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<h1 class="settitle" align="center">Bash Reference Manual</h1>

<div class="top" id="Top">
<div class="header">

Next: <a href="#Introduction" accesskey="n" rel="next">Introduction</a>, Previous: <a href="dir.html#Top" accesskey="p" rel="prev">(dir)</a>, Up: <a href="dir.html#Top" accesskey="u" rel="up">(dir)</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h1 class="top">Bash Features</h1>

This text is a brief description of the features that are present in
the Bash shell (version 5.2, 19 September 2022).
The Bash home page is <a href="http://www.gnu.org/software/bash/">http://www.gnu.org/software/bash/</a>.

This is Edition 5.2, last updated 19 September 2022,
of <cite>The GNU Bash Reference Manual</cite>,
for <code>Bash</code>, Version 5.2.

Bash contains features that appear in other popular shells, and some
features that only appear in Bash. Some of the shells that Bash has
borrowed concepts from are the Bourne Shell (<samp>sh</samp>), the Korn Shell
(<samp>ksh</samp>), and the C-shell (<samp>csh</samp> and its successor,
<samp>tcsh</samp>). The following menu breaks the features up into
categories, noting which features were inspired by other shells and
which are specific to Bash.

This manual is meant as a brief introduction to features found in
Bash. The Bash manual page should be used as the definitive
reference on shell behavior.

<div class="Contents_element" id="SEC_Contents">
<h2 class="contents-heading">Table of Contents</h2>

<ul class="no-bullet">
 <li><a id="toc-Introduction-1" href="#Introduction">1 Introduction</a>
 <ul class="no-bullet">
 <li><a id="toc-What-is-Bash_003f-1" href="#What-is-Bash_003f">1.1 What is Bash?</a></li>
 <li><a id="toc-What-is-a-shell_003f-1" href="#What-is-a-shell_003f">1.2 What is a shell?</a></li>
 </ul></li>
 <li><a id="toc-Definitions-1" href="#Definitions">2 Definitions</a></li>
 <li><a id="toc-Basic-Shell-Features-1" href="#Basic-Shell-Features">3 Basic Shell Features</a>
 <ul class="no-bullet">
 <li><a id="toc-Shell-Syntax-1" href="#Shell-Syntax">3.1 Shell Syntax</a>
 <ul class="no-bullet">
 <li><a id="toc-Shell-Operation-1" href="#Shell-Operation">3.1.1 Shell Operation</a></li>
 <li><a id="toc-Quoting-1" href="#Quoting">3.1.2 Quoting</a>
 <ul class="no-bullet">
 <li><a id="toc-Escape-Character-1" href="#Escape-Character">3.1.2.1 Escape Character</a></li>
 <li><a id="toc-Single-Quotes-1" href="#Single-Quotes">3.1.2.2 Single Quotes</a></li>
 <li><a id="toc-Double-Quotes-1" href="#Double-Quotes">3.1.2.3 Double Quotes</a></li>
 <li><a id="toc-ANSI_002dC-Quoting-1" href="#ANSI_002dC-Quoting">3.1.2.4 ANSI-C Quoting</a></li>
 <li><a id="toc-Locale_002dSpecific-Translation" href="#Locale-Translation">3.1.2.5 Locale-Specific Translation</a></li>
 </ul></li>
 <li><a id="toc-Comments-1" href="#Comments">3.1.3 Comments</a></li>
 </ul></li>
 <li><a id="toc-Shell-Commands-1" href="#Shell-Commands">3.2 Shell Commands</a>
 <ul class="no-bullet">
 <li><a id="toc-Reserved-Words-1" href="#Reserved-Words">3.2.1 Reserved Words</a></li>
 <li><a id="toc-Simple-Commands-1" href="#Simple-Commands">3.2.2 Simple Commands</a></li>
 <li><a id="toc-Pipelines-1" href="#Pipelines">3.2.3 Pipelines</a></li>
 <li><a id="toc-Lists-of-Commands" href="#Lists">3.2.4 Lists of Commands</a></li>
 <li><a id="toc-Compound-Commands-1" href="#Compound-Commands">3.2.5 Compound Commands</a>
 <ul class="no-bullet">
 <li><a id="toc-Looping-Constructs-1" href="#Looping-Constructs">3.2.5.1 Looping Constructs</a></li>
 <li><a id="toc-Conditional-Constructs-1" href="#Conditional-Constructs">3.2.5.2 Conditional Constructs</a></li>
 <li><a id="toc-Grouping-Commands" href="#Command-Grouping">3.2.5.3 Grouping Commands</a></li>
 </ul></li>
 <li><a id="toc-Coprocesses-1" href="#Coprocesses">3.2.6 Coprocesses</a></li>
 <li><a id="toc-GNU-Parallel-1" href="#GNU-Parallel">3.2.7 GNU Parallel</a></li>
 </ul></li>
 <li><a id="toc-Shell-Functions-1" href="#Shell-Functions">3.3 Shell Functions</a></li>
 <li><a id="toc-Shell-Parameters-1" href="#Shell-Parameters">3.4 Shell Parameters</a>
 <ul class="no-bullet">
 <li><a id="toc-Positional-Parameters-1" href="#Positional-Parameters">3.4.1 Positional Parameters</a></li>
 <li><a id="toc-Special-Parameters-1" href="#Special-Parameters">3.4.2 Special Parameters</a></li>
 </ul></li>
 <li><a id="toc-Shell-Expansions-1" href="#Shell-Expansions">3.5 Shell Expansions</a>
 <ul class="no-bullet">
 <li><a id="toc-Brace-Expansion-1" href="#Brace-Expansion">3.5.1 Brace Expansion</a></li>
 <li><a id="toc-Tilde-Expansion-1" href="#Tilde-Expansion">3.5.2 Tilde Expansion</a></li>
 <li><a id="toc-Shell-Parameter-Expansion-1" href="#Shell-Parameter-Expansion">3.5.3 Shell Parameter Expansion</a></li>
 <li><a id="toc-Command-Substitution-1" href="#Command-Substitution">3.5.4 Command Substitution</a></li>
 <li><a id="toc-Arithmetic-Expansion-1" href="#Arithmetic-Expansion">3.5.5 Arithmetic Expansion</a></li>
 <li><a id="toc-Process-Substitution-1" href="#Process-Substitution">3.5.6 Process Substitution</a></li>
 <li><a id="toc-Word-Splitting-1" href="#Word-Splitting">3.5.7 Word Splitting</a></li>
 <li><a id="toc-Filename-Expansion-1" href="#Filename-Expansion">3.5.8 Filename Expansion</a>
 <ul class="no-bullet">
 <li><a id="toc-Pattern-Matching-1" href="#Pattern-Matching">3.5.8.1 Pattern Matching</a></li>
 </ul></li>
 <li><a id="toc-Quote-Removal-1" href="#Quote-Removal">3.5.9 Quote Removal</a></li>
 </ul></li>
 <li><a id="toc-Redirections-1" href="#Redirections">3.6 Redirections</a>
 <ul class="no-bullet">
 <li><a id="toc-Redirecting-Input" href="#Redirecting-Input">3.6.1 Redirecting Input</a></li>
 <li><a id="toc-Redirecting-Output" href="#Redirecting-Output">3.6.2 Redirecting Output</a></li>
 <li><a id="toc-Appending-Redirected-Output" href="#Appending-Redirected-Output">3.6.3 Appending Redirected Output</a></li>
 <li><a id="toc-Redirecting-Standard-Output-and-Standard-Error" href="#Redirecting-Standard-Output-and-Standard-Error">3.6.4 Redirecting Standard Output and Standard Error</a></li>
 <li><a id="toc-Appending-Standard-Output-and-Standard-Error" href="#Appending-Standard-Output-and-Standard-Error">3.6.5 Appending Standard Output and Standard Error</a></li>
 <li><a id="toc-Here-Documents" href="#Here-Documents">3.6.6 Here Documents</a></li>
 <li><a id="toc-Here-Strings" href="#Here-Strings">3.6.7 Here Strings</a></li>
 <li><a id="toc-Duplicating-File-Descriptors" href="#Duplicating-File-Descriptors">3.6.8 Duplicating File Descriptors</a></li>
 <li><a id="toc-Moving-File-Descriptors" href="#Moving-File-Descriptors">3.6.9 Moving File Descriptors</a></li>
 <li><a id="toc-Opening-File-Descriptors-for-Reading-and-Writing" href="#Opening-File-Descriptors-for-Reading-and-Writing">3.6.10 Opening File Descriptors for Reading and Writing</a></li>
 </ul></li>
 <li><a id="toc-Executing-Commands-1" href="#Executing-Commands">3.7 Executing Commands</a>
 <ul class="no-bullet">
 <li><a id="toc-Simple-Command-Expansion-1" href="#Simple-Command-Expansion">3.7.1 Simple Command Expansion</a></li>
 <li><a id="toc-Command-Search-and-Execution-1" href="#Command-Search-and-Execution">3.7.2 Command Search and Execution</a></li>
 <li><a id="toc-Command-Execution-Environment-1" href="#Command-Execution-Environment">3.7.3 Command Execution Environment</a></li>
 <li><a id="toc-Environment-1" href="#Environment">3.7.4 Environment</a></li>
 <li><a id="toc-Exit-Status-1" href="#Exit-Status">3.7.5 Exit Status</a></li>
 <li><a id="toc-Signals-1" href="#Signals">3.7.6 Signals</a></li>
 </ul></li>
 <li><a id="toc-Shell-Scripts-1" href="#Shell-Scripts">3.8 Shell Scripts</a></li>
 </ul></li>
 <li><a id="toc-Shell-Builtin-Commands-1" href="#Shell-Builtin-Commands">4 Shell Builtin Commands</a>
 <ul class="no-bullet">
 <li><a id="toc-Bourne-Shell-Builtins-1" href="#Bourne-Shell-Builtins">4.1 Bourne Shell Builtins</a></li>
 <li><a id="toc-Bash-Builtin-Commands" href="#Bash-Builtins">4.2 Bash Builtin Commands</a></li>
 <li><a id="toc-Modifying-Shell-Behavior-1" href="#Modifying-Shell-Behavior">4.3 Modifying Shell Behavior</a>
 <ul class="no-bullet">
 <li><a id="toc-The-Set-Builtin-1" href="#The-Set-Builtin">4.3.1 The Set Builtin</a></li>
 <li><a id="toc-The-Shopt-Builtin-1" href="#The-Shopt-Builtin">4.3.2 The Shopt Builtin</a></li>
 </ul></li>
 <li><a id="toc-Special-Builtins-1" href="#Special-Builtins">4.4 Special Builtins</a></li>
 </ul></li>
 <li><a id="toc-Shell-Variables-1" href="#Shell-Variables">5 Shell Variables</a>
 <ul class="no-bullet">
 <li><a id="toc-Bourne-Shell-Variables-1" href="#Bourne-Shell-Variables">5.1 Bourne Shell Variables</a></li>
 <li><a id="toc-Bash-Variables-1" href="#Bash-Variables">5.2 Bash Variables</a></li>
 </ul></li>
 <li><a id="toc-Bash-Features-2" href="#Bash-Features">6 Bash Features</a>
 <ul class="no-bullet">
 <li><a id="toc-Invoking-Bash-1" href="#Invoking-Bash">6.1 Invoking Bash</a></li>
 <li><a id="toc-Bash-Startup-Files-1" href="#Bash-Startup-Files">6.2 Bash Startup Files</a></li>
 <li><a id="toc-Interactive-Shells-1" href="#Interactive-Shells">6.3 Interactive Shells</a>
 <ul class="no-bullet">
 <li><a id="toc-What-is-an-Interactive-Shell_003f-1" href="#What-is-an-Interactive-Shell_003f">6.3.1 What is an Interactive Shell?</a></li>
 <li><a id="toc-Is-this-Shell-Interactive_003f-1" href="#Is-this-Shell-Interactive_003f">6.3.2 Is this Shell Interactive?</a></li>
 <li><a id="toc-Interactive-Shell-Behavior-1" href="#Interactive-Shell-Behavior">6.3.3 Interactive Shell Behavior</a></li>
 </ul></li>
 <li><a id="toc-Bash-Conditional-Expressions-1" href="#Bash-Conditional-Expressions">6.4 Bash Conditional Expressions</a></li>
 <li><a id="toc-Shell-Arithmetic-1" href="#Shell-Arithmetic">6.5 Shell Arithmetic</a></li>
 <li><a id="toc-Aliases-1" href="#Aliases">6.6 Aliases</a></li>
 <li><a id="toc-Arrays-1" href="#Arrays">6.7 Arrays</a></li>
 <li><a id="toc-The-Directory-Stack-1" href="#The-Directory-Stack">6.8 The Directory Stack</a>
 <ul class="no-bullet">
 <li><a id="toc-Directory-Stack-Builtins-1" href="#Directory-Stack-Builtins">6.8.1 Directory Stack Builtins</a></li>
 </ul></li>
 <li><a id="toc-Controlling-the-Prompt-1" href="#Controlling-the-Prompt">6.9 Controlling the Prompt</a></li>
 <li><a id="toc-The-Restricted-Shell-1" href="#The-Restricted-Shell">6.10 The Restricted Shell</a></li>
 <li><a id="toc-Bash-POSIX-Mode-1" href="#Bash-POSIX-Mode">6.11 Bash POSIX Mode</a></li>
 <li><a id="toc-Shell-Compatibility-Mode-1" href="#Shell-Compatibility-Mode">6.12 Shell Compatibility Mode</a></li>
 </ul></li>
 <li><a id="toc-Job-Control-1" href="#Job-Control">7 Job Control</a>
 <ul class="no-bullet">
 <li><a id="toc-Job-Control-Basics-1" href="#Job-Control-Basics">7.1 Job Control Basics</a></li>
 <li><a id="toc-Job-Control-Builtins-1" href="#Job-Control-Builtins">7.2 Job Control Builtins</a></li>
 <li><a id="toc-Job-Control-Variables-1" href="#Job-Control-Variables">7.3 Job Control Variables</a></li>
 </ul></li>
 <li><a id="toc-Command-Line-Editing-1" href="#Command-Line-Editing">8 Command Line Editing</a>
 <ul class="no-bullet">
 <li><a id="toc-Introduction-to-Line-Editing" href="#Introduction-and-Notation">8.1 Introduction to Line Editing</a></li>
 <li><a id="toc-Readline-Interaction-1" href="#Readline-Interaction">8.2 Readline Interaction</a>
 <ul class="no-bullet">
 <li><a id="toc-Readline-Bare-Essentials-1" href="#Readline-Bare-Essentials">8.2.1 Readline Bare Essentials</a></li>
 <li><a id="toc-Readline-Movement-Commands-1" href="#Readline-Movement-Commands">8.2.2 Readline Movement Commands</a></li>
 <li><a id="toc-Readline-Killing-Commands-1" href="#Readline-Killing-Commands">8.2.3 Readline Killing Commands</a></li>
 <li><a id="toc-Readline-Arguments-1" href="#Readline-Arguments">8.2.4 Readline Arguments</a></li>
 <li><a id="toc-Searching-for-Commands-in-the-History" href="#Searching">8.2.5 Searching for Commands in the History</a></li>
 </ul></li>
 <li><a id="toc-Readline-Init-File-1" href="#Readline-Init-File">8.3 Readline Init File</a>
 <ul class="no-bullet">
 <li><a id="toc-Readline-Init-File-Syntax-1" href="#Readline-Init-File-Syntax">8.3.1 Readline Init File Syntax</a></li>
 <li><a id="toc-Conditional-Init-Constructs-1" href="#Conditional-Init-Constructs">8.3.2 Conditional Init Constructs</a></li>
 <li><a id="toc-Sample-Init-File-1" href="#Sample-Init-File">8.3.3 Sample Init File</a></li>
 </ul></li>
 <li><a id="toc-Bindable-Readline-Commands-1" href="#Bindable-Readline-Commands">8.4 Bindable Readline Commands</a>
 <ul class="no-bullet">
 <li><a id="toc-Commands-For-Moving-1" href="#Commands-For-Moving">8.4.1 Commands For Moving</a></li>
 <li><a id="toc-Commands-For-Manipulating-The-History" href="#Commands-For-History">8.4.2 Commands For Manipulating The History</a></li>
 <li><a id="toc-Commands-For-Changing-Text" href="#Commands-For-Text">8.4.3 Commands For Changing Text</a></li>
 <li><a id="toc-Killing-And-Yanking" href="#Commands-For-Killing">8.4.4 Killing And Yanking</a></li>
 <li><a id="toc-Specifying-Numeric-Arguments" href="#Numeric-Arguments">8.4.5 Specifying Numeric Arguments</a></li>
 <li><a id="toc-Letting-Readline-Type-For-You" href="#Commands-For-Completion">8.4.6 Letting Readline Type For You</a></li>
 <li><a id="toc-Keyboard-Macros-1" href="#Keyboard-Macros">8.4.7 Keyboard Macros</a></li>
 <li><a id="toc-Some-Miscellaneous-Commands" href="#Miscellaneous-Commands">8.4.8 Some Miscellaneous Commands</a></li>
 </ul></li>
 <li><a id="toc-Readline-vi-Mode-1" href="#Readline-vi-Mode">8.5 Readline vi Mode</a></li>
 <li><a id="toc-Programmable-Completion-1" href="#Programmable-Completion">8.6 Programmable Completion</a></li>
 <li><a id="toc-Programmable-Completion-Builtins-1" href="#Programmable-Completion-Builtins">8.7 Programmable Completion Builtins</a></li>
 <li><a id="toc-A-Programmable-Completion-Example-1" href="#A-Programmable-Completion-Example">8.8 A Programmable Completion Example</a></li>
 </ul></li>
 <li><a id="toc-Using-History-Interactively-1" href="#Using-History-Interactively">9 Using History Interactively</a>
 <ul class="no-bullet">
 <li><a id="toc-Bash-History-Facilities-1" href="#Bash-History-Facilities">9.1 Bash History Facilities</a></li>
 <li><a id="toc-Bash-History-Builtins-1" href="#Bash-History-Builtins">9.2 Bash History Builtins</a></li>
 <li><a id="toc-History-Expansion" href="#History-Interaction">9.3 History Expansion</a>
 <ul class="no-bullet">
 <li><a id="toc-Event-Designators-1" href="#Event-Designators">9.3.1 Event Designators</a></li>
 <li><a id="toc-Word-Designators-1" href="#Word-Designators">9.3.2 Word Designators</a></li>
 <li><a id="toc-Modifiers-1" href="#Modifiers">9.3.3 Modifiers</a></li>
 </ul></li>
 </ul></li>
 <li><a id="toc-Installing-Bash-1" href="#Installing-Bash">10 Installing Bash</a>
 <ul class="no-bullet">
 <li><a id="toc-Basic-Installation-1" href="#Basic-Installation">10.1 Basic Installation</a></li>
 <li><a id="toc-Compilers-and-Options-1" href="#Compilers-and-Options">10.2 Compilers and Options</a></li>
 <li><a id="toc-Compiling-For-Multiple-Architectures-1" href="#Compiling-For-Multiple-Architectures">10.3 Compiling For Multiple Architectures</a></li>
 <li><a id="toc-Installation-Names-1" href="#Installation-Names">10.4 Installation Names</a></li>
 <li><a id="toc-Specifying-the-System-Type-1" href="#Specifying-the-System-Type">10.5 Specifying the System Type</a></li>
 <li><a id="toc-Sharing-Defaults-1" href="#Sharing-Defaults">10.6 Sharing Defaults</a></li>
 <li><a id="toc-Operation-Controls-1" href="#Operation-Controls">10.7 Operation Controls</a></li>
 <li><a id="toc-Optional-Features-1" href="#Optional-Features">10.8 Optional Features</a></li>
 </ul></li>
 <li><a id="toc-Reporting-Bugs-1" href="#Reporting-Bugs">Appendix A Reporting Bugs</a></li>
 <li><a id="toc-Major-Differences-From-The-Bourne-Shell-1" href="#Major-Differences-From-The-Bourne-Shell">Appendix B Major Differences From The Bourne Shell</a>
 <ul class="no-bullet">
 <li><a id="toc-Implementation-Differences-From-The-SVR4_002e2-Shell" href="#Implementation-Differences-From-The-SVR4_002e2-Shell">B.1 Implementation Differences From The SVR4.2 Shell</a></li>
 </ul></li>
 <li><a id="toc-GNU-Free-Documentation-License-1" href="#GNU-Free-Documentation-License">Appendix C GNU Free Documentation License</a></li>
 <li><a id="toc-Indexes-1" href="#Indexes">Appendix D Indexes</a>
 <ul class="no-bullet">
 <li><a id="toc-Index-of-Shell-Builtin-Commands" href="#Builtin-Index" rel="index">D.1 Index of Shell Builtin Commands</a></li>
 <li><a id="toc-Index-of-Shell-Reserved-Words" href="#Reserved-Word-Index" rel="index">D.2 Index of Shell Reserved Words</a></li>
 <li><a id="toc-Parameter-and-Variable-Index" href="#Variable-Index" rel="index">D.3 Parameter and Variable Index</a></li>
 <li><a id="toc-Function-Index-1" href="#Function-Index" rel="index">D.4 Function Index</a></li>
 <li><a id="toc-Concept-Index-1" href="#Concept-Index" rel="index">D.5 Concept Index</a></li>
 </ul></li>
</ul>
</div>
</div>
<hr>
<div class="chapter" id="Introduction">
<div class="header">

Next: <a href="#Definitions" accesskey="n" rel="next">Definitions</a>, Up: <a href="#Top" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h2 class="chapter">1 Introduction</h2>

<ul class="section-toc">
<li><a href="#What-is-Bash_003f" accesskey="1">What is Bash?</a></li>
<li><a href="#What-is-a-shell_003f" accesskey="2">What is a shell?</a></li>
</ul>
<hr>
<div class="section" id="What-is-Bash_003f">
<div class="header">

Next: <a href="#What-is-a-shell_003f" accesskey="n" rel="next">What is a shell?</a>, Up: <a href="#Introduction" accesskey="u" rel="up">Introduction</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">1.1 What is Bash?</h3>

Bash is the shell, or command language interpreter,
for the GNU operating system.
The name is an acronym for the &lsquo;<samp>Bourne-Again SHell</samp>&rsquo;,
a pun on Stephen Bourne, the author of the direct ancestor of
the current Unix shell <code>sh</code>, 
which appeared in the Seventh Edition Bell Labs Research version
of Unix.

Bash is largely compatible with <code>sh</code> and incorporates useful
features from the Korn shell <code>ksh</code> and the C shell <code>csh</code>.
It is intended to be a conformant implementation of the IEEE
POSIX Shell and Tools portion of the IEEE POSIX
specification (IEEE Standard 1003.1).
It offers functional improvements over <code>sh</code> for both interactive and
programming use.

While the GNU operating system provides other shells, including
a version of <code>csh</code>, Bash is the default shell.
Like other GNU software, Bash is quite portable. It currently runs
on nearly every version of Unix and a few other operating systems -
independently-supported ports exist for MS-DOS, OS/2,
and Windows platforms.

<hr>
</div>
<div class="section" id="What-is-a-shell_003f">
<div class="header">

Previous: <a href="#What-is-Bash_003f" accesskey="p" rel="prev">What is Bash?</a>, Up: <a href="#Introduction" accesskey="u" rel="up">Introduction</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">1.2 What is a shell?</h3>

At its base, a shell is simply a macro processor that executes
commands. The term macro processor means functionality where text
and symbols are expanded to create larger expressions.

A Unix shell is both a command interpreter and a programming
language. As a command interpreter, the shell provides the user
interface to the rich set of GNU utilities. The programming
language features allow these utilities to be combined.
Files containing commands can be created, and become
commands themselves. These new commands have the same status as
system commands in directories such as <samp>/bin</samp>, allowing users
or groups to establish custom environments to automate their common
tasks.

Shells may be used interactively or non-interactively. In
interactive mode, they accept input typed from the keyboard.
When executing non-interactively, shells execute commands read
from a file.

A shell allows execution of GNU commands, both synchronously and
asynchronously.
The shell waits for synchronous commands to complete before accepting
more input; asynchronous commands continue to execute in parallel
with the shell while it reads and executes additional commands.
The redirection constructs permit
fine-grained control of the input and output of those commands.
Moreover, the shell allows control over the contents of commands&rsquo;
environments.

Shells also provide a small set of built-in
commands (builtins) implementing functionality impossible
or inconvenient to obtain via separate utilities.
For example, <code>cd</code>, <code>break</code>, <code>continue</code>, and
<code>exec</code> cannot be implemented outside of the shell because
they directly manipulate the shell itself.
The <code>history</code>, <code>getopts</code>, <code>kill</code>, or <code>pwd</code>
builtins, among others, could be implemented in separate utilities,
but they are more convenient to use as builtin commands.
All of the shell builtins are described in
subsequent sections.

While executing commands is essential, most of the power (and
complexity) of shells is due to their embedded programming
languages. Like any high-level language, the shell provides
variables, flow control constructs, quoting, and functions. 

Shells offer features geared specifically for
interactive use rather than to augment the programming language. 
These interactive features include job control, command line
editing, command history and aliases. Each of these features is
described in this manual.

<hr>
</div>
</div>
<div class="chapter" id="Definitions">
<div class="header">

Next: <a href="#Basic-Shell-Features" accesskey="n" rel="next">Basic Shell Features</a>, Previous: <a href="#Introduction" accesskey="p" rel="prev">Introduction</a>, Up: <a href="#Top" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h2 class="chapter">2 Definitions</h2>
These definitions are used throughout the remainder of this manual.

<dl compact="compact">
<dt id='index-POSIX'><code>POSIX</code><a href='#index-POSIX' class='copiable-anchor'> &para;</a></dt>
<dd>A family of open system standards based on Unix. Bash
is primarily concerned with the Shell and Utilities portion of the
POSIX 1003.1 standard. 

</dd>
<dt><code>blank</code></dt>
<dd>A space or tab character.

</dd>
<dt id='index-builtin-1'><code>builtin</code><a href='#index-builtin-1' class='copiable-anchor'> &para;</a></dt>
<dd>A command that is implemented internally by the shell itself, rather
than by an executable program somewhere in the file system.

</dd>
<dt id='index-control-operator'><code>control operator</code><a href='#index-control-operator' class='copiable-anchor'> &para;</a></dt>
<dd>A <code>token</code> that performs a control function. It is a <code>newline</code>
or one of the following:
&lsquo;<samp>||</samp>&rsquo;, &lsquo;<samp>&amp;&amp;</samp>&rsquo;, &lsquo;<samp>&amp;</samp>&rsquo;, &lsquo;<samp>;</samp>&rsquo;, &lsquo;<samp>;;</samp>&rsquo;, &lsquo;<samp>;&amp;</samp>&rsquo;, &lsquo;<samp>;;&amp;</samp>&rsquo;,
&lsquo;<samp>|</samp>&rsquo;, &lsquo;<samp>|&amp;</samp>&rsquo;, &lsquo;<samp>(</samp>&rsquo;, or &lsquo;<samp>)</samp>&rsquo;.

</dd>
<dt id='index-exit-status'><code>exit status</code><a href='#index-exit-status' class='copiable-anchor'> &para;</a></dt>
<dd>The value returned by a command to its caller. The value is restricted
to eight bits, so the maximum value is 255.

</dd>
<dt id='index-field'><code>field</code><a href='#index-field' class='copiable-anchor'> &para;</a></dt>
<dd>A unit of text that is the result of one of the shell expansions. After
expansion, when executing a command, the resulting fields are used as
the command name and arguments.

</dd>
<dt id='index-filename'><code>filename</code><a href='#index-filename' class='copiable-anchor'> &para;</a></dt>
<dd>A string of characters used to identify a file.

</dd>
<dt id='index-job'><code>job</code><a href='#index-job' class='copiable-anchor'> &para;</a></dt>
<dd>A set of processes comprising a pipeline, and any processes descended
from it, that are all in the same process group.

</dd>
<dt id='index-job-control'><code>job control</code><a href='#index-job-control' class='copiable-anchor'> &para;</a></dt>
<dd>A mechanism by which users can selectively stop (suspend) and restart
(resume) execution of processes.

</dd>
<dt id='index-metacharacter'><code>metacharacter</code><a href='#index-metacharacter' class='copiable-anchor'> &para;</a></dt>
<dd>A character that, when unquoted, separates words. A metacharacter is
a <code>space</code>, <code>tab</code>, <code>newline</code>, or one of the following characters:
&lsquo;<samp>|</samp>&rsquo;, &lsquo;<samp>&amp;</samp>&rsquo;, &lsquo;<samp>;</samp>&rsquo;, &lsquo;<samp>(</samp>&rsquo;, &lsquo;<samp>)</samp>&rsquo;, &lsquo;<samp>&lt;</samp>&rsquo;, or
&lsquo;<samp>&gt;</samp>&rsquo;.

</dd>
<dt id='index-name'><code>name</code><a href='#index-name' class='copiable-anchor'> &para;</a></dt>
<dd>
A <code>word</code> consisting solely of letters, numbers, and underscores,
and beginning with a letter or underscore. <code>Name</code>s are used as
shell variable and function names.
Also referred to as an <code>identifier</code>.

</dd>
<dt id='index-operator_002c-shell'><code>operator</code><a href='#index-operator_002c-shell' class='copiable-anchor'> &para;</a></dt>
<dd>A <code>control operator</code> or a <code>redirection operator</code>.
See <a href="#Redirections">Redirections</a>, for a list of redirection operators.
Operators contain at least one unquoted <code>metacharacter</code>.

</dd>
<dt id='index-process-group'><code>process group</code><a href='#index-process-group' class='copiable-anchor'> &para;</a></dt>
<dd>A collection of related processes each having the same process
group ID.

</dd>
<dt id='index-process-group-ID'><code>process group ID</code><a href='#index-process-group-ID' class='copiable-anchor'> &para;</a></dt>
<dd>A unique identifier that represents a <code>process group</code>
during its lifetime.

</dd>
<dt id='index-reserved-word'><code>reserved word</code><a href='#index-reserved-word' class='copiable-anchor'> &para;</a></dt>
<dd>A <code>word</code> that has a special meaning to the shell. Most reserved
words introduce shell flow control constructs, such as <code>for</code> and
<code>while</code>.

</dd>
<dt id='index-return-status'><code>return status</code><a href='#index-return-status' class='copiable-anchor'> &para;</a></dt>
<dd>A synonym for <code>exit status</code>.

</dd>
<dt id='index-signal'><code>signal</code><a href='#index-signal' class='copiable-anchor'> &para;</a></dt>
<dd>A mechanism by which a process may be notified by the kernel
of an event occurring in the system.

</dd>
<dt id='index-special-builtin'><code>special builtin</code><a href='#index-special-builtin' class='copiable-anchor'> &para;</a></dt>
<dd>A shell builtin command that has been classified as special by the
POSIX standard.

</dd>
<dt id='index-token'><code>token</code><a href='#index-token' class='copiable-anchor'> &para;</a></dt>
<dd>A sequence of characters considered a single unit by the shell.
It is either a <code>word</code> or an <code>operator</code>.

</dd>
<dt id='index-word'><code>word</code><a href='#index-word' class='copiable-anchor'> &para;</a></dt>
<dd>A sequence of characters treated as a unit by the shell.
Words may not include unquoted <code>metacharacters</code>.
</dd>
</dl>

<hr>
</div>
<div class="chapter" id="Basic-Shell-Features">
<div class="header">

Next: <a href="#Shell-Builtin-Commands" accesskey="n" rel="next">Shell Builtin Commands</a>, Previous: <a href="#Definitions" accesskey="p" rel="prev">Definitions</a>, Up: <a href="#Top" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h2 class="chapter">3 Basic Shell Features</h2>

Bash is an acronym for &lsquo;<samp>Bourne-Again SHell</samp>&rsquo;.
The Bourne shell is
the traditional Unix shell originally written by Stephen Bourne.
All of the Bourne shell builtin commands are available in Bash,
The rules for evaluation and quoting are taken from the POSIX
specification for the &lsquo;standard&rsquo; Unix shell.

This chapter briefly summarizes the shell&rsquo;s &lsquo;building blocks&rsquo;:
commands, control structures, shell functions, shell parameters,
shell expansions,
redirections, which are a way to direct input and output from
and to named files, and how the shell executes commands.

<ul class="section-toc">
<li><a href="#Shell-Syntax" accesskey="1">Shell Syntax</a></li>
<li><a href="#Shell-Commands" accesskey="2">Shell Commands</a></li>
<li><a href="#Shell-Functions" accesskey="3">Shell Functions</a></li>
<li><a href="#Shell-Parameters" accesskey="4">Shell Parameters</a></li>
<li><a href="#Shell-Expansions" accesskey="5">Shell Expansions</a></li>
<li><a href="#Redirections" accesskey="6">Redirections</a></li>
<li><a href="#Executing-Commands" accesskey="7">Executing Commands</a></li>
<li><a href="#Shell-Scripts" accesskey="8">Shell Scripts</a></li>
</ul>
<hr>
<div class="section" id="Shell-Syntax">
<div class="header">

Next: <a href="#Shell-Commands" accesskey="n" rel="next">Shell Commands</a>, Up: <a href="#Basic-Shell-Features" accesskey="u" rel="up">Basic Shell Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">3.1 Shell Syntax</h3>

When the shell reads input, it proceeds through a
sequence of operations. If the input indicates the beginning of a
comment, the shell ignores the comment symbol (&lsquo;<samp>#</samp>&rsquo;), and the rest
of that line.
 
Otherwise, roughly speaking, the shell reads its input and
divides the input into words and operators, employing the quoting rules
to select which meanings to assign various words and characters.

The shell then parses these tokens into commands and other constructs,
removes the special meaning of certain words or characters, expands
others, redirects input and output as needed, executes the specified
command, waits for the command&rsquo;s exit status, and makes that exit status
available for further inspection or processing.

<ul class="section-toc">
<li><a href="#Shell-Operation" accesskey="1">Shell Operation</a></li>
<li><a href="#Quoting" accesskey="2">Quoting</a></li>
<li><a href="#Comments" accesskey="3">Comments</a></li>
</ul>
<hr>
<div class="subsection" id="Shell-Operation">
<div class="header">

Next: <a href="#Quoting" accesskey="n" rel="next">Quoting</a>, Up: <a href="#Shell-Syntax" accesskey="u" rel="up">Shell Syntax</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.1.1 Shell Operation</h4>

The following is a brief description of the shell&rsquo;s operation when it
reads and executes a command. Basically, the shell does the
following:

<ol>
<li> Reads its input from a file (see <a href="#Shell-Scripts">Shell Scripts</a>), from a string
supplied as an argument to the <samp>-c</samp> invocation option
(see <a href="#Invoking-Bash">Invoking Bash</a>), or from the user&rsquo;s terminal.

</li><li> Breaks the input into words and operators, obeying the quoting rules
described in <a href="#Quoting">Quoting</a>. These tokens are separated by
<code>metacharacters</code>. Alias expansion is performed by this step
(see <a href="#Aliases">Aliases</a>).

</li><li> Parses the tokens into simple and compound commands
(see <a href="#Shell-Commands">Shell Commands</a>).

</li><li> Performs the various shell expansions (see <a href="#Shell-Expansions">Shell Expansions</a>), breaking
the expanded tokens into lists of filenames (see <a href="#Filename-Expansion">Filename Expansion</a>)
and commands and arguments.

</li><li> Performs any necessary redirections (see <a href="#Redirections">Redirections</a>) and removes
the redirection operators and their operands from the argument list.

</li><li> Executes the command (see <a href="#Executing-Commands">Executing Commands</a>).

</li><li> Optionally waits for the command to complete and collects its exit
status (see <a href="#Exit-Status">Exit Status</a>).

</li></ol>

<hr>
</div>
<div class="subsection" id="Quoting">
<div class="header">

Next: <a href="#Comments" accesskey="n" rel="next">Comments</a>, Previous: <a href="#Shell-Operation" accesskey="p" rel="prev">Shell Operation</a>, Up: <a href="#Shell-Syntax" accesskey="u" rel="up">Shell Syntax</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.1.2 Quoting</h4>

Quoting is used to remove the special meaning of certain
characters or words to the shell. Quoting can be used to
disable special treatment for special characters, to prevent
reserved words from being recognized as such, and to prevent
parameter expansion.

Each of the shell metacharacters (see <a href="#Definitions">Definitions</a>)
has special meaning to the shell and must be quoted if it is to
represent itself.
When the command history expansion facilities are being used
(see <a href="#History-Interaction">History Expansion</a>), the
history expansion character, usually &lsquo;<samp>!</samp>&rsquo;, must be quoted
to prevent history expansion. See <a href="#Bash-History-Facilities">Bash History Facilities</a>, for
more details concerning history expansion.

There are three quoting mechanisms: the
escape character, single quotes, and double quotes.

<ul class="section-toc">
<li><a href="#Escape-Character" accesskey="1">Escape Character</a></li>
<li><a href="#Single-Quotes" accesskey="2">Single Quotes</a></li>
<li><a href="#Double-Quotes" accesskey="3">Double Quotes</a></li>
<li><a href="#ANSI_002dC-Quoting" accesskey="4">ANSI-C Quoting</a></li>
<li><a href="#Locale-Translation" accesskey="5">Locale-Specific Translation</a></li>
</ul>
<hr>
<div class="subsubsection" id="Escape-Character">
<div class="header">

Next: <a href="#Single-Quotes" accesskey="n" rel="next">Single Quotes</a>, Up: <a href="#Quoting" accesskey="u" rel="up">Quoting</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsubsection">3.1.2.1 Escape Character</h4>
A non-quoted backslash &lsquo;<samp>\</samp>&rsquo; is the Bash escape character.
It preserves the literal value of the next character that follows,
with the exception of <code>newline</code>. If a <code>\newline</code> pair
appears, and the backslash itself is not quoted, the <code>\newline</code>
is treated as a line continuation (that is, it is removed from
the input stream and effectively ignored).

<hr>
</div>
<div class="subsubsection" id="Single-Quotes">
<div class="header">

Next: <a href="#Double-Quotes" accesskey="n" rel="next">Double Quotes</a>, Previous: <a href="#Escape-Character" accesskey="p" rel="prev">Escape Character</a>, Up: <a href="#Quoting" accesskey="u" rel="up">Quoting</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsubsection">3.1.2.2 Single Quotes</h4>

Enclosing characters in single quotes (&lsquo;<samp>'</samp>&rsquo;) preserves the literal value
of each character within the quotes. A single quote may not occur
between single quotes, even when preceded by a backslash.

<hr>
</div>
<div class="subsubsection" id="Double-Quotes">
<div class="header">

Next: <a href="#ANSI_002dC-Quoting" accesskey="n" rel="next">ANSI-C Quoting</a>, Previous: <a href="#Single-Quotes" accesskey="p" rel="prev">Single Quotes</a>, Up: <a href="#Quoting" accesskey="u" rel="up">Quoting</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsubsection">3.1.2.3 Double Quotes</h4>

Enclosing characters in double quotes (&lsquo;<samp>&quot;</samp>&rsquo;) preserves the literal value
of all characters within the quotes, with the exception of
&lsquo;<samp>$</samp>&rsquo;, &lsquo;<samp>`</samp>&rsquo;, &lsquo;<samp>\</samp>&rsquo;,
and, when history expansion is enabled, &lsquo;<samp>!</samp>&rsquo;.
When the shell is in
POSIX mode (see <a href="#Bash-POSIX-Mode">Bash POSIX Mode</a>),
the &lsquo;<samp>!</samp>&rsquo; has no special meaning
within double quotes, even when history expansion is enabled.
The characters &lsquo;<samp>$</samp>&rsquo; and &lsquo;<samp>`</samp>&rsquo;
retain their special meaning within double quotes (see <a href="#Shell-Expansions">Shell Expansions</a>).
The backslash retains its special meaning only when followed by one of
the following characters:
&lsquo;<samp>$</samp>&rsquo;, &lsquo;<samp>`</samp>&rsquo;, &lsquo;<samp>&quot;</samp>&rsquo;, &lsquo;<samp>\</samp>&rsquo;, or <code>newline</code>.
Within double quotes, backslashes that are followed by one of these
characters are removed. Backslashes preceding characters without a
special meaning are left unmodified.
A double quote may be quoted within double quotes by preceding it with
a backslash.
If enabled, history expansion will be performed unless an &lsquo;<samp>!</samp>&rsquo;
appearing in double quotes is escaped using a backslash.
The backslash preceding the &lsquo;<samp>!</samp>&rsquo; is not removed.

The special parameters &lsquo;<samp>*</samp>&rsquo; and &lsquo;<samp>@</samp>&rsquo; have special meaning
when in double quotes (see <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>).

<hr>
</div>
<div class="subsubsection" id="ANSI_002dC-Quoting">
<div class="header">

Next: <a href="#Locale-Translation" accesskey="n" rel="next">Locale-Specific Translation</a>, Previous: <a href="#Double-Quotes" accesskey="p" rel="prev">Double Quotes</a>, Up: <a href="#Quoting" accesskey="u" rel="up">Quoting</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsubsection">3.1.2.4 ANSI-C Quoting</h4>

Character sequences of the form $&rsquo;<var>string</var>&rsquo; are treated as a special
kind of single quotes.
The sequence expands to <var>string</var>, with backslash-escaped characters
in <var>string</var> replaced as specified by the ANSI C standard.
Backslash escape sequences, if present, are decoded as follows:

<dl compact="compact">
<dt><code>\a</code></dt>
<dd>alert (bell)
</dd>
<dt><code>\b</code></dt>
<dd>backspace
</dd>
<dt><code>\e</code></dt>
<dt><code>\E</code></dt>
<dd>an escape character (not ANSI C)
</dd>
<dt><code>\f</code></dt>
<dd>form feed
</dd>
<dt><code>\n</code></dt>
<dd>newline
</dd>
<dt><code>\r</code></dt>
<dd>carriage return
</dd>
<dt><code>\t</code></dt>
<dd>horizontal tab
</dd>
<dt><code>\v</code></dt>
<dd>vertical tab
</dd>
<dt><code>\\</code></dt>
<dd>backslash
</dd>
<dt><code>\'</code></dt>
<dd>single quote
</dd>
<dt><code>\&quot;</code></dt>
<dd>double quote
</dd>
<dt><code>\?</code></dt>
<dd>question mark
</dd>
<dt><code>\<var>nnn</var></code></dt>
<dd>the eight-bit character whose value is the octal value <var>nnn</var>
(one to three octal digits)
</dd>
<dt><code>\x<var>HH</var></code></dt>
<dd>the eight-bit character whose value is the hexadecimal value <var>HH</var>
(one or two hex digits)
</dd>
<dt><code>\u<var>HHHH</var></code></dt>
<dd>the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value
<var>HHHH</var> (one to four hex digits)
</dd>
<dt><code>\U<var>HHHHHHHH</var></code></dt>
<dd>the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value
<var>HHHHHHHH</var> (one to eight hex digits)
</dd>
<dt><code>\c<var>x</var></code></dt>
<dd>a control-<var>x</var> character
</dd>
</dl>

The expanded result is single-quoted, as if the dollar sign had not
been present.

<hr>
</div>
<div class="subsubsection" id="Locale-Translation">
<div class="header">

Previous: <a href="#ANSI_002dC-Quoting" accesskey="p" rel="prev">ANSI-C Quoting</a>, Up: <a href="#Quoting" accesskey="u" rel="up">Quoting</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsubsection">3.1.2.5 Locale-Specific Translation</h4>

Prefixing a double-quoted string with a dollar sign (&lsquo;<samp>$</samp>&rsquo;), such
as <tt>$&quot;hello, world&quot;</tt>,
will cause the string to be translated according to the current locale.
The <code>gettext</code> infrastructure performs the lookup and 
translation, using the <code>LC_MESSAGES</code>, <code>TEXTDOMAINDIR</code>,
and <code>TEXTDOMAIN</code> shell variables, as explained below.
See the gettext documentation for additional details not covered here.
If the current locale is <code>C</code> or <code>POSIX</code>,
if there are no translations available,
of if the string is not translated,
the dollar sign is ignored.
Since this is a form of double quoting, the string remains double-quoted
by default, whether or not it is translated and replaced.
If the <code>noexpand_translation</code> option is enabled
using the <code>shopt</code> builtin (see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>),
translated strings are single-quoted instead of double-quoted.

The rest of this section is a brief overview of how you use gettext to
create translations for strings in a shell script named <var>scriptname</var>.
There are more details in the gettext documentation.

<hr>
<div class="header">

 &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="node-heading">Creating Internationalized Scripts</h4>


Once you&rsquo;ve marked the strings in your script
that you want to translate using $&quot;...&quot;,
you create a gettext &quot;template&quot; file using the command

<div class="example">
<pre class="example">bash --dump-po-strings <var>scriptname</var> &gt; <var>domain</var>.pot
</pre></div>

The <var>domain</var> is your message domain.
It&rsquo;s just an arbitrary string that&rsquo;s used to identify the files gettext
needs, like a package or script name.
It needs to be unique among all
the message domains on systems where you install the translations, so
gettext knows which translations correspond to your script.
You&rsquo;ll use the template file to create translations for each target language.
The template file conventionally has the suffix &lsquo;<samp>.pot</samp>&rsquo;.

You copy this template file to a separate file for each target language
you want to support (called &quot;PO&quot; files, which use the suffix &lsquo;<samp>.po</samp>&rsquo;).
PO files use various naming conventions, but
when you are working to translate a template file into a particular
language, you first copy the template file to a file whose name is the
language you want to target, with the &lsquo;<samp>.po</samp>&rsquo; suffix.
For instance, the Spanish translations of your strings would be
in a file named &lsquo;<samp>es.po</samp>&rsquo;, and to get started using a message
domain named &quot;example,&quot; you would run

<div class="example">
<pre class="example">cp example.pot es.po
</pre></div>

Ultimately, PO files are often named <var>domain</var>.po and installed in
directories that contain multiple translation files for a particular language.

Whichever naming convention you choose, you will need to translate the
strings in the PO files into the appropriate languages.
This has to be done manually.

When you have the translations and PO files complete, you&rsquo;ll use the
gettext tools to produce what are called &quot;MO&quot; files, which are compiled
versions of the PO files the gettext tools use to look up translations
efficiently.
MO files are also called &quot;message catalog&quot; files.
You use the <code>msgfmt</code> program to do this.
For instance, if you had a file with Spanish translations, you could run

<div class="example">
<pre class="example">msgfmt -o es.mo es.po
</pre></div>

to produce the corresponding MO file.

Once you have the MO files, you decide where to install them and use the
<code>TEXTDOMAINDIR</code> shell variable to tell the gettext tools where they are.
Make sure to use the same message domain to name the MO files 
as you did for the PO files when you install them.





Your users will use the <code>LANG</code> or <code>LC_MESSAGES</code> shell variables to
select the desired language.

You set the <code>TEXTDOMAIN</code> variable to the script&rsquo;s message domain.
As above, you use the message domain to name your translation files.

You, or possibly your users, set the <code>TEXTDOMAINDIR</code> variable to the
name of a directory where the message catalog files are stored.
If you install the message files into the system&rsquo;s standard message catalog
directory, you don&rsquo;t need to worry about this variable.

The directory where the message catalog files are stored varies between
systems.
Some use the message catalog selected by the <code>LC_MESSAGES</code>
shell variable.
Others create the name of the message catalog from the value of the
<code>TEXTDOMAIN</code> shell variable, possibly adding the &lsquo;<samp>.mo</samp>&rsquo; suffix.
If you use the <code>TEXTDOMAIN</code> variable, you may need to set the
<code>TEXTDOMAINDIR</code> variable to the location of the message catalog files,
as above.
It&rsquo;s common to use both variables in this fashion:
<code>$TEXTDOMAINDIR</code>/<code>$LC_MESSAGES</code>/LC_MESSAGES/<code>$TEXTDOMAIN</code>.mo.

If you used that last convention, and you wanted to store the message
catalog files with Spanish (es) and Esperanto (eo) translations into a
local directory you use for custom translation files, you could run

<div class="example">
<pre class="example">TEXTDOMAIN=example
TEXTDOMAINDIR=/usr/local/share/locale

cp es.mo ${TEXTDOMAINDIR}/es/LC_MESSAGES/${TEXTDOMAIN}.mo
cp eo.mo ${TEXTDOMAINDIR}/eo/LC_MESSAGES/${TEXTDOMAIN}.mo
</pre></div>

When all of this is done, and the message catalog files containing the
compiled translations are installed in the correct location,
your users will be able to see translated strings
in any of the supported languages by setting the <code>LANG</code> or
<code>LC_MESSAGES</code> environment variables before running your script.

<hr>
</div>
</div>
<div class="subsection" id="Comments">
<div class="header">

Previous: <a href="#Quoting" accesskey="p" rel="prev">Quoting</a>, Up: <a href="#Shell-Syntax" accesskey="u" rel="up">Shell Syntax</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.1.3 Comments</h4>

In a non-interactive shell, or an interactive shell in which the
<code>interactive_comments</code> option to the <code>shopt</code>
builtin is enabled (see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>),
a word beginning with &lsquo;<samp>#</samp>&rsquo;
causes that word and all remaining characters on that line to
be ignored. An interactive shell without the <code>interactive_comments</code>
option enabled does not allow comments. The <code>interactive_comments</code>
option is on by default in interactive shells.
See <a href="#Interactive-Shells">Interactive Shells</a>, for a description of what makes
a shell interactive.

<hr>
</div>
</div>
<div class="section" id="Shell-Commands">
<div class="header">

Next: <a href="#Shell-Functions" accesskey="n" rel="next">Shell Functions</a>, Previous: <a href="#Shell-Syntax" accesskey="p" rel="prev">Shell Syntax</a>, Up: <a href="#Basic-Shell-Features" accesskey="u" rel="up">Basic Shell Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">3.2 Shell Commands</h3>

A simple shell command such as <code>echo a b c</code> consists of the command
itself followed by arguments, separated by spaces.

More complex shell commands are composed of simple commands arranged together
in a variety of ways: in a pipeline in which the output of one command
becomes the input of a second, in a loop or conditional construct, or in
some other grouping.

<ul class="section-toc">
<li><a href="#Reserved-Words" accesskey="1">Reserved Words</a></li>
<li><a href="#Simple-Commands" accesskey="2">Simple Commands</a></li>
<li><a href="#Pipelines" accesskey="3">Pipelines</a></li>
<li><a href="#Lists" accesskey="4">Lists of Commands</a></li>
<li><a href="#Compound-Commands" accesskey="5">Compound Commands</a></li>
<li><a href="#Coprocesses" accesskey="6">Coprocesses</a></li>
<li><a href="#GNU-Parallel" accesskey="7">GNU Parallel</a></li>
</ul>
<hr>
<div class="subsection" id="Reserved-Words">
<div class="header">

Next: <a href="#Simple-Commands" accesskey="n" rel="next">Simple Commands</a>, Up: <a href="#Shell-Commands" accesskey="u" rel="up">Shell Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.2.1 Reserved Words</h4>

Reserved words are words that have special meaning to the shell.
They are used to begin and end the shell&rsquo;s compound commands.

The following words are recognized as reserved when unquoted and 
the first word of a command (see below for exceptions):

<table>
<tr><td width="10%"><code>if</code></td><td width="10%"><code>then</code></td><td width="10%"><code>elif</code></td><td width="10%"><code>else</code></td><td width="12%"><code>fi</code></td><td width="10%"><code>time</code></td></tr>
<tr><td width="10%"><code>for</code></td><td width="10%"><code>in</code></td><td width="10%"><code>until</code></td><td width="10%"><code>while</code></td><td width="12%"><code>do</code></td><td width="10%"><code>done</code></td></tr>
<tr><td width="10%"><code>case</code></td><td width="10%"><code>esac</code></td><td width="10%"><code>coproc</code></td><td width="10%"><code>select</code></td><td width="12%"><code>function</code></td></tr>
<tr><td width="10%"><code>{</code></td><td width="10%"><code>}</code></td><td width="10%"><code>[[</code></td><td width="10%"><code>]]</code></td><td width="12%"><code>!</code></td></tr>
</table>

<code>in</code> is recognized as a reserved word if it is the third word of a
<code>case</code> or <code>select</code> command.
<code>in</code> and <code>do</code> are recognized as reserved
words if they are the third word in a <code>for</code> command.

<hr>
</div>
<div class="subsection" id="Simple-Commands">
<div class="header">

Next: <a href="#Pipelines" accesskey="n" rel="next">Pipelines</a>, Previous: <a href="#Reserved-Words" accesskey="p" rel="prev">Reserved Words</a>, Up: <a href="#Shell-Commands" accesskey="u" rel="up">Shell Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.2.2 Simple Commands</h4>

A simple command is the kind of command encountered most often.
It&rsquo;s just a sequence of words separated by <code>blank</code>s, terminated
by one of the shell&rsquo;s control operators (see <a href="#Definitions">Definitions</a>). The
first word generally specifies a command to be executed, with the
rest of the words being that command&rsquo;s arguments.

The return status (see <a href="#Exit-Status">Exit Status</a>) of a simple command is
its exit status as provided
by the POSIX 1003.1 <code>waitpid</code> function, or 128+<var>n</var> if
the command was terminated by signal <var>n</var>.

<hr>
</div>
<div class="subsection" id="Pipelines">
<div class="header">

Next: <a href="#Lists" accesskey="n" rel="next">Lists of Commands</a>, Previous: <a href="#Simple-Commands" accesskey="p" rel="prev">Simple Commands</a>, Up: <a href="#Shell-Commands" accesskey="u" rel="up">Shell Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.2.3 Pipelines</h4>

A <code>pipeline</code> is a sequence of one or more commands separated by
one of the control operators &lsquo;<samp>|</samp>&rsquo; or &lsquo;<samp>|&amp;</samp>&rsquo;.




The format for a pipeline is
<div class="example">
<pre class="example">[time [-p]] [!] <var>command1</var> [ | or |&amp; <var>command2</var> ] &hellip;
</pre></div>

The output of each command in the pipeline is connected via a pipe
to the input of the next command.
That is, each command reads the previous command&rsquo;s output. This
connection is performed before any redirections specified by
<var>command1</var>.

If &lsquo;<samp>|&amp;</samp>&rsquo; is used, <var>command1</var>&rsquo;s standard error, in addition to
its standard output, is connected to
<var>command2</var>&rsquo;s standard input through the pipe;
it is shorthand for <code>2&gt;&amp;1 |</code>.
This implicit redirection of the standard error to the standard output is
performed after any redirections specified by <var>command1</var>.

The reserved word <code>time</code> causes timing statistics
to be printed for the pipeline once it finishes.
The statistics currently consist of elapsed (wall-clock) time and
user and system time consumed by the command&rsquo;s execution.
The <samp>-p</samp> option changes the output format to that specified
by POSIX.
When the shell is in POSIX mode (see <a href="#Bash-POSIX-Mode">Bash POSIX Mode</a>),
it does not recognize <code>time</code> as a reserved word if the next
token begins with a &lsquo;<samp>-</samp>&rsquo;.
The <code>TIMEFORMAT</code> variable may be set to a format string that
specifies how the timing information should be displayed.
See <a href="#Bash-Variables">Bash Variables</a>, for a description of the available formats.
The use of <code>time</code> as a reserved word permits the timing of
shell builtins, shell functions, and pipelines. An external
<code>time</code> command cannot time these easily.

When the shell is in POSIX mode (see <a href="#Bash-POSIX-Mode">Bash POSIX Mode</a>), <code>time</code>
may be followed by a newline. In this case, the shell displays the
total user and system time consumed by the shell and its children.
The <code>TIMEFORMAT</code> variable may be used to specify the format of
the time information.

If the pipeline is not executed asynchronously (see <a href="#Lists">Lists of Commands</a>), the
shell waits for all commands in the pipeline to complete.

Each command in a multi-command pipeline,
where pipes are created,
is executed in its own subshell, which is a
separate process (see <a href="#Command-Execution-Environment">Command Execution Environment</a>).
If the <code>lastpipe</code> option is enabled using the <code>shopt</code> builtin
(see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>),
the last element of a pipeline may be run by the shell process
when job control is not active.

The exit
status of a pipeline is the exit status of the last command in the
pipeline, unless the <code>pipefail</code> option is enabled
(see <a href="#The-Set-Builtin">The Set Builtin</a>).
If <code>pipefail</code> is enabled, the pipeline&rsquo;s return status is the
value of the last (rightmost) command to exit with a non-zero status,
or zero if all commands exit successfully.
If the reserved word &lsquo;<samp>!</samp>&rsquo; precedes the pipeline, the
exit status is the logical negation of the exit status as described
above.
The shell waits for all commands in the pipeline to terminate before
returning a value.

<hr>
</div>
<div class="subsection" id="Lists">
<div class="header">

Next: <a href="#Compound-Commands" accesskey="n" rel="next">Compound Commands</a>, Previous: <a href="#Pipelines" accesskey="p" rel="prev">Pipelines</a>, Up: <a href="#Shell-Commands" accesskey="u" rel="up">Shell Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.2.4 Lists of Commands</h4>

A <code>list</code> is a sequence of one or more pipelines separated by one
of the operators &lsquo;<samp>;</samp>&rsquo;, &lsquo;<samp>&amp;</samp>&rsquo;, &lsquo;<samp>&amp;&amp;</samp>&rsquo;, or &lsquo;<samp>||</samp>&rsquo;,
and optionally terminated by one of &lsquo;<samp>;</samp>&rsquo;, &lsquo;<samp>&amp;</samp>&rsquo;, or a
<code>newline</code>.

Of these list operators, &lsquo;<samp>&amp;&amp;</samp>&rsquo; and &lsquo;<samp>||</samp>&rsquo;
have equal precedence, followed by &lsquo;<samp>;</samp>&rsquo; and &lsquo;<samp>&amp;</samp>&rsquo;,
which have equal precedence.

A sequence of one or more newlines may appear in a <code>list</code>
to delimit commands, equivalent to a semicolon.

If a command is terminated by the control operator &lsquo;<samp>&amp;</samp>&rsquo;,
the shell executes the command asynchronously in a subshell.
This is known as executing the command in the background,
and these are referred to as asynchronous commands.
The shell does not wait for the command to finish, and the return
status is 0 (true).
When job control is not active (see <a href="#Job-Control">Job Control</a>),
the standard input for asynchronous commands, in the absence of any
explicit redirections, is redirected from <code>/dev/null</code>.

Commands separated by a &lsquo;<samp>;</samp>&rsquo; are executed sequentially; the shell
waits for each command to terminate in turn. The return status is the
exit status of the last command executed.

AND and OR lists are sequences of one or more pipelines
separated by the control operators &lsquo;<samp>&amp;&amp;</samp>&rsquo; and &lsquo;<samp>||</samp>&rsquo;,
respectively. AND and OR lists are executed with left
associativity.

An AND list has the form
<div class="example">
<pre class="example"><var>command1</var> &amp;&amp; <var>command2</var>
</pre></div>

<var>command2</var> is executed if, and only if, <var>command1</var>
returns an exit status of zero (success).

An OR list has the form
<div class="example">
<pre class="example"><var>command1</var> || <var>command2</var>
</pre></div>

<var>command2</var> is executed if, and only if, <var>command1</var>
returns a non-zero exit status.

The return status of
AND and OR lists is the exit status of the last command
executed in the list.

<hr>
</div>
<div class="subsection" id="Compound-Commands">
<div class="header">

Next: <a href="#Coprocesses" accesskey="n" rel="next">Coprocesses</a>, Previous: <a href="#Lists" accesskey="p" rel="prev">Lists of Commands</a>, Up: <a href="#Shell-Commands" accesskey="u" rel="up">Shell Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.2.5 Compound Commands</h4>

Compound commands are the shell programming language constructs.
Each construct begins with a reserved word or control operator and is
terminated by a corresponding reserved word or operator.
Any redirections (see <a href="#Redirections">Redirections</a>) associated with a compound command
apply to all commands within that compound command unless explicitly overridden.

In most cases a list of commands in a compound command&rsquo;s description may be
separated from the rest of the command by one or more newlines, and may be
followed by a newline in place of a semicolon.

Bash provides looping constructs, conditional commands, and mechanisms
to group commands and execute them as a unit.

<ul class="section-toc">
<li><a href="#Looping-Constructs" accesskey="1">Looping Constructs</a></li>
<li><a href="#Conditional-Constructs" accesskey="2">Conditional Constructs</a></li>
<li><a href="#Command-Grouping" accesskey="3">Grouping Commands</a></li>
</ul>
<hr>
<div class="subsubsection" id="Looping-Constructs">
<div class="header">

Next: <a href="#Conditional-Constructs" accesskey="n" rel="next">Conditional Constructs</a>, Up: <a href="#Compound-Commands" accesskey="u" rel="up">Compound Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsubsection">3.2.5.1 Looping Constructs</h4>

Bash supports the following looping constructs.

Note that wherever a &lsquo;<samp>;</samp>&rsquo; appears in the description of a
command&rsquo;s syntax, it may be replaced with one or more newlines.

<dl compact="compact">
<dt id='index-until'><code>until</code><a href='#index-until' class='copiable-anchor'> &para;</a></dt>
<dd>

The syntax of the <code>until</code> command is:

<div class="example">
<pre class="example">until <var>test-commands</var>; do <var>consequent-commands</var>; done
</pre></div>

Execute <var>consequent-commands</var> as long as
<var>test-commands</var> has an exit status which is not zero.
The return status is the exit status of the last command executed
in <var>consequent-commands</var>, or zero if none was executed.

</dd>
<dt id='index-while'><code>while</code><a href='#index-while' class='copiable-anchor'> &para;</a></dt>
<dd>The syntax of the <code>while</code> command is:

<div class="example">
<pre class="example">while <var>test-commands</var>; do <var>consequent-commands</var>; done
</pre></div>

Execute <var>consequent-commands</var> as long as
<var>test-commands</var> has an exit status of zero.
The return status is the exit status of the last command executed
in <var>consequent-commands</var>, or zero if none was executed.

</dd>
<dt id='index-for'><code>for</code><a href='#index-for' class='copiable-anchor'> &para;</a></dt>
<dd>The syntax of the <code>for</code> command is:

<div class="example">
<pre class="example">for <var>name</var> [ [in [<var>words</var> &hellip;] ] ; ] do <var>commands</var>; done
</pre></div>

Expand <var>words</var> (see <a href="#Shell-Expansions">Shell Expansions</a>), and execute <var>commands</var>
once for each member
in the resultant list, with <var>name</var> bound to the current member.
If &lsquo;<samp>in <var>words</var></samp>&rsquo; is not present, the <code>for</code> command
executes the <var>commands</var> once for each positional parameter that is
set, as if &lsquo;<samp>in &quot;$@&quot;</samp>&rsquo; had been specified
(see <a href="#Special-Parameters">Special Parameters</a>).

The return status is the exit status of the last command that executes.
If there are no items in the expansion of <var>words</var>, no commands are
executed, and the return status is zero.

An alternate form of the <code>for</code> command is also supported:

<div class="example">
<pre class="example">for (( <var>expr1</var> ; <var>expr2</var> ; <var>expr3</var> )) ; do <var>commands</var> ; done
</pre></div>

First, the arithmetic expression <var>expr1</var> is evaluated according
to the rules described below (see <a href="#Shell-Arithmetic">Shell Arithmetic</a>).
The arithmetic expression <var>expr2</var> is then evaluated repeatedly
until it evaluates to zero. 
Each time <var>expr2</var> evaluates to a non-zero value, <var>commands</var> are
executed and the arithmetic expression <var>expr3</var> is evaluated. 
If any expression is omitted, it behaves as if it evaluates to 1.
The return value is the exit status of the last command in <var>commands</var>
that is executed, or false if any of the expressions is invalid.
</dd>
</dl>

The <code>break</code> and <code>continue</code> builtins (see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>)
may be used to control loop execution.

<hr>
</div>
<div class="subsubsection" id="Conditional-Constructs">
<div class="header">

Next: <a href="#Command-Grouping" accesskey="n" rel="next">Grouping Commands</a>, Previous: <a href="#Looping-Constructs" accesskey="p" rel="prev">Looping Constructs</a>, Up: <a href="#Compound-Commands" accesskey="u" rel="up">Compound Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsubsection">3.2.5.2 Conditional Constructs</h4>

<dl compact="compact">
<dt id='index-if'><code>if</code><a href='#index-if' class='copiable-anchor'> &para;</a></dt>
<dd>



The syntax of the <code>if</code> command is:

<div class="example">
<pre class="example">if <var>test-commands</var>; then
 <var>consequent-commands</var>;
[elif <var>more-test-commands</var>; then
 <var>more-consequents</var>;]
[else <var>alternate-consequents</var>;]
fi
</pre></div>

The <var>test-commands</var> list is executed, and if its return status is zero,
the <var>consequent-commands</var> list is executed.
If <var>test-commands</var> returns a non-zero status, each <code>elif</code> list
is executed in turn, and if its exit status is zero,
the corresponding <var>more-consequents</var> is executed and the 
command completes.
If &lsquo;<samp>else <var>alternate-consequents</var></samp>&rsquo; is present, and
the final command in the final <code>if</code> or <code>elif</code> clause
has a non-zero exit status, then <var>alternate-consequents</var> is executed.
The return status is the exit status of the last command executed, or
zero if no condition tested true.

</dd>
<dt id='index-case'><code>case</code><a href='#index-case' class='copiable-anchor'> &para;</a></dt>
<dd>

The syntax of the <code>case</code> command is:

<div class="example">
<pre class="example">case <var>word</var> in
 [ [(] <var>pattern</var> [| <var>pattern</var>]&hellip;) <var>command-list</var> ;;]&hellip;
esac
</pre></div>

<code>case</code> will selectively execute the <var>command-list</var> corresponding to
the first <var>pattern</var> that matches <var>word</var>.
The match is performed according
to the rules described below in <a href="#Pattern-Matching">Pattern Matching</a>.
If the <code>nocasematch</code> shell option
(see the description of <code>shopt</code> in <a href="#The-Shopt-Builtin">The Shopt Builtin</a>)
is enabled, the match is performed without regard to the case
of alphabetic characters.
The &lsquo;<samp>|</samp>&rsquo; is used to separate multiple patterns, and the &lsquo;<samp>)</samp>&rsquo;
operator terminates a pattern list.
A list of patterns and an associated command-list is known
as a <var>clause</var>.

Each clause must be terminated with &lsquo;<samp>;;</samp>&rsquo;, &lsquo;<samp>;&amp;</samp>&rsquo;, or &lsquo;<samp>;;&amp;</samp>&rsquo;.
The <var>word</var> undergoes tilde expansion, parameter expansion, command
substitution, arithmetic expansion, and quote removal
(see <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>)
before matching is attempted.
Each <var>pattern</var> undergoes tilde expansion, parameter expansion,
command substitution, arithmetic expansion, process substitution, and
quote removal.

There may be an arbitrary number of <code>case</code> clauses, each terminated
by a &lsquo;<samp>;;</samp>&rsquo;, &lsquo;<samp>;&amp;</samp>&rsquo;, or &lsquo;<samp>;;&amp;</samp>&rsquo;.
The first pattern that matches determines the
command-list that is executed.
It&rsquo;s a common idiom to use &lsquo;<samp>*</samp>&rsquo; as the final pattern to define the
default case, since that pattern will always match.

Here is an example using <code>case</code> in a script that could be used to
describe one interesting feature of an animal:

<div class="example">
<pre class="example">echo -n &quot;Enter the name of an animal: &quot;
read ANIMAL
echo -n &quot;The $ANIMAL has &quot;
case $ANIMAL in
 horse | dog | cat) echo -n &quot;four&quot;;;
 man | kangaroo ) echo -n &quot;two&quot;;;
 *) echo -n &quot;an unknown number of&quot;;;
esac
echo &quot; legs.&quot;
</pre></div>

If the &lsquo;<samp>;;</samp>&rsquo; operator is used, no subsequent matches are attempted after
the first pattern match.
Using &lsquo;<samp>;&amp;</samp>&rsquo; in place of &lsquo;<samp>;;</samp>&rsquo; causes execution to continue with
the <var>command-list</var> associated with the next clause, if any.
Using &lsquo;<samp>;;&amp;</samp>&rsquo; in place of &lsquo;<samp>;;</samp>&rsquo; causes the shell to test the patterns
in the next clause, if any, and execute any associated <var>command-list</var>
on a successful match,
continuing the case statement execution as if the pattern list had not matched.

The return status is zero if no <var>pattern</var> is matched. Otherwise, the
return status is the exit status of the <var>command-list</var> executed.

</dd>
<dt id='index-select'><code>select</code><a href='#index-select' class='copiable-anchor'> &para;</a></dt>
<dd>
The <code>select</code> construct allows the easy generation of menus.
It has almost the same syntax as the <code>for</code> command:

<div class="example">
<pre class="example">select <var>name</var> [in <var>words</var> &hellip;]; do <var>commands</var>; done
</pre></div>

The list of words following <code>in</code> is expanded, generating a list
of items, and the set of expanded words is printed on the standard
error output stream, each preceded by a number. If the
&lsquo;<samp>in <var>words</var></samp>&rsquo; is omitted, the positional parameters are printed,
as if &lsquo;<samp>in &quot;$@&quot;</samp>&rsquo; had been specified.
<code>select</code> then displays the <code>PS3</code>
prompt and reads a line from the standard input.
If the line consists of a number corresponding to one of the displayed
words, then the value of <var>name</var> is set to that word.
If the line is empty, the words and prompt are displayed again.
If <code>EOF</code> is read, the <code>select</code> command completes and returns 1.
Any other value read causes <var>name</var> to be set to null.
The line read is saved in the variable <code>REPLY</code>.

The <var>commands</var> are executed after each selection until a
<code>break</code> command is executed, at which
point the <code>select</code> command completes.

Here is an example that allows the user to pick a filename from the
current directory, and displays the name and index of the file
selected.

<div class="example">
<pre class="example">select fname in *;
do
	echo you picked $fname $$REPLY$
	break;
done
</pre></div>

</dd>
<dt><code>((&hellip;))</code></dt>
<dd><div class="example">
<pre class="example">(( <var>expression</var> ))
</pre></div>

The arithmetic <var>expression</var> is evaluated according to the rules
described below (see <a href="#Shell-Arithmetic">Shell Arithmetic</a>).
The <var>expression</var> undergoes the same expansions
as if it were within double quotes,
but double quote characters in <var>expression</var> are not treated specially
are removed.
If the value of the expression is non-zero, the return status is 0;
otherwise the return status is 1.

</dd>
<dt id='index-_005b_005b'><code>[[&hellip;]]</code><a href='#index-_005b_005b' class='copiable-anchor'> &para;</a></dt>
<dd>
<div class="example">
<pre class="example">[[ <var>expression</var> ]]
</pre></div>

Return a status of 0 or 1 depending on the evaluation of
the conditional expression <var>expression</var>.
Expressions are composed of the primaries described below in
<a href="#Bash-Conditional-Expressions">Bash Conditional Expressions</a>.
The words between the <code>[[</code> and <code>]]</code> do not undergo word splitting
and filename expansion.
The shell performs tilde expansion, parameter and
variable expansion, arithmetic expansion, command substitution, process
substitution, and quote removal on those words
(the expansions that would occur if the words were enclosed in double quotes).
Conditional operators such as &lsquo;<samp>-f</samp>&rsquo; must be unquoted to be recognized
as primaries.

When used with <code>[[</code>, the &lsquo;<samp>&lt;</samp>&rsquo; and &lsquo;<samp>&gt;</samp>&rsquo; operators sort
lexicographically using the current locale.

When the &lsquo;<samp>==</samp>&rsquo; and &lsquo;<samp>!=</samp>&rsquo; operators are used, the string to the
right of the operator is considered a pattern and matched according
to the rules described below in <a href="#Pattern-Matching">Pattern Matching</a>,
as if the <code>extglob</code> shell option were enabled.
The &lsquo;<samp>=</samp>&rsquo; operator is identical to &lsquo;<samp>==</samp>&rsquo;.
If the <code>nocasematch</code> shell option
(see the description of <code>shopt</code> in <a href="#The-Shopt-Builtin">The Shopt Builtin</a>)
is enabled, the match is performed without regard to the case
of alphabetic characters.
The return value is 0 if the string matches (&lsquo;<samp>==</samp>&rsquo;) or does not
match (&lsquo;<samp>!=</samp>&rsquo;) the pattern, and 1 otherwise.

If you quote any part of the pattern,
using any of the shell&rsquo;s quoting mechanisms,
the quoted portion is matched literally.
This means every character in the quoted portion matches itself,
instead of having any special pattern matching meaning.

An additional binary operator, &lsquo;<samp>=~</samp>&rsquo;, is available, with the same
precedence as &lsquo;<samp>==</samp>&rsquo; and &lsquo;<samp>!=</samp>&rsquo;.
When you use &lsquo;<samp>=~</samp>&rsquo;, the string to the right of the operator is considered
a POSIX extended regular expression pattern and matched accordingly
(using the POSIX <code>regcomp</code> and <code>regexec</code> interfaces
usually described in regex(3)).
The return value is 0 if the string matches the pattern, and 1 if it does not.
If the regular expression is syntactically incorrect, the conditional
expression returns 2.
If the <code>nocasematch</code> shell option
(see the description of <code>shopt</code> in <a href="#The-Shopt-Builtin">The Shopt Builtin</a>)
is enabled, the match is performed without regard to the case
of alphabetic characters.

You can quote any part of the pattern
to force the quoted portion to be matched literally
instead of as a regular expression (see above).
If the pattern is stored in a shell variable, quoting the variable
expansion forces the entire pattern to be matched literally.

The pattern will match if it matches any part of the string.
If you want to force the pattern to match the entire string,
anchor the pattern using the &lsquo;<samp>^</samp>&rsquo; and &lsquo;<samp>$</samp>&rsquo; regular expression
operators.

For example, the following will match a line
(stored in the shell variable <code>line</code>)
if there is a sequence of characters anywhere in the value consisting of
any number, including zero, of 
characters in the <code>space</code> character class,
immediately followed by zero or one instances of &lsquo;<samp>a</samp>&rsquo;,
then a &lsquo;<samp>b</samp>&rsquo;:

<div class="example">
<pre class="example">[[ $line =~ [[:space:]]*(a)?b ]]
</pre></div>

That means values for <code>line</code> like
&lsquo;<samp>aab</samp>&rsquo;, &lsquo;<samp> aaaaaab</samp>&rsquo;, &lsquo;<samp>xaby</samp>&rsquo;, and &lsquo;<samp> ab</samp>&rsquo;
will all match,
as will a line containing a &lsquo;<samp>b</samp>&rsquo; anywhere in its value.

If you want to match a character that&rsquo;s special to the regular expression
grammar (&lsquo;<samp>^$|[]()\.*+?</samp>&rsquo;), it has to be quoted to remove its special
meaning.
This means that in the pattern &lsquo;<samp>xxx.txt</samp>&rsquo;, the &lsquo;<samp>.</samp>&rsquo; matches any
character in the string (its usual regular expression meaning), but in the
pattern &lsquo;<samp>&quot;xxx.txt&quot;</samp>&rsquo;, it can only match a literal &lsquo;<samp>.</samp>&rsquo;.

Likewise, if you want to include a character in your pattern that has a
special meaning to the regular expression grammar, you must make sure it&rsquo;s
not quoted.
If you want to anchor a pattern at the beginning or end of the string,
for instance, you cannot quote the &lsquo;<samp>^</samp>&rsquo; or &lsquo;<samp>$</samp>&rsquo;
characters using any form of shell quoting.

If you want to match &lsquo;<samp>initial string</samp>&rsquo; at the start of a line,
the following will work:
<div class="example">
<pre class="example">[[ $line =~ ^&quot;initial string&quot; ]]
</pre></div>
but this will not:
<div class="example">
<pre class="example">[[ $line =~ &quot;^initial string&quot; ]]
</pre></div>
because in the second example the &lsquo;<samp>^</samp>&rsquo; is quoted and doesn&rsquo;t have its
usual special meaning.

It is sometimes difficult to specify a regular expression properly
without using quotes, or to keep track of the quoting used by regular
expressions while paying attention to
shell quoting and the shell&rsquo;s quote removal.
Storing the regular expression in a shell variable is often a useful
way to avoid problems with quoting characters that are special to the
shell.
For example, the following is equivalent to the pattern used above:

<div class="example">
<pre class="example">pattern='[[:space:]]*(a)?b'
[[ $line =~ $pattern ]]
</pre></div>

Shell programmers should take special care with backslashes, since
backslashes are used by both the shell and regular expressions to remove
the special meaning from the following character.
This means that after the shell&rsquo;s word expansions complete
(see <a href="#Shell-Expansions">Shell Expansions</a>),
any backslashes remaining in parts of the pattern
that were originally not quoted can remove the
special meaning of pattern characters.
If any part of the pattern is quoted, the shell does its best to ensure that
the regular expression treats those remaining backslashes as literal,
if they appeared in a quoted portion.

The following two sets of commands are not equivalent:

<div class="example">
<pre class="example">pattern='\.'

[[ . =~ $pattern ]]
[[ . =~ \. ]]

[[ . =~ &quot;$pattern&quot; ]]
[[ . =~ '\.' ]]
</pre></div>

The first two matches will succeed, but the second two will not, because
in the second two the backslash will be part of the pattern to be matched.
In the first two examples, the pattern passed to the regular expression
parser is &lsquo;<samp>\.</samp>&rsquo;. The backslash removes the special meaning from
&lsquo;<samp>.</samp>&rsquo;, so the literal &lsquo;<samp>.</samp>&rsquo; matches.
In the second two examples, the pattern passed to the regular expression
parser has the backslash quoted (e.g., &lsquo;<samp>\\\.</samp>&rsquo;), which will not match
the string, since it does not contain a backslash.
If the string in the first examples were anything other than &lsquo;<samp>.</samp>&rsquo;, say
&lsquo;<samp>a</samp>&rsquo;, the pattern would not match, because the quoted &lsquo;<samp>.</samp>&rsquo; in the
pattern loses its special meaning of matching any single character.

Bracket expressions in regular expressions can be sources of errors as well,
since characters that are normally special in regular expressions
lose their special meanings between brackets.
However, you can use bracket expressions to match special pattern characters
without quoting them, so they are sometimes useful for this purpose.

Though it might seem like a strange way to write it, the following pattern
will match a &lsquo;<samp>.</samp>&rsquo; in the string:

<div class="example">
<pre class="example">[[ . =~ [.] ]]
</pre></div>

The shell performs any word expansions before passing the pattern
to the regular expression functions,
so you can assume that the shell&rsquo;s quoting takes precedence.
As noted above, the regular expression parser will interpret any
unquoted backslashes remaining in the pattern after shell expansion
according to its own rules.
The intention is to avoid making shell programmers quote things twice
as much as possible, so shell quoting should be sufficient to quote
special pattern characters where that&rsquo;s necessary.

The array variable <code>BASH_REMATCH</code> records which parts of the string
matched the pattern.
The element of <code>BASH_REMATCH</code> with index 0 contains the portion of
the string matching the entire regular expression.
Substrings matched by parenthesized subexpressions within the regular
expression are saved in the remaining <code>BASH_REMATCH</code> indices.
The element of <code>BASH_REMATCH</code> with index <var>n</var> is the portion of the
string matching the <var>n</var>th parenthesized subexpression.

Bash sets
<code>BASH_REMATCH</code>
in the global scope; declaring it as a local variable will lead to
unexpected results.

Expressions may be combined using the following operators, listed
in decreasing order of precedence:

<dl compact="compact">
<dt><code>( <var>expression</var> )</code></dt>
<dd>Returns the value of <var>expression</var>.
This may be used to override the normal precedence of operators.

</dd>
<dt><code>! <var>expression</var></code></dt>
<dd>True if <var>expression</var> is false.

</dd>
<dt><code><var>expression1</var> &amp;&amp; <var>expression2</var></code></dt>
<dd>True if both <var>expression1</var> and <var>expression2</var> are true.

</dd>
<dt><code><var>expression1</var> || <var>expression2</var></code></dt>
<dd>True if either <var>expression1</var> or <var>expression2</var> is true.
</dd>
</dl>

The <code>&amp;&amp;</code> and <code>||</code> operators do not evaluate <var>expression2</var> if the
value of <var>expression1</var> is sufficient to determine the return
value of the entire conditional expression.
</dd>
</dl>

<hr>
</div>
<div class="subsubsection" id="Command-Grouping">
<div class="header">

Previous: <a href="#Conditional-Constructs" accesskey="p" rel="prev">Conditional Constructs</a>, Up: <a href="#Compound-Commands" accesskey="u" rel="up">Compound Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsubsection">3.2.5.3 Grouping Commands</h4>

Bash provides two ways to group a list of commands to be executed
as a unit. When commands are grouped, redirections may be applied
to the entire command list. For example, the output of all the
commands in the list may be redirected to a single stream.

<dl compact="compact">
<dt><code>()</code></dt>
<dd><div class="example">
<pre class="example">( <var>list</var> )
</pre></div>

Placing a list of commands between parentheses forces the shell to create
a subshell (see <a href="#Command-Execution-Environment">Command Execution Environment</a>), and each
of the commands in <var>list</var> is executed in that subshell environment.
Since the <var>list</var> is executed in a subshell, variable assignments do not
remain in effect after the subshell completes. 

</dd>
<dt id='index-_007b'><code>{}</code><a href='#index-_007b' class='copiable-anchor'> &para;</a></dt>
<dd>
<div class="example">
<pre class="example">{ <var>list</var>; }
</pre></div>

Placing a list of commands between curly braces causes the list to
be executed in the current shell context. No subshell is created.
The semicolon (or newline) following <var>list</var> is required.
</dd>
</dl>

In addition to the creation of a subshell, there is a subtle difference
between these two constructs due to historical reasons. The braces
are reserved words, so they must be separated from the <var>list</var>
by <code>blank</code>s or other shell metacharacters.
The parentheses are operators, and are
recognized as separate tokens by the shell even if they are not separated
from the <var>list</var> by whitespace.

The exit status of both of these constructs is the exit status of
<var>list</var>.

<hr>
</div>
</div>
<div class="subsection" id="Coprocesses">
<div class="header">

Next: <a href="#GNU-Parallel" accesskey="n" rel="next">GNU Parallel</a>, Previous: <a href="#Compound-Commands" accesskey="p" rel="prev">Compound Commands</a>, Up: <a href="#Shell-Commands" accesskey="u" rel="up">Shell Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.2.6 Coprocesses</h4>

A <code>coprocess</code> is a shell command preceded by the <code>coproc</code>
reserved word.
A coprocess is executed asynchronously in a subshell, as if the command
had been terminated with the &lsquo;<samp>&amp;</samp>&rsquo; control operator, with a two-way pipe
established between the executing shell and the coprocess.

The syntax for a coprocess is:

<div class="example">
<pre class="example">coproc [<var>NAME</var>] <var>command</var> [<var>redirections</var>]
</pre></div>

This creates a coprocess named <var>NAME</var>.
<var>command</var> may be either a simple command (see <a href="#Simple-Commands">Simple Commands</a>)
or a compound command (see <a href="#Compound-Commands">Compound Commands</a>).
<var>NAME</var> is a shell variable name.
If <var>NAME</var> is not supplied, the default name is <code>COPROC</code>.

The recommended form to use for a coprocess is

<div class="example">
<pre class="example">coproc <var>NAME</var> { <var>command</var>; }
</pre></div>

This form is recommended because simple commands result in the coprocess
always being named <code>COPROC</code>, and it is simpler to use and more complete
than the other compound commands.

There are other forms of coprocesses:

<div class="example">
<pre class="example">coproc <var>NAME</var> <var>compound-command</var>
coproc <var>compound-command</var>
coproc <var>simple-command</var>
</pre></div>

If <var>command</var> is a compound command, <var>NAME</var> is optional. The
word following <code>coproc</code> determines whether that word is interpreted
as a variable name: it is interpreted as <var>NAME</var> if it is not a
reserved word that introduces a compound command.
If <var>command</var> is a simple command, <var>NAME</var> is not allowed; this
is to avoid confusion between <var>NAME</var> and the first word of the simple
command.

When the coprocess is executed, the shell creates an array variable
(see <a href="#Arrays">Arrays</a>)
named <var>NAME</var> in the context of the executing shell.
The standard output of <var>command</var>
is connected via a pipe to a file descriptor in the executing shell,
and that file descriptor is assigned to <var>NAME</var>[0].
The standard input of <var>command</var>
is connected via a pipe to a file descriptor in the executing shell,
and that file descriptor is assigned to <var>NAME</var>[1].
This pipe is established before any redirections specified by the
command (see <a href="#Redirections">Redirections</a>).
The file descriptors can be utilized as arguments to shell commands
and redirections using standard word expansions.
Other than those created to execute command and process substitutions,
the file descriptors are not available in subshells.

The process ID of the shell spawned to execute the coprocess is
available as the value of the variable <code><var>NAME</var>_PID</code>.
The <code>wait</code>
builtin command may be used to wait for the coprocess to terminate.

Since the coprocess is created as an asynchronous command,
the <code>coproc</code> command always returns success.
The return status of a coprocess is the exit status of <var>command</var>.

<hr>
</div>
<div class="subsection" id="GNU-Parallel">
<div class="header">

Previous: <a href="#Coprocesses" accesskey="p" rel="prev">Coprocesses</a>, Up: <a href="#Shell-Commands" accesskey="u" rel="up">Shell Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.2.7 GNU Parallel</h4>

There are ways to run commands in parallel that are not built into Bash.
GNU Parallel is a tool to do just that.

GNU Parallel, as its name suggests, can be used to build and run commands
in parallel. You may run the same command with different arguments, whether
they are filenames, usernames, hostnames, or lines read from files. GNU
Parallel provides shorthand references to many of the most common operations
(input lines, various portions of the input line, different ways to specify
the input source, and so on). Parallel can replace <code>xargs</code> or feed
commands from its input sources to several different instances of Bash.

For a complete description, refer to the GNU Parallel documentation, which
is available at
<a href="https://www.gnu.org/software/parallel/parallel_tutorial.html">https://www.gnu.org/software/parallel/parallel_tutorial.html</a>.

<hr>
</div>
</div>
<div class="section" id="Shell-Functions">
<div class="header">

Next: <a href="#Shell-Parameters" accesskey="n" rel="next">Shell Parameters</a>, Previous: <a href="#Shell-Commands" accesskey="p" rel="prev">Shell Commands</a>, Up: <a href="#Basic-Shell-Features" accesskey="u" rel="up">Basic Shell Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">3.3 Shell Functions</h3>

Shell functions are a way to group commands for later execution
using a single name for the group. They are executed just like
a &quot;regular&quot; command.
When the name of a shell function is used as a simple command name,
the list of commands associated with that function name is executed.
Shell functions are executed in the current
shell context; no new process is created to interpret them.

Functions are declared using this syntax:

<div class="example">
<pre class="example"><var>fname</var> () <var>compound-command</var> [ <var>redirections</var> ]
</pre></div>

or

<div class="example">
<pre class="example">function <var>fname</var> [()] <var>compound-command</var> [ <var>redirections</var> ]
</pre></div>

This defines a shell function named <var>fname</var>. The reserved
word <code>function</code> is optional.
If the <code>function</code> reserved
word is supplied, the parentheses are optional.
The body of the function is the compound command
<var>compound-command</var> (see <a href="#Compound-Commands">Compound Commands</a>).
That command is usually a <var>list</var> enclosed between { and }, but
may be any compound command listed above.
If the <code>function</code> reserved word is used, but the
parentheses are not supplied, the braces are recommended.
<var>compound-command</var> is executed whenever <var>fname</var> is specified as the
name of a simple command.
When the shell is in POSIX mode (see <a href="#Bash-POSIX-Mode">Bash POSIX Mode</a>),
<var>fname</var> must be a valid shell name and
may not be the same as one of the special builtins
(see <a href="#Special-Builtins">Special Builtins</a>).
In default mode, a function name can be any unquoted shell word that does
not contain &lsquo;<samp>$</samp>&rsquo;.
Any redirections (see <a href="#Redirections">Redirections</a>) associated with the shell function
are performed when the function is executed.
A function definition may be deleted using the <samp>-f</samp> option to the
<code>unset</code> builtin (see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>).

The exit status of a function definition is zero unless a syntax error
occurs or a readonly function with the same name already exists.
When executed, the exit status of a function is the exit status of the
last command executed in the body.

Note that for historical reasons, in the most common usage the curly braces
that surround the body of the function must be separated from the body by
<code>blank</code>s or newlines.
This is because the braces are reserved words and are only recognized
as such when they are separated from the command list
by whitespace or another shell metacharacter.
Also, when using the braces, the <var>list</var> must be terminated by a semicolon,
a &lsquo;<samp>&amp;</samp>&rsquo;, or a newline.

When a function is executed, the arguments to the
function become the positional parameters
during its execution (see <a href="#Positional-Parameters">Positional Parameters</a>).
The special parameter &lsquo;<samp>#</samp>&rsquo; that expands to the number of
positional parameters is updated to reflect the change.
Special parameter <code>0</code> is unchanged.
The first element of the <code>FUNCNAME</code> variable is set to the
name of the function while the function is executing.

All other aspects of the shell execution
environment are identical between a function and its caller
with these exceptions:
the <code>DEBUG</code> and <code>RETURN</code> traps
are not inherited unless the function has been given the
<code>trace</code> attribute using the <code>declare</code> builtin or
the <code>-o functrace</code> option has been enabled with
the <code>set</code> builtin,
(in which case all functions inherit the <code>DEBUG</code> and <code>RETURN</code> traps),
and the <code>ERR</code> trap is not inherited unless the <code>-o errtrace</code>
shell option has been enabled.
See <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>, for the description of the
<code>trap</code> builtin.

The <code>FUNCNEST</code> variable, if set to a numeric value greater
than 0, defines a maximum function nesting level. Function
invocations that exceed the limit cause the entire command to
abort.

If the builtin command <code>return</code>
is executed in a function, the function completes and
execution resumes with the next command after the function
call.
Any command associated with the <code>RETURN</code> trap is executed
before execution resumes.
When a function completes, the values of the
positional parameters and the special parameter &lsquo;<samp>#</samp>&rsquo;
are restored to the values they had prior to the function&rsquo;s
execution. If a numeric argument is given to <code>return</code>,
that is the function&rsquo;s return status; otherwise the function&rsquo;s
return status is the exit status of the last command executed
before the <code>return</code>.

Variables local to the function may be declared with the
<code>local</code> builtin (local variables).
Ordinarily, variables and their values
are shared between a function and its caller.
These variables are visible only to
the function and the commands it invokes. This is particularly
important when a shell function calls other functions.

In the following description, the current scope is a currently-
executing function.
Previous scopes consist of that function&rsquo;s caller and so on,
back to the &quot;global&quot; scope, where the shell is not executing
any shell function.
Consequently, a local variable at the current local scope is a variable
declared using the <code>local</code> or <code>declare</code> builtins in the
function that is currently executing.

Local variables &quot;shadow&quot; variables with the same name declared at
previous scopes. For instance, a local variable declared in a function
hides a global variable of the same name: references and assignments
refer to the local variable, leaving the global variable unmodified.
When the function returns, the global variable is once again visible.

The shell uses dynamic scoping to control a variable&rsquo;s visibility
within functions.
With dynamic scoping, visible variables and their values
are a result of the sequence of function calls that caused execution
to reach the current function.
The value of a variable that a function sees depends
on its value within its caller, if any, whether that caller is
the &quot;global&quot; scope or another shell function.
This is also the value that a local variable
declaration &quot;shadows&quot;, and the value that is restored when the function
returns.

For example, if a variable <code>var</code> is declared as local in function
<code>func1</code>, and <code>func1</code> calls another function <code>func2</code>,
references to <code>var</code> made from within <code>func2</code> will resolve to the
local variable <code>var</code> from <code>func1</code>, shadowing any global variable
named <code>var</code>.

The following script demonstrates this behavior.
When executed, the script displays

<div class="example">
<pre class="example">In func2, var = func1 local
</pre></div>

<div class="example">
<pre class="example">func1()
{
 local var='func1 local'
 func2
}

func2()
{
    echo &quot;In func2, var = $var&quot;
}

var=global
func1
</pre></div>

The <code>unset</code> builtin also acts using the same dynamic scope: if a 
variable is local to the current scope, <code>unset</code> will unset it; 
otherwise the unset will refer to the variable found in any calling scope 
as described above.
If a variable at the current local scope is unset, it will remain so
(appearing as unset)
until it is reset in that scope or until the function returns.
Once the function returns, any instance of the variable at a previous
scope will become visible.
If the unset acts on a variable at a previous scope, any instance of a 
variable with that name that had been shadowed will become visible
(see below how <code>localvar_unset</code>shell option changes this behavior).

Function names and definitions may be listed with the
<samp>-f</samp> option to the <code>declare</code> (<code>typeset</code>)
builtin command (see <a href="#Bash-Builtins">Bash Builtin Commands</a>).
The <samp>-F</samp> option to <code>declare</code> or <code>typeset</code>
will list the function names only
(and optionally the source file and line number, if the <code>extdebug</code>
shell option is enabled).
Functions may be exported so that child shell processes
(those created when executing a separate shell invocation)
automatically have them defined with the
<samp>-f</samp> option to the <code>export</code> builtin
(see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>).

Functions may be recursive.
The <code>FUNCNEST</code> variable may be used to limit the depth of the
function call stack and restrict the number of function invocations.
By default, no limit is placed on the number of recursive calls.

<hr>
</div>
<div class="section" id="Shell-Parameters">
<div class="header">

Next: <a href="#Shell-Expansions" accesskey="n" rel="next">Shell Expansions</a>, Previous: <a href="#Shell-Functions" accesskey="p" rel="prev">Shell Functions</a>, Up: <a href="#Basic-Shell-Features" accesskey="u" rel="up">Basic Shell Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">3.4 Shell Parameters</h3>

A parameter is an entity that stores values.
It can be a <code>name</code>, a number, or one of the special characters
listed below.
A variable is a parameter denoted by a <code>name</code>.
A variable has a <code>value</code> and zero or more <code>attributes</code>.
Attributes are assigned using the <code>declare</code> builtin command
(see the description of the <code>declare</code> builtin in <a href="#Bash-Builtins">Bash Builtin Commands</a>).

A parameter is set if it has been assigned a value. The null string is
a valid value. Once a variable is set, it may be unset only by using
the <code>unset</code> builtin command.

A variable may be assigned to by a statement of the form
<div class="example">
<pre class="example"><var>name</var>=[<var>value</var>]
</pre></div>
If <var>value</var>
is not given, the variable is assigned the null string. All
<var>value</var>s undergo tilde expansion, parameter and variable expansion,
command substitution, arithmetic expansion, and quote
removal (see <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>).
If the variable has its <code>integer</code>
attribute set, then <var>value</var> 
is evaluated as an arithmetic expression even if the <code>$((&hellip;))</code>
expansion is not used (see <a href="#Arithmetic-Expansion">Arithmetic Expansion</a>).
Word splitting and filename expansion are not performed.
Assignment statements may also appear as arguments to the
<code>alias</code>, 
<code>declare</code>, <code>typeset</code>, <code>export</code>, <code>readonly</code>,
and <code>local</code> builtin commands (declaration commands).
When in POSIX mode (see <a href="#Bash-POSIX-Mode">Bash POSIX Mode</a>), these builtins may appear
in a command after one or more instances of the <code>command</code> builtin
and retain these assignment statement properties.

In the context where an assignment statement is assigning a value 
to a shell variable or array index (see <a href="#Arrays">Arrays</a>), the &lsquo;<samp>+=</samp>&rsquo;
operator can be used to 
append to or add to the variable&rsquo;s previous value.
This includes arguments to builtin commands such as <code>declare</code> that
accept assignment statements (declaration commands).
When &lsquo;<samp>+=</samp>&rsquo; is applied to a variable for which the <code>integer</code> attribute
has been set, <var>value</var> is evaluated as an arithmetic expression and
added to the variable&rsquo;s current value, which is also evaluated.
When &lsquo;<samp>+=</samp>&rsquo; is applied to an array variable using compound assignment
(see <a href="#Arrays">Arrays</a>), the
variable&rsquo;s value is not unset (as it is when using &lsquo;<samp>=</samp>&rsquo;), and new
values are appended to the array beginning at one greater than the array&rsquo;s
maximum index (for indexed arrays), or added as additional key-value pairs
in an associative array.
When applied to a string-valued variable, <var>value</var> is expanded and
appended to the variable&rsquo;s value.

A variable can be assigned the <code>nameref</code> attribute using the
<samp>-n</samp> option to the <code>declare</code> or <code>local</code> builtin commands
(see <a href="#Bash-Builtins">Bash Builtin Commands</a>)
to create a nameref, or a reference to another variable.
This allows variables to be manipulated indirectly.
Whenever the nameref variable is referenced, assigned to, unset, or has
its attributes modified (other than using or changing the nameref
attribute itself), the
operation is actually performed on the variable specified by the nameref
variable&rsquo;s value.
A nameref is commonly used within shell functions to refer to a variable
whose name is passed as an argument to the function.
For instance, if a variable name is passed to a shell function as its first
argument, running
<div class="example">
<pre class="example">declare -n ref=$1
</pre></div>
inside the function creates a nameref variable <code>ref</code> whose value is
the variable name passed as the first argument.
References and assignments to <code>ref</code>, and changes to its attributes,
are treated as references, assignments, and attribute modifications
to the variable whose name was passed as <code>$1</code>.

If the control variable in a <code>for</code> loop has the nameref attribute,
the list of words can be a list of shell variables, and a name reference
will be established for each word in the list, in turn, when the loop is
executed.
Array variables cannot be given the nameref attribute.
However, nameref variables can reference array variables and subscripted
array variables.
Namerefs can be unset using the <samp>-n</samp> option to the <code>unset</code> builtin
(see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>).
Otherwise, if <code>unset</code> is executed with the name of a nameref variable
as an argument, the variable referenced by the nameref variable will be unset.

<ul class="section-toc">
<li><a href="#Positional-Parameters" accesskey="1">Positional Parameters</a></li>
<li><a href="#Special-Parameters" accesskey="2">Special Parameters</a></li>
</ul>
<hr>
<div class="subsection" id="Positional-Parameters">
<div class="header">

Next: <a href="#Special-Parameters" accesskey="n" rel="next">Special Parameters</a>, Up: <a href="#Shell-Parameters" accesskey="u" rel="up">Shell Parameters</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.4.1 Positional Parameters</h4>

A positional parameter is a parameter denoted by one or more
digits, other than the single digit <code>0</code>. Positional parameters are
assigned from the shell&rsquo;s arguments when it is invoked,
and may be reassigned using the <code>set</code> builtin command.
Positional parameter <code>N</code> may be referenced as <code>${N}</code>, or
as <code>$N</code> when <code>N</code> consists of a single digit.
Positional parameters may not be assigned to with assignment statements.
The <code>set</code> and <code>shift</code> builtins are used to set and
unset them (see <a href="#Shell-Builtin-Commands">Shell Builtin Commands</a>).
The positional parameters are
temporarily replaced when a shell function is executed
(see <a href="#Shell-Functions">Shell Functions</a>).

When a positional parameter consisting of more than a single
digit is expanded, it must be enclosed in braces.

<hr>
</div>
<div class="subsection" id="Special-Parameters">
<div class="header">

Previous: <a href="#Positional-Parameters" accesskey="p" rel="prev">Positional Parameters</a>, Up: <a href="#Shell-Parameters" accesskey="u" rel="up">Shell Parameters</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.4.2 Special Parameters</h4>

The shell treats several parameters specially. These parameters may
only be referenced; assignment to them is not allowed.

<dl compact="compact">
<dt id='index-_002a'><code>*</code><a href='#index-_002a' class='copiable-anchor'> &para;</a></dt>
<dd>
($*) Expands to the positional parameters, starting from one.
When the expansion is not within double quotes, each positional parameter
expands to a separate word.
In contexts where it is performed, those words
are subject to further word splitting and filename expansion.
When the expansion occurs within double quotes, it expands to a single word
with the value of each parameter separated by the first character of the
<code>IFS</code> special variable. That is, <code>&quot;$*&quot;</code> is equivalent
to <code>&quot;$1<var>c</var>$2<var>c</var>&hellip;&quot;</code>, where <var>c</var>
is the first character of the value of the <code>IFS</code>
variable.
If <code>IFS</code> is unset, the parameters are separated by spaces.
If <code>IFS</code> is null, the parameters are joined without intervening
separators.

</dd>
<dt id='index-_0040'><code>@</code><a href='#index-_0040' class='copiable-anchor'> &para;</a></dt>
<dd>
($@) Expands to the positional parameters, starting from one.
In contexts where word splitting is performed, this expands each
positional parameter to a separate word; if not within double
quotes, these words are subject to word splitting.
In contexts where word splitting is not performed,
this expands to a single word
with each positional parameter separated by a space.
When the
expansion occurs within double quotes, and word splitting is performed,
each parameter expands to a
separate word. That is, <code>&quot;$@&quot;</code> is equivalent to
<code>&quot;$1&quot; &quot;$2&quot; &hellip;</code>.
If the double-quoted expansion occurs within a word, the expansion of
the first parameter is joined with the beginning part of the original
word, and the expansion of the last parameter is joined with the last
part of the original word.
When there are no positional parameters, <code>&quot;$@&quot;</code> and
<code>$@</code>
expand to nothing (i.e., they are removed).

</dd>
<dt id='index-_0023'><code>#</code><a href='#index-_0023' class='copiable-anchor'> &para;</a></dt>
<dd>
($#) Expands to the number of positional parameters in decimal.

</dd>
<dt id='index-_003f'><code>?</code><a href='#index-_003f' class='copiable-anchor'> &para;</a></dt>
<dd>
($?) Expands to the exit status of the most recently executed foreground
pipeline.

</dd>
<dt id='index-_002d'><code>-</code><a href='#index-_002d' class='copiable-anchor'> &para;</a></dt>
<dd>
($-, a hyphen.) Expands to the current option flags as specified upon
invocation, by the <code>set</code>
builtin command, or those set by the shell itself
(such as the <samp>-i</samp> option).

</dd>
<dt id='index-_0024'><code>$</code><a href='#index-_0024' class='copiable-anchor'> &para;</a></dt>
<dd>
($$) Expands to the process ID of the shell. In a subshell, it
expands to the process ID of the invoking shell, not the subshell.

</dd>
<dt id='index-_0021-1'><code>!</code><a href='#index-_0021-1' class='copiable-anchor'> &para;</a></dt>
<dd>
($!) Expands to the process ID of the job most recently placed into the
background, whether executed as an asynchronous command or using
the <code>bg</code> builtin (see <a href="#Job-Control-Builtins">Job Control Builtins</a>).

</dd>
<dt id='index-0'><code>0</code><a href='#index-0' class='copiable-anchor'> &para;</a></dt>
<dd>
($0) Expands to the name of the shell or shell script. This is set at
shell initialization. If Bash is invoked with a file of commands
(see <a href="#Shell-Scripts">Shell Scripts</a>), <code>$0</code> is set to the name of that file.
If Bash is started with the <samp>-c</samp> option (see <a href="#Invoking-Bash">Invoking Bash</a>),
then <code>$0</code> is set to the first argument after the string to be
executed, if one is present. Otherwise, it is set
to the filename used to invoke Bash, as given by argument zero.
</dd>
</dl>

<hr>
</div>
</div>
<div class="section" id="Shell-Expansions">
<div class="header">

Next: <a href="#Redirections" accesskey="n" rel="next">Redirections</a>, Previous: <a href="#Shell-Parameters" accesskey="p" rel="prev">Shell Parameters</a>, Up: <a href="#Basic-Shell-Features" accesskey="u" rel="up">Basic Shell Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">3.5 Shell Expansions</h3>

Expansion is performed on the command line after it has been split into
<code>token</code>s. There are seven kinds of expansion performed:

<ul>
<li> brace expansion
</li><li> tilde expansion
</li><li> parameter and variable expansion
</li><li> command substitution
</li><li> arithmetic expansion
</li><li> word splitting
</li><li> filename expansion
</li></ul>

The order of expansions is:
brace expansion;
tilde expansion, parameter and variable expansion, arithmetic expansion,
and command substitution (done in a left-to-right fashion);
word splitting;
and filename expansion.

On systems that can support it, there is an additional expansion
available: process substitution.
This is performed at the
same time as tilde, parameter, variable, and arithmetic expansion and
command substitution.

After these expansions are performed, quote characters present in the
original word are removed unless they have been quoted themselves
(quote removal).

Only brace expansion, word splitting, and filename expansion
can increase the number of words of the expansion; other expansions
expand a single word to a single word.
The only exceptions to this are the expansions of
<code>&quot;$@&quot;</code> and <code>$*</code> (see <a href="#Special-Parameters">Special Parameters</a>), and
<code>&quot;${<var>name</var>[@]}&quot;</code> and <code>${<var>name</var>[*]}</code>
(see <a href="#Arrays">Arrays</a>).

After all expansions, <code>quote removal</code> (see <a href="#Quote-Removal">Quote Removal</a>)
is performed.

<ul class="section-toc">
<li><a href="#Brace-Expansion" accesskey="1">Brace Expansion</a></li>
<li><a href="#Tilde-Expansion" accesskey="2">Tilde Expansion</a></li>
<li><a href="#Shell-Parameter-Expansion" accesskey="3">Shell Parameter Expansion</a></li>
<li><a href="#Command-Substitution" accesskey="4">Command Substitution</a></li>
<li><a href="#Arithmetic-Expansion" accesskey="5">Arithmetic Expansion</a></li>
<li><a href="#Process-Substitution" accesskey="6">Process Substitution</a></li>
<li><a href="#Word-Splitting" accesskey="7">Word Splitting</a></li>
<li><a href="#Filename-Expansion" accesskey="8">Filename Expansion</a></li>
<li><a href="#Quote-Removal" accesskey="9">Quote Removal</a></li>
</ul>
<hr>
<div class="subsection" id="Brace-Expansion">
<div class="header">

Next: <a href="#Tilde-Expansion" accesskey="n" rel="next">Tilde Expansion</a>, Up: <a href="#Shell-Expansions" accesskey="u" rel="up">Shell Expansions</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.5.1 Brace Expansion</h4>

Brace expansion is a mechanism by which arbitrary strings may be generated.
This mechanism is similar to
filename expansion (see <a href="#Filename-Expansion">Filename Expansion</a>),
but the filenames generated need not exist.
Patterns to be brace expanded take the form of an optional <var>preamble</var>,
followed by either a series of comma-separated strings or a sequence expression
between a pair of braces,
followed by an optional <var>postscript</var>.
The preamble is prefixed to each string contained within the braces, and
the postscript is then appended to each resulting string, expanding left
to right.

Brace expansions may be nested.
The results of each expanded string are not sorted; left to right order
is preserved.
For example,
<div class="example">
<pre class="example">bash$ echo a{d,c,b}e
ade ace abe
</pre></div>

A sequence expression takes the form <code>{<var>x</var>..<var>y</var>[..<var>incr</var>]}</code>,
where <var>x</var> and <var>y</var> are either integers or letters,
and <var>incr</var>, an optional increment, is an integer.
When integers are supplied, the expression expands to each number between
<var>x</var> and <var>y</var>, inclusive.
Supplied integers may be prefixed with &lsquo;<samp>0</samp>&rsquo; to force each term to have the
same width.
When either <var>x</var> or <var>y</var> begins with a zero, the shell
attempts to force all generated terms to contain the same number of digits,
zero-padding where necessary.
When letters are supplied, the expression expands to each character
lexicographically between <var>x</var> and <var>y</var>, inclusive,
using the default C locale.
Note that both <var>x</var> and <var>y</var> must be of the same type
(integer or letter).
When the increment is supplied, it is used as the difference between
each term. The default increment is 1 or -1 as appropriate.

Brace expansion is performed before any other expansions,
and any characters special to other expansions are preserved
in the result. It is strictly textual. Bash
does not apply any syntactic interpretation to the context of the
expansion or the text between the braces.

A correctly-formed brace expansion must contain unquoted opening
and closing braces, and at least one unquoted comma or a valid
sequence expression.
Any incorrectly formed brace expansion is left unchanged.

A { or &lsquo;<samp>,</samp>&rsquo; may be quoted with a backslash to prevent its
being considered part of a brace expression.
To avoid conflicts with parameter expansion, the string &lsquo;<samp>${</samp>&rsquo;
is not considered eligible for brace expansion,
and inhibits brace expansion until the closing &lsquo;<samp>}</samp>&rsquo;.

This construct is typically used as shorthand when the common
prefix of the strings to be generated is longer than in the
above example:
<div class="example">
<pre class="example">mkdir /usr/local/src/bash/{old,new,dist,bugs}
</pre></div>
or
<div class="example">
<pre class="example">chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}
</pre></div>

<hr>
</div>
<div class="subsection" id="Tilde-Expansion">
<div class="header">

Next: <a href="#Shell-Parameter-Expansion" accesskey="n" rel="next">Shell Parameter Expansion</a>, Previous: <a href="#Brace-Expansion" accesskey="p" rel="prev">Brace Expansion</a>, Up: <a href="#Shell-Expansions" accesskey="u" rel="up">Shell Expansions</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.5.2 Tilde Expansion</h4>

If a word begins with an unquoted tilde character (&lsquo;<samp>~</samp>&rsquo;), all of the
characters up to the first unquoted slash (or all characters,
if there is no unquoted slash) are considered a tilde-prefix.
If none of the characters in the tilde-prefix are quoted, the
characters in the tilde-prefix following the tilde are treated as a
possible login name.
If this login name is the null string, the tilde is replaced with the
value of the <code>HOME</code> shell variable.
If <code>HOME</code> is unset, the home directory of the user executing the
shell is substituted instead.
Otherwise, the tilde-prefix is replaced with the home directory
associated with the specified login name.

If the tilde-prefix is &lsquo;<samp>~+</samp>&rsquo;, the value of
the shell variable <code>PWD</code> replaces the tilde-prefix.
If the tilde-prefix is &lsquo;<samp>~-</samp>&rsquo;, the value of the shell variable
<code>OLDPWD</code>, if it is set, is substituted.

If the characters following the tilde in the tilde-prefix consist of a
number <var>N</var>, optionally prefixed by a &lsquo;<samp>+</samp>&rsquo; or a &lsquo;<samp>-</samp>&rsquo;,
the tilde-prefix is replaced with the
corresponding element from the directory stack, as it would be displayed
by the <code>dirs</code> builtin invoked with the characters following tilde
in the tilde-prefix as an argument (see <a href="#The-Directory-Stack">The Directory Stack</a>).
If the tilde-prefix, sans the tilde, consists of a number without a
leading &lsquo;<samp>+</samp>&rsquo; or &lsquo;<samp>-</samp>&rsquo;, &lsquo;<samp>+</samp>&rsquo; is assumed.

If the login name is invalid, or the tilde expansion fails, the word is
left unchanged.

Each variable assignment is checked for unquoted tilde-prefixes immediately
following a &lsquo;<samp>:</samp>&rsquo; or the first &lsquo;<samp>=</samp>&rsquo;.
In these cases, tilde expansion is also performed.
Consequently, one may use filenames with tildes in assignments to
<code>PATH</code>, <code>MAILPATH</code>, and <code>CDPATH</code>,
and the shell assigns the expanded value.

The following table shows how Bash treats unquoted tilde-prefixes:

<dl compact="compact">
<dt><code>~</code></dt>
<dd>The value of <code>$HOME</code>
</dd>
<dt><code>~/foo</code></dt>
<dd><samp>$HOME/foo</samp>

</dd>
<dt><code>~fred/foo</code></dt>
<dd>The subdirectory <code>foo</code> of the home directory of the user
<code>fred</code>

</dd>
<dt><code>~+/foo</code></dt>
<dd><samp>$PWD/foo</samp>

</dd>
<dt><code>~-/foo</code></dt>
<dd><samp>${OLDPWD-'~-'}/foo</samp>

</dd>
<dt><code>~<var>N</var></code></dt>
<dd>The string that would be displayed by &lsquo;<samp>dirs +<var>N</var></samp>&rsquo;

</dd>
<dt><code>~+<var>N</var></code></dt>
<dd>The string that would be displayed by &lsquo;<samp>dirs +<var>N</var></samp>&rsquo;

</dd>
<dt><code>~-<var>N</var></code></dt>
<dd>The string that would be displayed by &lsquo;<samp>dirs -<var>N</var></samp>&rsquo;
</dd>
</dl>

Bash also performs tilde expansion on words satisfying the conditions of
variable assignments (see <a href="#Shell-Parameters">Shell Parameters</a>)
when they appear as arguments to simple commands.
Bash does not do this, except for the declaration commands listed
above, when in POSIX mode.

<hr>
</div>
<div class="subsection" id="Shell-Parameter-Expansion">
<div class="header">

Next: <a href="#Command-Substitution" accesskey="n" rel="next">Command Substitution</a>, Previous: <a href="#Tilde-Expansion" accesskey="p" rel="prev">Tilde Expansion</a>, Up: <a href="#Shell-Expansions" accesskey="u" rel="up">Shell Expansions</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.5.3 Shell Parameter Expansion</h4>

The &lsquo;<samp>$</samp>&rsquo; character introduces parameter expansion,
command substitution, or arithmetic expansion. The parameter name
or symbol to be expanded may be enclosed in braces, which
are optional but serve to protect the variable to be expanded from
characters immediately following it which could be
interpreted as part of the name.

When braces are used, the matching ending brace is the first &lsquo;<samp>}</samp>&rsquo;
not escaped by a backslash or within a quoted string, and not within an
embedded arithmetic expansion, command substitution, or parameter
expansion.

The basic form of parameter expansion is ${<var>parameter</var>}.
The value of <var>parameter</var> is substituted.
The <var>parameter</var> is a shell parameter as described above
(see <a href="#Shell-Parameters">Shell Parameters</a>) or an array reference (see <a href="#Arrays">Arrays</a>).
The braces are required when <var>parameter</var>
is a positional parameter with more than one digit,
or when <var>parameter</var> is followed by a character that is not to be
interpreted as part of its name.

If the first character of <var>parameter</var> is an exclamation point (!),
and <var>parameter</var> is not a nameref,
it introduces a level of indirection.
Bash uses the value formed by expanding the rest of
<var>parameter</var> as the new <var>parameter</var>; this is then
expanded and that value is used in the rest of the expansion, rather
than the expansion of the original <var>parameter</var>.
This is known as <code>indirect expansion</code>.
The value is subject to tilde expansion,
parameter expansion, command substitution, and arithmetic expansion.
If <var>parameter</var> is a nameref, this expands to the name of the
variable referenced by <var>parameter</var> instead of performing the
complete indirect expansion.
The exceptions to this are the expansions of ${!<var>prefix</var>*}
and ${!<var>name</var>[@]}
described below.
The exclamation point must immediately follow the left brace in order to
introduce indirection.

In each of the cases below, <var>word</var> is subject to tilde expansion,
parameter expansion, command substitution, and arithmetic expansion.

When not performing substring expansion, using the form described
below (e.g., &lsquo;<samp>:-</samp>&rsquo;), Bash tests for a parameter that is unset or null.
Omitting the colon results in a test only for a parameter that is unset.
Put another way, if the colon is included,
the operator tests for both <var>parameter</var>&rsquo;s existence and that its value
is not null; if the colon is omitted, the operator tests only for existence.

<dl compact="compact">
<dt><code>${<var>parameter</var>:-<var>word</var>}</code></dt>
<dd>If <var>parameter</var> is unset or null, the expansion of
<var>word</var> is substituted. Otherwise, the value of
<var>parameter</var> is substituted.

<div class="example">
<pre class="example">$ v=123
$ echo ${v-unset}
123
</pre></div>

</dd>
<dt><code>${<var>parameter</var>:=<var>word</var>}</code></dt>
<dd>If <var>parameter</var>
is unset or null, the expansion of <var>word</var>
is assigned to <var>parameter</var>.
The value of <var>parameter</var> is then substituted. 
Positional parameters and special parameters may not be assigned to
in this way.

<div class="example">
<pre class="example">$ var=
$ : ${var:=DEFAULT}
$ echo $var
DEFAULT
</pre></div>

</dd>
<dt><code>${<var>parameter</var>:?<var>word</var>}</code></dt>
<dd>If <var>parameter</var>
is null or unset, the expansion of <var>word</var> (or a message
to that effect if <var>word</var>
is not present) is written to the standard error and the shell, if it
is not interactive, exits. Otherwise, the value of <var>parameter</var> is
substituted.

<div class="example">
<pre class="example">$ var=
$ : ${var:?var is unset or null}
bash: var: var is unset or null
</pre></div>

</dd>
<dt><code>${<var>parameter</var>:+<var>word</var>}</code></dt>
<dd>If <var>parameter</var>
is null or unset, nothing is substituted, otherwise the expansion of
<var>word</var> is substituted.

<div class="example">
<pre class="example">$ var=123
$ echo ${var:+var is set and not null}
var is set and not null
</pre></div>

</dd>
<dt><code>${<var>parameter</var>:<var>offset</var>}</code></dt>
<dt><code>${<var>parameter</var>:<var>offset</var>:<var>length</var>}</code></dt>
<dd>This is referred to as Substring Expansion.
It expands to up to <var>length</var> characters of the value of <var>parameter</var>
starting at the character specified by <var>offset</var>.
If <var>parameter</var> is &lsquo;<samp>@</samp>&rsquo; or &lsquo;<samp>*</samp>&rsquo;, an indexed array subscripted by
&lsquo;<samp>@</samp>&rsquo; or &lsquo;<samp>*</samp>&rsquo;, or an associative array name, the results differ as
described below.
If <var>length</var> is omitted, it expands to the substring of the value of
<var>parameter</var> starting at the character specified by <var>offset</var>
and extending to the end of the value.
<var>length</var> and <var>offset</var> are arithmetic expressions
(see <a href="#Shell-Arithmetic">Shell Arithmetic</a>).

If <var>offset</var> evaluates to a number less than zero, the value
is used as an offset in characters
from the end of the value of <var>parameter</var>.
If <var>length</var> evaluates to a number less than zero,
it is interpreted as an offset in characters
from the end of the value of <var>parameter</var> rather than
a number of characters, and the expansion is the characters between
<var>offset</var> and that result.
Note that a negative offset must be separated from the colon by at least
one space to avoid being confused with the &lsquo;<samp>:-</samp>&rsquo; expansion.

Here are some examples illustrating substring expansion on parameters and
subscripted arrays:

<pre class="verbatim">$ string=01234567890abcdefgh
$ echo ${string:7}
7890abcdefgh
$ echo ${string:7:0}

$ echo ${string:7:2}
78
$ echo ${string:7:-2}
7890abcdef
$ echo ${string: -7}
bcdefgh
$ echo ${string: -7:0}

$ echo ${string: -7:2}
bc
$ echo ${string: -7:-2}
bcdef
$ set -- 01234567890abcdefgh
$ echo ${1:7}
7890abcdefgh
$ echo ${1:7:0}

$ echo ${1:7:2}
78
$ echo ${1:7:-2}
7890abcdef
$ echo ${1: -7}
bcdefgh
$ echo ${1: -7:0}

$ echo ${1: -7:2}
bc
$ echo ${1: -7:-2}
bcdef
$ array[0]=01234567890abcdefgh
$ echo ${array[0]:7}
7890abcdefgh
$ echo ${array[0]:7:0}

$ echo ${array[0]:7:2}
78
$ echo ${array[0]:7:-2}
7890abcdef
$ echo ${array[0]: -7}
bcdefgh
$ echo ${array[0]: -7:0}

$ echo ${array[0]: -7:2}
bc
$ echo ${array[0]: -7:-2}
bcdef
</pre>
If <var>parameter</var> is &lsquo;<samp>@</samp>&rsquo; or &lsquo;<samp>*</samp>&rsquo;, the result is <var>length</var>
positional parameters beginning at <var>offset</var>.
A negative <var>offset</var> is taken relative to one greater than the greatest
positional parameter, so an offset of -1 evaluates to the last positional
parameter.
It is an expansion error if <var>length</var> evaluates to a number less than zero.

The following examples illustrate substring expansion using positional
parameters:

<pre class="verbatim">$ set -- 1 2 3 4 5 6 7 8 9 0 a b c d e f g h
$ echo ${@:7}
7 8 9 0 a b c d e f g h
$ echo ${@:7:0}

$ echo ${@:7:2}
7 8
$ echo ${@:7:-2}
bash: -2: substring expression &lt; 0
$ echo ${@: -7:2}
b c
$ echo ${@:0}
./bash 1 2 3 4 5 6 7 8 9 0 a b c d e f g h
$ echo ${@:0:2}
./bash 1
$ echo ${@: -7:0}

</pre>
If <var>parameter</var> is an indexed array name subscripted
by &lsquo;<samp>@</samp>&rsquo; or &lsquo;<samp>*</samp>&rsquo;, the result is the <var>length</var>
members of the array beginning with <code>${<var>parameter</var>[<var>offset</var>]}</code>.
A negative <var>offset</var> is taken relative to one greater than the maximum
index of the specified array.
It is an expansion error if <var>length</var> evaluates to a number less than zero.

These examples show how you can use substring expansion with indexed
arrays:

<pre class="verbatim">$ array=(0 1 2 3 4 5 6 7 8 9 0 a b c d e f g h)
$ echo ${array[@]:7}
7 8 9 0 a b c d e f g h
$ echo ${array[@]:7:2}
7 8
$ echo ${array[@]: -7:2}
b c
$ echo ${array[@]: -7:-2}
bash: -2: substring expression &lt; 0
$ echo ${array[@]:0}
0 1 2 3 4 5 6 7 8 9 0 a b c d e f g h
$ echo ${array[@]:0:2}
0 1
$ echo ${array[@]: -7:0}

</pre>
Substring expansion applied to an associative array produces undefined
results.

Substring indexing is zero-based unless the positional parameters
are used, in which case the indexing starts at 1 by default.
If <var>offset</var> is 0, and the positional parameters are used, <code>$0</code> is
prefixed to the list.

</dd>
<dt><code>${!<var>prefix</var>*}</code></dt>
<dt><code>${!<var>prefix</var>@}</code></dt>
<dd>Expands to the names of variables whose names begin with <var>prefix</var>,
separated by the first character of the <code>IFS</code> special variable.
When &lsquo;<samp>@</samp>&rsquo; is used and the expansion appears within double quotes, each
variable name expands to a separate word.

</dd>
<dt><code>${!<var>name</var>[@]}</code></dt>
<dt><code>${!<var>name</var>[*]}</code></dt>
<dd>If <var>name</var> is an array variable, expands to the list of array indices
(keys) assigned in <var>name</var>.
If <var>name</var> is not an array, expands to 0 if <var>name</var> is set and null
otherwise.
When &lsquo;<samp>@</samp>&rsquo; is used and the expansion appears within double quotes, each
key expands to a separate word.

</dd>
<dt><code>${#<var>parameter</var>}</code></dt>
<dd>The length in characters of the expanded value of <var>parameter</var> is
substituted.
If <var>parameter</var> is &lsquo;<samp>*</samp>&rsquo; or &lsquo;<samp>@</samp>&rsquo;, the value substituted
is the number of positional parameters.
If <var>parameter</var> is an array name subscripted by &lsquo;<samp>*</samp>&rsquo; or &lsquo;<samp>@</samp>&rsquo;, 
the value substituted is the number of elements in the array.
If <var>parameter</var>
is an indexed array name subscripted by a negative number, that number is
interpreted as relative to one greater than the maximum index of
<var>parameter</var>, so negative indices count back from the end of the
array, and an index of -1 references the last element.

</dd>
<dt><code>${<var>parameter</var>#<var>word</var>}</code></dt>
<dt><code>${<var>parameter</var>##<var>word</var>}</code></dt>
<dd>The <var>word</var>
is expanded to produce a pattern and matched according to the rules
described below (see <a href="#Pattern-Matching">Pattern Matching</a>). If the pattern matches
the beginning of the expanded value of <var>parameter</var>,
then the result of the expansion is the expanded value of <var>parameter</var>
with the shortest matching pattern (the &lsquo;<samp>#</samp>&rsquo; case) or the
longest matching pattern (the &lsquo;<samp>##</samp>&rsquo; case) deleted.
If <var>parameter</var> is &lsquo;<samp>@</samp>&rsquo; or &lsquo;<samp>*</samp>&rsquo;,
the pattern removal operation is applied to each positional
parameter in turn, and the expansion is the resultant list.
If <var>parameter</var> is an array variable subscripted with
&lsquo;<samp>@</samp>&rsquo; or &lsquo;<samp>*</samp>&rsquo;,
the pattern removal operation is applied to each member of the
array in turn, and the expansion is the resultant list.

</dd>
<dt><code>${<var>parameter</var>%<var>word</var>}</code></dt>
<dt><code>${<var>parameter</var>%%<var>word</var>}</code></dt>
<dd>The <var>word</var>
is expanded to produce a pattern and matched according to the rules
described below (see <a href="#Pattern-Matching">Pattern Matching</a>).
If the pattern matches a trailing portion of the expanded value of
<var>parameter</var>, then the result of the expansion is the value of
<var>parameter</var> with the shortest matching pattern (the &lsquo;<samp>%</samp>&rsquo; case)
or the longest matching pattern (the &lsquo;<samp>%%</samp>&rsquo; case) deleted.
If <var>parameter</var> is &lsquo;<samp>@</samp>&rsquo; or &lsquo;<samp>*</samp>&rsquo;,
the pattern removal operation is applied to each positional
parameter in turn, and the expansion is the resultant list.
If <var>parameter</var>
is an array variable subscripted with &lsquo;<samp>@</samp>&rsquo; or &lsquo;<samp>*</samp>&rsquo;,
the pattern removal operation is applied to each member of the
array in turn, and the expansion is the resultant list.

</dd>
<dt><code>${<var>parameter</var>/<var>pattern</var>/<var>string</var>}</code></dt>
<dt><code>${<var>parameter</var>//<var>pattern</var>/<var>string</var>}</code></dt>
<dt><code>${<var>parameter</var>/#<var>pattern</var>/<var>string</var>}</code></dt>
<dt><code>${<var>parameter</var>/%<var>pattern</var>/<var>string</var>}</code></dt>
<dd>The <var>pattern</var> is expanded to produce a pattern just as in
filename expansion.
<var>Parameter</var> is expanded and the longest match of <var>pattern</var>
against its value is replaced with <var>string</var>.
<var>string</var> undergoes tilde expansion, parameter and variable expansion,
arithmetic expansion, command and process substitution, and quote removal.
The match is performed according to the rules described below
(see <a href="#Pattern-Matching">Pattern Matching</a>).

In the first form above, only the first match is replaced.
If there are two slashes separating <var>parameter</var> and <var>pattern</var>
(the second form above), all matches of <var>pattern</var> are
replaced with <var>string</var>.
If <var>pattern</var> is preceded by &lsquo;<samp>#</samp>&rsquo; (the third form above),
it must match at the beginning of the expanded value of <var>parameter</var>.
If <var>pattern</var> is preceded by &lsquo;<samp>%</samp>&rsquo; (the fourth form above),
it must match at the end of the expanded value of <var>parameter</var>.
If the expansion of <var>string</var> is null,
matches of <var>pattern</var> are deleted.
If <var>string</var> is null,
matches of <var>pattern</var> are deleted
and the &lsquo;<samp>/</samp>&rsquo; following <var>pattern</var> may be omitted.

If the <code>patsub_replacement</code> shell option is enabled using <code>shopt</code>,
any unquoted instances of &lsquo;<samp>&amp;</samp>&rsquo; in <var>string</var> are replaced with the
matching portion of <var>pattern</var>.
This is intended to duplicate a common <code>sed</code> idiom.

Quoting any part of <var>string</var> inhibits replacement in the
expansion of the quoted portion, including replacement strings stored
in shell variables.
Backslash will escape &lsquo;<samp>&amp;</samp>&rsquo; in <var>string</var>; the backslash is removed
in order to permit a literal &lsquo;<samp>&amp;</samp>&rsquo; in the replacement string.
Users should take care if <var>string</var> is double-quoted to avoid
unwanted interactions between the backslash and double-quoting, since
backslash has special meaning within double quotes.
Pattern substitution performs the check for unquoted &lsquo;<samp>&amp;</samp>&rsquo; after
expanding <var>string</var>,
so users should ensure to properly quote any occurrences of &lsquo;<samp>&amp;</samp>&rsquo;
they want to be taken literally in the replacement
and ensure any instances of &lsquo;<samp>&amp;</samp>&rsquo; they want to be replaced are unquoted.

For instance,

<div class="example">
<pre class="example">var=abcdef
rep='&amp; '
echo ${var/abc/&amp; }
echo &quot;${var/abc/&amp; }&quot;
echo ${var/abc/$rep}
echo &quot;${var/abc/$rep}&quot;
</pre></div>

will display four lines of &quot;abc def&quot;, while

<div class="example">
<pre class="example">var=abcdef
rep='&amp; '
echo ${var/abc/\&amp; }
echo &quot;${var/abc/\&amp; }&quot;
echo ${var/abc/&quot;&amp; &quot;}
echo ${var/abc/&quot;$rep&quot;}
</pre></div>

will display four lines of &quot;&amp; def&quot;.
Like the pattern removal operators, double quotes surrounding the
replacement string quote the expanded characters, while double quotes
enclosing the entire parameter substitution do not, since
the expansion is performed in a
context that doesn&rsquo;t take any enclosing double quotes into account.

Since backslash can escape &lsquo;<samp>&amp;</samp>&rsquo;, it can also escape a backslash in
the replacement string.
This means that &lsquo;<samp>\\</samp>&rsquo; will insert a literal
backslash into the replacement, so these two <code>echo</code> commands

<div class="example">
<pre class="example">var=abcdef
rep='\\&amp;xyz'
echo ${var/abc/\\&amp;xyz}
echo ${var/abc/$rep}
</pre></div>

will both output &lsquo;<samp>\abcxyzdef</samp>&rsquo;.

It should rarely be necessary to enclose only <var>string</var> in double
quotes.

If the <code>nocasematch</code> shell option 
(see the description of <code>shopt</code> in <a href="#The-Shopt-Builtin">The Shopt Builtin</a>)
is enabled, the match is performed without regard to the case 
of alphabetic characters.
If <var>parameter</var> is &lsquo;<samp>@</samp>&rsquo; or &lsquo;<samp>*</samp>&rsquo;,
the substitution operation is applied to each positional
parameter in turn, and the expansion is the resultant list.
If <var>parameter</var>
is an array variable subscripted with &lsquo;<samp>@</samp>&rsquo; or &lsquo;<samp>*</samp>&rsquo;,
the substitution operation is applied to each member of the
array in turn, and the expansion is the resultant list.

</dd>
<dt><code>${<var>parameter</var>^<var>pattern</var>}</code></dt>
<dt><code>${<var>parameter</var>^^<var>pattern</var>}</code></dt>
<dt><code>${<var>parameter</var>,<var>pattern</var>}</code></dt>
<dt><code>${<var>parameter</var>,,<var>pattern</var>}</code></dt>
<dd>This expansion modifies the case of alphabetic characters in <var>parameter</var>.
The <var>pattern</var> is expanded to produce a pattern just as in
filename expansion.
Each character in the expanded value of <var>parameter</var> is tested against
<var>pattern</var>, and, if it matches the pattern, its case is converted.
The pattern should not attempt to match more than one character.

The &lsquo;<samp>^</samp>&rsquo; operator converts lowercase letters matching <var>pattern</var>
to uppercase; the &lsquo;<samp>,</samp>&rsquo; operator converts matching uppercase letters
to lowercase.
The &lsquo;<samp>^^</samp>&rsquo; and &lsquo;<samp>,,</samp>&rsquo; expansions convert each matched character in the
expanded value; the &lsquo;<samp>^</samp>&rsquo; and &lsquo;<samp>,</samp>&rsquo; expansions match and convert only
the first character in the expanded value.
If <var>pattern</var> is omitted, it is treated like a &lsquo;<samp>?</samp>&rsquo;, which matches
every character.

If <var>parameter</var> is &lsquo;<samp>@</samp>&rsquo; or &lsquo;<samp>*</samp>&rsquo;,
the case modification operation is applied to each positional
parameter in turn, and the expansion is the resultant list.
If <var>parameter</var>
is an array variable subscripted with &lsquo;<samp>@</samp>&rsquo; or &lsquo;<samp>*</samp>&rsquo;,
the case modification operation is applied to each member of the
array in turn, and the expansion is the resultant list.

</dd>
<dt><code>${<var>parameter</var>@<var>operator</var>}</code></dt>
<dd>The expansion is either a transformation of the value of <var>parameter</var>
or information about <var>parameter</var> itself, depending on the value of
<var>operator</var>. Each <var>operator</var> is a single letter:

<dl compact="compact">
<dt><code>U</code></dt>
<dd>The expansion is a string that is the value of <var>parameter</var> with lowercase
alphabetic characters converted to uppercase.
</dd>
<dt><code>u</code></dt>
<dd>The expansion is a string that is the value of <var>parameter</var> with the first
character converted to uppercase, if it is alphabetic.
</dd>
<dt><code>L</code></dt>
<dd>The expansion is a string that is the value of <var>parameter</var> with uppercase
alphabetic characters converted to lowercase.
</dd>
<dt><code>Q</code></dt>
<dd>The expansion is a string that is the value of <var>parameter</var> quoted in a
format that can be reused as input.
</dd>
<dt><code>E</code></dt>
<dd>The expansion is a string that is the value of <var>parameter</var> with backslash
escape sequences expanded as with the <code>$'&hellip;'</code> quoting mechanism.
</dd>
<dt><code>P</code></dt>
<dd>The expansion is a string that is the result of expanding the value of
<var>parameter</var> as if it were a prompt string (see <a href="#Controlling-the-Prompt">Controlling the Prompt</a>).
</dd>
<dt><code>A</code></dt>
<dd>The expansion is a string in the form of
an assignment statement or <code>declare</code> command that, if
evaluated, will recreate <var>parameter</var> with its attributes and value.
</dd>
<dt><code>K</code></dt>
<dd>Produces a possibly-quoted version of the value of <var>parameter</var>,
except that it prints the values of
indexed and associative arrays as a sequence of quoted key-value pairs
(see <a href="#Arrays">Arrays</a>).
</dd>
<dt><code>a</code></dt>
<dd>The expansion is a string consisting of flag values representing
<var>parameter</var>&rsquo;s attributes.
</dd>
<dt><code>k</code></dt>
<dd>Like the &lsquo;<samp>K</samp>&rsquo; transformation, but expands the keys and values of
indexed and associative arrays to separate words after word splitting.
</dd>
</dl>

If <var>parameter</var> is &lsquo;<samp>@</samp>&rsquo; or &lsquo;<samp>*</samp>&rsquo;,
the operation is applied to each positional
parameter in turn, and the expansion is the resultant list.
If <var>parameter</var>
is an array variable subscripted with &lsquo;<samp>@</samp>&rsquo; or &lsquo;<samp>*</samp>&rsquo;,
the operation is applied to each member of the
array in turn, and the expansion is the resultant list.

The result of the expansion is subject to word splitting and filename
expansion as described below.
</dd>
</dl>

<hr>
</div>
<div class="subsection" id="Command-Substitution">
<div class="header">

Next: <a href="#Arithmetic-Expansion" accesskey="n" rel="next">Arithmetic Expansion</a>, Previous: <a href="#Shell-Parameter-Expansion" accesskey="p" rel="prev">Shell Parameter Expansion</a>, Up: <a href="#Shell-Expansions" accesskey="u" rel="up">Shell Expansions</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.5.4 Command Substitution</h4>

Command substitution allows the output of a command to replace
the command itself.
Command substitution occurs when a command is enclosed as follows:
<div class="example">
<pre class="example">$(<var>command</var>)
</pre></div>
or
<div class="example">
<pre class="example">`<var>command</var>`
</pre></div>

Bash performs the expansion by executing <var>command</var> in a subshell environment
and replacing the command substitution with the standard output of the
command, with any trailing newlines deleted.
Embedded newlines are not deleted, but they may be removed during
word splitting.
The command substitution <code>$(cat <var>file</var>)</code> can be
replaced by the equivalent but faster <code>$(&lt; <var>file</var>)</code>.

When the old-style backquote form of substitution is used,
backslash retains its literal meaning except when followed by
&lsquo;<samp>$</samp>&rsquo;, &lsquo;<samp>`</samp>&rsquo;, or &lsquo;<samp>\</samp>&rsquo;. 
The first backquote not preceded by a backslash terminates the
command substitution.
When using the <code>$(<var>command</var>)</code> form, all characters between
the parentheses make up the command; none are treated specially.

Command substitutions may be nested. To nest when using the backquoted
form, escape the inner backquotes with backslashes.

If the substitution appears within double quotes, word splitting and
filename expansion are not performed on the results.

<hr>
</div>
<div class="subsection" id="Arithmetic-Expansion">
<div class="header">

Next: <a href="#Process-Substitution" accesskey="n" rel="next">Process Substitution</a>, Previous: <a href="#Command-Substitution" accesskey="p" rel="prev">Command Substitution</a>, Up: <a href="#Shell-Expansions" accesskey="u" rel="up">Shell Expansions</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.5.5 Arithmetic Expansion</h4>

Arithmetic expansion allows the evaluation of an arithmetic expression
and the substitution of the result. The format for arithmetic expansion is:

<div class="example">
<pre class="example">$(( <var>expression</var> ))
</pre></div>

The <var>expression</var> undergoes the same expansions
as if it were within double quotes,
but double quote characters in <var>expression</var> are not treated specially
and are removed.
All tokens in the expression undergo parameter and variable expansion,
command substitution, and quote removal.
The result is treated as the arithmetic expression to be evaluated.
Arithmetic expansions may be nested. 

The evaluation is performed according to the rules listed below
(see <a href="#Shell-Arithmetic">Shell Arithmetic</a>).
If the expression is invalid, Bash prints a message indicating
failure to the standard error and no substitution occurs.

<hr>
</div>
<div class="subsection" id="Process-Substitution">
<div class="header">

Next: <a href="#Word-Splitting" accesskey="n" rel="next">Word Splitting</a>, Previous: <a href="#Arithmetic-Expansion" accesskey="p" rel="prev">Arithmetic Expansion</a>, Up: <a href="#Shell-Expansions" accesskey="u" rel="up">Shell Expansions</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.5.6 Process Substitution</h4>

Process substitution allows a process&rsquo;s input or output to be
referred to using a filename.
It takes the form of 
<div class="example">
<pre class="example">&lt;(<var>list</var>)
</pre></div>
or
<div class="example">
<pre class="example">&gt;(<var>list</var>)
</pre></div>
The process <var>list</var> is run asynchronously, and its input or output 
appears as a filename.
This filename is
passed as an argument to the current command as the result of the
expansion.
If the <code>&gt;(<var>list</var>)</code> form is used, writing to
the file will provide input for <var>list</var>. If the
<code>&lt;(<var>list</var>)</code> form is used, the file passed as an
argument should be read to obtain the output of <var>list</var>.
Note that no space may appear between the <code>&lt;</code> or <code>&gt;</code>
and the left parenthesis, otherwise the construct would be interpreted
as a redirection.
Process substitution is supported on systems that support named
pipes (FIFOs) or the <samp>/dev/fd</samp> method of naming open files.

When available, process substitution is performed simultaneously with
parameter and variable expansion, command substitution, and arithmetic
expansion.

<hr>
</div>
<div class="subsection" id="Word-Splitting">
<div class="header">

Next: <a href="#Filename-Expansion" accesskey="n" rel="next">Filename Expansion</a>, Previous: <a href="#Process-Substitution" accesskey="p" rel="prev">Process Substitution</a>, Up: <a href="#Shell-Expansions" accesskey="u" rel="up">Shell Expansions</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.5.7 Word Splitting</h4>

The shell scans the results of parameter expansion, command substitution,
and arithmetic expansion that did not occur within double quotes for
word splitting.

The shell treats each character of <code>$IFS</code> as a delimiter, and splits
the results of the other expansions into words using these characters
as field terminators.
If <code>IFS</code> is unset, or its value is exactly <code>&lt;space&gt;&lt;tab&gt;&lt;newline&gt;</code>,
the default, then sequences of
<code> &lt;space&gt;</code>, <code>&lt;tab&gt;</code>, and <code>&lt;newline&gt;</code>
at the beginning and end of the results of the previous
expansions are ignored, and any sequence of <code>IFS</code>
characters not at the beginning or end serves to delimit words.
If <code>IFS</code> has a value other than the default, then sequences of
the whitespace characters <code>space</code>, <code>tab</code>, and <code>newline</code>
are ignored at the beginning and end of the
word, as long as the whitespace character is in the
value of <code>IFS</code> (an <code>IFS</code> whitespace character).
Any character in <code>IFS</code> that is not <code>IFS</code>
whitespace, along with any adjacent <code>IFS</code>
whitespace characters, delimits a field. A sequence of <code>IFS</code>
whitespace characters is also treated as a delimiter.
If the value of <code>IFS</code> is null, no word splitting occurs.

Explicit null arguments (<code>&quot;&quot;</code> or <code>''</code>) are retained
and passed to commands as empty strings.
Unquoted implicit null arguments, resulting from the expansion of
parameters that have no values, are removed.
If a parameter with no value is expanded within double quotes, a
null argument results and is retained
and passed to a command as an empty string.
When a quoted null argument appears as part of a word whose expansion is
non-null, the null argument is removed.
That is, the word
<code>-d''</code> becomes <code>-d</code> after word splitting and
null argument removal.

Note that if no expansion occurs, no splitting
is performed.

<hr>
</div>
<div class="subsection" id="Filename-Expansion">
<div class="header">

Next: <a href="#Quote-Removal" accesskey="n" rel="next">Quote Removal</a>, Previous: <a href="#Word-Splitting" accesskey="p" rel="prev">Word Splitting</a>, Up: <a href="#Shell-Expansions" accesskey="u" rel="up">Shell Expansions</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.5.8 Filename Expansion</h4>

After word splitting, unless the <samp>-f</samp> option has been set
(see <a href="#The-Set-Builtin">The Set Builtin</a>), Bash scans each word for the characters
&lsquo;<samp>*</samp>&rsquo;, &lsquo;<samp>?</samp>&rsquo;, and &lsquo;<samp>[</samp>&rsquo;.
If one of these characters appears, and is not quoted, then the word is
regarded as a <var>pattern</var>,
and replaced with an alphabetically sorted list of
filenames matching the pattern (see <a href="#Pattern-Matching">Pattern Matching</a>).
If no matching filenames are found,
and the shell option <code>nullglob</code> is disabled, the word is left
unchanged.
If the <code>nullglob</code> option is set, and no matches are found, the word
is removed.
If the <code>failglob</code> shell option is set, and no matches are found,
an error message is printed and the command is not executed.
If the shell option <code>nocaseglob</code> is enabled, the match is performed
without regard to the case of alphabetic characters.

When a pattern is used for filename expansion, the character &lsquo;<samp>.</samp>&rsquo;
at the start of a filename or immediately following a slash
must be matched explicitly, unless the shell option <code>dotglob</code> is set.
In order to match the filenames &lsquo;<samp>.</samp>&rsquo; and &lsquo;<samp>..</samp>&rsquo;,
the pattern must begin with &lsquo;<samp>.</samp>&rsquo; (for example, &lsquo;<samp>.?</samp>&rsquo;),
even if <code>dotglob</code> is set.
If the <code>globskipdots</code> shell option is enabled, the filenames
&lsquo;<samp>.</samp>&rsquo; and &lsquo;<samp>..</samp>&rsquo; are never matched, even if the pattern begins
with a &lsquo;<samp>.</samp>&rsquo;.
When not matching filenames, the &lsquo;<samp>.</samp>&rsquo; character is not treated specially.

When matching a filename, the slash character must always be
matched explicitly by a slash in the pattern, but in other matching
contexts it can be matched by a special pattern character as described
below (see <a href="#Pattern-Matching">Pattern Matching</a>).

See the description of <code>shopt</code> in <a href="#The-Shopt-Builtin">The Shopt Builtin</a>,
for a description of the <code>nocaseglob</code>, <code>nullglob</code>,
<code>globskipdots</code>,
<code>failglob</code>, and <code>dotglob</code> options.

The <code>GLOBIGNORE</code>
shell variable may be used to restrict the set of file names matching a
pattern. If <code>GLOBIGNORE</code>
is set, each matching file name that also matches one of the patterns in
<code>GLOBIGNORE</code> is removed from the list of matches.
If the <code>nocaseglob</code> option is set, the matching against the patterns in
<code>GLOBIGNORE</code> is performed without regard to case.
The filenames
<samp>.</samp> and <samp>..</samp>
are always ignored when <code>GLOBIGNORE</code>
is set and not null.
However, setting <code>GLOBIGNORE</code> to a non-null value has the effect of
enabling the <code>dotglob</code>
shell option, so all other filenames beginning with a
&lsquo;<samp>.</samp>&rsquo; will match.
To get the old behavior of ignoring filenames beginning with a
&lsquo;<samp>.</samp>&rsquo;, make &lsquo;<samp>.*</samp>&rsquo; one of the patterns in <code>GLOBIGNORE</code>.
The <code>dotglob</code> option is disabled when <code>GLOBIGNORE</code>
is unset.

<ul class="section-toc">
<li><a href="#Pattern-Matching" accesskey="1">Pattern Matching</a></li>
</ul>
<hr>
<div class="subsubsection" id="Pattern-Matching">
<div class="header">

Up: <a href="#Filename-Expansion" accesskey="u" rel="up">Filename Expansion</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsubsection">3.5.8.1 Pattern Matching</h4>

Any character that appears in a pattern, other than the special pattern
characters described below, matches itself.
The NUL character may not occur in a pattern.
A backslash escapes the following character; the
escaping backslash is discarded when matching.
The special pattern characters must be quoted if they are to be matched
literally.

The special pattern characters have the following meanings:
<dl compact="compact">
<dt><code>*</code></dt>
<dd>Matches any string, including the null string.
When the <code>globstar</code> shell option is enabled, and &lsquo;<samp>*</samp>&rsquo; is used in
a filename expansion context, two adjacent &lsquo;<samp>*</samp>&rsquo;s used as a single
pattern will match all files and zero or more directories and
subdirectories.
If followed by a &lsquo;<samp>/</samp>&rsquo;, two adjacent &lsquo;<samp>*</samp>&rsquo;s will match only
directories and subdirectories.
</dd>
<dt><code>?</code></dt>
<dd>Matches any single character.
</dd>
<dt><code>[&hellip;]</code></dt>
<dd>Matches any one of the enclosed characters. A pair of characters
separated by a hyphen denotes a <var>range expression</var>;
any character that falls between those two characters, inclusive,
using the current locale&rsquo;s collating sequence and character set,
is matched. If the first character following the
&lsquo;<samp>[</samp>&rsquo; is a &lsquo;<samp>!</samp>&rsquo; or a &lsquo;<samp>^</samp>&rsquo;
then any character not enclosed is matched. A &lsquo;<samp>-</samp>&rsquo;
may be matched by including it as the first or last character
in the set. A &lsquo;<samp>]</samp>&rsquo; may be matched by including it as the first
character in the set.
The sorting order of characters in range expressions,
and the characters included in the range,
are determined by
the current locale and the values of the
<code>LC_COLLATE</code> and <code>LC_ALL</code> shell variables, if set.

For example, in the default C locale, &lsquo;<samp>[a-dx-z]</samp>&rsquo; is equivalent to
&lsquo;<samp>[abcdxyz]</samp>&rsquo;. Many locales sort characters in dictionary order, and in
these locales &lsquo;<samp>[a-dx-z]</samp>&rsquo; is typically not equivalent to &lsquo;<samp>[abcdxyz]</samp>&rsquo;;
it might be equivalent to &lsquo;<samp>[aBbCcDdxYyZz]</samp>&rsquo;, for example. To obtain
the traditional interpretation of ranges in bracket expressions, you can
force the use of the C locale by setting the <code>LC_COLLATE</code> or
<code>LC_ALL</code> environment variable to the value &lsquo;<samp>C</samp>&rsquo;, or enable the
<code>globasciiranges</code> shell option.

Within &lsquo;<samp>[</samp>&rsquo; and &lsquo;<samp>]</samp>&rsquo;, character classes can be specified
using the syntax
<code>[:</code><var>class</var><code>:]</code>, where <var>class</var> is one of the
following classes defined in the POSIX standard:
<div class="example">
<pre class="example">alnum alpha ascii blank cntrl digit graph lower
print punct space upper word xdigit
</pre></div>
A character class matches any character belonging to that class.
The <code>word</code> character class matches letters, digits, and the character
&lsquo;<samp>_</samp>&rsquo;.

Within &lsquo;<samp>[</samp>&rsquo; and &lsquo;<samp>]</samp>&rsquo;, an equivalence class can be
specified using the syntax <code>[=</code><var>c</var><code>=]</code>, which
matches all characters with the same collation weight (as defined
by the current locale) as the character <var>c</var>.

Within &lsquo;<samp>[</samp>&rsquo; and &lsquo;<samp>]</samp>&rsquo;, the syntax <code>[.</code><var>symbol</var><code>.]</code>
matches the collating symbol <var>symbol</var>.
</dd>
</dl>

If the <code>extglob</code> shell option is enabled using the <code>shopt</code>
builtin, the shell recognizes several extended pattern matching operators.
In the following description, a <var>pattern-list</var> is a list of one
or more patterns separated by a &lsquo;<samp>|</samp>&rsquo;.
When matching filenames, the <code>dotglob</code> shell option determines
the set of filenames that are tested, as described above.
Composite patterns may be formed using one or more of the following
sub-patterns:

<dl compact="compact">
<dt><code>?(<var>pattern-list</var>)</code></dt>
<dd>Matches zero or one occurrence of the given patterns.

</dd>
<dt><code>*(<var>pattern-list</var>)</code></dt>
<dd>Matches zero or more occurrences of the given patterns.

</dd>
<dt><code>+(<var>pattern-list</var>)</code></dt>
<dd>Matches one or more occurrences of the given patterns.

</dd>
<dt><code>@(<var>pattern-list</var>)</code></dt>
<dd>Matches one of the given patterns.

</dd>
<dt><code>!(<var>pattern-list</var>)</code></dt>
<dd>Matches anything except one of the given patterns.
</dd>
</dl>

The <code>extglob</code> option changes the behavior of the parser, since the
parentheses are normally treated as operators with syntactic meaning.
To ensure that extended matching patterns are parsed correctly, make sure
that <code>extglob</code> is enabled before parsing constructs containing the
patterns, including shell functions and command substitutions.

When matching filenames, the <code>dotglob</code> shell option determines
the set of filenames that are tested:
when <code>dotglob</code> is enabled, the set of filenames includes all files
beginning with &lsquo;<samp>.</samp>&rsquo;, but the filenames
&lsquo;<samp>.</samp>&rsquo; and &lsquo;<samp>..</samp>&rsquo; must be matched by a
pattern or sub-pattern that begins with a dot;
when it is disabled, the set does not
include any filenames beginning with &ldquo;.&rdquo; unless the pattern
or sub-pattern begins with a &lsquo;<samp>.</samp>&rsquo;.
As above, &lsquo;<samp>.</samp>&rsquo; only has a special meaning when matching filenames. 

Complicated extended pattern matching against long strings is slow,
especially when the patterns contain alternations and the strings
contain multiple matches.
Using separate matches against shorter strings, or using arrays of
strings instead of a single long string, may be faster.

<hr>
</div>
</div>
<div class="subsection" id="Quote-Removal">
<div class="header">

Previous: <a href="#Filename-Expansion" accesskey="p" rel="prev">Filename Expansion</a>, Up: <a href="#Shell-Expansions" accesskey="u" rel="up">Shell Expansions</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.5.9 Quote Removal</h4>

After the preceding expansions, all unquoted occurrences of the
characters &lsquo;<samp>\</samp>&rsquo;, &lsquo;<samp>'</samp>&rsquo;, and &lsquo;<samp>&quot;</samp>&rsquo; that did not
result from one of the above expansions are removed.

<hr>
</div>
</div>
<div class="section" id="Redirections">
<div class="header">

Next: <a href="#Executing-Commands" accesskey="n" rel="next">Executing Commands</a>, Previous: <a href="#Shell-Expansions" accesskey="p" rel="prev">Shell Expansions</a>, Up: <a href="#Basic-Shell-Features" accesskey="u" rel="up">Basic Shell Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">3.6 Redirections</h3>

Before a command is executed, its input and output
may be redirected
using a special notation interpreted by the shell.
Redirection allows commands&rsquo; file handles to be
duplicated, opened, closed,
made to refer to different files,
and can change the files the command reads from and writes to.
Redirection may also be used to modify file handles in the
current shell execution environment. The following redirection
operators may precede or appear anywhere within a
simple command or may follow a command.
Redirections are processed in the order they appear, from
left to right.

Each redirection that may be preceded by a file descriptor number
may instead be preceded by a word of the form {<var>varname</var>}.
In this case, for each redirection operator except
&gt;&amp;- and &lt;&amp;-, the shell will allocate a file descriptor greater
than 10 and assign it to {<var>varname</var>}. If &gt;&amp;- or &lt;&amp;- is preceded
by {<var>varname</var>}, the value of <var>varname</var> defines the file
descriptor to close.
If {<var>varname</var>} is supplied, the redirection persists beyond
the scope of the command, allowing the shell programmer to manage
the file descriptor&rsquo;s lifetime manually.
The <code>varredir_close</code> shell option manages this behavior
(see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>).

In the following descriptions, if the file descriptor number is
omitted, and the first character of the redirection operator is
&lsquo;<samp>&lt;</samp>&rsquo;, the redirection refers to the standard input (file
descriptor 0). If the first character of the redirection operator
is &lsquo;<samp>&gt;</samp>&rsquo;, the redirection refers to the standard output (file
descriptor 1).

The word following the redirection operator in the following
descriptions, unless otherwise noted, is subjected to brace expansion,
tilde expansion, parameter expansion, command substitution, arithmetic
expansion, quote removal, filename expansion, and word splitting.
If it expands to more than one word, Bash reports an error.

Note that the order of redirections is significant. For example,
the command
<div class="example">
<pre class="example">ls &gt; <var>dirlist</var> 2&gt;&amp;1
</pre></div>
directs both standard output (file descriptor 1) and standard error
(file descriptor 2) to the file <var>dirlist</var>, while the command
<div class="example">
<pre class="example">ls 2&gt;&amp;1 &gt; <var>dirlist</var>
</pre></div>
directs only the standard output to file <var>dirlist</var>,
because the standard error was made a copy of the standard output
before the standard output was redirected to <var>dirlist</var>.

Bash handles several filenames specially when they are used in
redirections, as described in the following table.
If the operating system on which Bash is running provides these
special files, bash will use them; otherwise it will emulate them
internally with the behavior described below.

<dl compact="compact">
<dt><code>/dev/fd/<var>fd</var></code></dt>
<dd>If <var>fd</var> is a valid integer, file descriptor <var>fd</var> is duplicated.

</dd>
<dt><code>/dev/stdin</code></dt>
<dd>File descriptor 0 is duplicated.

</dd>
<dt><code>/dev/stdout</code></dt>
<dd>File descriptor 1 is duplicated.

</dd>
<dt><code>/dev/stderr</code></dt>
<dd>File descriptor 2 is duplicated.

</dd>
<dt><code>/dev/tcp/<var>host</var>/<var>port</var></code></dt>
<dd>If <var>host</var> is a valid hostname or Internet address, and <var>port</var>
is an integer port number or service name, Bash attempts to open
the corresponding TCP socket.

</dd>
<dt><code>/dev/udp/<var>host</var>/<var>port</var></code></dt>
<dd>If <var>host</var> is a valid hostname or Internet address, and <var>port</var>
is an integer port number or service name, Bash attempts to open 
the corresponding UDP socket.
</dd>
</dl>

A failure to open or create a file causes the redirection to fail.

Redirections using file descriptors greater than 9 should be used with
care, as they may conflict with file descriptors the shell uses
internally.

<ul class="section-toc">
<li><a href="#Redirecting-Input" accesskey="1">Redirecting Input</a></li>
<li><a href="#Redirecting-Output" accesskey="2">Redirecting Output</a></li>
<li><a href="#Appending-Redirected-Output" accesskey="3">Appending Redirected Output</a></li>
<li><a href="#Redirecting-Standard-Output-and-Standard-Error" accesskey="4">Redirecting Standard Output and Standard Error</a></li>
<li><a href="#Appending-Standard-Output-and-Standard-Error" accesskey="5">Appending Standard Output and Standard Error</a></li>
<li><a href="#Here-Documents" accesskey="6">Here Documents</a></li>
<li><a href="#Here-Strings" accesskey="7">Here Strings</a></li>
<li><a href="#Duplicating-File-Descriptors" accesskey="8">Duplicating File Descriptors</a></li>
<li><a href="#Moving-File-Descriptors" accesskey="9">Moving File Descriptors</a></li>
<li><a href="#Opening-File-Descriptors-for-Reading-and-Writing">Opening File Descriptors for Reading and Writing</a></li>
</ul>
<div class="subsection" id="Redirecting-Input">
<h4 class="subsection">3.6.1 Redirecting Input</h4>
Redirection of input causes the file whose name results from
the expansion of <var>word</var>
to be opened for reading on file descriptor <code>n</code>,
or the standard input (file descriptor 0) if <code>n</code>
is not specified.

The general format for redirecting input is:
<div class="example">
<pre class="example">[<var>n</var>]&lt;<var>word</var>
</pre></div>

</div>
<div class="subsection" id="Redirecting-Output">
<h4 class="subsection">3.6.2 Redirecting Output</h4>
Redirection of output causes the file whose name results from
the expansion of <var>word</var>
to be opened for writing on file descriptor <var>n</var>,
or the standard output (file descriptor 1) if <var>n</var>
is not specified. If the file does not exist it is created;
if it does exist it is truncated to zero size.

The general format for redirecting output is:
<div class="example">
<pre class="example">[<var>n</var>]&gt;[|]<var>word</var>
</pre></div>

If the redirection operator is &lsquo;<samp>&gt;</samp>&rsquo;, and the <code>noclobber</code>
option to the <code>set</code> builtin has been enabled, the redirection
will fail if the file whose name results from the expansion of
<var>word</var> exists and is a regular file.
If the redirection operator is &lsquo;<samp>&gt;|</samp>&rsquo;, or the redirection operator is
&lsquo;<samp>&gt;</samp>&rsquo; and the <code>noclobber</code> option is not enabled, the redirection
is attempted even if the file named by <var>word</var> exists.

</div>
<div class="subsection" id="Appending-Redirected-Output">
<h4 class="subsection">3.6.3 Appending Redirected Output</h4>
Redirection of output in this fashion
causes the file whose name results from
the expansion of <var>word</var>
to be opened for appending on file descriptor <var>n</var>,
or the standard output (file descriptor 1) if <var>n</var>
is not specified. If the file does not exist it is created.

The general format for appending output is:
<div class="example">
<pre class="example">[<var>n</var>]&gt;&gt;<var>word</var>
</pre></div>

</div>
<div class="subsection" id="Redirecting-Standard-Output-and-Standard-Error">
<h4 class="subsection">3.6.4 Redirecting Standard Output and Standard Error</h4>
This construct allows both the
standard output (file descriptor 1) and
the standard error output (file descriptor 2)
to be redirected to the file whose name is the
expansion of <var>word</var>.

There are two formats for redirecting standard output and
standard error:
<div class="example">
<pre class="example">&amp;&gt;<var>word</var>
</pre></div>
and
<div class="example">
<pre class="example">&gt;&amp;<var>word</var>
</pre></div>
Of the two forms, the first is preferred.
This is semantically equivalent to
<div class="example">
<pre class="example">&gt;<var>word</var> 2&gt;&amp;1
</pre></div>
When using the second form, <var>word</var> may not expand to a number or
&lsquo;<samp>-</samp>&rsquo;. If it does, other redirection operators apply
(see Duplicating File Descriptors below) for compatibility reasons.

</div>
<div class="subsection" id="Appending-Standard-Output-and-Standard-Error">
<h4 class="subsection">3.6.5 Appending Standard Output and Standard Error</h4>
This construct allows both the
standard output (file descriptor 1) and
the standard error output (file descriptor 2)
to be appended to the file whose name is the
expansion of <var>word</var>.

The format for appending standard output and standard error is:
<div class="example">
<pre class="example">&amp;&gt;&gt;<var>word</var>
</pre></div>
This is semantically equivalent to
<div class="example">
<pre class="example">&gt;&gt;<var>word</var> 2&gt;&amp;1
</pre></div>
(see Duplicating File Descriptors below).

</div>
<div class="subsection" id="Here-Documents">
<h4 class="subsection">3.6.6 Here Documents</h4>
This type of redirection instructs the shell to read input from the
current source until a line containing only <var>word</var>
(with no trailing blanks) is seen. All of
the lines read up to that point are then used as the standard
input (or file descriptor <var>n</var> if <var>n</var> is specified) for a command.

The format of here-documents is:
<div class="example">
<pre class="example">[<var>n</var>]&lt;&lt;[-]<var>word</var>
 <var>here-document</var>
<var>delimiter</var>
</pre></div>

No parameter and variable expansion, command substitution,
arithmetic expansion, or filename expansion is performed on
<var>word</var>. If any part of <var>word</var> is quoted, the
<var>delimiter</var> is the result of quote removal on <var>word</var>,
and the lines in the here-document are not expanded.
If <var>word</var> is unquoted,
all lines of the here-document are subjected to
parameter expansion, command substitution, and arithmetic expansion,
the character sequence <code>\newline</code> is ignored, and &lsquo;<samp>\</samp>&rsquo;
must be used to quote the characters
&lsquo;<samp>\</samp>&rsquo;, &lsquo;<samp>$</samp>&rsquo;, and &lsquo;<samp>`</samp>&rsquo;.

If the redirection operator is &lsquo;<samp>&lt;&lt;-</samp>&rsquo;,
then all leading tab characters are stripped from input lines and the
line containing <var>delimiter</var>.
This allows here-documents within shell scripts to be indented in a
natural fashion.

</div>
<div class="subsection" id="Here-Strings">
<h4 class="subsection">3.6.7 Here Strings</h4>
A variant of here documents, the format is:
<div class="example">
<pre class="example">[<var>n</var>]&lt;&lt;&lt; <var>word</var>
</pre></div>

The <var>word</var> undergoes
tilde expansion, parameter and variable expansion,
command substitution, arithmetic expansion, and quote removal.
Filename expansion and word splitting are not performed.
The result is supplied as a single string,
with a newline appended,
to the command on its
standard input (or file descriptor <var>n</var> if <var>n</var> is specified).

</div>
<div class="subsection" id="Duplicating-File-Descriptors">
<h4 class="subsection">3.6.8 Duplicating File Descriptors</h4>
The redirection operator
<div class="example">
<pre class="example">[<var>n</var>]&lt;&amp;<var>word</var>
</pre></div>
is used to duplicate input file descriptors.
If <var>word</var>
expands to one or more digits, the file descriptor denoted by <var>n</var>
is made to be a copy of that file descriptor.
If the digits in <var>word</var> do not specify a file descriptor open for
input, a redirection error occurs.
If <var>word</var>
evaluates to &lsquo;<samp>-</samp>&rsquo;, file descriptor <var>n</var> is closed.
If <var>n</var> is not specified, the standard input (file descriptor 0) is used.

The operator
<div class="example">
<pre class="example">[<var>n</var>]&gt;&amp;<var>word</var>
</pre></div>
is used similarly to duplicate output file descriptors. If
<var>n</var> is not specified, the standard output (file descriptor 1) is used.
If the digits in <var>word</var> do not specify a file descriptor open for
output, a redirection error occurs.
If <var>word</var>
evaluates to &lsquo;<samp>-</samp>&rsquo;, file descriptor <var>n</var> is closed.
As a special case, if <var>n</var> is omitted, and <var>word</var> does not
expand to one or more digits or &lsquo;<samp>-</samp>&rsquo;, the standard output and standard
error are redirected as described previously.

</div>
<div class="subsection" id="Moving-File-Descriptors">
<h4 class="subsection">3.6.9 Moving File Descriptors</h4>
The redirection operator
<div class="example">
<pre class="example">[<var>n</var>]&lt;&amp;<var>digit</var>-
</pre></div>
moves the file descriptor <var>digit</var> to file descriptor <var>n</var>,
or the standard input (file descriptor 0) if <var>n</var> is not specified.
<var>digit</var> is closed after being duplicated to <var>n</var>.

Similarly, the redirection operator
<div class="example">
<pre class="example">[<var>n</var>]&gt;&amp;<var>digit</var>-
</pre></div>
moves the file descriptor <var>digit</var> to file descriptor <var>n</var>,
or the standard output (file descriptor 1) if <var>n</var> is not specified.

</div>
<div class="subsection" id="Opening-File-Descriptors-for-Reading-and-Writing">
<h4 class="subsection">3.6.10 Opening File Descriptors for Reading and Writing</h4>
The redirection operator
<div class="example">
<pre class="example">[<var>n</var>]&lt;&gt;<var>word</var>
</pre></div>
causes the file whose name is the expansion of <var>word</var>
to be opened for both reading and writing on file descriptor
<var>n</var>, or on file descriptor 0 if <var>n</var>
is not specified. If the file does not exist, it is created.

<hr>
</div>
</div>
<div class="section" id="Executing-Commands">
<div class="header">

Next: <a href="#Shell-Scripts" accesskey="n" rel="next">Shell Scripts</a>, Previous: <a href="#Redirections" accesskey="p" rel="prev">Redirections</a>, Up: <a href="#Basic-Shell-Features" accesskey="u" rel="up">Basic Shell Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">3.7 Executing Commands</h3>

<ul class="section-toc">
<li><a href="#Simple-Command-Expansion" accesskey="1">Simple Command Expansion</a></li>
<li><a href="#Command-Search-and-Execution" accesskey="2">Command Search and Execution</a></li>
<li><a href="#Command-Execution-Environment" accesskey="3">Command Execution Environment</a></li>
<li><a href="#Environment" accesskey="4">Environment</a></li>
<li><a href="#Exit-Status" accesskey="5">Exit Status</a></li>
<li><a href="#Signals" accesskey="6">Signals</a></li>
</ul>
<hr>
<div class="subsection" id="Simple-Command-Expansion">
<div class="header">

Next: <a href="#Command-Search-and-Execution" accesskey="n" rel="next">Command Search and Execution</a>, Up: <a href="#Executing-Commands" accesskey="u" rel="up">Executing Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.7.1 Simple Command Expansion</h4>

When a simple command is executed, the shell performs the following
expansions, assignments, and redirections, from left to right, in
the following order.

<ol>
<li> The words that the parser has marked as variable assignments (those
preceding the command name) and redirections are saved for later
processing.

</li><li> The words that are not variable assignments or redirections are
expanded (see <a href="#Shell-Expansions">Shell Expansions</a>).
If any words remain after expansion, the first word
is taken to be the name of the command and the remaining words are
the arguments.

</li><li> Redirections are performed as described above (see <a href="#Redirections">Redirections</a>).

</li><li> The text after the &lsquo;<samp>=</samp>&rsquo; in each variable assignment undergoes tilde
expansion, parameter expansion, command substitution, arithmetic expansion,
and quote removal before being assigned to the variable.
</li></ol>

If no command name results, the variable assignments affect the current
shell environment.
In the case of such a command (one that consists only of assignment
statements and redirections), assignment statements are performed before
redirections.
Otherwise, the variables are added to the environment
of the executed command and do not affect the current shell environment.
If any of the assignments attempts to assign a value to a readonly variable,
an error occurs, and the command exits with a non-zero status.

If no command name results, redirections are performed, but do not
affect the current shell environment. A redirection error causes the
command to exit with a non-zero status.

If there is a command name left after expansion, execution proceeds as
described below. Otherwise, the command exits. If one of the expansions
contained a command substitution, the exit status of the command is
the exit status of the last command substitution performed. If there
were no command substitutions, the command exits with a status of zero.

<hr>
</div>
<div class="subsection" id="Command-Search-and-Execution">
<div class="header">

Next: <a href="#Command-Execution-Environment" accesskey="n" rel="next">Command Execution Environment</a>, Previous: <a href="#Simple-Command-Expansion" accesskey="p" rel="prev">Simple Command Expansion</a>, Up: <a href="#Executing-Commands" accesskey="u" rel="up">Executing Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.7.2 Command Search and Execution</h4>

After a command has been split into words, if it results in a
simple command and an optional list of arguments, the following
actions are taken.

<ol>
<li> If the command name contains no slashes, the shell attempts to
locate it. If there exists a shell function by that name, that
function is invoked as described in <a href="#Shell-Functions">Shell Functions</a>.

</li><li> If the name does not match a function, the shell searches for
it in the list of shell builtins. If a match is found, that
builtin is invoked.

</li><li> If the name is neither a shell function nor a builtin,
and contains no slashes, Bash searches each element of
<code>$PATH</code> for a directory containing an executable file
by that name. Bash uses a hash table to remember the full
pathnames of executable files to avoid multiple <code>PATH</code> searches
(see the description of <code>hash</code> in <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>).
A full search of the directories in <code>$PATH</code>
is performed only if the command is not found in the hash table.
If the search is unsuccessful, the shell searches for a defined shell
function named <code>command_not_found_handle</code>.
If that function exists, it is invoked in a separate execution environment
with the original command and
the original command&rsquo;s arguments as its arguments, and the function&rsquo;s
exit status becomes the exit status of that subshell.
If that function is not defined, the shell prints an error
message and returns an exit status of 127.

</li><li> If the search is successful, or if the command name contains
one or more slashes, the shell executes the named program in
a separate execution environment.
Argument 0 is set to the name given, and the remaining arguments
to the command are set to the arguments supplied, if any.

</li><li> If this execution fails because the file is not in executable
format, and the file is not a directory, it is assumed to be a
shell script and the shell executes it as described in
<a href="#Shell-Scripts">Shell Scripts</a>.

</li><li> If the command was not begun asynchronously, the shell waits for
the command to complete and collects its exit status.

</li></ol>

<hr>
</div>
<div class="subsection" id="Command-Execution-Environment">
<div class="header">

Next: <a href="#Environment" accesskey="n" rel="next">Environment</a>, Previous: <a href="#Command-Search-and-Execution" accesskey="p" rel="prev">Command Search and Execution</a>, Up: <a href="#Executing-Commands" accesskey="u" rel="up">Executing Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.7.3 Command Execution Environment</h4>

The shell has an execution environment, which consists of the
following:

<ul>
<li> open files inherited by the shell at invocation, as modified by
redirections supplied to the <code>exec</code> builtin

</li><li> the current working directory as set by <code>cd</code>, <code>pushd</code>, or
<code>popd</code>, or inherited by the shell at invocation

</li><li> the file creation mode mask as set by <code>umask</code> or inherited from
the shell&rsquo;s parent

</li><li> current traps set by <code>trap</code>

</li><li> shell parameters that are set by variable assignment or with <code>set</code>
or inherited from the shell&rsquo;s parent in the environment

</li><li> shell functions defined during execution or inherited from the shell&rsquo;s
parent in the environment

</li><li> options enabled at invocation (either by default or with command-line
arguments) or by <code>set</code>

</li><li> options enabled by <code>shopt</code> (see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>)

</li><li> shell aliases defined with <code>alias</code> (see <a href="#Aliases">Aliases</a>)

</li><li> various process IDs, including those of background jobs
(see <a href="#Lists">Lists of Commands</a>), the value of <code>$$</code>, and the value of
<code>$PPID</code>

</li></ul>

When a simple command other than a builtin or shell function
is to be executed, it
is invoked in a separate execution environment that consists of
the following. Unless otherwise noted, the values are inherited
from the shell.

<ul>
<li> the shell&rsquo;s open files, plus any modifications and additions specified
by redirections to the command

</li><li> the current working directory

</li><li> the file creation mode mask

</li><li> shell variables and functions marked for export, along with variables
exported for the command, passed in the environment (see <a href="#Environment">Environment</a>)

</li><li> traps caught by the shell are reset to the values inherited from the
shell&rsquo;s parent, and traps ignored by the shell are ignored

</li></ul>

A command invoked in this separate environment cannot affect the
shell&rsquo;s execution environment.

A subshell is a copy of the shell process.

Command substitution, commands grouped with parentheses,
and asynchronous commands are invoked in a
subshell environment that is a duplicate of the shell environment,
except that traps caught by the shell are reset to the values
that the shell inherited from its parent at invocation. Builtin
commands that are invoked as part of a pipeline are also executed
in a subshell environment. Changes made to the subshell environment
cannot affect the shell&rsquo;s execution environment.

Subshells spawned to execute command substitutions inherit the value of
the <samp>-e</samp> option from the parent shell. When not in POSIX mode,
Bash clears the <samp>-e</samp> option in such subshells.

If a command is followed by a &lsquo;<samp>&amp;</samp>&rsquo; and job control is not active, the
default standard input for the command is the empty file <samp>/dev/null</samp>.
Otherwise, the invoked command inherits the file descriptors of the calling
shell as modified by redirections.

<hr>
</div>
<div class="subsection" id="Environment">
<div class="header">

Next: <a href="#Exit-Status" accesskey="n" rel="next">Exit Status</a>, Previous: <a href="#Command-Execution-Environment" accesskey="p" rel="prev">Command Execution Environment</a>, Up: <a href="#Executing-Commands" accesskey="u" rel="up">Executing Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.7.4 Environment</h4>

When a program is invoked it is given an array of strings
called the environment.
This is a list of name-value pairs, of the form <code>name=value</code>.

Bash provides several ways to manipulate the environment.
On invocation, the shell scans its own environment and
creates a parameter for each name found, automatically marking
it for <code>export</code>
to child processes. Executed commands inherit the environment.
The <code>export</code> and &lsquo;<samp>declare -x</samp>&rsquo;
commands allow parameters and functions to be added to and
deleted from the environment. If the value of a parameter
in the environment is modified, the new value becomes part
of the environment, replacing the old. The environment
inherited by any executed command consists of the shell&rsquo;s
initial environment, whose values may be modified in the shell,
less any pairs removed by the <code>unset</code> and &lsquo;<samp>export -n</samp>&rsquo;
commands, plus any additions via the <code>export</code> and
&lsquo;<samp>declare -x</samp>&rsquo; commands.

The environment for any simple command
or function may be augmented temporarily by prefixing it with
parameter assignments, as described in <a href="#Shell-Parameters">Shell Parameters</a>.
These assignment statements affect only the environment seen
by that command.

If the <samp>-k</samp> option is set (see <a href="#The-Set-Builtin">The Set Builtin</a>), then all
parameter assignments are placed in the environment for a command,
not just those that precede the command name.

When Bash invokes an external command, the variable &lsquo;<samp>$_</samp>&rsquo;
is set to the full pathname of the command and passed to that
command in its environment.

<hr>
</div>
<div class="subsection" id="Exit-Status">
<div class="header">

Next: <a href="#Signals" accesskey="n" rel="next">Signals</a>, Previous: <a href="#Environment" accesskey="p" rel="prev">Environment</a>, Up: <a href="#Executing-Commands" accesskey="u" rel="up">Executing Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.7.5 Exit Status</h4>

The exit status of an executed command is the value returned by the
<code>waitpid</code> system call or equivalent function. Exit statuses 
fall between 0 and 255, though, as explained below, the shell may
use values above 125 specially. Exit statuses from shell builtins and
compound commands are also limited to this range. Under certain
circumstances, the shell will use special values to indicate specific
failure modes.

For the shell&rsquo;s purposes, a command which exits with a
zero exit status has succeeded.
A non-zero exit status indicates failure.
This seemingly counter-intuitive scheme is used so there
is one well-defined way to indicate success and a variety of
ways to indicate various failure modes.
When a command terminates on a fatal signal whose number is <var>N</var>,
Bash uses the value 128+<var>N</var> as the exit status.

If a command is not found, the child process created to
execute it returns a status of 127. If a command is found 
but is not executable, the return status is 126.

If a command fails because of an error during expansion or redirection,
the exit status is greater than zero.

The exit status is used by the Bash conditional commands
(see <a href="#Conditional-Constructs">Conditional Constructs</a>) and some of the list
constructs (see <a href="#Lists">Lists of Commands</a>).

All of the Bash builtins return an exit status of zero if they succeed
and a non-zero status on failure, so they may be used by the
conditional and list constructs.
All builtins return an exit status of 2 to indicate incorrect usage,
generally invalid options or missing arguments.

The exit status of the last command is available in the special
parameter $? (see <a href="#Special-Parameters">Special Parameters</a>).

<hr>
</div>
<div class="subsection" id="Signals">
<div class="header">

Previous: <a href="#Exit-Status" accesskey="p" rel="prev">Exit Status</a>, Up: <a href="#Executing-Commands" accesskey="u" rel="up">Executing Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">3.7.6 Signals</h4>

When Bash is interactive, in the absence of any traps, it ignores
<code>SIGTERM</code> (so that &lsquo;<samp>kill 0</samp>&rsquo; does not kill an interactive shell),
and <code>SIGINT</code>
is caught and handled (so that the <code>wait</code> builtin is interruptible).
When Bash receives a <code>SIGINT</code>, it breaks out of any executing loops.
In all cases, Bash ignores <code>SIGQUIT</code>.
If job control is in effect (see <a href="#Job-Control">Job Control</a>), Bash
ignores <code>SIGTTIN</code>, <code>SIGTTOU</code>, and <code>SIGTSTP</code>.

Non-builtin commands started by Bash have signal handlers set to the
values inherited by the shell from its parent.
When job control is not in effect, asynchronous commands
ignore <code>SIGINT</code> and <code>SIGQUIT</code> in addition to these inherited
handlers.
Commands run as a result of
command substitution ignore the keyboard-generated job control signals
<code>SIGTTIN</code>, <code>SIGTTOU</code>, and <code>SIGTSTP</code>.

The shell exits by default upon receipt of a <code>SIGHUP</code>.
Before exiting, an interactive shell resends the <code>SIGHUP</code> to
all jobs, running or stopped.
Stopped jobs are sent <code>SIGCONT</code> to ensure that they receive
the <code>SIGHUP</code>.
To prevent the shell from sending the <code>SIGHUP</code> signal to a
particular job, it should be removed
from the jobs table with the <code>disown</code>
builtin (see <a href="#Job-Control-Builtins">Job Control Builtins</a>) or marked
to not receive <code>SIGHUP</code> using <code>disown -h</code>.

If the <code>huponexit</code> shell option has been set with <code>shopt</code>
(see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>), Bash sends a <code>SIGHUP</code> to all jobs when
an interactive login shell exits.

If Bash is waiting for a command to complete and receives a signal
for which a trap has been set, the trap will not be executed until
the command completes.
When Bash is waiting for an asynchronous
command via the <code>wait</code> builtin, the reception of a signal for
which a trap has been set will cause the <code>wait</code> builtin to return
immediately with an exit status greater than 128, immediately after
which the trap is executed.

When job control is not enabled, and Bash is waiting for a foreground
command to complete, the shell receives keyboard-generated signals
such as <code>SIGINT</code> (usually generated by &lsquo;<samp>^C</samp>&rsquo;) that users
commonly intend to send to that command.
This happens because the shell and the command are in the same process
group as the terminal, and &lsquo;<samp>^C</samp>&rsquo; sends <code>SIGINT</code> to all processes
in that process group.
See <a href="#Job-Control">Job Control</a>, for a more in-depth discussion of process groups.

When Bash is running without job control enabled and receives <code>SIGINT</code>
while waiting for a foreground command, it waits until that foreground
command terminates and then decides what to do about the <code>SIGINT</code>:

<ol>
<li> If the command terminates due to the <code>SIGINT</code>, Bash concludes
that the user meant to end the entire script, and acts on the
<code>SIGINT</code> (e.g., by running a <code>SIGINT</code> trap or exiting itself);

</li><li> If the pipeline does not terminate due to <code>SIGINT</code>, the program
handled the <code>SIGINT</code> itself and did not treat it as a fatal signal.
In that case, Bash does not treat <code>SIGINT</code> as a fatal signal,
either, instead assuming that the <code>SIGINT</code> was used as part of the
program&rsquo;s normal operation (e.g., <code>emacs</code> uses it to abort editing
commands) or deliberately discarded. However, Bash will run any
trap set on <code>SIGINT</code>, as it does with any other trapped signal it
receives while it is waiting for the foreground command to
complete, for compatibility.
</li></ol>

<hr>
</div>
</div>
<div class="section" id="Shell-Scripts">
<div class="header">

Previous: <a href="#Executing-Commands" accesskey="p" rel="prev">Executing Commands</a>, Up: <a href="#Basic-Shell-Features" accesskey="u" rel="up">Basic Shell Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">3.8 Shell Scripts</h3>

A shell script is a text file containing shell commands. When such
a file is used as the first non-option argument when invoking Bash,
and neither the <samp>-c</samp> nor <samp>-s</samp> option is supplied
(see <a href="#Invoking-Bash">Invoking Bash</a>), 
Bash reads and executes commands from the file, then exits. This
mode of operation creates a non-interactive shell. The shell first
searches for the file in the current directory, and looks in the
directories in <code>$PATH</code> if not found there.

When Bash runs
a shell script, it sets the special parameter <code>0</code> to the name
of the file, rather than the name of the shell, and the positional
parameters are set to the remaining arguments, if any are given.
If no additional arguments are supplied, the positional parameters
are unset.

A shell script may be made executable by using the <code>chmod</code> command
to turn on the execute bit. When Bash finds such a file while
searching the <code>$PATH</code> for a command, it creates a
new instance of itself
to execute it.
In other words, executing
<div class="example">
<pre class="example">filename <var>arguments</var>
</pre></div>
is equivalent to executing
<div class="example">
<pre class="example">bash filename <var>arguments</var>
</pre></div>

if <code>filename</code> is an executable shell script.
This subshell reinitializes itself, so that the effect is as if a
new shell had been invoked to interpret the script, with the
exception that the locations of commands remembered by the parent
(see the description of <code>hash</code> in <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>)
are retained by the child.

Most versions of Unix make this a part of the operating system&rsquo;s command
execution mechanism. If the first line of a script begins with
the two characters &lsquo;<samp>#!</samp>&rsquo;, the remainder of the line specifies
an interpreter for the program and, depending on the operating system, one
or more optional arguments for that interpreter.
Thus, you can specify Bash, <code>awk</code>, Perl, or some other
interpreter and write the rest of the script file in that language.

The arguments to the interpreter
consist of one or more optional arguments following the interpreter
name on the first line of the script file, followed by the name of
the script file, followed by the rest of the arguments supplied to the
script.
The details of how the interpreter line is split into an interpreter name
and a set of arguments vary across systems.
Bash will perform this action on operating systems that do not handle it
themselves.
Note that some older versions of Unix limit the interpreter
name and a single argument to a maximum of 32 characters, so it&rsquo;s not
portable to assume that using more than one argument will work.

Bash scripts often begin with <code>#! /bin/bash</code> (assuming that
Bash has been installed in <samp>/bin</samp>), since this ensures that
Bash will be used to interpret the script, even if it is executed
under another shell. It&rsquo;s a common idiom to use <code>env</code> to find
<code>bash</code> even if it&rsquo;s been installed in another directory:
<code>#!/usr/bin/env bash</code> will find the first occurrence of <code>bash</code>
in <code>$PATH</code>.

<hr>
</div>
</div>
<div class="chapter" id="Shell-Builtin-Commands">
<div class="header">

Next: <a href="#Shell-Variables" accesskey="n" rel="next">Shell Variables</a>, Previous: <a href="#Basic-Shell-Features" accesskey="p" rel="prev">Basic Shell Features</a>, Up: <a href="#Top" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h2 class="chapter">4 Shell Builtin Commands</h2>

Builtin commands are contained within the shell itself.
When the name of a builtin command is used as the first word of
a simple command (see <a href="#Simple-Commands">Simple Commands</a>), the shell executes
the command directly, without invoking another program.
Builtin commands are necessary to implement functionality impossible
or inconvenient to obtain with separate utilities.

This section briefly describes the builtins which Bash inherits from
the Bourne Shell, as well as the builtin commands which are unique
to or have been extended in Bash.

Several builtin commands are described in other chapters: builtin
commands which provide the Bash interface to the job control
facilities (see <a href="#Job-Control-Builtins">Job Control Builtins</a>), the directory stack
(see <a href="#Directory-Stack-Builtins">Directory Stack Builtins</a>), the command history
(see <a href="#Bash-History-Builtins">Bash History Builtins</a>), and the programmable completion
facilities (see <a href="#Programmable-Completion-Builtins">Programmable Completion Builtins</a>).

Many of the builtins have been extended by POSIX or Bash.

Unless otherwise noted, each builtin command documented as accepting
options preceded by &lsquo;<samp>-</samp>&rsquo; accepts &lsquo;<samp>--</samp>&rsquo;
to signify the end of the options.
The <code>:</code>, <code>true</code>, <code>false</code>, and <code>test</code>/<code>[</code>
builtins do not accept options and do not treat &lsquo;<samp>--</samp>&rsquo; specially.
The <code>exit</code>, <code>logout</code>, <code>return</code>,
<code>break</code>, <code>continue</code>, <code>let</code>,
and <code>shift</code> builtins accept and process arguments beginning
with &lsquo;<samp>-</samp>&rsquo; without requiring &lsquo;<samp>--</samp>&rsquo;.
Other builtins that accept arguments but are not specified as accepting
options interpret arguments beginning with &lsquo;<samp>-</samp>&rsquo; as invalid options and
require &lsquo;<samp>--</samp>&rsquo; to prevent this interpretation.

<ul class="section-toc">
<li><a href="#Bourne-Shell-Builtins" accesskey="1">Bourne Shell Builtins</a></li>
<li><a href="#Bash-Builtins" accesskey="2">Bash Builtin Commands</a></li>
<li><a href="#Modifying-Shell-Behavior" accesskey="3">Modifying Shell Behavior</a></li>
<li><a href="#Special-Builtins" accesskey="4">Special Builtins</a></li>
</ul>
<hr>
<div class="section" id="Bourne-Shell-Builtins">
<div class="header">

Next: <a href="#Bash-Builtins" accesskey="n" rel="next">Bash Builtin Commands</a>, Up: <a href="#Shell-Builtin-Commands" accesskey="u" rel="up">Shell Builtin Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">4.1 Bourne Shell Builtins</h3>

The following shell builtin commands are inherited from the Bourne Shell.
These commands are implemented as specified by the POSIX standard.

<dl compact="compact">
<dt id='index-_003a'><code>: (a colon)</code><a href='#index-_003a' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">: [<var>arguments</var>]
</pre></div>

Do nothing beyond expanding <var>arguments</var> and performing redirections.
The return status is zero.

</dd>
<dt id='index-_002e'><code>. (a period)</code><a href='#index-_002e' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">. <var>filename</var> [<var>arguments</var>]
</pre></div>

Read and execute commands from the <var>filename</var> argument in the
current shell context. If <var>filename</var> does not contain a slash,
the <code>PATH</code> variable is used to find <var>filename</var>,
but <var>filename</var> does not need to be executable.
When Bash is not in POSIX mode, it searches the current directory
if <var>filename</var> is not found in <code>$PATH</code>.
If any <var>arguments</var> are supplied, they become the positional
parameters when <var>filename</var> is executed. Otherwise the positional
parameters are unchanged.
If the <samp>-T</samp> option is enabled, <code>.</code> inherits any trap on
<code>DEBUG</code>; if it is not, any <code>DEBUG</code> trap string is saved and
restored around the call to <code>.</code>, and <code>.</code> unsets the
<code>DEBUG</code> trap while it executes.
If <samp>-T</samp> is not set, and the sourced file changes
the <code>DEBUG</code> trap, the new value is retained when <code>.</code> completes.
The return status is the exit status of the last command executed, or
zero if no commands are executed. If <var>filename</var> is not found, or
cannot be read, the return status is non-zero.
This builtin is equivalent to <code>source</code>.

</dd>
<dt id='index-break'><code>break</code><a href='#index-break' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">break [<var>n</var>]
</pre></div>

Exit from a <code>for</code>, <code>while</code>, <code>until</code>, or <code>select</code> loop.
If <var>n</var> is supplied, the <var>n</var>th enclosing loop is exited.
<var>n</var> must be greater than or equal to 1.
The return status is zero unless <var>n</var> is not greater than or equal to 1.

</dd>
<dt id='index-cd'><code>cd</code><a href='#index-cd' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">cd [-L|[-P [-e]] [-@] [<var>directory</var>]
</pre></div>

Change the current working directory to <var>directory</var>.
If <var>directory</var> is not supplied, the value of the <code>HOME</code>
shell variable is used.
If the shell variable
<code>CDPATH</code> exists, it is used as a search path:
each directory name in <code>CDPATH</code> is searched for
<var>directory</var>, with alternative directory names in <code>CDPATH</code>
separated by a colon (&lsquo;<samp>:</samp>&rsquo;).
If <var>directory</var> begins with a slash, <code>CDPATH</code> is not used.

The <samp>-P</samp> option means to not follow symbolic links: symbolic links
are resolved while <code>cd</code> is traversing <var>directory</var> and before
processing an instance of &lsquo;<samp>..</samp>&rsquo; in <var>directory</var>.

By default, or when the <samp>-L</samp> option is supplied, symbolic links
in <var>directory</var> are resolved after <code>cd</code> processes an instance
of &lsquo;<samp>..</samp>&rsquo; in <var>directory</var>.

If &lsquo;<samp>..</samp>&rsquo; appears in <var>directory</var>, it is processed by removing the
immediately preceding pathname component, back to a slash or the beginning
of <var>directory</var>.

If the <samp>-e</samp> option is supplied with <samp>-P</samp>
and the current working directory cannot be successfully determined
after a successful directory change, <code>cd</code> will return an unsuccessful
status.

On systems that support it, the <samp>-@</samp> option presents the extended
attributes associated with a file as a directory. 

If <var>directory</var> is &lsquo;<samp>-</samp>&rsquo;, it is converted to <code>$OLDPWD</code>
before the directory change is attempted.

If a non-empty directory name from <code>CDPATH</code> is used, or if
&lsquo;<samp>-</samp>&rsquo; is the first argument, and the directory change is
successful, the absolute pathname of the new working directory is
written to the standard output.

If the directory change is successful, <code>cd</code> sets the value of the
<code>PWD</code> environment variable to the new directory name, and sets the
<code>OLDPWD</code> environment variable to the value of the current working
directory before the change.

The return status is zero if the directory is successfully changed,
non-zero otherwise.

</dd>
<dt id='index-continue'><code>continue</code><a href='#index-continue' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">continue [<var>n</var>]
</pre></div>

Resume the next iteration of an enclosing <code>for</code>, <code>while</code>,
<code>until</code>, or <code>select</code> loop.
If <var>n</var> is supplied, the execution of the <var>n</var>th enclosing loop
is resumed.
<var>n</var> must be greater than or equal to 1.
The return status is zero unless <var>n</var> is not greater than or equal to 1.

</dd>
<dt id='index-eval'><code>eval</code><a href='#index-eval' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">eval [<var>arguments</var>]
</pre></div>

The arguments are concatenated together into a single command, which is
then read and executed, and its exit status returned as the exit status
of <code>eval</code>.
If there are no arguments or only empty arguments, the return status is
zero.

</dd>
<dt id='index-exec'><code>exec</code><a href='#index-exec' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">exec [-cl] [-a <var>name</var>] [<var>command</var> [<var>arguments</var>]]
</pre></div>

If <var>command</var>
is supplied, it replaces the shell without creating a new process.
If the <samp>-l</samp> option is supplied, the shell places a dash at the
beginning of the zeroth argument passed to <var>command</var>.
This is what the <code>login</code> program does.
The <samp>-c</samp> option causes <var>command</var> to be executed with an empty
environment.
If <samp>-a</samp> is supplied, the shell passes <var>name</var> as the zeroth
argument to <var>command</var>.
If <var>command</var>
cannot be executed for some reason, a non-interactive shell exits,
unless the <code>execfail</code> shell option
is enabled. In that case, it returns failure.
An interactive shell returns failure if the file cannot be executed.
A subshell exits unconditionally if <code>exec</code> fails.
If no <var>command</var> is specified, redirections may be used to affect
the current shell environment. If there are no redirection errors, the
return status is zero; otherwise the return status is non-zero.

</dd>
<dt id='index-exit'><code>exit</code><a href='#index-exit' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">exit [<var>n</var>]
</pre></div>

Exit the shell, returning a status of <var>n</var> to the shell&rsquo;s parent.
If <var>n</var> is omitted, the exit status is that of the last command executed.
Any trap on <code>EXIT</code> is executed before the shell terminates.

</dd>
<dt id='index-export'><code>export</code><a href='#index-export' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">export [-fn] [-p] [<var>name</var>[=<var>value</var>]]
</pre></div>

Mark each <var>name</var> to be passed to child processes
in the environment. If the <samp>-f</samp> option is supplied, the <var>name</var>s
refer to shell functions; otherwise the names refer to shell variables.
The <samp>-n</samp> option means to no longer mark each <var>name</var> for export.
If no <var>name</var>s are supplied, or if the <samp>-p</samp> option is given, a
list of names of all exported variables is displayed.
The <samp>-p</samp> option displays output in a form that may be reused as input.
If a variable name is followed by =<var>value</var>, the value of
the variable is set to <var>value</var>.

The return status is zero unless an invalid option is supplied, one of
the names is not a valid shell variable name, or <samp>-f</samp> is supplied
with a name that is not a shell function.

</dd>
<dt id='index-getopts'><code>getopts</code><a href='#index-getopts' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">getopts <var>optstring</var> <var>name</var> [<var>arg</var> &hellip;]
</pre></div>

<code>getopts</code> is used by shell scripts to parse positional parameters.
<var>optstring</var> contains the option characters to be recognized; if a
character is followed by a colon, the option is expected to have an
argument, which should be separated from it by whitespace.
The colon (&lsquo;<samp>:</samp>&rsquo;) and question mark (&lsquo;<samp>?</samp>&rsquo;) may not be
used as option characters.
Each time it is invoked, <code>getopts</code>
places the next option in the shell variable <var>name</var>, initializing
<var>name</var> if it does not exist,
and the index of the next argument to be processed into the
variable <code>OPTIND</code>.
<code>OPTIND</code> is initialized to 1 each time the shell or a shell script
is invoked.
When an option requires an argument,
<code>getopts</code> places that argument into the variable <code>OPTARG</code>.
The shell does not reset <code>OPTIND</code> automatically; it must be manually
reset between multiple calls to <code>getopts</code> within the same shell
invocation if a new set of parameters is to be used.

When the end of options is encountered, <code>getopts</code> exits with a
return value greater than zero.
<code>OPTIND</code> is set to the index of the first non-option argument,
and <var>name</var> is set to &lsquo;<samp>?</samp>&rsquo;.

<code>getopts</code>
normally parses the positional parameters, but if more arguments are
supplied as <var>arg</var> values, <code>getopts</code> parses those instead.

<code>getopts</code> can report errors in two ways. If the first character of
<var>optstring</var> is a colon, <var>silent</var>
error reporting is used. In normal operation, diagnostic messages
are printed when invalid options or missing option arguments are
encountered.
If the variable <code>OPTERR</code>
is set to 0, no error messages will be displayed, even if the first
character of <code>optstring</code> is not a colon.

If an invalid option is seen,
<code>getopts</code> places &lsquo;<samp>?</samp>&rsquo; into <var>name</var> and, if not silent,
prints an error message and unsets <code>OPTARG</code>.
If <code>getopts</code> is silent, the option character found is placed in
<code>OPTARG</code> and no diagnostic message is printed.

If a required argument is not found, and <code>getopts</code>
is not silent, a question mark (&lsquo;<samp>?</samp>&rsquo;) is placed in <var>name</var>,
<code>OPTARG</code> is unset, and a diagnostic message is printed.
If <code>getopts</code> is silent, then a colon (&lsquo;<samp>:</samp>&rsquo;) is placed in
<var>name</var> and <code>OPTARG</code> is set to the option character found.

</dd>
<dt id='index-hash'><code>hash</code><a href='#index-hash' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">hash [-r] [-p <var>filename</var>] [-dt] [<var>name</var>]
</pre></div>

Each time <code>hash</code> is invoked, it remembers the full pathnames of the
commands specified as <var>name</var> arguments,
so they need not be searched for on subsequent invocations.
The commands are found by searching through the directories listed in
<code>$PATH</code>.
Any previously-remembered pathname is discarded.
The <samp>-p</samp> option inhibits the path search, and <var>filename</var> is
used as the location of <var>name</var>.
The <samp>-r</samp> option causes the shell to forget all remembered locations.
The <samp>-d</samp> option causes the shell to forget the remembered location
of each <var>name</var>.
If the <samp>-t</samp> option is supplied, the full pathname to which each
<var>name</var> corresponds is printed. If multiple <var>name</var> arguments are
supplied with <samp>-t</samp>, the <var>name</var> is printed before the hashed
full pathname.
The <samp>-l</samp> option causes output to be displayed in a format
that may be reused as input.
If no arguments are given, or if only <samp>-l</samp> is supplied,
information about remembered commands is printed.
The return status is zero unless a <var>name</var> is not found or an invalid
option is supplied.

</dd>
<dt id='index-pwd'><code>pwd</code><a href='#index-pwd' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">pwd [-LP]
</pre></div>

Print the absolute pathname of the current working directory.
If the <samp>-P</samp> option is supplied, the pathname printed will not
contain symbolic links.
If the <samp>-L</samp> option is supplied, the pathname printed may contain
symbolic links.
The return status is zero unless an error is encountered while
determining the name of the current directory or an invalid option
is supplied.

</dd>
<dt id='index-readonly'><code>readonly</code><a href='#index-readonly' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">readonly [-aAf] [-p] [<var>name</var>[=<var>value</var>]] &hellip;
</pre></div>

Mark each <var>name</var> as readonly.
The values of these names may not be changed by subsequent assignment.
If the <samp>-f</samp> option is supplied, each <var>name</var> refers to a shell
function.
The <samp>-a</samp> option means each <var>name</var> refers to an indexed
array variable; the <samp>-A</samp> option means each <var>name</var> refers
to an associative array variable.
If both options are supplied, <samp>-A</samp> takes precedence.
If no <var>name</var> arguments are given, or if the <samp>-p</samp>
option is supplied, a list of all readonly names is printed.
The other options may be used to restrict the output to a subset of
the set of readonly names.
The <samp>-p</samp> option causes output to be displayed in a format that
may be reused as input.
If a variable name is followed by =<var>value</var>, the value of
the variable is set to <var>value</var>.
The return status is zero unless an invalid option is supplied, one of
the <var>name</var> arguments is not a valid shell variable or function name,
or the <samp>-f</samp> option is supplied with a name that is not a shell function.

</dd>
<dt id='index-return'><code>return</code><a href='#index-return' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">return [<var>n</var>]
</pre></div>

Cause a shell function to stop executing and return the value <var>n</var>
to its caller.
If <var>n</var> is not supplied, the return value is the exit status of the
last command executed in the function.
If <code>return</code> is executed by a trap handler, the last command used to
determine the status is the last command executed before the trap handler.
If <code>return</code> is executed during a <code>DEBUG</code> trap, the last command
used to determine the status is the last command executed by the trap
handler before <code>return</code> was invoked.
<code>return</code> may also be used to terminate execution of a script
being executed with the <code>.</code> (<code>source</code>) builtin,
returning either <var>n</var> or
the exit status of the last command executed within the script as the exit
status of the script.
If <var>n</var> is supplied, the return value is its least significant
8 bits.
Any command associated with the <code>RETURN</code> trap is executed
before execution resumes after the function or script.
The return status is non-zero if <code>return</code> is supplied a non-numeric
argument or is used outside a function
and not during the execution of a script by <code>.</code> or <code>source</code>.

</dd>
<dt id='index-shift'><code>shift</code><a href='#index-shift' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">shift [<var>n</var>]
</pre></div>

Shift the positional parameters to the left by <var>n</var>.
The positional parameters from <var>n</var>+1 &hellip; <code>$#</code> are
renamed to <code>$1</code> &hellip; <code>$#</code>-<var>n</var>.
Parameters represented by the numbers <code>$#</code> down to <code>$#</code>-<var>n</var>+1
are unset.
<var>n</var> must be a non-negative number less than or equal to <code>$#</code>.
If <var>n</var> is zero or greater than <code>$#</code>, the positional parameters
are not changed.
If <var>n</var> is not supplied, it is assumed to be 1.
The return status is zero unless <var>n</var> is greater than <code>$#</code> or
less than zero, non-zero otherwise.

</dd>
<dt id='index-test'><code>test</code><a href='#index-test' class='copiable-anchor'> &para;</a></dt>
<dt><code>[</code></dt>
<dd>
<div class="example">
<pre class="example">test <var>expr</var>
</pre></div>

Evaluate a conditional expression <var>expr</var> and return a status of 0
(true) or 1 (false).
Each operator and operand must be a separate argument.
Expressions are composed of the primaries described below in
<a href="#Bash-Conditional-Expressions">Bash Conditional Expressions</a>.
<code>test</code> does not accept any options, nor does it accept and ignore
an argument of <samp>--</samp> as signifying the end of options.

When the <code>[</code> form is used, the last argument to the command must
be a <code>]</code>.

Expressions may be combined using the following operators, listed in
decreasing order of precedence.
The evaluation depends on the number of arguments; see below.
Operator precedence is used when there are five or more arguments.

<dl compact="compact">
<dt><code>! <var>expr</var></code></dt>
<dd>True if <var>expr</var> is false.

</dd>
<dt><code>( <var>expr</var> )</code></dt>
<dd>Returns the value of <var>expr</var>.
This may be used to override the normal precedence of operators.

</dd>
<dt><code><var>expr1</var> -a <var>expr2</var></code></dt>
<dd>True if both <var>expr1</var> and <var>expr2</var> are true.

</dd>
<dt><code><var>expr1</var> -o <var>expr2</var></code></dt>
<dd>True if either <var>expr1</var> or <var>expr2</var> is true.
</dd>
</dl>

The <code>test</code> and <code>[</code> builtins evaluate conditional
expressions using a set of rules based on the number of arguments.

<dl compact="compact">
<dt>0 arguments</dt>
<dd>The expression is false.

</dd>
<dt>1 argument</dt>
<dd>The expression is true if, and only if, the argument is not null.

</dd>
<dt>2 arguments</dt>
<dd>If the first argument is &lsquo;<samp>!</samp>&rsquo;, the expression is true if and
only if the second argument is null.
If the first argument is one of the unary conditional operators
(see <a href="#Bash-Conditional-Expressions">Bash Conditional Expressions</a>), the expression
is true if the unary test is true.
If the first argument is not a valid unary operator, the expression is
false.

</dd>
<dt>3 arguments</dt>
<dd>The following conditions are applied in the order listed.

<ol>
<li> If the second argument is one of the binary conditional
operators (see <a href="#Bash-Conditional-Expressions">Bash Conditional Expressions</a>), the
result of the expression is the result of the binary test using the
first and third arguments as operands.
The &lsquo;<samp>-a</samp>&rsquo; and &lsquo;<samp>-o</samp>&rsquo; operators are considered binary operators
when there are three arguments.
</li><li> If the first argument is &lsquo;<samp>!</samp>&rsquo;, the value is the negation of
the two-argument test using the second and third arguments.
</li><li> If the first argument is exactly &lsquo;<samp>(</samp>&rsquo; and the third argument is
exactly &lsquo;<samp>)</samp>&rsquo;, the result is the one-argument test of the second
argument.
</li><li> Otherwise, the expression is false.
</li></ol>

</dd>
<dt>4 arguments</dt>
<dd>The following conditions are applied in the order listed.

<ol>
<li> If the first argument is &lsquo;<samp>!</samp>&rsquo;, the result is the negation of
the three-argument expression composed of the remaining arguments.
</li><li> If the first argument is exactly &lsquo;<samp>(</samp>&rsquo; and the fourth argument is
exactly &lsquo;<samp>)</samp>&rsquo;, the result is the two-argument test of the second
and third arguments.
</li><li> Otherwise, the expression is parsed and evaluated according to
precedence using the rules listed above.
</li></ol>

</dd>
<dt>5 or more arguments</dt>
<dd>The expression is parsed and evaluated according to precedence
using the rules listed above.
</dd>
</dl>

When used with <code>test</code> or &lsquo;<samp>[</samp>&rsquo;, the &lsquo;<samp>&lt;</samp>&rsquo; and &lsquo;<samp>&gt;</samp>&rsquo;
operators sort lexicographically using ASCII ordering.

</dd>
<dt id='index-times'><code>times</code><a href='#index-times' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">times
</pre></div>

Print out the user and system times used by the shell and its children.
The return status is zero.

</dd>
<dt id='index-trap'><code>trap</code><a href='#index-trap' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">trap [-lp] [<var>arg</var>] [<var>sigspec</var> &hellip;]
</pre></div>

The commands in <var>arg</var> are to be read and executed when the
shell receives signal <var>sigspec</var>. If <var>arg</var> is absent (and
there is a single <var>sigspec</var>) or
equal to &lsquo;<samp>-</samp>&rsquo;, each specified signal&rsquo;s disposition is reset
to the value it had when the shell was started.
If <var>arg</var> is the null string, then the signal specified by
each <var>sigspec</var> is ignored by the shell and commands it invokes.
If <var>arg</var> is not present and <samp>-p</samp> has been supplied,
the shell displays the trap commands associated with each <var>sigspec</var>.
If no arguments are supplied, or
only <samp>-p</samp> is given, <code>trap</code> prints the list of commands
associated with each signal number in a form that may be reused as
shell input.
The <samp>-l</samp> option causes the shell to print a list of signal names
and their corresponding numbers.
Each <var>sigspec</var> is either a signal name or a signal number.
Signal names are case insensitive and the <code>SIG</code> prefix is optional.

If a <var>sigspec</var>
is <code>0</code> or <code>EXIT</code>, <var>arg</var> is executed when the shell exits.
If a <var>sigspec</var> is <code>DEBUG</code>, the command <var>arg</var> is executed
before every simple command, <code>for</code> command, <code>case</code> command,
<code>select</code> command, every arithmetic <code>for</code> command, and before
the first command executes in a shell function.
Refer to the description of the <code>extdebug</code> option to the
<code>shopt</code> builtin (see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>) for details of its
effect on the <code>DEBUG</code> trap.
If a <var>sigspec</var> is <code>RETURN</code>, the command <var>arg</var> is executed
each time a shell function or a script executed with the <code>.</code> or
<code>source</code> builtins finishes executing.

If a <var>sigspec</var> is <code>ERR</code>, the command <var>arg</var> 
is executed whenever
a pipeline (which may consist of a single simple
command), a list, or a compound command returns a
non-zero exit status,
subject to the following conditions.
The <code>ERR</code> trap is not executed if the failed command is part of the
command list immediately following an <code>until</code> or <code>while</code> keyword,
part of the test following the <code>if</code> or <code>elif</code> reserved words,
part of a command executed in a <code>&amp;&amp;</code> or <code>||</code> list
except the command following the final <code>&amp;&amp;</code> or <code>||</code>,
any command in a pipeline but the last,
or if the command&rsquo;s return
status is being inverted using <code>!</code>.
These are the same conditions obeyed by the <code>errexit</code> (<samp>-e</samp>)
option.

Signals ignored upon entry to the shell cannot be trapped or reset.
Trapped signals that are not being ignored are reset to their original
values in a subshell or subshell environment when one is created.

The return status is zero unless a <var>sigspec</var> does not specify a
valid signal.

</dd>
<dt id='index-umask'><code>umask</code><a href='#index-umask' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">umask [-p] [-S] [<var>mode</var>]
</pre></div>

Set the shell process&rsquo;s file creation mask to <var>mode</var>. If
<var>mode</var> begins with a digit, it is interpreted as an octal number;
if not, it is interpreted as a symbolic mode mask similar
to that accepted by the <code>chmod</code> command. If <var>mode</var> is
omitted, the current value of the mask is printed. If the <samp>-S</samp>
option is supplied without a <var>mode</var> argument, the mask is printed
in a symbolic format.
If the <samp>-p</samp> option is supplied, and <var>mode</var>
is omitted, the output is in a form that may be reused as input.
The return status is zero if the mode is successfully changed or if
no <var>mode</var> argument is supplied, and non-zero otherwise.

Note that when the mode is interpreted as an octal number, each number
of the umask is subtracted from <code>7</code>. Thus, a umask of <code>022</code>
results in permissions of <code>755</code>.

</dd>
<dt id='index-unset'><code>unset</code><a href='#index-unset' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">unset [-fnv] [<var>name</var>]
</pre></div>

Remove each variable or function <var>name</var>.
If the <samp>-v</samp> option is given, each
<var>name</var> refers to a shell variable and that variable is removed.
If the <samp>-f</samp> option is given, the <var>name</var>s refer to shell
functions, and the function definition is removed.
If the <samp>-n</samp> option is supplied, and <var>name</var> is a variable with
the <code>nameref</code> attribute, <var>name</var> will be unset rather than the
variable it references.
<samp>-n</samp> has no effect if the <samp>-f</samp> option is supplied.
If no options are supplied, each <var>name</var> refers to a variable; if
there is no variable by that name, a function with that name, if any, is
unset.
Readonly variables and functions may not be unset.
Some shell variables lose their special behavior if they are unset; such
behavior is noted in the description of the individual variables.
The return status is zero unless a <var>name</var> is readonly or may not be unset.
</dd>
</dl>

<hr>
</div>
<div class="section" id="Bash-Builtins">
<div class="header">

Next: <a href="#Modifying-Shell-Behavior" accesskey="n" rel="next">Modifying Shell Behavior</a>, Previous: <a href="#Bourne-Shell-Builtins" accesskey="p" rel="prev">Bourne Shell Builtins</a>, Up: <a href="#Shell-Builtin-Commands" accesskey="u" rel="up">Shell Builtin Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">4.2 Bash Builtin Commands</h3>

This section describes builtin commands which are unique to
or have been extended in Bash.
Some of these commands are specified in the POSIX standard.

<dl compact="compact">
<dt id='index-alias'><code>alias</code><a href='#index-alias' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">alias [-p] [<var>name</var>[=<var>value</var>] &hellip;]
</pre></div>

Without arguments or with the <samp>-p</samp> option, <code>alias</code> prints
the list of aliases on the standard output in a form that allows
them to be reused as input.
If arguments are supplied, an alias is defined for each <var>name</var>
whose <var>value</var> is given. If no <var>value</var> is given, the name
and value of the alias is printed.
Aliases are described in <a href="#Aliases">Aliases</a>.

</dd>
<dt id='index-bind'><code>bind</code><a href='#index-bind' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">bind [-m <var>keymap</var>] [-lpsvPSVX]
bind [-m <var>keymap</var>] [-q <var>function</var>] [-u <var>function</var>] [-r <var>keyseq</var>]
bind [-m <var>keymap</var>] -f <var>filename</var>
bind [-m <var>keymap</var>] -x <var>keyseq:shell-command</var>
bind [-m <var>keymap</var>] <var>keyseq:function-name</var>
bind [-m <var>keymap</var>] <var>keyseq:readline-command</var>
bind <var>readline-command-line</var>
</pre></div>

Display current Readline (see <a href="#Command-Line-Editing">Command Line Editing</a>)
key and function bindings,
bind a key sequence to a Readline function or macro,
or set a Readline variable.
Each non-option argument is a command as it would appear in a
Readline initialization file (see <a href="#Readline-Init-File">Readline Init File</a>),
but each binding or command must be passed as a separate argument; e.g.,
&lsquo;<samp>&quot;\C-x\C-r&quot;:re-read-init-file</samp>&rsquo;.

Options, if supplied, have the following meanings:

<dl compact="compact">
<dt><code>-m <var>keymap</var></code></dt>
<dd>Use <var>keymap</var> as the keymap to be affected by
the subsequent bindings. Acceptable <var>keymap</var>
names are
<code>emacs</code>,
<code>emacs-standard</code>,
<code>emacs-meta</code>,
<code>emacs-ctlx</code>,
<code>vi</code>,
<code>vi-move</code>,
<code>vi-command</code>, and
<code>vi-insert</code>.
<code>vi</code> is equivalent to <code>vi-command</code> (<code>vi-move</code> is also a
synonym); <code>emacs</code> is equivalent to <code>emacs-standard</code>.

</dd>
<dt><code>-l</code></dt>
<dd>List the names of all Readline functions.

</dd>
<dt><code>-p</code></dt>
<dd>Display Readline function names and bindings in such a way that they
can be used as input or in a Readline initialization file.

</dd>
<dt><code>-P</code></dt>
<dd>List current Readline function names and bindings.

</dd>
<dt><code>-v</code></dt>
<dd>Display Readline variable names and values in such a way that they
can be used as input or in a Readline initialization file.

</dd>
<dt><code>-V</code></dt>
<dd>List current Readline variable names and values.

</dd>
<dt><code>-s</code></dt>
<dd>Display Readline key sequences bound to macros and the strings they output
in such a way that they can be used as input or in a Readline
initialization file.

</dd>
<dt><code>-S</code></dt>
<dd>Display Readline key sequences bound to macros and the strings they output.

</dd>
<dt><code>-f <var>filename</var></code></dt>
<dd>Read key bindings from <var>filename</var>.

</dd>
<dt><code>-q <var>function</var></code></dt>
<dd>Query about which keys invoke the named <var>function</var>.

</dd>
<dt><code>-u <var>function</var></code></dt>
<dd>Unbind all keys bound to the named <var>function</var>.

</dd>
<dt><code>-r <var>keyseq</var></code></dt>
<dd>Remove any current binding for <var>keyseq</var>.

</dd>
<dt><code>-x <var>keyseq:shell-command</var></code></dt>
<dd>Cause <var>shell-command</var> to be executed whenever <var>keyseq</var> is
entered.
When <var>shell-command</var> is executed, the shell sets the
<code>READLINE_LINE</code> variable to the contents of the Readline line
buffer and the <code>READLINE_POINT</code> and <code>READLINE_MARK</code> variables
to the current location of the insertion point and the saved insertion
point (the <var>mark</var>), respectively.
The shell assigns any numeric argument the user supplied to the
<code>READLINE_ARGUMENT</code> variable.
If there was no argument, that variable is not set.
If the executed command changes the value of any of <code>READLINE_LINE</code>,
<code>READLINE_POINT</code>, or <code>READLINE_MARK</code>, those new values will be
reflected in the editing state.

</dd>
<dt><code>-X</code></dt>
<dd>List all key sequences bound to shell commands and the associated commands
in a format that can be reused as input.
</dd>
</dl>

The return status is zero unless an invalid option is supplied or an
error occurs.

</dd>
<dt id='index-builtin'><code>builtin</code><a href='#index-builtin' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">builtin [<var>shell-builtin</var> [<var>args</var>]]
</pre></div>

Run a shell builtin, passing it <var>args</var>, and return its exit status.
This is useful when defining a shell function with the same
name as a shell builtin, retaining the functionality of the builtin within
the function.
The return status is non-zero if <var>shell-builtin</var> is not a shell
builtin command.

</dd>
<dt id='index-caller'><code>caller</code><a href='#index-caller' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">caller [<var>expr</var>]
</pre></div>

Returns the context of any active subroutine call (a shell function or
a script executed with the <code>.</code> or <code>source</code> builtins).

Without <var>expr</var>, <code>caller</code> displays the line number and source
filename of the current subroutine call.
If a non-negative integer is supplied as <var>expr</var>, <code>caller</code>
displays the line number, subroutine name, and source file corresponding
to that position in the current execution call stack. This extra
information may be used, for example, to print a stack trace. The
current frame is frame 0.

The return value is 0 unless the shell is not executing a subroutine
call or <var>expr</var> does not correspond to a valid position in the
call stack.

</dd>
<dt id='index-command'><code>command</code><a href='#index-command' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">command [-pVv] <var>command</var> [<var>arguments</var> &hellip;]
</pre></div>

Runs <var>command</var> with <var>arguments</var> ignoring any shell function
named <var>command</var>.
Only shell builtin commands or commands found by searching the
<code>PATH</code> are executed.
If there is a shell function named <code>ls</code>, running &lsquo;<samp>command ls</samp>&rsquo;
within the function will execute the external command <code>ls</code>
instead of calling the function recursively.
The <samp>-p</samp> option means to use a default value for <code>PATH</code>
that is guaranteed to find all of the standard utilities.
The return status in this case is 127 if <var>command</var> cannot be
found or an error occurred, and the exit status of <var>command</var>
otherwise.

If either the <samp>-V</samp> or <samp>-v</samp> option is supplied, a
description of <var>command</var> is printed. The <samp>-v</samp> option
causes a single word indicating the command or file name used to
invoke <var>command</var> to be displayed; the <samp>-V</samp> option produces
a more verbose description. In this case, the return status is
zero if <var>command</var> is found, and non-zero if not.

</dd>
<dt id='index-declare'><code>declare</code><a href='#index-declare' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">declare [-aAfFgiIlnrtux] [-p] [<var>name</var>[=<var>value</var>] &hellip;]
</pre></div>

Declare variables and give them attributes. If no <var>name</var>s
are given, then display the values of variables instead. 

The <samp>-p</samp> option will display the attributes and values of each
<var>name</var>.
When <samp>-p</samp> is used with <var>name</var> arguments, additional options,
other than <samp>-f</samp> and <samp>-F</samp>, are ignored.

When <samp>-p</samp> is supplied without <var>name</var> arguments, <code>declare</code>
will display the attributes and values of all variables having the
attributes specified by the additional options.
If no other options are supplied with <samp>-p</samp>, <code>declare</code> will
display the attributes and values of all shell variables. The <samp>-f</samp>
option will restrict the display to shell functions.

The <samp>-F</samp> option inhibits the display of function definitions;
only the function name and attributes are printed.
If the <code>extdebug</code> shell option is enabled using <code>shopt</code>
(see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>), the source file name and line number where
each <var>name</var> is defined are displayed as well.
<samp>-F</samp> implies <samp>-f</samp>.

The <samp>-g</samp> option forces variables to be created or modified at
the global scope, even when <code>declare</code> is executed in a shell function.
It is ignored in all other cases.

The <samp>-I</samp> option causes local variables to inherit the attributes
(except the <code>nameref</code> attribute)
and value of any existing variable with the same
<var>name</var> at a surrounding scope.
If there is no existing variable, the local variable is initially unset.

The following options can be used to restrict output to variables with
the specified attributes or to give variables attributes:

<dl compact="compact">
<dt><code>-a</code></dt>
<dd>Each <var>name</var> is an indexed array variable (see <a href="#Arrays">Arrays</a>).

</dd>
<dt><code>-A</code></dt>
<dd>Each <var>name</var> is an associative array variable (see <a href="#Arrays">Arrays</a>).

</dd>
<dt><code>-f</code></dt>
<dd>Use function names only.

</dd>
<dt><code>-i</code></dt>
<dd>The variable is to be treated as
an integer; arithmetic evaluation (see <a href="#Shell-Arithmetic">Shell Arithmetic</a>) is
performed when the variable is assigned a value.

</dd>
<dt><code>-l</code></dt>
<dd>When the variable is assigned a value, all upper-case characters are
converted to lower-case.
The upper-case attribute is disabled.

</dd>
<dt><code>-n</code></dt>
<dd>Give each <var>name</var> the <code>nameref</code> attribute, making
it a name reference to another variable.
That other variable is defined by the value of <var>name</var>.
All references, assignments, and attribute modifications
to <var>name</var>, except for those using or changing the
<samp>-n</samp> attribute itself, are performed on the variable referenced by
<var>name</var>&rsquo;s value.
The nameref attribute cannot be applied to array variables.

</dd>
<dt><code>-r</code></dt>
<dd>Make <var>name</var>s readonly. These names cannot then be assigned values
by subsequent assignment statements or unset.

</dd>
<dt><code>-t</code></dt>
<dd>Give each <var>name</var> the <code>trace</code> attribute.
Traced functions inherit the <code>DEBUG</code> and <code>RETURN</code> traps from
the calling shell.
The trace attribute has no special meaning for variables.

</dd>
<dt><code>-u</code></dt>
<dd>When the variable is assigned a value, all lower-case characters are
converted to upper-case.
The lower-case attribute is disabled.

</dd>
<dt><code>-x</code></dt>
<dd>Mark each <var>name</var> for export to subsequent commands via
the environment.
</dd>
</dl>

Using &lsquo;<samp>+</samp>&rsquo; instead of &lsquo;<samp>-</samp>&rsquo; turns off the attribute instead,
with the exceptions that &lsquo;<samp>+a</samp>&rsquo; and &lsquo;<samp>+A</samp>&rsquo;
may not be used to destroy array variables and &lsquo;<samp>+r</samp>&rsquo; will not
remove the readonly attribute.
When used in a function, <code>declare</code> makes each <var>name</var> local,
as with the <code>local</code> command, unless the <samp>-g</samp> option is used.
If a variable name is followed by =<var>value</var>, the value of the variable
is set to <var>value</var>.

When using <samp>-a</samp> or <samp>-A</samp> and the compound assignment syntax to 
create array variables, additional attributes do not take effect until
subsequent assignments.

The return status is zero unless an invalid option is encountered,
an attempt is made to define a function using &lsquo;<samp>-f foo=bar</samp>&rsquo;,
an attempt is made to assign a value to a readonly variable,
an attempt is made to assign a value to an array variable without
using the compound assignment syntax (see <a href="#Arrays">Arrays</a>),
one of the <var>name</var>s is not a valid shell variable name,
an attempt is made to turn off readonly status for a readonly variable,
an attempt is made to turn off array status for an array variable,
or an attempt is made to display a non-existent function with <samp>-f</samp>.

</dd>
<dt id='index-echo'><code>echo</code><a href='#index-echo' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">echo [-neE] [<var>arg</var> &hellip;]
</pre></div>

Output the <var>arg</var>s, separated by spaces, terminated with a
newline.
The return status is 0 unless a write error occurs.
If <samp>-n</samp> is specified, the trailing newline is suppressed.
If the <samp>-e</samp> option is given, interpretation of the following
backslash-escaped characters is enabled.
The <samp>-E</samp> option disables the interpretation of these escape characters,
even on systems where they are interpreted by default.
The <code>xpg_echo</code> shell option may be used to
dynamically determine whether or not <code>echo</code> expands these
escape characters by default.
<code>echo</code> does not interpret <samp>--</samp> to mean the end of options.

<code>echo</code> interprets the following escape sequences:
<dl compact="compact">
<dt><code>\a</code></dt>
<dd>alert (bell)
</dd>
<dt><code>\b</code></dt>
<dd>backspace
</dd>
<dt><code>\c</code></dt>
<dd>suppress further output
</dd>
<dt><code>\e</code></dt>
<dt><code>\E</code></dt>
<dd>escape
</dd>
<dt><code>\f</code></dt>
<dd>form feed
</dd>
<dt><code>\n</code></dt>
<dd>new line
</dd>
<dt><code>\r</code></dt>
<dd>carriage return
</dd>
<dt><code>\t</code></dt>
<dd>horizontal tab
</dd>
<dt><code>\v</code></dt>
<dd>vertical tab
</dd>
<dt><code>\\</code></dt>
<dd>backslash
</dd>
<dt><code>\0<var>nnn</var></code></dt>
<dd>the eight-bit character whose value is the octal value <var>nnn</var>
(zero to three octal digits)
</dd>
<dt><code>\x<var>HH</var></code></dt>
<dd>the eight-bit character whose value is the hexadecimal value <var>HH</var>
(one or two hex digits)
</dd>
<dt><code>\u<var>HHHH</var></code></dt>
<dd>the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value
<var>HHHH</var> (one to four hex digits)
</dd>
<dt><code>\U<var>HHHHHHHH</var></code></dt>
<dd>the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value
<var>HHHHHHHH</var> (one to eight hex digits)
</dd>
</dl>

</dd>
<dt id='index-enable'><code>enable</code><a href='#index-enable' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">enable [-a] [-dnps] [-f <var>filename</var>] [<var>name</var> &hellip;]
</pre></div>

Enable and disable builtin shell commands.
Disabling a builtin allows a disk command which has the same name
as a shell builtin to be executed without specifying a full pathname,
even though the shell normally searches for builtins before disk commands.
If <samp>-n</samp> is used, the <var>name</var>s become disabled. Otherwise
<var>name</var>s are enabled. For example, to use the <code>test</code> binary
found via <code>$PATH</code> instead of the shell builtin version, type
&lsquo;<samp>enable -n test</samp>&rsquo;.

If the <samp>-p</samp> option is supplied, or no <var>name</var> arguments appear,
a list of shell builtins is printed. With no other arguments, the list
consists of all enabled shell builtins.
The <samp>-a</samp> option means to list
each builtin with an indication of whether or not it is enabled. 

The <samp>-f</samp> option means to load the new builtin command <var>name</var>
from shared object <var>filename</var>, on systems that support dynamic loading.
Bash will use the value of the <code>BASH_LOADABLES_PATH</code> variable as a
colon-separated list of directories in which to search for <var>filename</var>.
The default is system-dependent.
The <samp>-d</samp> option will delete a builtin loaded with <samp>-f</samp>.

If there are no options, a list of the shell builtins is displayed.
The <samp>-s</samp> option restricts <code>enable</code> to the POSIX special
builtins. If <samp>-s</samp> is used with <samp>-f</samp>, the new builtin becomes
a special builtin (see <a href="#Special-Builtins">Special Builtins</a>).

If no options are supplied and a <var>name</var> is not a shell builtin,
<code>enable</code> will attempt to load <var>name</var> from a shared object named
<var>name</var>, as if the command were
&lsquo;<samp>enable -f <var>name</var> <var>name</var></samp>&rsquo;.

The return status is zero unless a <var>name</var> is not a shell builtin
or there is an error loading a new builtin from a shared object.

</dd>
<dt id='index-help'><code>help</code><a href='#index-help' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">help [-dms] [<var>pattern</var>]
</pre></div>

Display helpful information about builtin commands.
If <var>pattern</var> is specified, <code>help</code> gives detailed help
on all commands matching <var>pattern</var>, otherwise a list of
the builtins is printed.

Options, if supplied, have the following meanings:

<dl compact="compact">
<dt><code>-d</code></dt>
<dd>Display a short description of each <var>pattern</var>
</dd>
<dt><code>-m</code></dt>
<dd>Display the description of each <var>pattern</var> in a manpage-like format
</dd>
<dt><code>-s</code></dt>
<dd>Display only a short usage synopsis for each <var>pattern</var>
</dd>
</dl>

The return status is zero unless no command matches <var>pattern</var>.

</dd>
<dt id='index-let'><code>let</code><a href='#index-let' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">let <var>expression</var> [<var>expression</var> &hellip;]
</pre></div>

The <code>let</code> builtin allows arithmetic to be performed on shell
variables. Each <var>expression</var> is evaluated according to the
rules given below in <a href="#Shell-Arithmetic">Shell Arithmetic</a>. If the
last <var>expression</var> evaluates to 0, <code>let</code> returns 1;
otherwise 0 is returned.

</dd>
<dt id='index-local'><code>local</code><a href='#index-local' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">local [<var>option</var>] <var>name</var>[=<var>value</var>] &hellip;
</pre></div>

For each argument, a local variable named <var>name</var> is created,
and assigned <var>value</var>.
The <var>option</var> can be any of the options accepted by <code>declare</code>.
<code>local</code> can only be used within a function; it makes the variable
<var>name</var> have a visible scope restricted to that function and its
children.
If <var>name</var> is &lsquo;<samp>-</samp>&rsquo;, the set of shell options is made local to the
function in which <code>local</code> is invoked: shell options changed using
the <code>set</code> builtin inside the function are restored to their original
values when the function returns.
The restore is effected as if a series of <code>set</code> commands were executed
to restore the values that were in place before the function.
The return status is zero unless <code>local</code> is used outside
a function, an invalid <var>name</var> is supplied, or <var>name</var> is a
readonly variable.

</dd>
<dt id='index-logout'><code>logout</code><a href='#index-logout' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">logout [<var>n</var>]
</pre></div>

Exit a login shell, returning a status of <var>n</var> to the shell&rsquo;s
parent.

</dd>
<dt id='index-mapfile'><code>mapfile</code><a href='#index-mapfile' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">mapfile [-d <var>delim</var>] [-n <var>count</var>] [-O <var>origin</var>] [-s <var>count</var>]
 [-t] [-u <var>fd</var>] [-C <var>callback</var>] [-c <var>quantum</var>] [<var>array</var>]
</pre></div>

Read lines from the standard input into the indexed array variable <var>array</var>,
or from file descriptor <var>fd</var>
if the <samp>-u</samp> option is supplied.
The variable <code>MAPFILE</code> is the default <var>array</var>.
Options, if supplied, have the following meanings:

<dl compact="compact">
<dt><code>-d</code></dt>
<dd>The first character of <var>delim</var> is used to terminate each input line,
rather than newline.
If <var>delim</var> is the empty string, <code>mapfile</code> will terminate a line
when it reads a NUL character.
</dd>
<dt><code>-n</code></dt>
<dd>Copy at most <var>count</var> lines. If <var>count</var> is 0, all lines are copied.
</dd>
<dt><code>-O</code></dt>
<dd>Begin assigning to <var>array</var> at index <var>origin</var>.
The default index is 0.
</dd>
<dt><code>-s</code></dt>
<dd>Discard the first <var>count</var> lines read.
</dd>
<dt><code>-t</code></dt>
<dd>Remove a trailing <var>delim</var> (default newline) from each line read.
</dd>
<dt><code>-u</code></dt>
<dd>Read lines from file descriptor <var>fd</var> instead of the standard input.
</dd>
<dt><code>-C</code></dt>
<dd>Evaluate <var>callback</var> each time <var>quantum</var> lines are read.
The <samp>-c</samp> option specifies <var>quantum</var>.
</dd>
<dt><code>-c</code></dt>
<dd>Specify the number of lines read between each call to <var>callback</var>.
</dd>
</dl>

If <samp>-C</samp> is specified without <samp>-c</samp>,
the default quantum is 5000.
When <var>callback</var> is evaluated, it is supplied the index of the next
array element to be assigned and the line to be assigned to that element
as additional arguments.
<var>callback</var> is evaluated after the line is read but before the
array element is assigned.

If not supplied with an explicit origin, <code>mapfile</code> will clear <var>array</var>
before assigning to it.

<code>mapfile</code> returns successfully unless an invalid option or option
argument is supplied, <var>array</var> is invalid or unassignable, or <var>array</var>
is not an indexed array.

</dd>
<dt id='index-printf'><code>printf</code><a href='#index-printf' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">printf [-v <var>var</var>] <var>format</var> [<var>arguments</var>]
</pre></div>

Write the formatted <var>arguments</var> to the standard output under the
control of the <var>format</var>.
The <samp>-v</samp> option causes the output to be assigned to the variable
<var>var</var> rather than being printed to the standard output.

The <var>format</var> is a character string which contains three types of objects:
plain characters, which are simply copied to standard output, character
escape sequences, which are converted and copied to the standard output, and
format specifications, each of which causes printing of the next successive
<var>argument</var>.
In addition to the standard <code>printf(1)</code> formats, <code>printf</code>
interprets the following extensions:

<dl compact="compact">
<dt><code>%b</code></dt>
<dd>Causes <code>printf</code> to expand backslash escape sequences in the
corresponding <var>argument</var> in the same way as <code>echo -e</code>
(see <a href="#Bash-Builtins">Bash Builtin Commands</a>).
</dd>
<dt><code>%q</code></dt>
<dd>Causes <code>printf</code> to output the
corresponding <var>argument</var> in a format that can be reused as shell input.
</dd>
<dt><code>%Q</code></dt>
<dd>like <code>%q</code>, but applies any supplied precision to the <var>argument</var>
before quoting it.
</dd>
<dt><code>%(<var>datefmt</var>)T</code></dt>
<dd>Causes <code>printf</code> to output the date-time string resulting from using
<var>datefmt</var> as a format string for <code>strftime</code>(3).
The corresponding <var>argument</var> is an integer representing the number of
seconds since the epoch.
Two special argument values may be used: -1 represents the current
time, and -2 represents the time the shell was invoked.
If no argument is specified, conversion behaves as if -1 had been given.
This is an exception to the usual <code>printf</code> behavior.
</dd>
</dl>

The %b, %q, and %T directives all use the field width and precision
arguments from the format specification and write that many bytes from 
(or use that wide a field for) the expanded argument, which usually
contains more characters than the original.

Arguments to non-string format specifiers are treated as C language constants,
except that a leading plus or minus sign is allowed, and if the leading
character is a single or double quote, the value is the ASCII value of
the following character.

The <var>format</var> is reused as necessary to consume all of the <var>arguments</var>.
If the <var>format</var> requires more <var>arguments</var> than are supplied, the
extra format specifications behave as if a zero value or null string, as
appropriate, had been supplied. The return value is zero on success,
non-zero on failure.

</dd>
<dt id='index-read'><code>read</code><a href='#index-read' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">read [-ers] [-a <var>aname</var>] [-d <var>delim</var>] [-i <var>text</var>] [-n <var>nchars</var>]
 [-N <var>nchars</var>] [-p <var>prompt</var>] [-t <var>timeout</var>] [-u <var>fd</var>] [<var>name</var> &hellip;]
</pre></div>

One line is read from the standard input, or from the file descriptor
<var>fd</var> supplied as an argument to the <samp>-u</samp> option,
split into words as described above in <a href="#Word-Splitting">Word Splitting</a>,
and the first word
is assigned to the first <var>name</var>, the second word to the second <var>name</var>,
and so on.
If there are more words than names,
the remaining words and their intervening delimiters are assigned
to the last <var>name</var>.
If there are fewer words read from the input stream than names,
the remaining names are assigned empty values.
The characters in the value of the <code>IFS</code> variable
are used to split the line into words using the same rules the shell
uses for expansion (described above in <a href="#Word-Splitting">Word Splitting</a>).
The backslash character &lsquo;<samp>\</samp>&rsquo; may be used to remove any special
meaning for the next character read and for line continuation.

Options, if supplied, have the following meanings:

<dl compact="compact">
<dt><code>-a <var>aname</var></code></dt>
<dd>The words are assigned to sequential indices of the array variable
<var>aname</var>, starting at 0.
All elements are removed from <var>aname</var> before the assignment.
Other <var>name</var> arguments are ignored.

</dd>
<dt><code>-d <var>delim</var></code></dt>
<dd>The first character of <var>delim</var> is used to terminate the input line,
rather than newline.
If <var>delim</var> is the empty string, <code>read</code> will terminate a line
when it reads a NUL character.

</dd>
<dt><code>-e</code></dt>
<dd>Readline (see <a href="#Command-Line-Editing">Command Line Editing</a>) is used to obtain the line.
Readline uses the current (or default, if line editing was not previously
active) editing settings, but uses Readline&rsquo;s default filename completion.

</dd>
<dt><code>-i <var>text</var></code></dt>
<dd>If Readline is being used to read the line, <var>text</var> is placed into
the editing buffer before editing begins.

</dd>
<dt><code>-n <var>nchars</var></code></dt>
<dd><code>read</code> returns after reading <var>nchars</var> characters rather than
waiting for a complete line of input, but honors a delimiter if fewer
than <var>nchars</var> characters are read before the delimiter.

</dd>
<dt><code>-N <var>nchars</var></code></dt>
<dd><code>read</code> returns after reading exactly <var>nchars</var> characters rather
than waiting for a complete line of input, unless EOF is encountered or
<code>read</code> times out.
Delimiter characters encountered in the input are
not treated specially and do not cause <code>read</code> to return until
<var>nchars</var> characters are read.
The result is not split on the characters in <code>IFS</code>; the intent is
that the variable is assigned exactly the characters read
(with the exception of backslash; see the <samp>-r</samp> option below).

</dd>
<dt><code>-p <var>prompt</var></code></dt>
<dd>Display <var>prompt</var>, without a trailing newline, before attempting
to read any input.
The prompt is displayed only if input is coming from a terminal.

</dd>
<dt><code>-r</code></dt>
<dd>If this option is given, backslash does not act as an escape character.
The backslash is considered to be part of the line.
In particular, a backslash-newline pair may not then be used as a line
continuation.

</dd>
<dt><code>-s</code></dt>
<dd>Silent mode. If input is coming from a terminal, characters are
not echoed.

</dd>
<dt><code>-t <var>timeout</var></code></dt>
<dd>Cause <code>read</code> to time out and return failure if a complete line of
input (or a specified number of characters)
is not read within <var>timeout</var> seconds.
<var>timeout</var> may be a decimal number with a fractional portion following
the decimal point.
This option is only effective if <code>read</code> is reading input from a
terminal, pipe, or other special file; it has no effect when reading
from regular files.
If <code>read</code> times out, <code>read</code> saves any partial input read into
the specified variable <var>name</var>.
If <var>timeout</var> is 0, <code>read</code> returns immediately, without trying to
read any data.
The exit status is 0 if input is available on the specified file descriptor,
or the read will return EOF,
non-zero otherwise.
The exit status is greater than 128 if the timeout is exceeded.

</dd>
<dt><code>-u <var>fd</var></code></dt>
<dd>Read input from file descriptor <var>fd</var>.
</dd>
</dl>

If no <var>name</var>s are supplied, the line read,
without the ending delimiter but otherwise unmodified,
is assigned to the
variable <code>REPLY</code>.
The exit status is zero, unless end-of-file is encountered, <code>read</code>
times out (in which case the status is greater than 128),
a variable assignment error (such as assigning to a readonly variable) occurs,
or an invalid file descriptor is supplied as the argument to <samp>-u</samp>.

</dd>
<dt id='index-readarray'><code>readarray</code><a href='#index-readarray' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">readarray [-d <var>delim</var>] [-n <var>count</var>] [-O <var>origin</var>] [-s <var>count</var>]
 [-t] [-u <var>fd</var>] [-C <var>callback</var>] [-c <var>quantum</var>] [<var>array</var>]
</pre></div>

Read lines from the standard input into the indexed array variable <var>array</var>,
or from file descriptor <var>fd</var>
if the <samp>-u</samp> option is supplied.

A synonym for <code>mapfile</code>.

</dd>
<dt id='index-source'><code>source</code><a href='#index-source' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">source <var>filename</var>
</pre></div>

A synonym for <code>.</code> (see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>).

</dd>
<dt id='index-type'><code>type</code><a href='#index-type' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">type [-afptP] [<var>name</var> &hellip;]
</pre></div>

For each <var>name</var>, indicate how it would be interpreted if used as a
command name.

If the <samp>-t</samp> option is used, <code>type</code> prints a single word
which is one of &lsquo;<samp>alias</samp>&rsquo;, &lsquo;<samp>function</samp>&rsquo;, &lsquo;<samp>builtin</samp>&rsquo;,
&lsquo;<samp>file</samp>&rsquo; or &lsquo;<samp>keyword</samp>&rsquo;,
if <var>name</var> is an alias, shell function, shell builtin,
disk file, or shell reserved word, respectively.
If the <var>name</var> is not found, then nothing is printed, and
<code>type</code> returns a failure status.

If the <samp>-p</samp> option is used, <code>type</code> either returns the name
of the disk file that would be executed, or nothing if <samp>-t</samp>
would not return &lsquo;<samp>file</samp>&rsquo;.

The <samp>-P</samp> option forces a path search for each <var>name</var>, even if
<samp>-t</samp> would not return &lsquo;<samp>file</samp>&rsquo;.

If a command is hashed, <samp>-p</samp> and <samp>-P</samp> print the hashed value,
which is not necessarily the file that appears first in <code>$PATH</code>.

If the <samp>-a</samp> option is used, <code>type</code> returns all of the places
that contain an executable named <var>file</var>.
This includes aliases and functions, if and only if the <samp>-p</samp> option
is not also used.

If the <samp>-f</samp> option is used, <code>type</code> does not attempt to find
shell functions, as with the <code>command</code> builtin.

The return status is zero if all of the <var>name</var>s are found, non-zero
if any are not found.

</dd>
<dt id='index-typeset'><code>typeset</code><a href='#index-typeset' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">typeset [-afFgrxilnrtux] [-p] [<var>name</var>[=<var>value</var>] &hellip;]
</pre></div>

The <code>typeset</code> command is supplied for compatibility with the Korn
shell.
It is a synonym for the <code>declare</code> builtin command.

</dd>
<dt id='index-ulimit'><code>ulimit</code><a href='#index-ulimit' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">ulimit [-HS] -a
ulimit [-HS] [-bcdefiklmnpqrstuvxPRT] [<var>limit</var>]
</pre></div>

<code>ulimit</code> provides control over the resources available to processes
started by the shell, on systems that allow such control. If an
option is given, it is interpreted as follows:

<dl compact="compact">
<dt><code>-S</code></dt>
<dd>Change and report the soft limit associated with a resource.

</dd>
<dt><code>-H</code></dt>
<dd>Change and report the hard limit associated with a resource.

</dd>
<dt><code>-a</code></dt>
<dd>All current limits are reported; no limits are set.

</dd>
<dt><code>-b</code></dt>
<dd>The maximum socket buffer size.

</dd>
<dt><code>-c</code></dt>
<dd>The maximum size of core files created.

</dd>
<dt><code>-d</code></dt>
<dd>The maximum size of a process&rsquo;s data segment.

</dd>
<dt><code>-e</code></dt>
<dd>The maximum scheduling priority (&quot;nice&quot;).

</dd>
<dt><code>-f</code></dt>
<dd>The maximum size of files written by the shell and its children.

</dd>
<dt><code>-i</code></dt>
<dd>The maximum number of pending signals.

</dd>
<dt><code>-k</code></dt>
<dd>The maximum number of kqueues that may be allocated.

</dd>
<dt><code>-l</code></dt>
<dd>The maximum size that may be locked into memory.

</dd>
<dt><code>-m</code></dt>
<dd>The maximum resident set size (many systems do not honor this limit).

</dd>
<dt><code>-n</code></dt>
<dd>The maximum number of open file descriptors (most systems do not
allow this value to be set).

</dd>
<dt><code>-p</code></dt>
<dd>The pipe buffer size.

</dd>
<dt><code>-q</code></dt>
<dd>The maximum number of bytes in POSIX message queues.

</dd>
<dt><code>-r</code></dt>
<dd>The maximum real-time scheduling priority.

</dd>
<dt><code>-s</code></dt>
<dd>The maximum stack size.

</dd>
<dt><code>-t</code></dt>
<dd>The maximum amount of cpu time in seconds.

</dd>
<dt><code>-u</code></dt>
<dd>The maximum number of processes available to a single user.

</dd>
<dt><code>-v</code></dt>
<dd>The maximum amount of virtual memory available to the shell, and, on
some systems, to its children.

</dd>
<dt><code>-x</code></dt>
<dd>The maximum number of file locks.

</dd>
<dt><code>-P</code></dt>
<dd>The maximum number of pseudoterminals.

</dd>
<dt><code>-R</code></dt>
<dd>The maximum time a real-time process can run before blocking, in microseconds.

</dd>
<dt><code>-T</code></dt>
<dd>The maximum number of threads.
</dd>
</dl>

If <var>limit</var> is given, and the <samp>-a</samp> option is not used,
<var>limit</var> is the new value of the specified resource.
The special <var>limit</var> values <code>hard</code>, <code>soft</code>, and
<code>unlimited</code> stand for the current hard limit, the current soft limit,
and no limit, respectively.
A hard limit cannot be increased by a non-root user once it is set;
a soft limit may be increased up to the value of the hard limit.
Otherwise, the current value of the soft limit for the specified resource
is printed, unless the <samp>-H</samp> option is supplied.
When more than one
resource is specified, the limit name and unit, if appropriate,
are printed before the value.
When setting new limits, if neither <samp>-H</samp> nor <samp>-S</samp> is supplied,
both the hard and soft limits are set.
If no option is given, then <samp>-f</samp> is assumed. Values are in 1024-byte
increments, except for
<samp>-t</samp>, which is in seconds;
<samp>-R</samp>, which is in microseconds;
<samp>-p</samp>, which is in units of 512-byte blocks;
<samp>-P</samp>,
<samp>-T</samp>,
<samp>-b</samp>,
<samp>-k</samp>,
<samp>-n</samp> and <samp>-u</samp>, which are unscaled values;
and, when in POSIX Mode (see <a href="#Bash-POSIX-Mode">Bash POSIX Mode</a>),
<samp>-c</samp> and <samp>-f</samp>, which are in 512-byte increments.

The return status is zero unless an invalid option or argument is supplied,
or an error occurs while setting a new limit.

</dd>
<dt id='index-unalias'><code>unalias</code><a href='#index-unalias' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">unalias [-a] [<var>name</var> &hellip; ]
</pre></div>

Remove each <var>name</var> from the list of aliases. If <samp>-a</samp> is
supplied, all aliases are removed.
Aliases are described in <a href="#Aliases">Aliases</a>.
</dd>
</dl>

<hr>
</div>
<div class="section" id="Modifying-Shell-Behavior">
<div class="header">

Next: <a href="#Special-Builtins" accesskey="n" rel="next">Special Builtins</a>, Previous: <a href="#Bash-Builtins" accesskey="p" rel="prev">Bash Builtin Commands</a>, Up: <a href="#Shell-Builtin-Commands" accesskey="u" rel="up">Shell Builtin Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">4.3 Modifying Shell Behavior</h3>

<ul class="section-toc">
<li><a href="#The-Set-Builtin" accesskey="1">The Set Builtin</a></li>
<li><a href="#The-Shopt-Builtin" accesskey="2">The Shopt Builtin</a></li>
</ul>
<hr>
<div class="subsection" id="The-Set-Builtin">
<div class="header">

Next: <a href="#The-Shopt-Builtin" accesskey="n" rel="next">The Shopt Builtin</a>, Up: <a href="#Modifying-Shell-Behavior" accesskey="u" rel="up">Modifying Shell Behavior</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">4.3.1 The Set Builtin</h4>

This builtin is so complicated that it deserves its own section. <code>set</code>
allows you to change the values of shell options and set the positional
parameters, or to display the names and values of shell variables.

<dl compact="compact">
<dt id='index-set'><code>set</code><a href='#index-set' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">set [-abefhkmnptuvxBCEHPT] [-o <var>option-name</var>] [--] [-] [<var>argument</var> &hellip;]
set [+abefhkmnptuvxBCEHPT] [+o <var>option-name</var>] [--] [-] [<var>argument</var> &hellip;]
</pre></div>

If no options or arguments are supplied, <code>set</code> displays the names
and values of all shell variables and functions, sorted according to the
current locale, in a format that may be reused as input
for setting or resetting the currently-set variables.
Read-only variables cannot be reset.
In POSIX mode, only shell variables are listed.

When options are supplied, they set or unset shell attributes.
Options, if specified, have the following meanings:

<dl compact="compact">
<dt><code>-a</code></dt>
<dd>Each variable or function that is created or modified is given the
export attribute and marked for export to the environment of
subsequent commands.

</dd>
<dt><code>-b</code></dt>
<dd>Cause the status of terminated background jobs to be reported
immediately, rather than before printing the next primary prompt.

</dd>
<dt><code>-e</code></dt>
<dd>Exit immediately if
a pipeline (see <a href="#Pipelines">Pipelines</a>), which may consist of a single simple command
(see <a href="#Simple-Commands">Simple Commands</a>),
a list (see <a href="#Lists">Lists of Commands</a>),
or a compound command (see <a href="#Compound-Commands">Compound Commands</a>)
returns a non-zero status.
The shell does not exit if the command that fails is part of the
command list immediately following a <code>while</code> or <code>until</code> keyword,
part of the test in an <code>if</code> statement,
part of any command executed in a <code>&amp;&amp;</code> or <code>||</code> list except
the command following the final <code>&amp;&amp;</code> or <code>||</code>,
any command in a pipeline but the last,
or if the command&rsquo;s return status is being inverted with <code>!</code>.
If a compound command other than a subshell
returns a non-zero status because a command failed
while <samp>-e</samp> was being ignored, the shell does not exit.
A trap on <code>ERR</code>, if set, is executed before the shell exits.

This option applies to the shell environment and each subshell environment
separately (see <a href="#Command-Execution-Environment">Command Execution Environment</a>), and may cause
subshells to exit before executing all the commands in the subshell.

If a compound command or shell function executes in a context where
<samp>-e</samp> is being ignored,
none of the commands executed within the compound command or function body
will be affected by the <samp>-e</samp> setting, even if <samp>-e</samp> is set
and a command returns a failure status.
If a compound command or shell function sets <samp>-e</samp> while executing in
a context where <samp>-e</samp> is ignored, that setting will not have any
effect until the compound command or the command containing the function
call completes.

</dd>
<dt><code>-f</code></dt>
<dd>Disable filename expansion (globbing).

</dd>
<dt><code>-h</code></dt>
<dd>Locate and remember (hash) commands as they are looked up for execution.
This option is enabled by default.

</dd>
<dt><code>-k</code></dt>
<dd>All arguments in the form of assignment statements are placed
in the environment for a command, not just those that precede
the command name.

</dd>
<dt><code>-m</code></dt>
<dd>Job control is enabled (see <a href="#Job-Control">Job Control</a>).
All processes run in a separate process group.
When a background job completes, the shell prints a line
containing its exit status.

</dd>
<dt><code>-n</code></dt>
<dd>Read commands but do not execute them.
This may be used to check a script for syntax errors.
This option is ignored by interactive shells.

</dd>
<dt><code>-o <var>option-name</var></code></dt>
<dd>
Set the option corresponding to <var>option-name</var>:

<dl compact="compact">
<dt><code>allexport</code></dt>
<dd>Same as <code>-a</code>.

</dd>
<dt><code>braceexpand</code></dt>
<dd>Same as <code>-B</code>.

</dd>
<dt><code>emacs</code></dt>
<dd>Use an <code>emacs</code>-style line editing interface (see <a href="#Command-Line-Editing">Command Line Editing</a>).
This also affects the editing interface used for <code>read -e</code>.

</dd>
<dt><code>errexit</code></dt>
<dd>Same as <code>-e</code>.

</dd>
<dt><code>errtrace</code></dt>
<dd>Same as <code>-E</code>.

</dd>
<dt><code>functrace</code></dt>
<dd>Same as <code>-T</code>.

</dd>
<dt><code>hashall</code></dt>
<dd>Same as <code>-h</code>.

</dd>
<dt><code>histexpand</code></dt>
<dd>Same as <code>-H</code>.

</dd>
<dt><code>history</code></dt>
<dd>Enable command history, as described in <a href="#Bash-History-Facilities">Bash History Facilities</a>.
This option is on by default in interactive shells.

</dd>
<dt><code>ignoreeof</code></dt>
<dd>An interactive shell will not exit upon reading EOF.

</dd>
<dt><code>keyword</code></dt>
<dd>Same as <code>-k</code>.

</dd>
<dt><code>monitor</code></dt>
<dd>Same as <code>-m</code>.

</dd>
<dt><code>noclobber</code></dt>
<dd>Same as <code>-C</code>.

</dd>
<dt><code>noexec</code></dt>
<dd>Same as <code>-n</code>.

</dd>
<dt><code>noglob</code></dt>
<dd>Same as <code>-f</code>.

</dd>
<dt><code>nolog</code></dt>
<dd>Currently ignored.

</dd>
<dt><code>notify</code></dt>
<dd>Same as <code>-b</code>.

</dd>
<dt><code>nounset</code></dt>
<dd>Same as <code>-u</code>.

</dd>
<dt><code>onecmd</code></dt>
<dd>Same as <code>-t</code>.

</dd>
<dt><code>physical</code></dt>
<dd>Same as <code>-P</code>.

</dd>
<dt><code>pipefail</code></dt>
<dd>If set, the return value of a pipeline is the value of the last
(rightmost) command to exit with a non-zero status, or zero if all
commands in the pipeline exit successfully.
This option is disabled by default.

</dd>
<dt><code>posix</code></dt>
<dd>Change the behavior of Bash where the default operation differs
from the POSIX standard to match the standard
(see <a href="#Bash-POSIX-Mode">Bash POSIX Mode</a>).
This is intended to make Bash behave as a strict superset of that
standard.

</dd>
<dt><code>privileged</code></dt>
<dd>Same as <code>-p</code>.

</dd>
<dt><code>verbose</code></dt>
<dd>Same as <code>-v</code>.

</dd>
<dt><code>vi</code></dt>
<dd>Use a <code>vi</code>-style line editing interface.
This also affects the editing interface used for <code>read -e</code>.

</dd>
<dt><code>xtrace</code></dt>
<dd>Same as <code>-x</code>.
</dd>
</dl>

</dd>
<dt><code>-p</code></dt>
<dd>Turn on privileged mode.
In this mode, the <code>$BASH_ENV</code> and <code>$ENV</code> files are not
processed, shell functions are not inherited from the environment,
and the <code>SHELLOPTS</code>, <code>BASHOPTS</code>, <code>CDPATH</code> and <code>GLOBIGNORE</code>
variables, if they appear in the environment, are ignored.
If the shell is started with the effective user (group) id not equal to the
real user (group) id, and the <samp>-p</samp> option is not supplied, these actions
are taken and the effective user id is set to the real user id.
If the <samp>-p</samp> option is supplied at startup, the effective user id is
not reset.
Turning this option off causes the effective user
and group ids to be set to the real user and group ids.

</dd>
<dt><code>-r</code></dt>
<dd>Enable restricted shell mode.
This option cannot be unset once it has been set.

</dd>
<dt><code>-t</code></dt>
<dd>Exit after reading and executing one command.

</dd>
<dt><code>-u</code></dt>
<dd>Treat unset variables and parameters other than the special parameters
&lsquo;<samp>@</samp>&rsquo; or &lsquo;<samp>*</samp>&rsquo;,
or array variables subscripted with &lsquo;<samp>@</samp>&rsquo; or &lsquo;<samp>*</samp>&rsquo;,
as an error when performing parameter expansion.
An error message will be written to the standard error, and a non-interactive
shell will exit.

</dd>
<dt><code>-v</code></dt>
<dd>Print shell input lines as they are read.

</dd>
<dt><code>-x</code></dt>
<dd>Print a trace of simple commands, <code>for</code> commands, <code>case</code>
commands, <code>select</code> commands, and arithmetic <code>for</code> commands
and their arguments or associated word lists after they are
expanded and before they are executed. The value of the <code>PS4</code>
variable is expanded and the resultant value is printed before
the command and its expanded arguments.

</dd>
<dt><code>-B</code></dt>
<dd>The shell will perform brace expansion (see <a href="#Brace-Expansion">Brace Expansion</a>).
This option is on by default.

</dd>
<dt><code>-C</code></dt>
<dd>Prevent output redirection using &lsquo;<samp>&gt;</samp>&rsquo;, &lsquo;<samp>&gt;&amp;</samp>&rsquo;, and &lsquo;<samp>&lt;&gt;</samp>&rsquo;
from overwriting existing files.

</dd>
<dt><code>-E</code></dt>
<dd>If set, any trap on <code>ERR</code> is inherited by shell functions, command
substitutions, and commands executed in a subshell environment.
The <code>ERR</code> trap is normally not inherited in such cases.

</dd>
<dt><code>-H</code></dt>
<dd>Enable &lsquo;<samp>!</samp>&rsquo; style history substitution (see <a href="#History-Interaction">History Expansion</a>).
This option is on by default for interactive shells.

</dd>
<dt><code>-P</code></dt>
<dd>If set, do not resolve symbolic links when performing commands such as
<code>cd</code> which change the current directory. The physical directory
is used instead. By default, Bash follows
the logical chain of directories when performing commands
which change the current directory.

For example, if <samp>/usr/sys</samp> is a symbolic link to <samp>/usr/local/sys</samp>
then:
<div class="example">
<pre class="example">$ cd /usr/sys; echo $PWD
/usr/sys
$ cd ..; pwd
/usr
</pre></div>

If <code>set -P</code> is on, then:
<div class="example">
<pre class="example">$ cd /usr/sys; echo $PWD
/usr/local/sys
$ cd ..; pwd
/usr/local
</pre></div>

</dd>
<dt><code>-T</code></dt>
<dd>If set, any trap on <code>DEBUG</code> and <code>RETURN</code> are inherited by
shell functions, command substitutions, and commands executed
in a subshell environment.
The <code>DEBUG</code> and <code>RETURN</code> traps are normally not inherited
in such cases.

</dd>
<dt><code>--</code></dt>
<dd>If no arguments follow this option, then the positional parameters are
unset. Otherwise, the positional parameters are set to the
<var>arguments</var>, even if some of them begin with a &lsquo;<samp>-</samp>&rsquo;.

</dd>
<dt><code>-</code></dt>
<dd>Signal the end of options, cause all remaining <var>arguments</var>
to be assigned to the positional parameters. The <samp>-x</samp>
and <samp>-v</samp> options are turned off.
If there are no arguments, the positional parameters remain unchanged.
</dd>
</dl>

Using &lsquo;<samp>+</samp>&rsquo; rather than &lsquo;<samp>-</samp>&rsquo; causes these options to be
turned off. The options can also be used upon invocation of the
shell. The current set of options may be found in <code>$-</code>.

The remaining N <var>arguments</var> are positional parameters and are
assigned, in order, to <code>$1</code>, <code>$2</code>, &hellip; <code>$N</code>.
The special parameter <code>#</code> is set to N.

The return status is always zero unless an invalid option is supplied.
</dd>
</dl>

<hr>
</div>
<div class="subsection" id="The-Shopt-Builtin">
<div class="header">

Previous: <a href="#The-Set-Builtin" accesskey="p" rel="prev">The Set Builtin</a>, Up: <a href="#Modifying-Shell-Behavior" accesskey="u" rel="up">Modifying Shell Behavior</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">4.3.2 The Shopt Builtin</h4>

This builtin allows you to change additional shell optional behavior.

<dl compact="compact">
<dt id='index-shopt'><code>shopt</code><a href='#index-shopt' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">shopt [-pqsu] [-o] [<var>optname</var> &hellip;]
</pre></div>

Toggle the values of settings controlling optional shell behavior.
The settings can be either those listed below, or, if the
<samp>-o</samp> option is used, those available with the <samp>-o</samp>
option to the <code>set</code> builtin command (see <a href="#The-Set-Builtin">The Set Builtin</a>).
With no options, or with the <samp>-p</samp> option, a list of all settable
options is displayed, with an indication of whether or not each is set;
if <var>optname</var>s are supplied, the output is restricted to those options.
The <samp>-p</samp> option causes output to be displayed in a form that
may be reused as input.
Other options have the following meanings:

<dl compact="compact">
<dt><code>-s</code></dt>
<dd>Enable (set) each <var>optname</var>.

</dd>
<dt><code>-u</code></dt>
<dd>Disable (unset) each <var>optname</var>.

</dd>
<dt><code>-q</code></dt>
<dd>Suppresses normal output; the return status
indicates whether the <var>optname</var> is set or unset.
If multiple <var>optname</var> arguments are given with <samp>-q</samp>,
the return status is zero if all <var>optname</var>s are enabled;
non-zero otherwise.

</dd>
<dt><code>-o</code></dt>
<dd>Restricts the values of
<var>optname</var> to be those defined for the <samp>-o</samp> option to the
<code>set</code> builtin (see <a href="#The-Set-Builtin">The Set Builtin</a>).
</dd>
</dl>

If either <samp>-s</samp> or <samp>-u</samp>
is used with no <var>optname</var> arguments, <code>shopt</code> shows only
those options which are set or unset, respectively.

Unless otherwise noted, the <code>shopt</code> options are disabled (off)
by default.

The return status when listing options is zero if all <var>optname</var>s
are enabled, non-zero otherwise. When setting or unsetting options,
the return status is zero unless an <var>optname</var> is not a valid shell
option.

The list of <code>shopt</code> options is:
<dl compact="compact">
<dt><code>assoc_expand_once</code></dt>
<dd>If set, the shell suppresses multiple evaluation of associative array
subscripts during arithmetic expression evaluation, while executing
builtins that can perform variable assignments,
and while executing builtins that perform array dereferencing.

</dd>
<dt><code>autocd</code></dt>
<dd>If set, a command name that is the name of a directory is executed as if
it were the argument to the <code>cd</code> command.
This option is only used by interactive shells.

</dd>
<dt><code>cdable_vars</code></dt>
<dd>If this is set, an argument to the <code>cd</code> builtin command that
is not a directory is assumed to be the name of a variable whose
value is the directory to change to.

</dd>
<dt><code>cdspell</code></dt>
<dd>If set, minor errors in the spelling of a directory component in a
<code>cd</code> command will be corrected.
The errors checked for are transposed characters,
a missing character, and a character too many.
If a correction is found, the corrected path is printed,
and the command proceeds.
This option is only used by interactive shells.

</dd>
<dt><code>checkhash</code></dt>
<dd>If this is set, Bash checks that a command found in the hash
table exists before trying to execute it. If a hashed command no
longer exists, a normal path search is performed.

</dd>
<dt><code>checkjobs</code></dt>
<dd>If set, Bash lists the status of any stopped and running jobs before
exiting an interactive shell. If any jobs are running, this causes
the exit to be deferred until a second exit is attempted without an
intervening command (see <a href="#Job-Control">Job Control</a>).
The shell always postpones exiting if any jobs are stopped.

</dd>
<dt><code>checkwinsize</code></dt>
<dd>If set, Bash checks the window size after each external (non-builtin)
command and, if necessary, updates the values of 
<code>LINES</code> and <code>COLUMNS</code>.
This option is enabled by default.

</dd>
<dt><code>cmdhist</code></dt>
<dd>If set, Bash
attempts to save all lines of a multiple-line
command in the same history entry. This allows
easy re-editing of multi-line commands.
This option is enabled by default, but only has an effect if command
history is enabled (see <a href="#Bash-History-Facilities">Bash History Facilities</a>).

</dd>
<dt><code>compat31</code></dt>
<dt><code>compat32</code></dt>
<dt><code>compat40</code></dt>
<dt><code>compat41</code></dt>
<dt><code>compat42</code></dt>
<dt><code>compat43</code></dt>
<dt><code>compat44</code></dt>
<dd>These control aspects of the shell&rsquo;s compatibility mode
(see <a href="#Shell-Compatibility-Mode">Shell Compatibility Mode</a>).

</dd>
<dt><code>complete_fullquote</code></dt>
<dd>If set, Bash
quotes all shell metacharacters in filenames and directory names when
performing completion.
If not set, Bash
removes metacharacters such as the dollar sign from the set of
characters that will be quoted in completed filenames
when these metacharacters appear in shell variable references in words to be
completed.
This means that dollar signs in variable names that expand to directories
will not be quoted;
however, any dollar signs appearing in filenames will not be quoted, either.
This is active only when bash is using backslashes to quote completed
filenames.
This variable is set by default, which is the default Bash behavior in
versions through 4.2.

</dd>
<dt><code>direxpand</code></dt>
<dd>If set, Bash
replaces directory names with the results of word expansion when performing
filename completion. This changes the contents of the Readline editing
buffer.
If not set, Bash attempts to preserve what the user typed.

</dd>
<dt><code>dirspell</code></dt>
<dd>If set, Bash
attempts spelling correction on directory names during word completion 
if the directory name initially supplied does not exist.

</dd>
<dt><code>dotglob</code></dt>
<dd>If set, Bash includes filenames beginning with a &lsquo;.&rsquo; in
the results of filename expansion.
The filenames &lsquo;<samp>.</samp>&rsquo; and &lsquo;<samp>..</samp>&rsquo; must always be matched explicitly,
even if <code>dotglob</code> is set.

</dd>
<dt><code>execfail</code></dt>
<dd>If this is set, a non-interactive shell will not exit if
it cannot execute the file specified as an argument to the <code>exec</code>
builtin command. An interactive shell does not exit if <code>exec</code>
fails.

</dd>
<dt><code>expand_aliases</code></dt>
<dd>If set, aliases are expanded as described below under Aliases,
<a href="#Aliases">Aliases</a>.
This option is enabled by default for interactive shells.

</dd>
<dt><code>extdebug</code></dt>
<dd>If set at shell invocation,
or in a shell startup file,
arrange to execute the debugger profile
before the shell starts, identical to the <samp>--debugger</samp> option.
If set after invocation, behavior intended for use by debuggers is enabled:

<ol>
<li> The <samp>-F</samp> option to the <code>declare</code> builtin (see <a href="#Bash-Builtins">Bash Builtin Commands</a>)
displays the source file name and line number corresponding to each function
name supplied as an argument.

</li><li> If the command run by the <code>DEBUG</code> trap returns a non-zero value, the
next command is skipped and not executed.

</li><li> If the command run by the <code>DEBUG</code> trap returns a value of 2, and the
shell is executing in a subroutine (a shell function or a shell script
executed by the <code>.</code> or <code>source</code> builtins), the shell simulates
a call to <code>return</code>.

</li><li> <code>BASH_ARGC</code> and <code>BASH_ARGV</code> are updated as described in their
descriptions (see <a href="#Bash-Variables">Bash Variables</a>).

</li><li> Function tracing is enabled: command substitution, shell functions, and
subshells invoked with <code>( <var>command</var> )</code> inherit the
<code>DEBUG</code> and <code>RETURN</code> traps.

</li><li> Error tracing is enabled: command substitution, shell functions, and
subshells invoked with <code>( <var>command</var> )</code> inherit the
<code>ERR</code> trap.
</li></ol>

</dd>
<dt><code>extglob</code></dt>
<dd>If set, the extended pattern matching features described above
(see <a href="#Pattern-Matching">Pattern Matching</a>) are enabled.

</dd>
<dt><code>extquote</code></dt>
<dd>If set, <code>$'<var>string</var>'</code> and <code>$&quot;<var>string</var>&quot;</code> quoting is 
performed within <code>${<var>parameter</var>}</code> expansions 
enclosed in double quotes. This option is enabled by default. 

</dd>
<dt><code>failglob</code></dt>
<dd>If set, patterns which fail to match filenames during filename expansion
result in an expansion error.

</dd>
<dt><code>force_fignore</code></dt>
<dd>If set, the suffixes specified by the <code>FIGNORE</code> shell variable
cause words to be ignored when performing word completion even if
the ignored words are the only possible completions.
See <a href="#Bash-Variables">Bash Variables</a>, for a description of <code>FIGNORE</code>.
This option is enabled by default.

</dd>
<dt><code>globasciiranges</code></dt>
<dd>If set, range expressions used in pattern matching bracket expressions
(see <a href="#Pattern-Matching">Pattern Matching</a>)
behave as if in the traditional C locale when performing
comparisons. That is, the current locale&rsquo;s collating sequence
is not taken into account, so
&lsquo;<samp>b</samp>&rsquo; will not collate between &lsquo;<samp>A</samp>&rsquo; and &lsquo;<samp>B</samp>&rsquo;,
and upper-case and lower-case ASCII characters will collate together. 

</dd>
<dt><code>globskipdots</code></dt>
<dd>If set, filename expansion will never match the filenames
&lsquo;<samp>.</samp>&rsquo; and &lsquo;<samp>..</samp>&rsquo;,
even if the pattern begins with a &lsquo;<samp>.</samp>&rsquo;.
This option is enabled by default.

</dd>
<dt><code>globstar</code></dt>
<dd>If set, the pattern &lsquo;<samp>**</samp>&rsquo; used in a filename expansion context will
match all files and zero or more directories and subdirectories.
If the pattern is followed by a &lsquo;<samp>/</samp>&rsquo;, only directories and
subdirectories match.

</dd>
<dt><code>gnu_errfmt</code></dt>
<dd>If set, shell error messages are written in the standard GNU error
message format.

</dd>
<dt><code>histappend</code></dt>
<dd>If set, the history list is appended to the file named by the value
of the <code>HISTFILE</code>
variable when the shell exits, rather than overwriting the file.

</dd>
<dt><code>histreedit</code></dt>
<dd>If set, and Readline
is being used, a user is given the opportunity to re-edit a
failed history substitution.

</dd>
<dt><code>histverify</code></dt>
<dd>If set, and Readline
is being used, the results of history substitution are not immediately
passed to the shell parser. Instead, the resulting line is loaded into
the Readline editing buffer, allowing further modification.

</dd>
<dt><code>hostcomplete</code></dt>
<dd>If set, and Readline is being used, Bash will attempt to perform
hostname completion when a word containing a &lsquo;<samp>@</samp>&rsquo; is being
completed (see <a href="#Commands-For-Completion">Letting Readline Type For You</a>). This option is enabled
by default.

</dd>
<dt><code>huponexit</code></dt>
<dd>If set, Bash will send <code>SIGHUP</code> to all jobs when an interactive
login shell exits (see <a href="#Signals">Signals</a>).

</dd>
<dt><code>inherit_errexit</code></dt>
<dd>If set, command substitution inherits the value of the <code>errexit</code> option,
instead of unsetting it in the subshell environment.
This option is enabled when POSIX mode is enabled.

</dd>
<dt><code>interactive_comments</code></dt>
<dd>Allow a word beginning with &lsquo;<samp>#</samp>&rsquo;
to cause that word and all remaining characters on that
line to be ignored in an interactive shell.
This option is enabled by default.

</dd>
<dt><code>lastpipe</code></dt>
<dd>If set, and job control is not active, the shell runs the last command of
a pipeline not executed in the background in the current shell environment.

</dd>
<dt><code>lithist</code></dt>
<dd>If enabled, and the <code>cmdhist</code>
option is enabled, multi-line commands are saved to the history with
embedded newlines rather than using semicolon separators where possible.

</dd>
<dt><code>localvar_inherit</code></dt>
<dd>If set, local variables inherit the value and attributes of a variable of
the same name that exists at a previous scope before any new value is
assigned. The <code>nameref</code> attribute is not inherited.

</dd>
<dt><code>localvar_unset</code></dt>
<dd>If set, calling <code>unset</code> on local variables in previous function scopes
marks them so subsequent lookups find them unset until that function
returns. This is identical to the behavior of unsetting local variables
at the current function scope.

</dd>
<dt><code>login_shell</code></dt>
<dd>The shell sets this option if it is started as a login shell
(see <a href="#Invoking-Bash">Invoking Bash</a>).
The value may not be changed.

</dd>
<dt><code>mailwarn</code></dt>
<dd>If set, and a file that Bash is checking for mail has been
accessed since the last time it was checked, the message
<code>&quot;The mail in <var>mailfile</var> has been read&quot;</code> is displayed.

</dd>
<dt><code>no_empty_cmd_completion</code></dt>
<dd>If set, and Readline is being used, Bash will not attempt to search
the <code>PATH</code> for possible completions when completion is attempted
on an empty line.

</dd>
<dt><code>nocaseglob</code></dt>
<dd>If set, Bash matches filenames in a case-insensitive fashion when
performing filename expansion.

</dd>
<dt><code>nocasematch</code></dt>
<dd>If set, Bash matches patterns in a case-insensitive fashion when
performing matching while executing <code>case</code> or <code>[[</code>
conditional commands (see <a href="#Conditional-Constructs">Conditional Constructs</a>,
when performing pattern substitution word expansions,
or when filtering possible completions as part of programmable completion.

</dd>
<dt><code>noexpand_translation</code></dt>
<dd>If set, Bash
encloses the translated results of $&quot;...&quot; quoting in single quotes
instead of double quotes.
If the string is not translated, this has no effect.

</dd>
<dt><code>nullglob</code></dt>
<dd>If set, Bash allows filename patterns which match no
files to expand to a null string, rather than themselves.

</dd>
<dt><code>patsub_replacement</code></dt>
<dd>If set, Bash
expands occurrences of &lsquo;<samp>&amp;</samp>&rsquo; in the replacement string of pattern
substitution to the text matched by the pattern, as described
above (see <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>).
This option is enabled by default.

</dd>
<dt><code>progcomp</code></dt>
<dd>If set, the programmable completion facilities
(see <a href="#Programmable-Completion">Programmable Completion</a>) are enabled.
This option is enabled by default.

</dd>
<dt><code>progcomp_alias</code></dt>
<dd>If set, and programmable completion is enabled, Bash treats a command
name that doesn&rsquo;t have any completions as a possible alias and attempts
alias expansion. If it has an alias, Bash attempts programmable
completion using the command word resulting from the expanded alias.

</dd>
<dt><code>promptvars</code></dt>
<dd>If set, prompt strings undergo
parameter expansion, command substitution, arithmetic
expansion, and quote removal after being expanded
as described below (see <a href="#Controlling-the-Prompt">Controlling the Prompt</a>).
This option is enabled by default.

</dd>
<dt><code>restricted_shell</code></dt>
<dd>The shell sets this option if it is started in restricted mode
(see <a href="#The-Restricted-Shell">The Restricted Shell</a>).
The value may not be changed.
This is not reset when the startup files are executed, allowing
the startup files to discover whether or not a shell is restricted.

</dd>
<dt><code>shift_verbose</code></dt>
<dd>If this is set, the <code>shift</code>
builtin prints an error message when the shift count exceeds the
number of positional parameters.

</dd>
<dt><code>sourcepath</code></dt>
<dd>If set, the <code>.</code> (<code>source</code>) builtin uses the value of <code>PATH</code>
to find the directory containing the file supplied as an argument.
This option is enabled by default.

</dd>
<dt><code>varredir_close</code></dt>
<dd>If set, the shell automatically closes file descriptors assigned using the
<code>{varname}</code> redirection syntax (see <a href="#Redirections">Redirections</a>) instead of
leaving them open when the command completes.

</dd>
<dt><code>xpg_echo</code></dt>
<dd>If set, the <code>echo</code> builtin expands backslash-escape sequences
by default.

</dd>
</dl>
</dd>
</dl>

<hr>
</div>
</div>
<div class="section" id="Special-Builtins">
<div class="header">

Previous: <a href="#Modifying-Shell-Behavior" accesskey="p" rel="prev">Modifying Shell Behavior</a>, Up: <a href="#Shell-Builtin-Commands" accesskey="u" rel="up">Shell Builtin Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">4.4 Special Builtins</h3>

For historical reasons, the POSIX standard has classified
several builtin commands as special.
When Bash is executing in POSIX mode, the special builtins
differ from other builtin commands in three respects:

<ol>
<li> Special builtins are found before shell functions during command lookup.

</li><li> If a special builtin returns an error status, a non-interactive shell exits.

</li><li> Assignment statements preceding the command stay in effect in the shell
environment after the command completes.
</li></ol>

When Bash is not executing in POSIX mode, these builtins behave no
differently than the rest of the Bash builtin commands.
The Bash POSIX mode is described in <a href="#Bash-POSIX-Mode">Bash POSIX Mode</a>. 

These are the POSIX special builtins:
<div class="example">
<pre class="example">break : . continue eval exec exit export readonly return set
shift trap unset
</pre></div>

<hr>
</div>
</div>
<div class="chapter" id="Shell-Variables">
<div class="header">

Next: <a href="#Bash-Features" accesskey="n" rel="next">Bash Features</a>, Previous: <a href="#Shell-Builtin-Commands" accesskey="p" rel="prev">Shell Builtin Commands</a>, Up: <a href="#Top" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h2 class="chapter">5 Shell Variables</h2>

This chapter describes the shell variables that Bash uses.
Bash automatically assigns default values to a number of variables.

<ul class="section-toc">
<li><a href="#Bourne-Shell-Variables" accesskey="1">Bourne Shell Variables</a></li>
<li><a href="#Bash-Variables" accesskey="2">Bash Variables</a></li>
</ul>
<hr>
<div class="section" id="Bourne-Shell-Variables">
<div class="header">

Next: <a href="#Bash-Variables" accesskey="n" rel="next">Bash Variables</a>, Up: <a href="#Shell-Variables" accesskey="u" rel="up">Shell Variables</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">5.1 Bourne Shell Variables</h3>

Bash uses certain shell variables in the same way as the Bourne shell.
In some cases, Bash assigns a default value to the variable.

<dl compact="compact">
<dt id='index-CDPATH'><code>CDPATH</code><a href='#index-CDPATH' class='copiable-anchor'> &para;</a></dt>
<dd>A colon-separated list of directories used as a search path for
the <code>cd</code> builtin command.

</dd>
<dt id='index-HOME'><code>HOME</code><a href='#index-HOME' class='copiable-anchor'> &para;</a></dt>
<dd>The current user&rsquo;s home directory; the default for the <code>cd</code> builtin
command.
The value of this variable is also used by tilde expansion
(see <a href="#Tilde-Expansion">Tilde Expansion</a>).

</dd>
<dt id='index-IFS'><code>IFS</code><a href='#index-IFS' class='copiable-anchor'> &para;</a></dt>
<dd>A list of characters that separate fields; used when the shell splits
words as part of expansion.

</dd>
<dt id='index-MAIL'><code>MAIL</code><a href='#index-MAIL' class='copiable-anchor'> &para;</a></dt>
<dd>If this parameter is set to a filename or directory name
and the <code>MAILPATH</code> variable
is not set, Bash informs the user of the arrival of mail in
the specified file or Maildir-format directory.

</dd>
<dt id='index-MAILPATH'><code>MAILPATH</code><a href='#index-MAILPATH' class='copiable-anchor'> &para;</a></dt>
<dd>A colon-separated list of filenames which the shell periodically checks
for new mail.
Each list entry can specify the message that is printed when new mail
arrives in the mail file by separating the filename from the message with
a &lsquo;<samp>?</samp>&rsquo;.
When used in the text of the message, <code>$_</code> expands to the name of
the current mail file.

</dd>
<dt id='index-OPTARG'><code>OPTARG</code><a href='#index-OPTARG' class='copiable-anchor'> &para;</a></dt>
<dd>The value of the last option argument processed by the <code>getopts</code> builtin.

</dd>
<dt id='index-OPTIND'><code>OPTIND</code><a href='#index-OPTIND' class='copiable-anchor'> &para;</a></dt>
<dd>The index of the last option argument processed by the <code>getopts</code> builtin.

</dd>
<dt id='index-PATH'><code>PATH</code><a href='#index-PATH' class='copiable-anchor'> &para;</a></dt>
<dd>A colon-separated list of directories in which the shell looks for
commands.
A zero-length (null) directory name in the value of <code>PATH</code> indicates the
current directory.
A null directory name may appear as two adjacent colons, or as an initial
or trailing colon.

</dd>
<dt id='index-PS1'><code>PS1</code><a href='#index-PS1' class='copiable-anchor'> &para;</a></dt>
<dd>The primary prompt string. The default value is &lsquo;<samp>\s-\v\$ </samp>&rsquo;.
See <a href="#Controlling-the-Prompt">Controlling the Prompt</a>, for the complete list of escape
sequences that are expanded before <code>PS1</code> is displayed.

</dd>
<dt id='index-PS2'><code>PS2</code><a href='#index-PS2' class='copiable-anchor'> &para;</a></dt>
<dd>The secondary prompt string. The default value is &lsquo;<samp>&gt; </samp>&rsquo;.
<code>PS2</code> is expanded in the same way as <code>PS1</code> before being
displayed.

</dd>
</dl>

<hr>
</div>
<div class="section" id="Bash-Variables">
<div class="header">

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<h3 class="section">5.2 Bash Variables</h3>

These variables are set or used by Bash, but other shells
do not normally treat them specially.

A few variables used by Bash are described in different chapters:
variables for controlling the job control facilities
(see <a href="#Job-Control-Variables">Job Control Variables</a>).

<dl compact="compact">
<dt id='index-_005f'><code>_</code><a href='#index-_005f' class='copiable-anchor'> &para;</a></dt>
<dd>
($_, an underscore.)
At shell startup, set to the pathname used to invoke the
shell or shell script being executed as passed in the environment
or argument list.
Subsequently, expands to the last argument to the previous simple
command executed in the foreground, after expansion. 
Also set to the full pathname used to invoke each command executed
and placed in the environment exported to that command.
When checking mail, this parameter holds the name of the mail file.

</dd>
<dt id='index-BASH'><code>BASH</code><a href='#index-BASH' class='copiable-anchor'> &para;</a></dt>
<dd>The full pathname used to execute the current instance of Bash.

</dd>
<dt id='index-BASHOPTS'><code>BASHOPTS</code><a href='#index-BASHOPTS' class='copiable-anchor'> &para;</a></dt>
<dd>A colon-separated list of enabled shell options. Each word in
the list is a valid argument for the <samp>-s</samp> option to the
<code>shopt</code> builtin command (see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>).
The options appearing in <code>BASHOPTS</code> are those reported
as &lsquo;<samp>on</samp>&rsquo; by &lsquo;<samp>shopt</samp>&rsquo;.
If this variable is in the environment when Bash
starts up, each shell option in the list will be enabled before
reading any startup files. This variable is readonly.

</dd>
<dt id='index-BASHPID'><code>BASHPID</code><a href='#index-BASHPID' class='copiable-anchor'> &para;</a></dt>
<dd>Expands to the process ID of the current Bash process.
This differs from <code>$$</code> under certain circumstances, such as subshells
that do not require Bash to be re-initialized.
Assignments to <code>BASHPID</code> have no effect.
If <code>BASHPID</code>
is unset, it loses its special properties, even if it is
subsequently reset.

</dd>
<dt id='index-BASH_005fALIASES'><code>BASH_ALIASES</code><a href='#index-BASH_005fALIASES' class='copiable-anchor'> &para;</a></dt>
<dd>An associative array variable whose members correspond to the internal
list of aliases as maintained by the <code>alias</code> builtin.
(see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>).
Elements added to this array appear in the alias list; however,
unsetting array elements currently does not cause aliases to be removed
from the alias list.
If <code>BASH_ALIASES</code>
is unset, it loses its special properties, even if it is
subsequently reset.

</dd>
<dt id='index-BASH_005fARGC'><code>BASH_ARGC</code><a href='#index-BASH_005fARGC' class='copiable-anchor'> &para;</a></dt>
<dd>An array variable whose values are the number of parameters in each
frame of the current bash execution call stack. The number of
parameters to the current subroutine (shell function or script executed
with <code>.</code> or <code>source</code>) is at the top of the stack. When a
subroutine is executed, the number of parameters passed is pushed onto
<code>BASH_ARGC</code>.
The shell sets <code>BASH_ARGC</code> only when in extended debugging mode
(see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>
for a description of the <code>extdebug</code> option to the <code>shopt</code>
builtin).
Setting <code>extdebug</code> after the shell has started to execute a script,
or referencing this variable when <code>extdebug</code> is not set,
may result in inconsistent values.

</dd>
<dt id='index-BASH_005fARGV'><code>BASH_ARGV</code><a href='#index-BASH_005fARGV' class='copiable-anchor'> &para;</a></dt>
<dd>An array variable containing all of the parameters in the current bash
execution call stack. The final parameter of the last subroutine call
is at the top of the stack; the first parameter of the initial call is
at the bottom. When a subroutine is executed, the parameters supplied
are pushed onto <code>BASH_ARGV</code>.
The shell sets <code>BASH_ARGV</code> only when in extended debugging mode
(see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>
for a description of the <code>extdebug</code> option to the <code>shopt</code>
builtin).
Setting <code>extdebug</code> after the shell has started to execute a script,
or referencing this variable when <code>extdebug</code> is not set,
may result in inconsistent values.

</dd>
<dt id='index-BASH_005fARGV0'><code>BASH_ARGV0</code><a href='#index-BASH_005fARGV0' class='copiable-anchor'> &para;</a></dt>
<dd>When referenced, this variable expands to the name of the shell or shell
script (identical to <code>$0</code>; See <a href="#Special-Parameters">Special Parameters</a>,
for the description of special parameter 0).
Assignment to <code>BASH_ARGV0</code>
causes the value assigned to also be assigned to <code>$0</code>.
If <code>BASH_ARGV0</code>
is unset, it loses its special properties, even if it is
subsequently reset.

</dd>
<dt id='index-BASH_005fCMDS'><code>BASH_CMDS</code><a href='#index-BASH_005fCMDS' class='copiable-anchor'> &para;</a></dt>
<dd>An associative array variable whose members correspond to the internal
hash table of commands as maintained by the <code>hash</code> builtin
(see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>).
Elements added to this array appear in the hash table; however,
unsetting array elements currently does not cause command names to be removed
from the hash table.
If <code>BASH_CMDS</code>
is unset, it loses its special properties, even if it is
subsequently reset.

</dd>
<dt id='index-BASH_005fCOMMAND'><code>BASH_COMMAND</code><a href='#index-BASH_005fCOMMAND' class='copiable-anchor'> &para;</a></dt>
<dd>The command currently being executed or about to be executed, unless the
shell is executing a command as the result of a trap,
in which case it is the command executing at the time of the trap.
If <code>BASH_COMMAND</code>
is unset, it loses its special properties, even if it is
subsequently reset.

</dd>
<dt id='index-BASH_005fCOMPAT'><code>BASH_COMPAT</code><a href='#index-BASH_005fCOMPAT' class='copiable-anchor'> &para;</a></dt>
<dd>The value is used to set the shell&rsquo;s compatibility level.
See <a href="#Shell-Compatibility-Mode">Shell Compatibility Mode</a>, for a description of the various
compatibility levels and their effects.
The value may be a decimal number (e.g., 4.2) or an integer (e.g., 42)
corresponding to the desired compatibility level.
If <code>BASH_COMPAT</code> is unset or set to the empty string, the compatibility
level is set to the default for the current version.
If <code>BASH_COMPAT</code> is set to a value that is not one of the valid
compatibility levels, the shell prints an error message and sets the
compatibility level to the default for the current version.
The valid values correspond to the compatibility levels
described below (see <a href="#Shell-Compatibility-Mode">Shell Compatibility Mode</a>).
For example, 4.2 and 42 are valid values that correspond
to the <code>compat42</code> <code>shopt</code> option
and set the compatibility level to 42.
The current version is also a valid value.

</dd>
<dt id='index-BASH_005fENV'><code>BASH_ENV</code><a href='#index-BASH_005fENV' class='copiable-anchor'> &para;</a></dt>
<dd>If this variable is set when Bash is invoked to execute a shell
script, its value is expanded and used as the name of a startup file
to read before executing the script. See <a href="#Bash-Startup-Files">Bash Startup Files</a>.

</dd>
<dt id='index-BASH_005fEXECUTION_005fSTRING'><code>BASH_EXECUTION_STRING</code><a href='#index-BASH_005fEXECUTION_005fSTRING' class='copiable-anchor'> &para;</a></dt>
<dd>The command argument to the <samp>-c</samp> invocation option.

</dd>
<dt id='index-BASH_005fLINENO'><code>BASH_LINENO</code><a href='#index-BASH_005fLINENO' class='copiable-anchor'> &para;</a></dt>
<dd>An array variable whose members are the line numbers in source files
where each corresponding member of <code>FUNCNAME</code> was invoked.
<code>${BASH_LINENO[$i]}</code> is the line number in the source file
(<code>${BASH_SOURCE[$i+1]}</code>) where
<code>${FUNCNAME[$i]}</code> was called (or <code>${BASH_LINENO[$i-1]}</code> if
referenced within another shell function). 
Use <code>LINENO</code> to obtain the current line number.

</dd>
<dt id='index-BASH_005fLOADABLES_005fPATH'><code>BASH_LOADABLES_PATH</code><a href='#index-BASH_005fLOADABLES_005fPATH' class='copiable-anchor'> &para;</a></dt>
<dd>A colon-separated list of directories in which the shell looks for
dynamically loadable builtins specified by the
<code>enable</code> command.

</dd>
<dt id='index-BASH_005fREMATCH'><code>BASH_REMATCH</code><a href='#index-BASH_005fREMATCH' class='copiable-anchor'> &para;</a></dt>
<dd>An array variable whose members are assigned by the &lsquo;<samp>=~</samp>&rsquo; binary
operator to the <code>[[</code> conditional command
(see <a href="#Conditional-Constructs">Conditional Constructs</a>).
The element with index 0 is the portion of the string
matching the entire regular expression.
The element with index <var>n</var> is the portion of the
string matching the <var>n</var>th parenthesized subexpression.

</dd>
<dt id='index-BASH_005fSOURCE'><code>BASH_SOURCE</code><a href='#index-BASH_005fSOURCE' class='copiable-anchor'> &para;</a></dt>
<dd>An array variable whose members are the source filenames where the
corresponding shell function names in the <code>FUNCNAME</code> array
variable are defined.
The shell function <code>${FUNCNAME[$i]}</code> is defined in the file
<code>${BASH_SOURCE[$i]}</code> and called from <code>${BASH_SOURCE[$i+1]}</code>

</dd>
<dt id='index-BASH_005fSUBSHELL'><code>BASH_SUBSHELL</code><a href='#index-BASH_005fSUBSHELL' class='copiable-anchor'> &para;</a></dt>
<dd>Incremented by one within each subshell or subshell environment when
the shell begins executing in that environment.
The initial value is 0.
If <code>BASH_SUBSHELL</code>
is unset, it loses its special properties, even if it is
subsequently reset.

</dd>
<dt id='index-BASH_005fVERSINFO'><code>BASH_VERSINFO</code><a href='#index-BASH_005fVERSINFO' class='copiable-anchor'> &para;</a></dt>
<dd>A readonly array variable (see <a href="#Arrays">Arrays</a>)
whose members hold version information for this instance of Bash.
The values assigned to the array members are as follows:

<dl compact="compact">
<dt><code>BASH_VERSINFO[0]</code></dt>
<dd>The major version number (the release).

</dd>
<dt><code>BASH_VERSINFO[1]</code></dt>
<dd>The minor version number (the version).

</dd>
<dt><code>BASH_VERSINFO[2]</code></dt>
<dd>The patch level.

</dd>
<dt><code>BASH_VERSINFO[3]</code></dt>
<dd>The build version.

</dd>
<dt><code>BASH_VERSINFO[4]</code></dt>
<dd>The release status (e.g., <code>beta1</code>).

</dd>
<dt><code>BASH_VERSINFO[5]</code></dt>
<dd>The value of <code>MACHTYPE</code>.
</dd>
</dl>

</dd>
<dt id='index-BASH_005fVERSION'><code>BASH_VERSION</code><a href='#index-BASH_005fVERSION' class='copiable-anchor'> &para;</a></dt>
<dd>The version number of the current instance of Bash.

</dd>
<dt id='index-BASH_005fXTRACEFD'><code>BASH_XTRACEFD</code><a href='#index-BASH_005fXTRACEFD' class='copiable-anchor'> &para;</a></dt>
<dd>If set to an integer corresponding to a valid file descriptor, Bash
will write the trace output generated when &lsquo;<samp>set -x</samp>&rsquo;
is enabled to that file descriptor.
This allows tracing output to be separated from diagnostic and error
messages.
The file descriptor is closed when <code>BASH_XTRACEFD</code> is unset or assigned
a new value.
Unsetting <code>BASH_XTRACEFD</code> or assigning it the empty string causes the
trace output to be sent to the standard error.
Note that setting <code>BASH_XTRACEFD</code> to 2 (the standard error file
descriptor) and then unsetting it will result in the standard error
being closed.

</dd>
<dt id='index-CHILD_005fMAX'><code>CHILD_MAX</code><a href='#index-CHILD_005fMAX' class='copiable-anchor'> &para;</a></dt>
<dd>Set the number of exited child status values for the shell to remember.
Bash will not allow this value to be decreased below a POSIX-mandated
minimum, and there is a maximum value (currently 8192) that this may
not exceed.
The minimum value is system-dependent.

</dd>
<dt id='index-COLUMNS'><code>COLUMNS</code><a href='#index-COLUMNS' class='copiable-anchor'> &para;</a></dt>
<dd>Used by the <code>select</code> command to determine the terminal width
when printing selection lists.
Automatically set if the <code>checkwinsize</code> option is enabled
(see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>), or in an interactive shell upon receipt of a
<code>SIGWINCH</code>.

</dd>
<dt id='index-COMP_005fCWORD'><code>COMP_CWORD</code><a href='#index-COMP_005fCWORD' class='copiable-anchor'> &para;</a></dt>
<dd>An index into <code>${COMP_WORDS}</code> of the word containing the current
cursor position.
This variable is available only in shell functions invoked by the
programmable completion facilities (see <a href="#Programmable-Completion">Programmable Completion</a>).

</dd>
<dt id='index-COMP_005fLINE'><code>COMP_LINE</code><a href='#index-COMP_005fLINE' class='copiable-anchor'> &para;</a></dt>
<dd>The current command line.
This variable is available only in shell functions and external
commands invoked by the
programmable completion facilities (see <a href="#Programmable-Completion">Programmable Completion</a>).

</dd>
<dt id='index-COMP_005fPOINT'><code>COMP_POINT</code><a href='#index-COMP_005fPOINT' class='copiable-anchor'> &para;</a></dt>
<dd>The index of the current cursor position relative to the beginning of
the current command.
If the current cursor position is at the end of the current command,
the value of this variable is equal to <code>${#COMP_LINE}</code>.
This variable is available only in shell functions and external
commands invoked by the
programmable completion facilities (see <a href="#Programmable-Completion">Programmable Completion</a>).

</dd>
<dt id='index-COMP_005fTYPE'><code>COMP_TYPE</code><a href='#index-COMP_005fTYPE' class='copiable-anchor'> &para;</a></dt>
<dd>Set to an integer value corresponding to the type of completion attempted
that caused a completion function to be called:
<tt class="key">TAB</tt>, for normal completion,
&lsquo;<samp>?</samp>&rsquo;, for listing completions after successive tabs,
&lsquo;<samp>!</samp>&rsquo;, for listing alternatives on partial word completion,
&lsquo;<samp>@</samp>&rsquo;, to list completions if the word is not unmodified,
or
&lsquo;<samp>%</samp>&rsquo;, for menu completion.
This variable is available only in shell functions and external
commands invoked by the
programmable completion facilities (see <a href="#Programmable-Completion">Programmable Completion</a>).

</dd>
<dt id='index-COMP_005fKEY'><code>COMP_KEY</code><a href='#index-COMP_005fKEY' class='copiable-anchor'> &para;</a></dt>
<dd>The key (or final key of a key sequence) used to invoke the current
completion function.

</dd>
<dt id='index-COMP_005fWORDBREAKS'><code>COMP_WORDBREAKS</code><a href='#index-COMP_005fWORDBREAKS' class='copiable-anchor'> &para;</a></dt>
<dd>The set of characters that the Readline library treats as word
separators when performing word completion.
If <code>COMP_WORDBREAKS</code>
is unset, it loses its special properties,
even if it is subsequently reset.

</dd>
<dt id='index-COMP_005fWORDS'><code>COMP_WORDS</code><a href='#index-COMP_005fWORDS' class='copiable-anchor'> &para;</a></dt>
<dd>An array variable consisting of the individual
words in the current command line.
The line is split into words as Readline would split it, using
<code>COMP_WORDBREAKS</code> as described above.
This variable is available only in shell functions invoked by the
programmable completion facilities (see <a href="#Programmable-Completion">Programmable Completion</a>).

</dd>
<dt id='index-COMPREPLY'><code>COMPREPLY</code><a href='#index-COMPREPLY' class='copiable-anchor'> &para;</a></dt>
<dd>An array variable from which Bash reads the possible completions
generated by a shell function invoked by the programmable completion
facility (see <a href="#Programmable-Completion">Programmable Completion</a>).
Each array element contains one possible completion.

</dd>
<dt id='index-COPROC'><code>COPROC</code><a href='#index-COPROC' class='copiable-anchor'> &para;</a></dt>
<dd>An array variable created to hold the file descriptors
for output from and input to an unnamed coprocess (see <a href="#Coprocesses">Coprocesses</a>).

</dd>
<dt id='index-DIRSTACK'><code>DIRSTACK</code><a href='#index-DIRSTACK' class='copiable-anchor'> &para;</a></dt>
<dd>An array variable containing the current contents of the directory stack.
Directories appear in the stack in the order they are displayed by the
<code>dirs</code> builtin.
Assigning to members of this array variable may be used to modify
directories already in the stack, but the <code>pushd</code> and <code>popd</code>
builtins must be used to add and remove directories.
Assignment to this variable will not change the current directory.
If <code>DIRSTACK</code>
is unset, it loses its special properties, even if
it is subsequently reset.

</dd>
<dt id='index-EMACS'><code>EMACS</code><a href='#index-EMACS' class='copiable-anchor'> &para;</a></dt>
<dd>If Bash finds this variable in the environment when the shell
starts with value &lsquo;<samp>t</samp>&rsquo;, it assumes that the shell is running in an
Emacs shell buffer and disables line editing.

</dd>
<dt id='index-ENV'><code>ENV</code><a href='#index-ENV' class='copiable-anchor'> &para;</a></dt>
<dd>Expanded and executed similarly to <code>BASH_ENV</code>
(see <a href="#Bash-Startup-Files">Bash Startup Files</a>)
when an interactive shell is invoked in
POSIX Mode (see <a href="#Bash-POSIX-Mode">Bash POSIX Mode</a>).

</dd>
<dt id='index-EPOCHREALTIME'><code>EPOCHREALTIME</code><a href='#index-EPOCHREALTIME' class='copiable-anchor'> &para;</a></dt>
<dd>Each time this parameter is referenced, it expands to the number of seconds
since the Unix Epoch as a floating point value with micro-second granularity
(see the documentation for the C library function <code>time</code> for the
definition of Epoch).
Assignments to <code>EPOCHREALTIME</code> are ignored.
If <code>EPOCHREALTIME</code>
is unset, it loses its special properties, even if
it is subsequently reset.

</dd>
<dt id='index-EPOCHSECONDS'><code>EPOCHSECONDS</code><a href='#index-EPOCHSECONDS' class='copiable-anchor'> &para;</a></dt>
<dd>Each time this parameter is referenced, it expands to the number of seconds
since the Unix Epoch (see the documentation for the C library function
<code>time</code> for the definition of Epoch).
Assignments to <code>EPOCHSECONDS</code> are ignored.
If <code>EPOCHSECONDS</code>
is unset, it loses its special properties, even if
it is subsequently reset.

</dd>
<dt id='index-EUID'><code>EUID</code><a href='#index-EUID' class='copiable-anchor'> &para;</a></dt>
<dd>The numeric effective user id of the current user. This variable
is readonly.

</dd>
<dt id='index-EXECIGNORE'><code>EXECIGNORE</code><a href='#index-EXECIGNORE' class='copiable-anchor'> &para;</a></dt>
<dd>A colon-separated list of shell patterns (see <a href="#Pattern-Matching">Pattern Matching</a>)
defining the list of filenames to be ignored by command search using
<code>PATH</code>.
Files whose full pathnames match one of these patterns are not considered
executable files for the purposes of completion and command execution
via <code>PATH</code> lookup.
This does not affect the behavior of the <code>[</code>, <code>test</code>, and <code>[[</code>
commands.
Full pathnames in the command hash table are not subject to <code>EXECIGNORE</code>.
Use this variable to ignore shared library files that have the executable
bit set, but are not executable files.
The pattern matching honors the setting of the <code>extglob</code> shell 
option.

</dd>
<dt id='index-FCEDIT'><code>FCEDIT</code><a href='#index-FCEDIT' class='copiable-anchor'> &para;</a></dt>
<dd>The editor used as a default by the <samp>-e</samp> option to the <code>fc</code>
builtin command.

</dd>
<dt id='index-FIGNORE'><code>FIGNORE</code><a href='#index-FIGNORE' class='copiable-anchor'> &para;</a></dt>
<dd>A colon-separated list of suffixes to ignore when performing
filename completion.
A filename whose suffix matches one of the entries in 
<code>FIGNORE</code>
is excluded from the list of matched filenames. A sample
value is &lsquo;<samp>.o:~</samp>&rsquo;

</dd>
<dt id='index-FUNCNAME'><code>FUNCNAME</code><a href='#index-FUNCNAME' class='copiable-anchor'> &para;</a></dt>
<dd>An array variable containing the names of all shell functions
currently in the execution call stack.
The element with index 0 is the name of any currently-executing
shell function.
The bottom-most element (the one with the highest index)
is <code>&quot;main&quot;</code>.
This variable exists only when a shell function is executing.
Assignments to <code>FUNCNAME</code> have no effect.
If <code>FUNCNAME</code>
is unset, it loses its special properties, even if
it is subsequently reset.

This variable can be used with <code>BASH_LINENO</code> and <code>BASH_SOURCE</code>.
Each element of <code>FUNCNAME</code> has corresponding elements in
<code>BASH_LINENO</code> and <code>BASH_SOURCE</code> to describe the call stack.
For instance, <code>${FUNCNAME[$i]}</code> was called from the file
<code>${BASH_SOURCE[$i+1]}</code> at line number <code>${BASH_LINENO[$i]}</code>.
The <code>caller</code> builtin displays the current call stack using this
information.

</dd>
<dt id='index-FUNCNEST'><code>FUNCNEST</code><a href='#index-FUNCNEST' class='copiable-anchor'> &para;</a></dt>
<dd>If set to a numeric value greater than 0, defines a maximum function
nesting level. Function invocations that exceed this nesting level
will cause the current command to abort.

</dd>
<dt id='index-GLOBIGNORE'><code>GLOBIGNORE</code><a href='#index-GLOBIGNORE' class='copiable-anchor'> &para;</a></dt>
<dd>A colon-separated list of patterns defining the set of file names to
be ignored by filename expansion.
If a file name matched by a filename expansion pattern also matches one
of the patterns in <code>GLOBIGNORE</code>, it is removed from the list
of matches.
The pattern matching honors the setting of the <code>extglob</code> shell
option.

</dd>
<dt id='index-GROUPS'><code>GROUPS</code><a href='#index-GROUPS' class='copiable-anchor'> &para;</a></dt>
<dd>An array variable containing the list of groups of which the current 
user is a member.
Assignments to <code>GROUPS</code> have no effect.
If <code>GROUPS</code>
is unset, it loses its special properties, even if it is
subsequently reset.

</dd>
<dt id='index-histchars'><code>histchars</code><a href='#index-histchars' class='copiable-anchor'> &para;</a></dt>
<dd>Up to three characters which control history expansion, quick
substitution, and tokenization (see <a href="#History-Interaction">History Expansion</a>).
The first character is the
history expansion character, that is, the character which signifies the
start of a history expansion, normally &lsquo;<samp>!</samp>&rsquo;. The second character is the
character which signifies &lsquo;quick substitution&rsquo; when seen as the first
character on a line, normally &lsquo;<samp>^</samp>&rsquo;. The optional third character is the
character which indicates that the remainder of the line is a comment when
found as the first character of a word, usually &lsquo;<samp>#</samp>&rsquo;. The history
comment character causes history substitution to be skipped for the
remaining words on the line. It does not necessarily cause the shell
parser to treat the rest of the line as a comment.

</dd>
<dt id='index-HISTCMD'><code>HISTCMD</code><a href='#index-HISTCMD' class='copiable-anchor'> &para;</a></dt>
<dd>The history number, or index in the history list, of the current
command.
Assignments to <code>HISTCMD</code> are ignored.
If <code>HISTCMD</code>
is unset, it loses its special properties,
even if it is subsequently reset.

</dd>
<dt id='index-HISTCONTROL'><code>HISTCONTROL</code><a href='#index-HISTCONTROL' class='copiable-anchor'> &para;</a></dt>
<dd>A colon-separated list of values controlling how commands are saved on
the history list.
If the list of values includes &lsquo;<samp>ignorespace</samp>&rsquo;, lines which begin
with a space character are not saved in the history list.
A value of &lsquo;<samp>ignoredups</samp>&rsquo; causes lines which match the previous
history entry to not be saved.
A value of &lsquo;<samp>ignoreboth</samp>&rsquo; is shorthand for
&lsquo;<samp>ignorespace</samp>&rsquo; and &lsquo;<samp>ignoredups</samp>&rsquo;.
A value of &lsquo;<samp>erasedups</samp>&rsquo; causes all previous lines matching the
current line to be removed from the history list before that line
is saved.
Any value not in the above list is ignored.
If <code>HISTCONTROL</code> is unset, or does not include a valid value, 
all lines read by the shell parser are saved on the history list, 
subject to the value of <code>HISTIGNORE</code>.
The second and subsequent lines of a multi-line compound command are
not tested, and are added to the history regardless of the value of
<code>HISTCONTROL</code>.

</dd>
<dt id='index-HISTFILE'><code>HISTFILE</code><a href='#index-HISTFILE' class='copiable-anchor'> &para;</a></dt>
<dd>The name of the file to which the command history is saved. The
default value is <samp>~/.bash_history</samp>.

</dd>
<dt id='index-HISTFILESIZE'><code>HISTFILESIZE</code><a href='#index-HISTFILESIZE' class='copiable-anchor'> &para;</a></dt>
<dd>The maximum number of lines contained in the history file.
When this variable is assigned a value, the history file is truncated,
if necessary, to contain no more than that number of lines
by removing the oldest entries.
The history file is also truncated to this size after
writing it when a shell exits.
If the value is 0, the history file is truncated to zero size.
Non-numeric values and numeric values less than zero inhibit truncation.
The shell sets the default value to the value of <code>HISTSIZE</code>
after reading any startup files.

</dd>
<dt id='index-HISTIGNORE'><code>HISTIGNORE</code><a href='#index-HISTIGNORE' class='copiable-anchor'> &para;</a></dt>
<dd>A colon-separated list of patterns used to decide which command
lines should be saved on the history list. Each pattern is
anchored at the beginning of the line and must match the complete
line (no implicit &lsquo;<samp>*</samp>&rsquo; is appended). Each pattern is tested
against the line after the checks specified by <code>HISTCONTROL</code>
are applied. In addition to the normal shell pattern matching
characters, &lsquo;<samp>&amp;</samp>&rsquo; matches the previous history line. &lsquo;<samp>&amp;</samp>&rsquo;
may be escaped using a backslash; the backslash is removed
before attempting a match. 
The second and subsequent lines of a multi-line compound command are
not tested, and are added to the history regardless of the value of
<code>HISTIGNORE</code>.
The pattern matching honors the setting of the <code>extglob</code> shell
option.

<code>HISTIGNORE</code> subsumes the function of <code>HISTCONTROL</code>. A
pattern of &lsquo;<samp>&amp;</samp>&rsquo; is identical to <code>ignoredups</code>, and a
pattern of &lsquo;<samp>[ ]*</samp>&rsquo; is identical to <code>ignorespace</code>. 
Combining these two patterns, separating them with a colon,
provides the functionality of <code>ignoreboth</code>. 

</dd>
<dt id='index-HISTSIZE'><code>HISTSIZE</code><a href='#index-HISTSIZE' class='copiable-anchor'> &para;</a></dt>
<dd>The maximum number of commands to remember on the history list.
If the value is 0, commands are not saved in the history list.
Numeric values less than zero result in every command being saved
on the history list (there is no limit).
The shell sets the default value to 500 after reading any startup files.

</dd>
<dt id='index-HISTTIMEFORMAT'><code>HISTTIMEFORMAT</code><a href='#index-HISTTIMEFORMAT' class='copiable-anchor'> &para;</a></dt>
<dd>If this variable is set and not null, its value is used as a format string
for <code>strftime</code> to print the time stamp associated with each history
entry displayed by the <code>history</code> builtin.
If this variable is set, time stamps are written to the history file so
they may be preserved across shell sessions.
This uses the history comment character to distinguish timestamps from
other history lines.

</dd>
<dt id='index-HOSTFILE'><code>HOSTFILE</code><a href='#index-HOSTFILE' class='copiable-anchor'> &para;</a></dt>
<dd>Contains the name of a file in the same format as <samp>/etc/hosts</samp> that
should be read when the shell needs to complete a hostname.
The list of possible hostname completions may be changed while the shell
is running;
the next time hostname completion is attempted after the
value is changed, Bash adds the contents of the new file to the
existing list.
If <code>HOSTFILE</code> is set, but has no value, or does not name a readable file,
Bash attempts to read 
<samp>/etc/hosts</samp> to obtain the list of possible hostname completions.
When <code>HOSTFILE</code> is unset, the hostname list is cleared.

</dd>
<dt id='index-HOSTNAME'><code>HOSTNAME</code><a href='#index-HOSTNAME' class='copiable-anchor'> &para;</a></dt>
<dd>The name of the current host.

</dd>
<dt id='index-HOSTTYPE'><code>HOSTTYPE</code><a href='#index-HOSTTYPE' class='copiable-anchor'> &para;</a></dt>
<dd>A string describing the machine Bash is running on.

</dd>
<dt id='index-IGNOREEOF'><code>IGNOREEOF</code><a href='#index-IGNOREEOF' class='copiable-anchor'> &para;</a></dt>
<dd>Controls the action of the shell on receipt of an <code>EOF</code> character
as the sole input. If set, the value denotes the number
of consecutive <code>EOF</code> characters that can be read as the
first character on an input line
before the shell will exit. If the variable exists but does not
have a numeric value, or has no value, then the default is 10.
If the variable does not exist, then <code>EOF</code> signifies the end of 
input to the shell. This is only in effect for interactive shells.

</dd>
<dt id='index-INPUTRC'><code>INPUTRC</code><a href='#index-INPUTRC' class='copiable-anchor'> &para;</a></dt>
<dd>The name of the Readline initialization file, overriding the default
of <samp>~/.inputrc</samp>.

</dd>
<dt id='index-INSIDE_005fEMACS'><code>INSIDE_EMACS</code><a href='#index-INSIDE_005fEMACS' class='copiable-anchor'> &para;</a></dt>
<dd>If Bash finds this variable in the environment when the shell
starts, it assumes that the shell is running in an Emacs shell buffer
and may disable line editing depending on the value of <code>TERM</code>.

</dd>
<dt id='index-LANG-1'><code>LANG</code><a href='#index-LANG-1' class='copiable-anchor'> &para;</a></dt>
<dd>Used to determine the locale category for any category not specifically
selected with a variable starting with <code>LC_</code>.

</dd>
<dt id='index-LC_005fALL'><code>LC_ALL</code><a href='#index-LC_005fALL' class='copiable-anchor'> &para;</a></dt>
<dd>This variable overrides the value of <code>LANG</code> and any other
<code>LC_</code> variable specifying a locale category.

</dd>
<dt id='index-LC_005fCOLLATE'><code>LC_COLLATE</code><a href='#index-LC_005fCOLLATE' class='copiable-anchor'> &para;</a></dt>
<dd>This variable determines the collation order used when sorting the
results of filename expansion, and
determines the behavior of range expressions, equivalence classes,
and collating sequences within filename expansion and pattern matching
(see <a href="#Filename-Expansion">Filename Expansion</a>).

</dd>
<dt id='index-LC_005fCTYPE'><code>LC_CTYPE</code><a href='#index-LC_005fCTYPE' class='copiable-anchor'> &para;</a></dt>
<dd>This variable determines the interpretation of characters and the
behavior of character classes within filename expansion and pattern
matching (see <a href="#Filename-Expansion">Filename Expansion</a>).

</dd>
<dt id='index-LC_005fMESSAGES-1'><code>LC_MESSAGES</code><a href='#index-LC_005fMESSAGES-1' class='copiable-anchor'> &para;</a></dt>
<dd>This variable determines the locale used to translate double-quoted
strings preceded by a &lsquo;<samp>$</samp>&rsquo; (see <a href="#Locale-Translation">Locale-Specific Translation</a>).

</dd>
<dt id='index-LC_005fNUMERIC'><code>LC_NUMERIC</code><a href='#index-LC_005fNUMERIC' class='copiable-anchor'> &para;</a></dt>
<dd>This variable determines the locale category used for number formatting.

</dd>
<dt id='index-LC_005fTIME'><code>LC_TIME</code><a href='#index-LC_005fTIME' class='copiable-anchor'> &para;</a></dt>
<dd>This variable determines the locale category used for data and time
formatting.

</dd>
<dt id='index-LINENO'><code>LINENO</code><a href='#index-LINENO' class='copiable-anchor'> &para;</a></dt>
<dd>The line number in the script or shell function currently executing.
If <code>LINENO</code>
is unset, it loses its special properties, even if it is
subsequently reset.

</dd>
<dt id='index-LINES'><code>LINES</code><a href='#index-LINES' class='copiable-anchor'> &para;</a></dt>
<dd>Used by the <code>select</code> command to determine the column length
for printing selection lists.
Automatically set if the <code>checkwinsize</code> option is enabled
(see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>), or in an interactive shell upon receipt of a
<code>SIGWINCH</code>.

</dd>
<dt id='index-MACHTYPE'><code>MACHTYPE</code><a href='#index-MACHTYPE' class='copiable-anchor'> &para;</a></dt>
<dd>A string that fully describes the system type on which Bash
is executing, in the standard GNU <var>cpu-company-system</var> format.

</dd>
<dt id='index-MAILCHECK'><code>MAILCHECK</code><a href='#index-MAILCHECK' class='copiable-anchor'> &para;</a></dt>
<dd>How often (in seconds) that the shell should check for mail in the
files specified in the <code>MAILPATH</code> or <code>MAIL</code> variables.
The default is 60 seconds. When it is time to check
for mail, the shell does so before displaying the primary prompt.
If this variable is unset, or set to a value that is not a number
greater than or equal to zero, the shell disables mail checking.

</dd>
<dt id='index-MAPFILE'><code>MAPFILE</code><a href='#index-MAPFILE' class='copiable-anchor'> &para;</a></dt>
<dd>An array variable created to hold the text read by the
<code>mapfile</code> builtin when no variable name is supplied.

</dd>
<dt id='index-OLDPWD'><code>OLDPWD</code><a href='#index-OLDPWD' class='copiable-anchor'> &para;</a></dt>
<dd>The previous working directory as set by the <code>cd</code> builtin.

</dd>
<dt id='index-OPTERR'><code>OPTERR</code><a href='#index-OPTERR' class='copiable-anchor'> &para;</a></dt>
<dd>If set to the value 1, Bash displays error messages
generated by the <code>getopts</code> builtin command.

</dd>
<dt id='index-OSTYPE'><code>OSTYPE</code><a href='#index-OSTYPE' class='copiable-anchor'> &para;</a></dt>
<dd>A string describing the operating system Bash is running on.

</dd>
<dt id='index-PIPESTATUS'><code>PIPESTATUS</code><a href='#index-PIPESTATUS' class='copiable-anchor'> &para;</a></dt>
<dd>An array variable (see <a href="#Arrays">Arrays</a>)
containing a list of exit status values from the processes
in the most-recently-executed foreground pipeline (which may
contain only a single command).

</dd>
<dt id='index-POSIXLY_005fCORRECT'><code>POSIXLY_CORRECT</code><a href='#index-POSIXLY_005fCORRECT' class='copiable-anchor'> &para;</a></dt>
<dd>If this variable is in the environment when Bash starts, the shell
enters POSIX mode (see <a href="#Bash-POSIX-Mode">Bash POSIX Mode</a>) before reading the
startup files, as if the <samp>--posix</samp> invocation option had been supplied.
If it is set while the shell is running, Bash enables POSIX mode,
as if the command
<div class="example">
<pre class="example"><code>set -o posix</code>
</pre></div>
had been executed.
When the shell enters POSIX mode, it sets this variable if it was
not already set.

</dd>
<dt id='index-PPID'><code>PPID</code><a href='#index-PPID' class='copiable-anchor'> &para;</a></dt>
<dd>The process ID of the shell&rsquo;s parent process. This variable
is readonly.

</dd>
<dt id='index-PROMPT_005fCOMMAND'><code>PROMPT_COMMAND</code><a href='#index-PROMPT_005fCOMMAND' class='copiable-anchor'> &para;</a></dt>
<dd>If this variable is set, and is an array,
the value of each set element is interpreted as a command to execute
before printing the primary prompt (<code>$PS1</code>).
If this is set but not an array variable,
its value is used as a command to execute instead.

</dd>
<dt id='index-PROMPT_005fDIRTRIM'><code>PROMPT_DIRTRIM</code><a href='#index-PROMPT_005fDIRTRIM' class='copiable-anchor'> &para;</a></dt>
<dd>If set to a number greater than zero, the value is used as the number of
trailing directory components to retain when expanding the <code>\w</code> and
<code>\W</code> prompt string escapes (see <a href="#Controlling-the-Prompt">Controlling the Prompt</a>).
Characters removed are replaced with an ellipsis.

</dd>
<dt id='index-PS0'><code>PS0</code><a href='#index-PS0' class='copiable-anchor'> &para;</a></dt>
<dd>The value of this parameter is expanded like <code>PS1</code>
and displayed by interactive shells after reading a command
and before the command is executed.

</dd>
<dt id='index-PS3'><code>PS3</code><a href='#index-PS3' class='copiable-anchor'> &para;</a></dt>
<dd>The value of this variable is used as the prompt for the
<code>select</code> command. If this variable is not set, the
<code>select</code> command prompts with &lsquo;<samp>#? </samp>&rsquo;

</dd>
<dt id='index-PS4'><code>PS4</code><a href='#index-PS4' class='copiable-anchor'> &para;</a></dt>
<dd>The value of this parameter is expanded like <code>PS1</code>
and the expanded value is the prompt printed before the command line
is echoed when the <samp>-x</samp> option is set (see <a href="#The-Set-Builtin">The Set Builtin</a>).
The first character of the expanded value is replicated multiple times,
as necessary, to indicate multiple levels of indirection.
The default is &lsquo;<samp>+ </samp>&rsquo;.

</dd>
<dt id='index-PWD'><code>PWD</code><a href='#index-PWD' class='copiable-anchor'> &para;</a></dt>
<dd>The current working directory as set by the <code>cd</code> builtin.

</dd>
<dt id='index-RANDOM'><code>RANDOM</code><a href='#index-RANDOM' class='copiable-anchor'> &para;</a></dt>
<dd>Each time this parameter is referenced, it expands to a random integer
between 0 and 32767. Assigning a value to this
variable seeds the random number generator.
If <code>RANDOM</code>
is unset, it loses its special properties, even if it is
subsequently reset.

</dd>
<dt id='index-READLINE_005fARGUMENT'><code>READLINE_ARGUMENT</code><a href='#index-READLINE_005fARGUMENT' class='copiable-anchor'> &para;</a></dt>
<dd>Any numeric argument given to a Readline command that was defined using
&lsquo;<samp>bind -x</samp>&rsquo; (see <a href="#Bash-Builtins">Bash Builtin Commands</a>
when it was invoked.

</dd>
<dt id='index-READLINE_005fLINE'><code>READLINE_LINE</code><a href='#index-READLINE_005fLINE' class='copiable-anchor'> &para;</a></dt>
<dd>The contents of the Readline line buffer, for use
with &lsquo;<samp>bind -x</samp>&rsquo; (see <a href="#Bash-Builtins">Bash Builtin Commands</a>).

</dd>
<dt id='index-READLINE_005fMARK'><code>READLINE_MARK</code><a href='#index-READLINE_005fMARK' class='copiable-anchor'> &para;</a></dt>
<dd>The position of the mark (saved insertion point) in the
Readline line buffer, for use
with &lsquo;<samp>bind -x</samp>&rsquo; (see <a href="#Bash-Builtins">Bash Builtin Commands</a>).
The characters between the insertion point and the mark are often
called the region.

</dd>
<dt id='index-READLINE_005fPOINT'><code>READLINE_POINT</code><a href='#index-READLINE_005fPOINT' class='copiable-anchor'> &para;</a></dt>
<dd>The position of the insertion point in the Readline line buffer, for use
with &lsquo;<samp>bind -x</samp>&rsquo; (see <a href="#Bash-Builtins">Bash Builtin Commands</a>).

</dd>
<dt id='index-REPLY'><code>REPLY</code><a href='#index-REPLY' class='copiable-anchor'> &para;</a></dt>
<dd>The default variable for the <code>read</code> builtin.

</dd>
<dt id='index-SECONDS'><code>SECONDS</code><a href='#index-SECONDS' class='copiable-anchor'> &para;</a></dt>
<dd>This variable expands to the number of seconds since the shell was started. 
Assignment to this variable resets the count to the value assigned, and the
expanded value becomes the value assigned plus the number of seconds
since the assignment.
The number of seconds at shell invocation and the current time are always
determined by querying the system clock.
If <code>SECONDS</code>
is unset, it loses its special properties,
even if it is subsequently reset.

</dd>
<dt id='index-SHELL'><code>SHELL</code><a href='#index-SHELL' class='copiable-anchor'> &para;</a></dt>
<dd>This environment variable expands to the full pathname to the shell.
If it is not set when the shell starts,
Bash assigns to it the full pathname of the current user&rsquo;s login shell.

</dd>
<dt id='index-SHELLOPTS'><code>SHELLOPTS</code><a href='#index-SHELLOPTS' class='copiable-anchor'> &para;</a></dt>
<dd>A colon-separated list of enabled shell options. Each word in
the list is a valid argument for the <samp>-o</samp> option to the
<code>set</code> builtin command (see <a href="#The-Set-Builtin">The Set Builtin</a>).
The options appearing in <code>SHELLOPTS</code> are those reported
as &lsquo;<samp>on</samp>&rsquo; by &lsquo;<samp>set -o</samp>&rsquo;.
If this variable is in the environment when Bash
starts up, each shell option in the list will be enabled before
reading any startup files. This variable is readonly.

</dd>
<dt id='index-SHLVL'><code>SHLVL</code><a href='#index-SHLVL' class='copiable-anchor'> &para;</a></dt>
<dd>Incremented by one each time a new instance of Bash is started. This is
intended to be a count of how deeply your Bash shells are nested.

</dd>
<dt id='index-SRANDOM'><code>SRANDOM</code><a href='#index-SRANDOM' class='copiable-anchor'> &para;</a></dt>
<dd>This variable expands to a 32-bit pseudo-random number each time it is
referenced. The random number generator is not linear on systems that
support <samp>/dev/urandom</samp> or <code>arc4random</code>, so each returned number
has no relationship to the numbers preceding it.
The random number generator cannot be seeded, so assignments to this
variable have no effect.
If <code>SRANDOM</code>
is unset, it loses its special properties,
even if it is subsequently reset.

</dd>
<dt id='index-TIMEFORMAT'><code>TIMEFORMAT</code><a href='#index-TIMEFORMAT' class='copiable-anchor'> &para;</a></dt>
<dd>The value of this parameter is used as a format string specifying
how the timing information for pipelines prefixed with the <code>time</code>
reserved word should be displayed.
The &lsquo;<samp>%</samp>&rsquo; character introduces an
escape sequence that is expanded to a time value or other
information.
The escape sequences and their meanings are as
follows; the braces denote optional portions. 

<dl compact="compact">
<dt><code>%%</code></dt>
<dd>A literal &lsquo;<samp>%</samp>&rsquo;.

</dd>
<dt><code>%[<var>p</var>][l]R</code></dt>
<dd>The elapsed time in seconds. 

</dd>
<dt><code>%[<var>p</var>][l]U</code></dt>
<dd>The number of CPU seconds spent in user mode. 

</dd>
<dt><code>%[<var>p</var>][l]S</code></dt>
<dd>The number of CPU seconds spent in system mode. 

</dd>
<dt><code>%P</code></dt>
<dd>The CPU percentage, computed as (%U + %S) / %R. 
</dd>
</dl>

The optional <var>p</var> is a digit specifying the precision, the number of
fractional digits after a decimal point.
A value of 0 causes no decimal point or fraction to be output.
At most three places after the decimal point may be specified; values
of <var>p</var> greater than 3 are changed to 3.
If <var>p</var> is not specified, the value 3 is used. 

The optional <code>l</code> specifies a longer format, including minutes, of
the form <var>MM</var>m<var>SS</var>.<var>FF</var>s.
The value of <var>p</var> determines whether or not the fraction is included. 

If this variable is not set, Bash acts as if it had the value
<div class="example">
<pre class="example"><code>$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'</code>
</pre></div>
If the value is null, no timing information is displayed.
A trailing newline is added when the format string is displayed.

</dd>
<dt id='index-TMOUT'><code>TMOUT</code><a href='#index-TMOUT' class='copiable-anchor'> &para;</a></dt>
<dd>If set to a value greater than zero, <code>TMOUT</code> is treated as the
default timeout for the <code>read</code> builtin (see <a href="#Bash-Builtins">Bash Builtin Commands</a>).
The <code>select</code> command (see <a href="#Conditional-Constructs">Conditional Constructs</a>) terminates
if input does not arrive after <code>TMOUT</code> seconds when input is coming
from a terminal.

In an interactive shell, the value is interpreted as
the number of seconds to wait for a line of input after issuing
the primary prompt.
Bash
terminates after waiting for that number of seconds if a complete
line of input does not arrive.

</dd>
<dt id='index-TMPDIR'><code>TMPDIR</code><a href='#index-TMPDIR' class='copiable-anchor'> &para;</a></dt>
<dd>If set, Bash uses its value as the name of a directory in which
Bash creates temporary files for the shell&rsquo;s use.

</dd>
<dt id='index-UID'><code>UID</code><a href='#index-UID' class='copiable-anchor'> &para;</a></dt>
<dd>The numeric real user id of the current user. This variable is readonly.

</dd>
</dl>

<hr>
</div>
</div>
<div class="chapter" id="Bash-Features">
<div class="header">

Next: <a href="#Job-Control" accesskey="n" rel="next">Job Control</a>, Previous: <a href="#Shell-Variables" accesskey="p" rel="prev">Shell Variables</a>, Up: <a href="#Top" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h2 class="chapter">6 Bash Features</h2>

This chapter describes features unique to Bash.

<ul class="section-toc">
<li><a href="#Invoking-Bash" accesskey="1">Invoking Bash</a></li>
<li><a href="#Bash-Startup-Files" accesskey="2">Bash Startup Files</a></li>
<li><a href="#Interactive-Shells" accesskey="3">Interactive Shells</a></li>
<li><a href="#Bash-Conditional-Expressions" accesskey="4">Bash Conditional Expressions</a></li>
<li><a href="#Shell-Arithmetic" accesskey="5">Shell Arithmetic</a></li>
<li><a href="#Aliases" accesskey="6">Aliases</a></li>
<li><a href="#Arrays" accesskey="7">Arrays</a></li>
<li><a href="#The-Directory-Stack" accesskey="8">The Directory Stack</a></li>
<li><a href="#Controlling-the-Prompt" accesskey="9">Controlling the Prompt</a></li>
<li><a href="#The-Restricted-Shell">The Restricted Shell</a></li>
<li><a href="#Bash-POSIX-Mode">Bash POSIX Mode</a></li>
<li><a href="#Shell-Compatibility-Mode">Shell Compatibility Mode</a></li>
</ul>
<hr>
<div class="section" id="Invoking-Bash">
<div class="header">

Next: <a href="#Bash-Startup-Files" accesskey="n" rel="next">Bash Startup Files</a>, Up: <a href="#Bash-Features" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">6.1 Invoking Bash</h3>

<div class="example">
<pre class="example">bash [long-opt] [-ir] [-abefhkmnptuvxdBCDHP] [-o <var>option</var>]
 [-O <var>shopt_option</var>] [<var>argument</var> &hellip;]
bash [long-opt] [-abefhkmnptuvxdBCDHP] [-o <var>option</var>]
 [-O <var>shopt_option</var>] -c <var>string</var> [<var>argument</var> &hellip;]
bash [long-opt] -s [-abefhkmnptuvxdBCDHP] [-o <var>option</var>]
 [-O <var>shopt_option</var>] [<var>argument</var> &hellip;]
</pre></div>

All of the single-character options used with the <code>set</code> builtin
(see <a href="#The-Set-Builtin">The Set Builtin</a>) can be used as options when the shell is invoked.
In addition, there are several multi-character
options that you can use. These options must appear on the command
line before the single-character options to be recognized. 

<dl compact="compact">
<dt><code>--debugger</code></dt>
<dd>Arrange for the debugger profile to be executed before the shell
starts. Turns on extended debugging mode (see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>
for a description of the <code>extdebug</code> option to the <code>shopt</code>
builtin).

</dd>
<dt><code>--dump-po-strings</code></dt>
<dd>A list of all double-quoted strings preceded by &lsquo;<samp>$</samp>&rsquo;
is printed on the standard output
in the GNU <code>gettext</code> PO (portable object) file format.
Equivalent to <samp>-D</samp> except for the output format.

</dd>
<dt><code>--dump-strings</code></dt>
<dd>Equivalent to <samp>-D</samp>.

</dd>
<dt><code>--help</code></dt>
<dd>Display a usage message on standard output and exit successfully.

</dd>
<dt><code>--init-file <var>filename</var></code></dt>
<dt><code>--rcfile <var>filename</var></code></dt>
<dd>Execute commands from <var>filename</var> (instead of <samp>~/.bashrc</samp>)
in an interactive shell.

</dd>
<dt><code>--login</code></dt>
<dd>Equivalent to <samp>-l</samp>.

</dd>
<dt><code>--noediting</code></dt>
<dd>Do not use the GNU Readline library (see <a href="#Command-Line-Editing">Command Line Editing</a>)
to read command lines when the shell is interactive.

</dd>
<dt><code>--noprofile</code></dt>
<dd>Don&rsquo;t load the system-wide startup file <samp>/etc/profile</samp>
or any of the personal initialization files
<samp>~/.bash_profile</samp>, <samp>~/.bash_login</samp>, or <samp>~/.profile</samp>
when Bash is invoked as a login shell.

</dd>
<dt><code>--norc</code></dt>
<dd>Don&rsquo;t read the <samp>~/.bashrc</samp> initialization file in an
interactive shell. This is on by default if the shell is
invoked as <code>sh</code>.

</dd>
<dt><code>--posix</code></dt>
<dd>Change the behavior of Bash where the default operation differs
from the POSIX standard to match the standard. This
is intended to make Bash behave as a strict superset of that
standard. See <a href="#Bash-POSIX-Mode">Bash POSIX Mode</a>, for a description of the Bash
POSIX mode.

</dd>
<dt><code>--restricted</code></dt>
<dd>Make the shell a restricted shell (see <a href="#The-Restricted-Shell">The Restricted Shell</a>).

</dd>
<dt><code>--verbose</code></dt>
<dd>Equivalent to <samp>-v</samp>. Print shell input lines as they&rsquo;re read.

</dd>
<dt><code>--version</code></dt>
<dd>Show version information for this instance of
Bash on the standard output and exit successfully.
</dd>
</dl>

There are several single-character options that may be supplied at
invocation which are not available with the <code>set</code> builtin.

<dl compact="compact">
<dt><code>-c</code></dt>
<dd>Read and execute commands from the first non-option argument
<var>command_string</var>, then exit. 
If there are arguments after the <var>command_string</var>,
the first argument is assigned to <code>$0</code>
and any remaining arguments are assigned to the positional parameters.
The assignment to <code>$0</code> sets the name of the shell, which is used
in warning and error messages.

</dd>
<dt><code>-i</code></dt>
<dd>Force the shell to run interactively. Interactive shells are
described in <a href="#Interactive-Shells">Interactive Shells</a>.

</dd>
<dt><code>-l</code></dt>
<dd>Make this shell act as if it had been directly invoked by login.
When the shell is interactive, this is equivalent to starting a
login shell with &lsquo;<samp>exec -l bash</samp>&rsquo;.
When the shell is not interactive, the login shell startup files will
be executed.
&lsquo;<samp>exec bash -l</samp>&rsquo; or &lsquo;<samp>exec bash --login</samp>&rsquo;
will replace the current shell with a Bash login shell.
See <a href="#Bash-Startup-Files">Bash Startup Files</a>, for a description of the special behavior
of a login shell.

</dd>
<dt><code>-r</code></dt>
<dd>Make the shell a restricted shell (see <a href="#The-Restricted-Shell">The Restricted Shell</a>).

</dd>
<dt><code>-s</code></dt>
<dd>If this option is present, or if no arguments remain after option
processing, then commands are read from the standard input.
This option allows the positional parameters to be set
when invoking an interactive shell or when reading input
through a pipe.

</dd>
<dt><code>-D</code></dt>
<dd>A list of all double-quoted strings preceded by &lsquo;<samp>$</samp>&rsquo;
is printed on the standard output.
These are the strings that
are subject to language translation when the current locale
is not <code>C</code> or <code>POSIX</code> (see <a href="#Locale-Translation">Locale-Specific Translation</a>).
This implies the <samp>-n</samp> option; no commands will be executed.

</dd>
<dt><code>[-+]O [<var>shopt_option</var>]</code></dt>
<dd><var>shopt_option</var> is one of the shell options accepted by the
<code>shopt</code> builtin (see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>).
If <var>shopt_option</var> is present, <samp>-O</samp> sets the value of that option;
<samp>+O</samp> unsets it. 
If <var>shopt_option</var> is not supplied, the names and values of the shell
options accepted by <code>shopt</code> are printed on the standard output.
If the invocation option is <samp>+O</samp>, the output is displayed in a format
that may be reused as input.

</dd>
<dt><code>--</code></dt>
<dd>A <code>--</code> signals the end of options and disables further option
processing.
Any arguments after the <code>--</code> are treated as filenames and arguments.
</dd>
</dl>

A login shell is one whose first character of argument zero is
&lsquo;<samp>-</samp>&rsquo;, or one invoked with the <samp>--login</samp> option.


An interactive shell is one started without non-option arguments,
unless <samp>-s</samp> is specified,
without specifying the <samp>-c</samp> option, and whose input and output are both
connected to terminals (as determined by <code>isatty(3)</code>), or one
started with the <samp>-i</samp> option. See <a href="#Interactive-Shells">Interactive Shells</a>, for more
information.

If arguments remain after option processing, and neither the
<samp>-c</samp> nor the <samp>-s</samp>
option has been supplied, the first argument is assumed to
be the name of a file containing shell commands (see <a href="#Shell-Scripts">Shell Scripts</a>).
When Bash is invoked in this fashion, <code>$0</code>
is set to the name of the file, and the positional parameters
are set to the remaining arguments.
Bash reads and executes commands from this file, then exits. 
Bash&rsquo;s exit status is the exit status of the last command executed
in the script. If no commands are executed, the exit status is 0.

<hr>
</div>
<div class="section" id="Bash-Startup-Files">
<div class="header">

Next: <a href="#Interactive-Shells" accesskey="n" rel="next">Interactive Shells</a>, Previous: <a href="#Invoking-Bash" accesskey="p" rel="prev">Invoking Bash</a>, Up: <a href="#Bash-Features" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">6.2 Bash Startup Files</h3>

This section describes how Bash executes its startup files.
If any of the files exist but cannot be read, Bash reports an error.
Tildes are expanded in filenames as described above under
Tilde Expansion (see <a href="#Tilde-Expansion">Tilde Expansion</a>).

Interactive shells are described in <a href="#Interactive-Shells">Interactive Shells</a>.

<h4 class="subsubheading">Invoked as an interactive login shell, or with <samp>--login</samp></h4>

When Bash is invoked as an interactive login shell, or as a
non-interactive shell with the <samp>--login</samp> option, it first reads and
executes commands from the file <samp>/etc/profile</samp>, if that file exists.
After reading that file, it looks for <samp>~/.bash_profile</samp>,
<samp>~/.bash_login</samp>, and <samp>~/.profile</samp>, in that order, and reads
and executes commands from the first one that exists and is readable.
The <samp>--noprofile</samp> option may be used when the shell is started to
inhibit this behavior.

When an interactive login shell exits,
or a non-interactive login shell executes the <code>exit</code> builtin command,
Bash reads and executes commands from
the file <samp>~/.bash_logout</samp>, if it exists.

<h4 class="subsubheading">Invoked as an interactive non-login shell</h4>

When an interactive shell that is not a login shell is started, Bash
reads and executes commands from <samp>~/.bashrc</samp>, if that file exists.
This may be inhibited by using the <samp>--norc</samp> option.
The <samp>--rcfile <var>file</var></samp> option will force Bash to read and
execute commands from <var>file</var> instead of <samp>~/.bashrc</samp>.

So, typically, your <samp>~/.bash_profile</samp> contains the line
<div class="example">
<pre class="example"><code>if [ -f ~/.bashrc ]; then . ~/.bashrc; fi</code>
</pre></div>
after (or before) any login-specific initializations.

<h4 class="subsubheading">Invoked non-interactively</h4>

When Bash is started non-interactively, to run a shell script,
for example, it looks for the variable <code>BASH_ENV</code> in the environment,
expands its value if it appears there, and uses the expanded value as
the name of a file to read and execute. Bash behaves as if the
following command were executed:
<div class="example">
<pre class="example"><code>if [ -n &quot;$BASH_ENV&quot; ]; then . &quot;$BASH_ENV&quot;; fi</code>
</pre></div>
but the value of the <code>PATH</code> variable is not used to search for the
filename.

As noted above, if a non-interactive shell is invoked with the
<samp>--login</samp> option, Bash attempts to read and execute commands from the
login shell startup files. 

<h4 class="subsubheading">Invoked with name <code>sh</code></h4>

If Bash is invoked with the name <code>sh</code>, it tries to mimic the
startup behavior of historical versions of <code>sh</code> as closely as
possible, while conforming to the POSIX standard as well.

When invoked as an interactive login shell, or as a non-interactive
shell with the <samp>--login</samp> option, it first attempts to read
and execute commands from <samp>/etc/profile</samp> and <samp>~/.profile</samp>, in
that order.
The <samp>--noprofile</samp> option may be used to inhibit this behavior.
When invoked as an interactive shell with the name <code>sh</code>, Bash
looks for the variable <code>ENV</code>, expands its value if it is defined,
and uses the expanded value as the name of a file to read and execute.
Since a shell invoked as <code>sh</code> does not attempt to read and execute
commands from any other startup files, the <samp>--rcfile</samp> option has
no effect.
A non-interactive shell invoked with the name <code>sh</code> does not attempt
to read any other startup files.

When invoked as <code>sh</code>, Bash enters POSIX mode after
the startup files are read.

<h4 class="subsubheading">Invoked in POSIX mode</h4>

When Bash is started in POSIX mode, as with the
<samp>--posix</samp> command line option, it follows the POSIX standard
for startup files.
In this mode, interactive shells expand the <code>ENV</code> variable
and commands are read and executed from the file whose name is the
expanded value.
No other startup files are read.

<h4 class="subsubheading">Invoked by remote shell daemon</h4>

Bash attempts to determine when it is being run with its standard input
connected to a network connection, as when executed by
the historical remote shell daemon, usually <code>rshd</code>,
or the secure shell daemon <code>sshd</code>.
If Bash
determines it is being run non-interactively in this fashion,
it reads and executes commands from <samp>~/.bashrc</samp>, if that
file exists and is readable.
It will not do this if invoked as <code>sh</code>.
The <samp>--norc</samp> option may be used to inhibit this behavior, and the
<samp>--rcfile</samp> option may be used to force another file to be read, but
neither <code>rshd</code> nor <code>sshd</code> generally invoke the shell with those
options or allow them to be specified.

<h4 class="subsubheading">Invoked with unequal effective and real UID/GIDs</h4>

If Bash is started with the effective user (group) id not equal to the
real user (group) id, and the <samp>-p</samp> option is not supplied, no startup
files are read, shell functions are not inherited from the environment,
the <code>SHELLOPTS</code>, <code>BASHOPTS</code>, <code>CDPATH</code>, and <code>GLOBIGNORE</code>
variables, if they appear in the environment, are ignored, and the effective
user id is set to the real user id.
If the <samp>-p</samp> option is supplied at invocation, the startup behavior is
the same, but the effective user id is not reset.

<hr>
</div>
<div class="section" id="Interactive-Shells">
<div class="header">

Next: <a href="#Bash-Conditional-Expressions" accesskey="n" rel="next">Bash Conditional Expressions</a>, Previous: <a href="#Bash-Startup-Files" accesskey="p" rel="prev">Bash Startup Files</a>, Up: <a href="#Bash-Features" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">6.3 Interactive Shells</h3>

<ul class="section-toc">
<li><a href="#What-is-an-Interactive-Shell_003f" accesskey="1">What is an Interactive Shell?</a></li>
<li><a href="#Is-this-Shell-Interactive_003f" accesskey="2">Is this Shell Interactive?</a></li>
<li><a href="#Interactive-Shell-Behavior" accesskey="3">Interactive Shell Behavior</a></li>
</ul>
<hr>
<div class="subsection" id="What-is-an-Interactive-Shell_003f">
<div class="header">

Next: <a href="#Is-this-Shell-Interactive_003f" accesskey="n" rel="next">Is this Shell Interactive?</a>, Up: <a href="#Interactive-Shells" accesskey="u" rel="up">Interactive Shells</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">6.3.1 What is an Interactive Shell?</h4>

An interactive shell
is one started without non-option arguments
(unless <samp>-s</samp> is specified)
and without specifying the <samp>-c</samp> option,
whose input and error output are both
connected to terminals (as determined by <code>isatty(3)</code>),
or one started with the <samp>-i</samp> option.

An interactive shell generally reads from and writes to a user&rsquo;s
terminal.

The <samp>-s</samp> invocation option may be used to set the positional parameters
when an interactive shell is started.

<hr>
</div>
<div class="subsection" id="Is-this-Shell-Interactive_003f">
<div class="header">

Next: <a href="#Interactive-Shell-Behavior" accesskey="n" rel="next">Interactive Shell Behavior</a>, Previous: <a href="#What-is-an-Interactive-Shell_003f" accesskey="p" rel="prev">What is an Interactive Shell?</a>, Up: <a href="#Interactive-Shells" accesskey="u" rel="up">Interactive Shells</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">6.3.2 Is this Shell Interactive?</h4>

To determine within a startup script whether or not Bash is
running interactively,
test the value of the &lsquo;<samp>-</samp>&rsquo; special parameter.
It contains <code>i</code> when the shell is interactive. For example:

<div class="example">
<pre class="example">case &quot;$-&quot; in
*i*)	echo This shell is interactive ;;
*)	echo This shell is not interactive ;;
esac
</pre></div>

Alternatively, startup scripts may examine the variable
<code>PS1</code>; it is unset in non-interactive shells, and set in
interactive shells. Thus:

<div class="example">
<pre class="example">if [ -z &quot;$PS1&quot; ]; then
 echo This shell is not interactive
else
 echo This shell is interactive
fi
</pre></div>

<hr>
</div>
<div class="subsection" id="Interactive-Shell-Behavior">
<div class="header">

Previous: <a href="#Is-this-Shell-Interactive_003f" accesskey="p" rel="prev">Is this Shell Interactive?</a>, Up: <a href="#Interactive-Shells" accesskey="u" rel="up">Interactive Shells</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">6.3.3 Interactive Shell Behavior</h4>

When the shell is running interactively, it changes its behavior in
several ways.

<ol>
<li> Startup files are read and executed as described in <a href="#Bash-Startup-Files">Bash Startup Files</a>.

</li><li> Job Control (see <a href="#Job-Control">Job Control</a>) is enabled by default. When job
control is in effect, Bash ignores the keyboard-generated job control
signals <code>SIGTTIN</code>, <code>SIGTTOU</code>, and <code>SIGTSTP</code>.

</li><li> Bash expands and displays <code>PS1</code> before reading the first line
of a command, and expands and displays <code>PS2</code> before reading the
second and subsequent lines of a multi-line command.
Bash expands and displays <code>PS0</code> after it reads a command but before
executing it.
See <a href="#Controlling-the-Prompt">Controlling the Prompt</a>, for a complete list of prompt
string escape sequences.

</li><li> Bash executes the values of the set elements of the <code>PROMPT_COMMAND</code>
array variable as commands before printing the primary prompt, <code>$PS1</code>
(see <a href="#Bash-Variables">Bash Variables</a>).

</li><li> Readline (see <a href="#Command-Line-Editing">Command Line Editing</a>) is used to read commands from
the user&rsquo;s terminal.

</li><li> Bash inspects the value of the <code>ignoreeof</code> option to <code>set -o</code>
instead of exiting immediately when it receives an <code>EOF</code> on its
standard input when reading a command (see <a href="#The-Set-Builtin">The Set Builtin</a>).

</li><li> Command history (see <a href="#Bash-History-Facilities">Bash History Facilities</a>)
and history expansion (see <a href="#History-Interaction">History Expansion</a>)
are enabled by default.
Bash will save the command history to the file named by <code>$HISTFILE</code>
when a shell with history enabled exits.

</li><li> Alias expansion (see <a href="#Aliases">Aliases</a>) is performed by default.

</li><li> In the absence of any traps, Bash ignores <code>SIGTERM</code>
(see <a href="#Signals">Signals</a>).

</li><li> In the absence of any traps, <code>SIGINT</code> is caught and handled
(see <a href="#Signals">Signals</a>).
<code>SIGINT</code> will interrupt some shell builtins.

</li><li> An interactive login shell sends a <code>SIGHUP</code> to all jobs on exit
if the <code>huponexit</code> shell option has been enabled (see <a href="#Signals">Signals</a>).

</li><li> The <samp>-n</samp> invocation option is ignored, and &lsquo;<samp>set -n</samp>&rsquo; has
no effect (see <a href="#The-Set-Builtin">The Set Builtin</a>).

</li><li> Bash will check for mail periodically, depending on the values of the
<code>MAIL</code>, <code>MAILPATH</code>, and <code>MAILCHECK</code> shell variables
(see <a href="#Bash-Variables">Bash Variables</a>).

</li><li> Expansion errors due to references to unbound shell variables after
&lsquo;<samp>set -u</samp>&rsquo; has been enabled will not cause the shell to exit
(see <a href="#The-Set-Builtin">The Set Builtin</a>).

</li><li> The shell will not exit on expansion errors caused by <var>var</var> being unset
or null in <code>${<var>var</var>:?<var>word</var>}</code> expansions
(see <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>).

</li><li> Redirection errors encountered by shell builtins will not cause the
shell to exit.

</li><li> When running in POSIX mode, a special builtin returning an error
status will not cause the shell to exit (see <a href="#Bash-POSIX-Mode">Bash POSIX Mode</a>).

</li><li> A failed <code>exec</code> will not cause the shell to exit
(see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>).

</li><li> Parser syntax errors will not cause the shell to exit.

</li><li> If the <code>cdspell</code> shell option is enabled, the shell will attempt
simple spelling correction for directory arguments to the <code>cd</code>
builtin (see the description of the <code>cdspell</code>
option to the <code>shopt</code> builtin in <a href="#The-Shopt-Builtin">The Shopt Builtin</a>).
The <code>cdspell</code> option is only effective in interactive shells.

</li><li> The shell will check the value of the <code>TMOUT</code> variable and exit
if a command is not read within the specified number of seconds after
printing <code>$PS1</code> (see <a href="#Bash-Variables">Bash Variables</a>).

</li></ol>

<hr>
</div>
</div>
<div class="section" id="Bash-Conditional-Expressions">
<div class="header">

Next: <a href="#Shell-Arithmetic" accesskey="n" rel="next">Shell Arithmetic</a>, Previous: <a href="#Interactive-Shells" accesskey="p" rel="prev">Interactive Shells</a>, Up: <a href="#Bash-Features" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">6.4 Bash Conditional Expressions</h3>

Conditional expressions are used by the <code>[[</code> compound command
(see <a href="#Conditional-Constructs">Conditional Constructs</a>)
and the <code>test</code> and <code>[</code> builtin commands
(see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>).
The <code>test</code>
and <code>[</code> commands determine their behavior based on the number
of arguments; see the descriptions of those commands for any other
command-specific actions.

Expressions may be unary or binary,
and are formed from the following primaries.
Unary expressions are often used to examine the status of a file.
There are string operators and numeric comparison operators as well.
Bash handles several filenames specially when they are used in
expressions.
If the operating system on which Bash is running provides these
special files, Bash will use them; otherwise it will emulate them
internally with this behavior:
If the <var>file</var> argument to one of the primaries is of the form
<samp>/dev/fd/<var>N</var></samp>, then file descriptor <var>N</var> is checked.
If the <var>file</var> argument to one of the primaries is one of
<samp>/dev/stdin</samp>, <samp>/dev/stdout</samp>, or <samp>/dev/stderr</samp>, file
descriptor 0, 1, or 2, respectively, is checked.

When used with <code>[[</code>, the &lsquo;<samp>&lt;</samp>&rsquo; and &lsquo;<samp>&gt;</samp>&rsquo; operators sort
lexicographically using the current locale.
The <code>test</code> command uses ASCII ordering.

Unless otherwise specified, primaries that operate on files follow symbolic
links and operate on the target of the link, rather than the link itself.

<dl compact="compact">
<dt><code>-a <var>file</var></code></dt>
<dd>True if <var>file</var> exists.

</dd>
<dt><code>-b <var>file</var></code></dt>
<dd>True if <var>file</var> exists and is a block special file.

</dd>
<dt><code>-c <var>file</var></code></dt>
<dd>True if <var>file</var> exists and is a character special file.

</dd>
<dt><code>-d <var>file</var></code></dt>
<dd>True if <var>file</var> exists and is a directory.

</dd>
<dt><code>-e <var>file</var></code></dt>
<dd>True if <var>file</var> exists.

</dd>
<dt><code>-f <var>file</var></code></dt>
<dd>True if <var>file</var> exists and is a regular file.

</dd>
<dt><code>-g <var>file</var></code></dt>
<dd>True if <var>file</var> exists and its set-group-id bit is set.

</dd>
<dt><code>-h <var>file</var></code></dt>
<dd>True if <var>file</var> exists and is a symbolic link.

</dd>
<dt><code>-k <var>file</var></code></dt>
<dd>True if <var>file</var> exists and its &quot;sticky&quot; bit is set.

</dd>
<dt><code>-p <var>file</var></code></dt>
<dd>True if <var>file</var> exists and is a named pipe (FIFO).

</dd>
<dt><code>-r <var>file</var></code></dt>
<dd>True if <var>file</var> exists and is readable.

</dd>
<dt><code>-s <var>file</var></code></dt>
<dd>True if <var>file</var> exists and has a size greater than zero.

</dd>
<dt><code>-t <var>fd</var></code></dt>
<dd>True if file descriptor <var>fd</var> is open and refers to a terminal.

</dd>
<dt><code>-u <var>file</var></code></dt>
<dd>True if <var>file</var> exists and its set-user-id bit is set.

</dd>
<dt><code>-w <var>file</var></code></dt>
<dd>True if <var>file</var> exists and is writable.

</dd>
<dt><code>-x <var>file</var></code></dt>
<dd>True if <var>file</var> exists and is executable.

</dd>
<dt><code>-G <var>file</var></code></dt>
<dd>True if <var>file</var> exists and is owned by the effective group id.

</dd>
<dt><code>-L <var>file</var></code></dt>
<dd>True if <var>file</var> exists and is a symbolic link.

</dd>
<dt><code>-N <var>file</var></code></dt>
<dd>True if <var>file</var> exists and has been modified since it was last read.

</dd>
<dt><code>-O <var>file</var></code></dt>
<dd>True if <var>file</var> exists and is owned by the effective user id.

</dd>
<dt><code>-S <var>file</var></code></dt>
<dd>True if <var>file</var> exists and is a socket.

</dd>
<dt><code><var>file1</var> -ef <var>file2</var></code></dt>
<dd>True if <var>file1</var> and <var>file2</var> refer to the same device and
inode numbers.

</dd>
<dt><code><var>file1</var> -nt <var>file2</var></code></dt>
<dd>True if <var>file1</var> is newer (according to modification date)
than <var>file2</var>, or if <var>file1</var> exists and <var>file2</var> does not.

</dd>
<dt><code><var>file1</var> -ot <var>file2</var></code></dt>
<dd>True if <var>file1</var> is older than <var>file2</var>,
or if <var>file2</var> exists and <var>file1</var> does not.

</dd>
<dt><code>-o <var>optname</var></code></dt>
<dd>True if the shell option <var>optname</var> is enabled.
The list of options appears in the description of the <samp>-o</samp>
option to the <code>set</code> builtin (see <a href="#The-Set-Builtin">The Set Builtin</a>).

</dd>
<dt><code>-v <var>varname</var></code></dt>
<dd>True if the shell variable <var>varname</var> is set (has been assigned a value).

</dd>
<dt><code>-R <var>varname</var></code></dt>
<dd>True if the shell variable <var>varname</var> is set and is a name reference.

</dd>
<dt><code>-z <var>string</var></code></dt>
<dd>True if the length of <var>string</var> is zero.

</dd>
<dt><code>-n <var>string</var></code></dt>
<dt><code><var>string</var></code></dt>
<dd>True if the length of <var>string</var> is non-zero.

</dd>
<dt><code><var>string1</var> == <var>string2</var></code></dt>
<dt><code><var>string1</var> = <var>string2</var></code></dt>
<dd>True if the strings are equal.
When used with the <code>[[</code> command, this performs pattern matching as
described above (see <a href="#Conditional-Constructs">Conditional Constructs</a>).

&lsquo;<samp>=</samp>&rsquo; should be used with the <code>test</code> command for POSIX conformance.

</dd>
<dt><code><var>string1</var> != <var>string2</var></code></dt>
<dd>True if the strings are not equal.

</dd>
<dt><code><var>string1</var> &lt; <var>string2</var></code></dt>
<dd>True if <var>string1</var> sorts before <var>string2</var> lexicographically.

</dd>
<dt><code><var>string1</var> &gt; <var>string2</var></code></dt>
<dd>True if <var>string1</var> sorts after <var>string2</var> lexicographically.

</dd>
<dt><code><var>arg1</var> OP <var>arg2</var></code></dt>
<dd><code>OP</code> is one of 
&lsquo;<samp>-eq</samp>&rsquo;, &lsquo;<samp>-ne</samp>&rsquo;, &lsquo;<samp>-lt</samp>&rsquo;, &lsquo;<samp>-le</samp>&rsquo;, &lsquo;<samp>-gt</samp>&rsquo;, or &lsquo;<samp>-ge</samp>&rsquo;.
These arithmetic binary operators return true if <var>arg1</var>
is equal to, not equal to, less than, less than or equal to,
greater than, or greater than or equal to <var>arg2</var>,
respectively. <var>Arg1</var> and <var>arg2</var>
may be positive or negative integers.
When used with the <code>[[</code> command, <var>Arg1</var> and <var>Arg2</var>
are evaluated as arithmetic expressions (see <a href="#Shell-Arithmetic">Shell Arithmetic</a>).
</dd>
</dl>

<hr>
</div>
<div class="section" id="Shell-Arithmetic">
<div class="header">

Next: <a href="#Aliases" accesskey="n" rel="next">Aliases</a>, Previous: <a href="#Bash-Conditional-Expressions" accesskey="p" rel="prev">Bash Conditional Expressions</a>, Up: <a href="#Bash-Features" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">6.5 Shell Arithmetic</h3>

The shell allows arithmetic expressions to be evaluated, as one of
the shell expansions or by using the <code>((</code> compound command, the
<code>let</code> builtin, or the <samp>-i</samp> option to the <code>declare</code> builtin.

Evaluation is done in fixed-width integers with no check for overflow,
though division by 0 is trapped and flagged as an error.
The operators and their precedence, associativity, and values
are the same as in the C language.
The following list of operators is grouped into levels of
equal-precedence operators.
The levels are listed in order of decreasing precedence. 

<dl compact="compact">
<dt><code><var>id</var>++ <var>id</var>--</code></dt>
<dd>variable post-increment and post-decrement 

</dd>
<dt><code>++<var>id</var> --<var>id</var></code></dt>
<dd>variable pre-increment and pre-decrement

</dd>
<dt><code>- +</code></dt>
<dd>unary minus and plus

</dd>
<dt><code>! ~</code></dt>
<dd>logical and bitwise negation

</dd>
<dt><code>**</code></dt>
<dd>exponentiation

</dd>
<dt><code>* / %</code></dt>
<dd>multiplication, division, remainder

</dd>
<dt><code>+ -</code></dt>
<dd>addition, subtraction

</dd>
<dt><code>&lt;&lt; &gt;&gt;</code></dt>
<dd>left and right bitwise shifts

</dd>
<dt><code>&lt;= &gt;= &lt; &gt;</code></dt>
<dd>comparison

</dd>
<dt><code>== !=</code></dt>
<dd>equality and inequality

</dd>
<dt><code>&amp;</code></dt>
<dd>bitwise AND

</dd>
<dt><code>^</code></dt>
<dd>bitwise exclusive OR

</dd>
<dt><code>|</code></dt>
<dd>bitwise OR

</dd>
<dt><code>&amp;&amp;</code></dt>
<dd>logical AND

</dd>
<dt><code>||</code></dt>
<dd>logical OR

</dd>
<dt><code>expr ? expr : expr</code></dt>
<dd>conditional operator

</dd>
<dt><code>= *= /= %= += -= &lt;&lt;= &gt;&gt;= &amp;= ^= |=</code></dt>
<dd>assignment

</dd>
<dt><code>expr1 , expr2</code></dt>
<dd>comma
</dd>
</dl>

Shell variables are allowed as operands; parameter expansion is
performed before the expression is evaluated. 
Within an expression, shell variables may also be referenced by name
without using the parameter expansion syntax.
A shell variable that is null or unset evaluates to 0 when referenced
by name without using the parameter expansion syntax.
The value of a variable is evaluated as an arithmetic expression
when it is referenced, or when a variable which has been given the 
<code>integer</code> attribute using &lsquo;<samp>declare -i</samp>&rsquo; is assigned a value.
A null value evaluates to 0.
A shell variable need not have its <code>integer</code> attribute turned on
to be used in an expression.

Integer constants follow the C language definition, without suffixes or
character constants.
Constants with a leading 0 are interpreted as octal numbers.
A leading &lsquo;<samp>0x</samp>&rsquo; or &lsquo;<samp>0X</samp>&rsquo; denotes hexadecimal. Otherwise,
numbers take the form [<var>base</var><code>#</code>]<var>n</var>, where the optional <var>base</var>
is a decimal number between 2 and 64 representing the arithmetic
base, and <var>n</var> is a number in that base.
If <var>base</var><code>#</code> is omitted, then base 10 is used.
When specifying <var>n</var>,
if a non-digit is required,
the digits greater than 9 are represented by the lowercase letters,
the uppercase letters, &lsquo;<samp>@</samp>&rsquo;, and &lsquo;<samp>_</samp>&rsquo;, in that order.
If <var>base</var> is less than or equal to 36, lowercase and uppercase
letters may be used interchangeably to represent numbers between 10
and 35.

Operators are evaluated in order of precedence. Sub-expressions in
parentheses are evaluated first and may override the precedence
rules above.

<hr>
</div>
<div class="section" id="Aliases">
<div class="header">

Next: <a href="#Arrays" accesskey="n" rel="next">Arrays</a>, Previous: <a href="#Shell-Arithmetic" accesskey="p" rel="prev">Shell Arithmetic</a>, Up: <a href="#Bash-Features" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">6.6 Aliases</h3>

Aliases allow a string to be substituted for a word when it is used
as the first word of a simple command.
The shell maintains a list of aliases that may be set and unset with
the <code>alias</code> and <code>unalias</code> builtin commands.

The first word of each simple command, if unquoted, is checked to see
if it has an alias.
If so, that word is replaced by the text of the alias.
The characters &lsquo;<samp>/</samp>&rsquo;, &lsquo;<samp>$</samp>&rsquo;, &lsquo;<samp>`</samp>&rsquo;, &lsquo;<samp>=</samp>&rsquo; and any of the
shell metacharacters or quoting characters listed above may not appear
in an alias name.
The replacement text may contain any valid
shell input, including shell metacharacters.
The first word of the replacement text is tested for
aliases, but a word that is identical to an alias being expanded
is not expanded a second time.
This means that one may alias <code>ls</code> to <code>&quot;ls -F&quot;</code>,
for instance, and Bash does not try to recursively expand the
replacement text.
If the last character of the alias value is a
<code>blank</code>, then the next command word following the
alias is also checked for alias expansion.

Aliases are created and listed with the <code>alias</code>
command, and removed with the <code>unalias</code> command.

There is no mechanism for using arguments in the replacement text,
as in <code>csh</code>.
If arguments are needed, use a shell function
(see <a href="#Shell-Functions">Shell Functions</a>).

Aliases are not expanded when the shell is not interactive,
unless the <code>expand_aliases</code> shell option is set using
<code>shopt</code> (see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>).

The rules concerning the definition and use of aliases are
somewhat confusing. Bash
always reads at least one complete line of input,
and all lines that make up a compound command,
before executing any of the commands on that line or the compound command.
Aliases are expanded when a
command is read, not when it is executed. Therefore, an
alias definition appearing on the same line as another
command does not take effect until the next line of input is read.
The commands following the alias definition
on that line are not affected by the new alias.
This behavior is also an issue when functions are executed.
Aliases are expanded when a function definition is read,
not when the function is executed, because a function definition
is itself a command. As a consequence, aliases
defined in a function are not available until after that
function is executed. To be safe, always put
alias definitions on a separate line, and do not use <code>alias</code>
in compound commands.

For almost every purpose, shell functions are preferred over aliases.

<hr>
</div>
<div class="section" id="Arrays">
<div class="header">

Next: <a href="#The-Directory-Stack" accesskey="n" rel="next">The Directory Stack</a>, Previous: <a href="#Aliases" accesskey="p" rel="prev">Aliases</a>, Up: <a href="#Bash-Features" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">6.7 Arrays</h3>

Bash provides one-dimensional indexed and associative array variables.
Any variable may be used as an indexed array;
the <code>declare</code> builtin will explicitly declare an array.
There is no maximum
limit on the size of an array, nor any requirement that members
be indexed or assigned contiguously.
Indexed arrays are referenced using integers (including arithmetic
expressions (see <a href="#Shell-Arithmetic">Shell Arithmetic</a>)) and are zero-based;
associative arrays use arbitrary strings.
Unless otherwise noted, indexed array indices must be non-negative integers.

An indexed array is created automatically if any variable is assigned to
using the syntax
<div class="example">
<pre class="example"><var>name</var>[<var>subscript</var>]=<var>value</var>
</pre></div>

The <var>subscript</var>
is treated as an arithmetic expression that must evaluate to a number.
To explicitly declare an array, use
<div class="example">
<pre class="example">declare -a <var>name</var>
</pre></div>
The syntax
<div class="example">
<pre class="example">declare -a <var>name</var>[<var>subscript</var>]
</pre></div>
is also accepted; the <var>subscript</var> is ignored.

Associative arrays are created using
<div class="example">
<pre class="example">declare -A <var>name</var>
</pre></div>

Attributes may be
specified for an array variable using the <code>declare</code> and
<code>readonly</code> builtins. Each attribute applies to all members of
an array.

Arrays are assigned to using compound assignments of the form
<div class="example">
<pre class="example"><var>name</var>=(<var>value1</var> <var>value2</var> &hellip; )
</pre></div>
where each
<var>value</var> may be of the form <code>[<var>subscript</var>]=</code><var>string</var>.
Indexed array assignments do not require anything but <var>string</var>.
When assigning to indexed arrays, if
the optional subscript is supplied, that index is assigned to;
otherwise the index of the element assigned is the last index assigned
to by the statement plus one. Indexing starts at zero.

Each <var>value</var> in the list undergoes all the shell expansions
described above (see <a href="#Shell-Expansions">Shell Expansions</a>).

When assigning to an associative array, the words in a compound assignment
may be either assignment statements, for which the subscript is required,
or a list of words that is interpreted as a sequence of alternating keys
and values:
<var>name</var>=(<var>key1</var> <var>value1</var> <var>key2</var> <var>value2</var> &hellip; ).
These are treated identically to
<var>name</var>=( [<var>key1</var>]=<var>value1</var> [<var>key2</var>]=<var>value2</var> &hellip; ).
The first word in the list determines how the remaining words
are interpreted; all assignments in a list must be of the same type.
When using key/value pairs, the keys may not be missing or empty;
a final missing value is treated like the empty string.

This syntax is also accepted by the <code>declare</code>
builtin. Individual array elements may be assigned to using the
<code><var>name</var>[<var>subscript</var>]=<var>value</var></code> syntax introduced above.

When assigning to an indexed array, if <var>name</var>
is subscripted by a negative number, that number is
interpreted as relative to one greater than the maximum index of
<var>name</var>, so negative indices count back from the end of the
array, and an index of -1 references the last element.

The &lsquo;<samp>+=</samp>&rsquo; operator will append to an array variable when assigning
using the compound assignment syntax; see <a href="#Shell-Parameters">Shell Parameters</a> above.

Any element of an array may be referenced using
<code>${<var>name</var>[<var>subscript</var>]}</code>.
The braces are required to avoid
conflicts with the shell&rsquo;s filename expansion operators. If the
<var>subscript</var> is &lsquo;<samp>@</samp>&rsquo; or &lsquo;<samp>*</samp>&rsquo;, the word expands to all members
of the array <var>name</var>. These subscripts differ only when the word
appears within double quotes.
If the word is double-quoted,
<code>${<var>name</var>[*]}</code> expands to a single word with
the value of each array member separated by the first character of the
<code>IFS</code> variable, and <code>${<var>name</var>[@]}</code> expands each element of
<var>name</var> to a separate word. When there are no array members,
<code>${<var>name</var>[@]}</code> expands to nothing.
If the double-quoted expansion occurs within a word, the expansion of
the first parameter is joined with the beginning part of the original
word, and the expansion of the last parameter is joined with the last
part of the original word.
This is analogous to the
expansion of the special parameters &lsquo;<samp>@</samp>&rsquo; and &lsquo;<samp>*</samp>&rsquo;. 
<code>${#<var>name</var>[<var>subscript</var>]}</code> expands to the length of
<code>${<var>name</var>[<var>subscript</var>]}</code>.
If <var>subscript</var> is &lsquo;<samp>@</samp>&rsquo; or
&lsquo;<samp>*</samp>&rsquo;, the expansion is the number of elements in the array. 
If the <var>subscript</var>
used to reference an element of an indexed array
evaluates to a number less than zero, it is
interpreted as relative to one greater than the maximum index of the array,
so negative indices count back from the end of the array,
and an index of -1 refers to the last element.

Referencing an array variable without a subscript is equivalent to
referencing with a subscript of 0.
Any reference to a variable using a valid subscript is legal, and
<code>bash</code> will create an array if necessary.

An array variable is considered set if a subscript has been assigned a
value. The null string is a valid value.

It is possible to obtain the keys (indices) of an array as well as the values.
${!<var>name</var>[@]} and ${!<var>name</var>[*]} expand to the indices
assigned in array variable <var>name</var>.
The treatment when in double quotes is similar to the expansion of the
special parameters &lsquo;<samp>@</samp>&rsquo; and &lsquo;<samp>*</samp>&rsquo; within double quotes.

The <code>unset</code> builtin is used to destroy arrays.
<code>unset <var>name</var>[<var>subscript</var>]</code>
destroys the array element at index <var>subscript</var>.
Negative subscripts to indexed arrays are interpreted as described above.
Unsetting the last element of an array variable does not unset the variable.
<code>unset <var>name</var></code>, where <var>name</var> is an array, removes the
entire array.
<code>unset <var>name</var>[<var>subscript</var>]</code> behaves differently
depending on the array type when given a
subscript of &lsquo;<samp>*</samp>&rsquo; or &lsquo;<samp>@</samp>&rsquo;.
When <var>name</var> is an associative array, it removes the element with key
&lsquo;<samp>*</samp>&rsquo; or &lsquo;<samp>@</samp>&rsquo;.
If <var>name</var> is an indexed array, <code>unset</code> removes all of the elements,
but does not remove the array itself.

When using a variable name with a subscript as an argument to a command,
such as with <code>unset</code>, without using the word expansion syntax
described above, the argument is subject to the shell&rsquo;s filename expansion.
If filename expansion is not desired, the argument should be quoted.

The <code>declare</code>, <code>local</code>, and <code>readonly</code>
builtins each accept a <samp>-a</samp> option to specify an indexed
array and a <samp>-A</samp> option to specify an associative array.
If both options are supplied, <samp>-A</samp> takes precedence.
The <code>read</code> builtin accepts a <samp>-a</samp>
option to assign a list of words read from the standard input
to an array, and can read values from the standard input into
individual array elements. The <code>set</code> and <code>declare</code>
builtins display array values in a way that allows them to be
reused as input.

<hr>
</div>
<div class="section" id="The-Directory-Stack">
<div class="header">

Next: <a href="#Controlling-the-Prompt" accesskey="n" rel="next">Controlling the Prompt</a>, Previous: <a href="#Arrays" accesskey="p" rel="prev">Arrays</a>, Up: <a href="#Bash-Features" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">6.8 The Directory Stack</h3>

The directory stack is a list of recently-visited directories. The
<code>pushd</code> builtin adds directories to the stack as it changes
the current directory, and the <code>popd</code> builtin removes specified
directories from the stack and changes the current directory to
the directory removed. The <code>dirs</code> builtin displays the contents
of the directory stack. The current directory is always the &quot;top&quot;
of the directory stack.

The contents of the directory stack are also visible
as the value of the <code>DIRSTACK</code> shell variable.

<ul class="section-toc">
<li><a href="#Directory-Stack-Builtins" accesskey="1">Directory Stack Builtins</a></li>
</ul>
<hr>
<div class="subsection" id="Directory-Stack-Builtins">
<div class="header">

Up: <a href="#The-Directory-Stack" accesskey="u" rel="up">The Directory Stack</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">6.8.1 Directory Stack Builtins</h4>

Display the list of currently remembered directories. Directories
are added to the list with the <code>pushd</code> command; the
<code>popd</code> command removes directories from the list.
The current directory is always the first directory in the stack.

<dl compact="compact">
<dt><code>-c</code></dt>
<dd>Clears the directory stack by deleting all of the elements.
</dd>
<dt><code>-l</code></dt>
<dd>Produces a listing using full pathnames;
the default listing format uses a tilde to denote the home directory.
</dd>
<dt><code>-p</code></dt>
<dd>Causes <code>dirs</code> to print the directory stack with one entry per
line.
</dd>
<dt><code>-v</code></dt>
<dd>Causes <code>dirs</code> to print the directory stack with one entry per
line, prefixing each entry with its index in the stack.
</dd>
<dt><code>+<var>N</var></code></dt>
<dd>Displays the <var>N</var>th directory (counting from the left of the
list printed by <code>dirs</code> when invoked without options), starting
with zero.
</dd>
<dt><code>-<var>N</var></code></dt>
<dd>Displays the <var>N</var>th directory (counting from the right of the
list printed by <code>dirs</code> when invoked without options), starting
with zero.
</dd>
</dl>

</dd>
<dt id='index-popd'><code>popd</code><a href='#index-popd' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">popd [-n] [+<var>N</var> | -<var>N</var>]
</pre></div>

Removes elements from the directory stack.
The elements are numbered from 0 starting at the first directory
listed by <code>dirs</code>;
that is, <code>popd</code> is equivalent to <code>popd +0</code>.

When no arguments are given, <code>popd</code>
removes the top directory from the stack and changes to
the new top directory.

Arguments, if supplied, have the following meanings:

<dl compact="compact">
<dt><code>-n</code></dt>
<dd>Suppresses the normal change of directory when removing directories
from the stack, so that only the stack is manipulated.
</dd>
<dt><code>+<var>N</var></code></dt>
<dd>Removes the <var>N</var>th directory (counting from the left of the
list printed by <code>dirs</code>), starting with zero, from the stack.
</dd>
<dt><code>-<var>N</var></code></dt>
<dd>Removes the <var>N</var>th directory (counting from the right of the
list printed by <code>dirs</code>), starting with zero, from the stack.
</dd>
</dl>

If the top element of the directory stack is modified, and
the <samp>-n</samp> option was not supplied, <code>popd</code> uses the <code>cd</code>
builtin to change to the directory at the top of the stack.
If the <code>cd</code> fails, <code>popd</code> returns a non-zero value.

Otherwise, <code>popd</code> returns an unsuccessful status if
an invalid option is encountered, the directory stack
is empty, or a non-existent directory stack entry is specified.

If the <code>popd</code> command is successful,
Bash runs <code>dirs</code> to show the final contents of the directory stack,
and the return status is 0.


</dd>
<dt><code>pushd</code></dt>
<dd><div class="example">
<pre class="example">pushd [-n] [<var>+N</var> | <var>-N</var> | <var>dir</var>]
</pre></div>

Adds a directory to the top of the directory stack, or rotates
the stack, making the new top of the stack the current working
directory.
With no arguments, <code>pushd</code> exchanges the top two elements
of the directory stack.

Arguments, if supplied, have the following meanings:

<dl compact="compact">
<dt><code>-n</code></dt>
<dd>Suppresses the normal change of directory when rotating or
adding directories to the stack, so that only the stack is manipulated.
</dd>
<dt><code>+<var>N</var></code></dt>
<dd>Brings the <var>N</var>th directory (counting from the left of the
list printed by <code>dirs</code>, starting with zero) to the top of
the list by rotating the stack.
</dd>
<dt><code>-<var>N</var></code></dt>
<dd>Brings the <var>N</var>th directory (counting from the right of the
list printed by <code>dirs</code>, starting with zero) to the top of
the list by rotating the stack.
</dd>
<dt><code><var>dir</var></code></dt>
<dd>Makes <var>dir</var> be the top of the stack.
</dd>
</dl>

After the stack has been modified, if the <samp>-n</samp> option was not
supplied, <code>pushd</code> uses the <code>cd</code> builtin to change to the
directory at the top of the stack.
If the <code>cd</code> fails, <code>pushd</code> returns a non-zero value.

Otherwise, if no arguments are supplied, <code>pushd</code> returns 0 unless the
directory stack is empty.
When rotating the directory stack, <code>pushd</code> returns 0 unless
the directory stack is empty or a non-existent directory stack element
is specified.

If the <code>pushd</code> command is successful,
Bash runs <code>dirs</code> to show the final contents of the directory stack.

</dd>
</dl>

<hr>
</div>
</div>
<div class="section" id="Controlling-the-Prompt">
<div class="header">

Next: <a href="#The-Restricted-Shell" accesskey="n" rel="next">The Restricted Shell</a>, Previous: <a href="#The-Directory-Stack" accesskey="p" rel="prev">The Directory Stack</a>, Up: <a href="#Bash-Features" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">6.9 Controlling the Prompt</h3>

Bash examines the value of the array variable <code>PROMPT_COMMAND</code> just before
printing each primary prompt.
If any elements in <code>PROMPT_COMMAND</code> are set and non-null, Bash
executes each value, in numeric order,
just as if it had been typed on the command line.

In addition, the following table describes the special characters which
can appear in the prompt variables <code>PS0</code>, <code>PS1</code>, <code>PS2</code>, and
<code>PS4</code>:

<dl compact="compact">
<dt><code>\a</code></dt>
<dd>A bell character.
</dd>
<dt><code>\d</code></dt>
<dd>The date, in &quot;Weekday Month Date&quot; format (e.g., &quot;Tue May 26&quot;).
</dd>
<dt><code>\D{<var>format</var>}</code></dt>
<dd>The <var>format</var> is passed to <code>strftime</code>(3) and the result is inserted
into the prompt string; an empty <var>format</var> results in a locale-specific
time representation. The braces are required.
</dd>
<dt><code>\e</code></dt>
<dd>An escape character.
</dd>
<dt><code>\h</code></dt>
<dd>The hostname, up to the first &lsquo;.&rsquo;.
</dd>
<dt><code>\H</code></dt>
<dd>The hostname.
</dd>
<dt><code>\j</code></dt>
<dd>The number of jobs currently managed by the shell.
</dd>
<dt><code>\l</code></dt>
<dd>The basename of the shell&rsquo;s terminal device name.
</dd>
<dt><code>\n</code></dt>
<dd>A newline.
</dd>
<dt><code>\r</code></dt>
<dd>A carriage return.
</dd>
<dt><code>\s</code></dt>
<dd>The name of the shell, the basename of <code>$0</code> (the portion
following the final slash).
</dd>
<dt><code>\t</code></dt>
<dd>The time, in 24-hour HH:MM:SS format.
</dd>
<dt><code>\T</code></dt>
<dd>The time, in 12-hour HH:MM:SS format.
</dd>
<dt><code>\@</code></dt>
<dd>The time, in 12-hour am/pm format.
</dd>
<dt><code>\A</code></dt>
<dd>The time, in 24-hour HH:MM format.
</dd>
<dt><code>\u</code></dt>
<dd>The username of the current user.
</dd>
<dt><code>\v</code></dt>
<dd>The version of Bash (e.g., 2.00) 
</dd>
<dt><code>\V</code></dt>
<dd>The release of Bash, version + patchlevel (e.g., 2.00.0)
</dd>
<dt><code>\w</code></dt>
<dd>The value of the <code>PWD</code> shell variable (<code>$PWD</code>),
with <code>$HOME</code> abbreviated with a tilde
(uses the <code>$PROMPT_DIRTRIM</code> variable).
</dd>
<dt><code>\W</code></dt>
<dd>The basename of <code>$PWD</code>, with <code>$HOME</code> abbreviated with a tilde.
</dd>
<dt><code>\!</code></dt>
<dd>The history number of this command.
</dd>
<dt><code>\#</code></dt>
<dd>The command number of this command.
</dd>
<dt><code>\$</code></dt>
<dd>If the effective uid is 0, <code>#</code>, otherwise <code>$</code>.
</dd>
<dt><code>\<var>nnn</var></code></dt>
<dd>The character whose ASCII code is the octal value <var>nnn</var>.
</dd>
<dt><code>\\</code></dt>
<dd>A backslash.
</dd>
<dt><code>\[</code></dt>
<dd>Begin a sequence of non-printing characters. This could be used to
embed a terminal control sequence into the prompt.
</dd>
<dt><code>\]</code></dt>
<dd>End a sequence of non-printing characters.
</dd>
</dl>

The command number and the history number are usually different:
the history number of a command is its position in the history
list, which may include commands restored from the history file
(see <a href="#Bash-History-Facilities">Bash History Facilities</a>), while the command number is
the position in the sequence of commands executed during the current
shell session.

After the string is decoded, it is expanded via
parameter expansion, command substitution, arithmetic
expansion, and quote removal, subject to the value of the
<code>promptvars</code> shell option (see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>).
This can have unwanted side effects if escaped portions of the string
appear within command substitution or contain characters special to
word expansion.

<hr>
</div>
<div class="section" id="The-Restricted-Shell">
<div class="header">

Next: <a href="#Bash-POSIX-Mode" accesskey="n" rel="next">Bash POSIX Mode</a>, Previous: <a href="#Controlling-the-Prompt" accesskey="p" rel="prev">Controlling the Prompt</a>, Up: <a href="#Bash-Features" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">6.10 The Restricted Shell</h3>

If Bash is started with the name <code>rbash</code>, or the
<samp>--restricted</samp>
or
<samp>-r</samp>
option is supplied at invocation, the shell becomes restricted.
A restricted shell is used to
set up an environment more controlled than the standard shell.
A restricted shell behaves identically to <code>bash</code>
with the exception that the following are disallowed or not performed:

<ul>
<li> Changing directories with the <code>cd</code> builtin.
</li><li> Setting or unsetting the values of the <code>SHELL</code>, <code>PATH</code>,
<code>HISTFILE</code>,
<code>ENV</code>, or <code>BASH_ENV</code> variables.
</li><li> Specifying command names containing slashes.
</li><li> Specifying a filename containing a slash as an argument to the <code>.</code>
builtin command.
</li><li> Specifying a filename containing a slash as an argument to the <code>history</code>
builtin command.
</li><li> Specifying a filename containing a slash as an argument to the <samp>-p</samp>
option to the <code>hash</code> builtin command.
</li><li> Importing function definitions from the shell environment at startup.
</li><li> Parsing the value of <code>SHELLOPTS</code> from the shell environment at startup.
</li><li> Redirecting output using the &lsquo;<samp>&gt;</samp>&rsquo;, &lsquo;<samp>&gt;|</samp>&rsquo;, &lsquo;<samp>&lt;&gt;</samp>&rsquo;, &lsquo;<samp>&gt;&amp;</samp>&rsquo;,
&lsquo;<samp>&amp;&gt;</samp>&rsquo;, and &lsquo;<samp>&gt;&gt;</samp>&rsquo; redirection operators.
</li><li> Using the <code>exec</code> builtin to replace the shell with another command.
</li><li> Adding or deleting builtin commands with the
<samp>-f</samp> and <samp>-d</samp> options to the <code>enable</code> builtin.
</li><li> Using the <code>enable</code> builtin command to enable disabled shell builtins.
</li><li> Specifying the <samp>-p</samp> option to the <code>command</code> builtin.
</li><li> Turning off restricted mode with &lsquo;<samp>set +r</samp>&rsquo; or &lsquo;<samp>shopt -u restricted_shell</samp>&rsquo;.
</li></ul>

These restrictions are enforced after any startup files are read.

When a command that is found to be a shell script is executed
(see <a href="#Shell-Scripts">Shell Scripts</a>), <code>rbash</code> turns off any restrictions in
the shell spawned to execute the script.

The restricted shell mode is only one component of a useful restricted
environment. It should be accompanied by setting <code>PATH</code> to a value
that allows execution of only a few verified commands (commands that
allow shell escapes are particularly vulnerable), changing the current
directory to a non-writable directory other than <code>$HOME</code> after login,
not allowing the restricted shell to execute shell scripts, and cleaning
the environment of variables that cause some commands to modify their
behavior (e.g., <code>VISUAL</code> or <code>PAGER</code>).

Modern systems provide more secure ways to implement a restricted environment,
such as <code>jails</code>, <code>zones</code>, or <code>containers</code>.

<hr>
</div>
<div class="section" id="Bash-POSIX-Mode">
<div class="header">

Next: <a href="#Shell-Compatibility-Mode" accesskey="n" rel="next">Shell Compatibility Mode</a>, Previous: <a href="#The-Restricted-Shell" accesskey="p" rel="prev">The Restricted Shell</a>, Up: <a href="#Bash-Features" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">6.11 Bash POSIX Mode</h3>

Starting Bash with the <samp>--posix</samp> command-line option or executing
&lsquo;<samp>set -o posix</samp>&rsquo; while Bash is running will cause Bash to conform more
closely to the POSIX standard by changing the behavior to
match that specified by POSIX in areas where the Bash default differs.

When invoked as <code>sh</code>, Bash enters POSIX mode after reading the
startup files.

The following list is what&rsquo;s changed when &lsquo;POSIX mode&rsquo; is in effect:

<ol>
<li> Bash ensures that the <code>POSIXLY_CORRECT</code> variable is set.

</li><li> When a command in the hash table no longer exists, Bash will re-search
<code>$PATH</code> to find the new location. This is also available with
&lsquo;<samp>shopt -s checkhash</samp>&rsquo;.

</li><li> Bash will not insert a command without the execute bit set into the
command hash table, even if it returns it as a (last-ditch) result
from a <code>$PATH</code> search.

</li><li> The message printed by the job control code and builtins when a job
exits with a non-zero status is &lsquo;Done(status)&rsquo;.

</li><li> The message printed by the job control code and builtins when a job
is stopped is &lsquo;Stopped(<var>signame</var>)&rsquo;, where <var>signame</var> is, for
example, <code>SIGTSTP</code>.

</li><li> Alias expansion is always enabled, even in non-interactive shells.

</li><li> Reserved words appearing in a context where reserved words are recognized
do not undergo alias expansion.

</li><li> Alias expansion is performed when initially parsing a command substitution.
The default mode generally defers it, when enabled, until the command
substitution is executed. This means that command substitution will not
expand aliases that are defined after the command substitution is initially
parsed (e.g., as part of a function definition).

</li><li> The POSIX <code>PS1</code> and <code>PS2</code> expansions of &lsquo;<samp>!</samp>&rsquo; to
the history number and &lsquo;<samp>!!</samp>&rsquo; to &lsquo;<samp>!</samp>&rsquo; are enabled,
and parameter expansion is performed on the values of <code>PS1</code> and
<code>PS2</code> regardless of the setting of the <code>promptvars</code> option.

</li><li> The POSIX startup files are executed (<code>$ENV</code>) rather than
the normal Bash files.

</li><li> Tilde expansion is only performed on assignments preceding a command
name, rather than on all assignment statements on the line.

</li><li> The default history file is <samp>~/.sh_history</samp> (this is the
default value of <code>$HISTFILE</code>).

</li><li> Redirection operators do not perform filename expansion on the word
in the redirection unless the shell is interactive.

</li><li> Redirection operators do not perform word splitting on the word in the
redirection.

</li><li> Function names must be valid shell <code>name</code>s. That is, they may not
contain characters other than letters, digits, and underscores, and
may not start with a digit. Declaring a function with an invalid name
causes a fatal syntax error in non-interactive shells.

</li><li> Function names may not be the same as one of the POSIX special
builtins.

</li><li> POSIX special builtins are found before shell functions
during command lookup.

</li><li> When printing shell function definitions (e.g., by <code>type</code>), Bash does
not print the <code>function</code> keyword.

</li><li> Literal tildes that appear as the first character in elements of
the <code>PATH</code> variable are not expanded as described above
under <a href="#Tilde-Expansion">Tilde Expansion</a>.

</li><li> The <code>time</code> reserved word may be used by itself as a command. When
used in this way, it displays timing statistics for the shell and its
completed children. The <code>TIMEFORMAT</code> variable controls the format
of the timing information.

</li><li> When parsing and expanding a ${&hellip;} expansion that appears within
double quotes, single quotes are no longer special and cannot be used to
quote a closing brace or other special character, unless the operator is
one of those defined to perform pattern removal. In this case, they do
not have to appear as matched pairs.

</li><li> The parser does not recognize <code>time</code> as a reserved word if the next
token begins with a &lsquo;<samp>-</samp>&rsquo;.

</li><li> The &lsquo;<samp>!</samp>&rsquo; character does not introduce history expansion within a
double-quoted string, even if the <code>histexpand</code> option is enabled.

</li><li> If a POSIX special builtin returns an error status, a
non-interactive shell exits. The fatal errors are those listed in
the POSIX standard, and include things like passing incorrect options,
redirection errors, variable assignment errors for assignments preceding
the command name, and so on.

</li><li> A non-interactive shell exits with an error status if a variable
assignment error occurs when no command name follows the assignment
statements.
A variable assignment error occurs, for example, when trying to assign
a value to a readonly variable.

</li><li> A non-interactive shell exits with an error status if a variable
assignment error occurs in an assignment statement preceding a special
builtin, but not with any other simple command. For any other simple
command, the shell aborts execution of that command, and execution continues
at the top level (&quot;the shell shall not perform any further processing of the
command in which the error occurred&quot;).

</li><li> A non-interactive shell exits with an error status if the iteration
variable in a <code>for</code> statement or the selection variable in a
<code>select</code> statement is a readonly variable.

</li><li> Non-interactive shells exit if <var>filename</var> in <code>.</code> <var>filename</var>
is not found.

</li><li> Non-interactive shells exit if a syntax error in an arithmetic expansion
results in an invalid expression.

</li><li> Non-interactive shells exit if a parameter expansion error occurs.

</li><li> Non-interactive shells exit if there is a syntax error in a script read
with the <code>.</code> or <code>source</code> builtins, or in a string processed by
the <code>eval</code> builtin.

</li><li> While variable indirection is available, it may not be applied to the
&lsquo;<samp>#</samp>&rsquo; and &lsquo;<samp>?</samp>&rsquo; special parameters.

</li><li> Expanding the &lsquo;<samp>*</samp>&rsquo; special parameter in a pattern context where the
expansion is double-quoted does not treat the <code>$*</code> as if it were
double-quoted.

</li><li> Assignment statements preceding POSIX special builtins
persist in the shell environment after the builtin completes.

</li><li> The <code>command</code> builtin does not prevent builtins that take assignment
statements as arguments from expanding them as assignment statements;
when not in POSIX mode, assignment builtins lose their assignment
statement expansion properties when preceded by <code>command</code>.

</li><li> The <code>bg</code> builtin uses the required format to describe each job placed
in the background, which does not include an indication of whether the job
is the current or previous job.

</li><li> The output of &lsquo;<samp>kill -l</samp>&rsquo; prints all the signal names on a single line,
separated by spaces, without the &lsquo;<samp>SIG</samp>&rsquo; prefix.

</li><li> The <code>kill</code> builtin does not accept signal names with a &lsquo;<samp>SIG</samp>&rsquo;
prefix.

</li><li> The <code>export</code> and <code>readonly</code> builtin commands display their
output in the format required by POSIX.

</li><li> The <code>trap</code> builtin displays signal names without the leading
<code>SIG</code>.

</li><li> The <code>trap</code> builtin doesn&rsquo;t check the first argument for a possible
signal specification and revert the signal handling to the original
disposition if it is, unless that argument consists solely of digits and
is a valid signal number. If users want to reset the handler for a given
signal to the original disposition, they should use &lsquo;<samp>-</samp>&rsquo; as the
first argument.

</li><li> <code>trap -p</code> displays signals whose dispositions are set to SIG_DFL and
those that were ignored when the shell started.

</li><li> The <code>.</code> and <code>source</code> builtins do not search the current directory
for the filename argument if it is not found by searching <code>PATH</code>.

</li><li> Enabling POSIX mode has the effect of setting the
<code>inherit_errexit</code> option, so
subshells spawned to execute command substitutions inherit the value of
the <samp>-e</samp> option from the parent shell.
When the <code>inherit_errexit</code> option is not enabled,
Bash clears the <samp>-e</samp> option in such subshells.

</li><li> Enabling POSIX mode has the effect of setting the
<code>shift_verbose</code> option, so numeric arguments to <code>shift</code>
that exceed the number of positional parameters will result in an
error message.

</li><li> When the <code>alias</code> builtin displays alias definitions, it does not
display them with a leading &lsquo;<samp>alias </samp>&rsquo; unless the <samp>-p</samp> option
is supplied.

</li><li> When the <code>set</code> builtin is invoked without options, it does not display
shell function names and definitions.

</li><li> When the <code>set</code> builtin is invoked without options, it displays
variable values without quotes, unless they contain shell metacharacters,
even if the result contains nonprinting characters.

</li><li> When the <code>cd</code> builtin is invoked in logical mode, and the pathname
constructed from <code>$PWD</code> and the directory name supplied as an argument
does not refer to an existing directory, <code>cd</code> will fail instead of
falling back to physical mode.

</li><li> When the <code>cd</code> builtin cannot change a directory because the
length of the pathname 
constructed from <code>$PWD</code> and the directory name supplied as an argument
exceeds <code>PATH_MAX</code> when all symbolic links are expanded, <code>cd</code> will
fail instead of attempting to use only the supplied directory name.

</li><li> The <code>pwd</code> builtin verifies that the value it prints is the same as the
current directory, even if it is not asked to check the file system with the
<samp>-P</samp> option.

</li><li> When listing the history, the <code>fc</code> builtin does not include an
indication of whether or not a history entry has been modified.

</li><li> The default editor used by <code>fc</code> is <code>ed</code>.

</li><li> The <code>type</code> and <code>command</code> builtins will not report a non-executable
file as having been found, though the shell will attempt to execute such a
file if it is the only so-named file found in <code>$PATH</code>.

</li><li> The <code>vi</code> editing mode will invoke the <code>vi</code> editor directly when
the &lsquo;<samp>v</samp>&rsquo; command is run, instead of checking <code>$VISUAL</code> and
<code>$EDITOR</code>.

</li><li> When the <code>xpg_echo</code> option is enabled, Bash does not attempt to interpret
any arguments to <code>echo</code> as options. Each argument is displayed, after
escape characters are converted.

</li><li> The <code>ulimit</code> builtin uses a block size of 512 bytes for the <samp>-c</samp>
and <samp>-f</samp> options.

</li><li> The arrival of <code>SIGCHLD</code> when a trap is set on <code>SIGCHLD</code> does
not interrupt the <code>wait</code> builtin and cause it to return immediately.
The trap command is run once for each child that exits.

</li><li> The <code>read</code> builtin may be interrupted by a signal for which a trap
has been set.
If Bash receives a trapped signal while executing <code>read</code>, the trap
handler executes and <code>read</code> returns an exit status greater than 128.

</li><li> The <code>printf</code> builtin uses <code>double</code> (via <code>strtod</code>) to convert
arguments corresponding to floating point conversion specifiers, instead of
<code>long double</code> if it&rsquo;s available. The &lsquo;<samp>L</samp>&rsquo; length modifier forces
<code>printf</code> to use <code>long double</code> if it&rsquo;s available.

</li><li> Bash removes an exited background process&rsquo;s status from the list of such
statuses after the <code>wait</code> builtin is used to obtain it.

</li></ol>

There is other POSIX behavior that Bash does not implement by
default even when in POSIX mode.
Specifically:

<ol>
<li> The <code>fc</code> builtin checks <code>$EDITOR</code> as a program to edit history
entries if <code>FCEDIT</code> is unset, rather than defaulting directly to
<code>ed</code>. <code>fc</code> uses <code>ed</code> if <code>EDITOR</code> is unset.

</li><li> As noted above, Bash requires the <code>xpg_echo</code> option to be enabled for
the <code>echo</code> builtin to be fully conformant.

</li></ol>

Bash can be configured to be POSIX-conformant by default, by specifying
the <samp>--enable-strict-posix-default</samp> to <code>configure</code> when building
(see <a href="#Optional-Features">Optional Features</a>).

<hr>
</div>
<div class="section" id="Shell-Compatibility-Mode">
<div class="header">

Previous: <a href="#Bash-POSIX-Mode" accesskey="p" rel="prev">Bash POSIX Mode</a>, Up: <a href="#Bash-Features" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">6.12 Shell Compatibility Mode</h3>

Bash-4.0 introduced the concept of a shell compatibility level,
specified as a set of options to the shopt builtin
(<code>compat31</code>,
<code>compat32</code>,
<code>compat40</code>,
<code>compat41</code>,
and so on).
There is only one current
compatibility level &ndash; each option is mutually exclusive.
The compatibility level is intended to allow users to select behavior
from previous versions that is incompatible with newer versions
while they migrate scripts to use current features and
behavior. It&rsquo;s intended to be a temporary solution.

This section does not mention behavior that is standard for a particular
version (e.g., setting <code>compat32</code> means that quoting the rhs of the regexp
matching operator quotes special regexp characters in the word, which is
default behavior in bash-3.2 and subsequent versions). 

If a user enables, say, <code>compat32</code>, it may affect the behavior of other
compatibility levels up to and including the current compatibility level.
The idea is that each compatibility level controls behavior that changed
in that version of Bash,
but that behavior may have been present in earlier versions.
For instance, the change to use locale-based comparisons with the <code>[[</code>
command came in bash-4.1, and earlier versions used ASCII-based comparisons,
so enabling <code>compat32</code> will enable ASCII-based comparisons as well.
That granularity may not be sufficient for
all uses, and as a result users should employ compatibility levels carefully.
Read the documentation for a particular feature to find out the
current behavior.

Bash-4.3 introduced a new shell variable: <code>BASH_COMPAT</code>.
The value assigned
to this variable (a decimal version number like 4.2, or an integer
corresponding to the <code>compat</code><var>NN</var> option, like 42) determines the
compatibility level.

Starting with bash-4.4, Bash has begun deprecating older compatibility
levels.
Eventually, the options will be removed in favor of <code>BASH_COMPAT</code>.

Bash-5.0 is the final version for which there will be an individual shopt
option for the previous version. Users should use <code>BASH_COMPAT</code>
on bash-5.0 and later versions.

The following table describes the behavior changes controlled by each
compatibility level setting.
The <code>compat</code><var>NN</var> tag is used as shorthand for setting the
compatibility level
to <var>NN</var> using one of the following mechanisms.
For versions prior to bash-5.0, the compatibility level may be set using
the corresponding <code>compat</code><var>NN</var> shopt option.
For bash-4.3 and later versions, the <code>BASH_COMPAT</code> variable is preferred,
and it is required for bash-5.1 and later versions.

<dl compact="compact">
<dt><code>compat31</code></dt>
<dd><ul>
<li> quoting the rhs of the <code>[[</code> command&rsquo;s regexp matching operator (=~)
has no special effect
</li></ul>

</dd>
<dt><code>compat32</code></dt>
<dd><ul>
<li> interrupting a command list such as &quot;a ; b ; c&quot; causes the execution
of the next command in the list (in bash-4.0 and later versions,
the shell acts as if it received the interrupt, so
interrupting one command in a list aborts the execution of the
entire list)
</li></ul>

</dd>
<dt><code>compat40</code></dt>
<dd><ul>
<li> the &lsquo;<samp>&lt;</samp>&rsquo; and &lsquo;<samp>&gt;</samp>&rsquo; operators to the <code>[[</code> command do not
consider the current locale when comparing strings; they use ASCII
ordering.
Bash versions prior to bash-4.1 use ASCII collation and strcmp(3);
bash-4.1 and later use the current locale&rsquo;s collation sequence and
strcoll(3).
</li></ul>

</dd>
<dt><code>compat41</code></dt>
<dd><ul>
<li> in posix mode, <code>time</code> may be followed by options and still be
recognized as a reserved word (this is POSIX interpretation 267)
</li><li> in posix mode, the parser requires that an even number of single
quotes occur in the <var>word</var> portion of a double-quoted ${&hellip;}
parameter expansion and treats them specially, so that characters within
the single quotes are considered quoted
(this is POSIX interpretation 221)
</li></ul>

</dd>
<dt><code>compat42</code></dt>
<dd><ul>
<li> the replacement string in double-quoted pattern substitution does not
undergo quote removal, as it does in versions after bash-4.2
</li><li> in posix mode, single quotes are considered special when expanding
the <var>word</var> portion of a double-quoted ${&hellip;} parameter expansion
and can be used to quote a closing brace or other special character
(this is part of POSIX interpretation 221);
in later versions, single quotes
are not special within double-quoted word expansions
</li></ul>

</dd>
<dt><code>compat43</code></dt>
<dd><ul>
<li> the shell does not print a warning message if an attempt is made to
use a quoted compound assignment as an argument to declare
(e.g., declare -a foo=&rsquo;(1 2)&rsquo;). Later versions warn that this usage is
deprecated
</li><li> word expansion errors are considered non-fatal errors that cause the
current command to fail, even in posix mode
(the default behavior is to make them fatal errors that cause the shell
to exit)
</li><li> when executing a shell function, the loop state (while/until/etc.)
is not reset, so <code>break</code> or <code>continue</code> in that function will break
or continue loops in the calling context. Bash-4.4 and later reset
the loop state to prevent this
</li></ul>

</dd>
<dt><code>compat44</code></dt>
<dd><ul>
<li> the shell sets up the values used by <code>BASH_ARGV</code> and <code>BASH_ARGC</code>
so they can expand to the shell&rsquo;s positional parameters even if extended
debugging mode is not enabled
</li><li> a subshell inherits loops from its parent context, so <code>break</code>
or <code>continue</code> will cause the subshell to exit.
Bash-5.0 and later reset the loop state to prevent the exit
</li><li> variable assignments preceding builtins like <code>export</code> and <code>readonly</code>
that set attributes continue to affect variables with the same
name in the calling environment even if the shell is not in posix
mode
</li></ul>

</dd>
<dt><code>compat50 (set using BASH_COMPAT)</code></dt>
<dd><ul>
<li> Bash-5.1 changed the way <code>$RANDOM</code> is generated to introduce slightly
more randomness. If the shell compatibility level is set to 50 or
lower, it reverts to the method from bash-5.0 and previous versions,
so seeding the random number generator by assigning a value to
<code>RANDOM</code> will produce the same sequence as in bash-5.0
</li><li> If the command hash table is empty, Bash versions prior to bash-5.1
printed an informational message to that effect, even when producing
output that can be reused as input. Bash-5.1 suppresses that message
when the <samp>-l</samp> option is supplied.
</li></ul>

</dd>
<dt><code>compat51 (set using BASH_COMPAT)</code></dt>
<dd><ul>
<li> The <code>unset</code> builtin will unset the array <code>a</code> given an argument like
&lsquo;<samp>a[@]</samp>&rsquo;.
Bash-5.2 will unset an element with key &lsquo;<samp>@</samp>&rsquo; (associative arrays)
or remove all the elements without unsetting the array (indexed arrays)
</li><li> arithmetic commands ( ((...)) ) and the expressions in an arithmetic for
statement can be expanded more than once
</li><li> expressions used as arguments to arithmetic operators in the <code>[[</code>
conditional command can be expanded more than once
</li><li> the expressions in substring parameter brace expansion can be
expanded more than once
</li><li> the expressions in the $(( ... )) word expansion can be expanded
more than once
</li><li> arithmetic expressions used as indexed array subscripts can be
expanded more than once
</li><li> <code>test -v</code>, when given an argument of &lsquo;<samp>A[@]</samp>&rsquo;, where <var>A</var> is
an existing associative array, will return true if the array has any set
elements.
Bash-5.2 will look for and report on a key named &lsquo;<samp>@</samp>&rsquo;
</li><li> the ${<var>parameter</var>[:]=<var>value</var>} word expansion will return
<var>value</var>, before any variable-specific transformations have been
performed (e.g., converting to lowercase).
Bash-5.2 will return the final value assigned to the variable.
</li><li> Parsing command substitutions will behave as if extended glob
(see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>)
is enabled, so that parsing a command substitution containing an extglob
pattern (say, as part of a shell function) will not fail.
This assumes the intent is to enable extglob before the command is executed
and word expansions are performed.
It will fail at word expansion time if extglob hasn&rsquo;t been
enabled by the time the command is executed.
</li></ul>
</dd>
</dl>

<hr>
</div>
</div>
<div class="chapter" id="Job-Control">
<div class="header">

Next: <a href="#Command-Line-Editing" accesskey="n" rel="next">Command Line Editing</a>, Previous: <a href="#Bash-Features" accesskey="p" rel="prev">Bash Features</a>, Up: <a href="#Top" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h2 class="chapter">7 Job Control</h2>

This chapter discusses what job control is, how it works, and how
Bash allows you to access its facilities.

<ul class="section-toc">
<li><a href="#Job-Control-Basics" accesskey="1">Job Control Basics</a></li>
<li><a href="#Job-Control-Builtins" accesskey="2">Job Control Builtins</a></li>
<li><a href="#Job-Control-Variables" accesskey="3">Job Control Variables</a></li>
</ul>
<hr>
<div class="section" id="Job-Control-Basics">
<div class="header">

Next: <a href="#Job-Control-Builtins" accesskey="n" rel="next">Job Control Builtins</a>, Up: <a href="#Job-Control" accesskey="u" rel="up">Job Control</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">7.1 Job Control Basics</h3>

Job control
refers to the ability to selectively stop (suspend)
the execution of processes and continue (resume)
their execution at a later point. A user typically employs
this facility via an interactive interface supplied jointly
by the operating system kernel&rsquo;s terminal driver and Bash.

The shell associates a <var>job</var> with each pipeline. It keeps a
table of currently executing jobs, which may be listed with the
<code>jobs</code> command. When Bash starts a job
asynchronously, it prints a line that looks
like:
<div class="example">
<pre class="example">[1] 25647
</pre></div>
indicating that this job is job number 1 and that the process ID
of the last process in the pipeline associated with this job is
25647. All of the processes in a single pipeline are members of
the same job. Bash uses the <var>job</var> abstraction as the
basis for job control. 

To facilitate the implementation of the user interface to job
control, the operating system maintains the notion of a current terminal
process group ID. Members of this process group (processes whose
process group ID is equal to the current terminal process group
ID) receive keyboard-generated signals such as <code>SIGINT</code>. 
These processes are said to be in the foreground. Background
processes are those whose process group ID differs from the
terminal&rsquo;s; such processes are immune to keyboard-generated
signals. Only foreground processes are allowed to read from or, if
the user so specifies with <code>stty tostop</code>, write to the terminal.
Background processes which attempt to
read from (write to when <code>stty tostop</code> is in effect) the
terminal are sent a <code>SIGTTIN</code> (<code>SIGTTOU</code>)
signal by the kernel&rsquo;s terminal driver,
which, unless caught, suspends the process. 

If the operating system on which Bash is running supports
job control, Bash contains facilities to use it. Typing the
suspend character (typically &lsquo;<samp>^Z</samp>&rsquo;, Control-Z) while a
process is running causes that process to be stopped and returns
control to Bash. Typing the delayed suspend character
(typically &lsquo;<samp>^Y</samp>&rsquo;, Control-Y) causes the process to be stopped
when it attempts to read input from the terminal, and control to
be returned to Bash. The user then manipulates the state of
this job, using the <code>bg</code> command to continue it in the
background, the <code>fg</code> command to continue it in the
foreground, or the <code>kill</code> command to kill it. A &lsquo;<samp>^Z</samp>&rsquo;
takes effect immediately, and has the additional side effect of
causing pending output and typeahead to be discarded. 

There are a number of ways to refer to a job in the shell. The
character &lsquo;<samp>%</samp>&rsquo; introduces a job specification (jobspec).

Job number <code>n</code> may be referred to as &lsquo;<samp>%n</samp>&rsquo;.
The symbols &lsquo;<samp>%%</samp>&rsquo; and &lsquo;<samp>%+</samp>&rsquo; refer to the shell&rsquo;s notion of the
current job, which is the last job stopped while it was in the foreground
or started in the background.
A single &lsquo;<samp>%</samp>&rsquo; (with no accompanying job specification) also refers
to the current job.
The previous job may be referenced using &lsquo;<samp>%-</samp>&rsquo;.
If there is only a single job, &lsquo;<samp>%+</samp>&rsquo; and &lsquo;<samp>%-</samp>&rsquo; can both be used
to refer to that job.
In output pertaining to jobs (e.g., the output of the <code>jobs</code>
command), the current job is always flagged with a &lsquo;<samp>+</samp>&rsquo;, and the
previous job with a &lsquo;<samp>-</samp>&rsquo;. 

A job may also be referred to
using a prefix of the name used to start it, or using a substring
that appears in its command line. For example, &lsquo;<samp>%ce</samp>&rsquo; refers
to a stopped job whose command name begins with &lsquo;<samp>ce</samp>&rsquo;.
Using &lsquo;<samp>%?ce</samp>&rsquo;, on the
other hand, refers to any job containing the string &lsquo;<samp>ce</samp>&rsquo; in
its command line. If the prefix or substring matches more than one job,
Bash reports an error.

Simply naming a job can be used to bring it into the foreground:
&lsquo;<samp>%1</samp>&rsquo; is a synonym for &lsquo;<samp>fg %1</samp>&rsquo;, bringing job 1 from the
background into the foreground. Similarly, &lsquo;<samp>%1 &amp;</samp>&rsquo; resumes
job 1 in the background, equivalent to &lsquo;<samp>bg %1</samp>&rsquo;

The shell learns immediately whenever a job changes state. 
Normally, Bash waits until it is about to print a prompt
before reporting changes in a job&rsquo;s status so as to not interrupt
any other output.
If the <samp>-b</samp> option to the <code>set</code> builtin is enabled,
Bash reports such changes immediately (see <a href="#The-Set-Builtin">The Set Builtin</a>).
Any trap on <code>SIGCHLD</code> is executed for each child process
that exits.

If an attempt to exit Bash is made while jobs are stopped, (or running, if
the <code>checkjobs</code> option is enabled &ndash; see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>), the
shell prints a warning message, and if the <code>checkjobs</code> option is
enabled, lists the jobs and their statuses.
The <code>jobs</code> command may then be used to inspect their status.
If a second attempt to exit is made without an intervening command,
Bash does not print another warning, and any stopped jobs are terminated.

When the shell is waiting for a job or process using the <code>wait</code>
builtin, and job control is enabled, <code>wait</code> will return when the
job changes state. The <samp>-f</samp> option causes <code>wait</code> to wait
until the job or process terminates before returning.

<hr>
</div>
<div class="section" id="Job-Control-Builtins">
<div class="header">

Next: <a href="#Job-Control-Variables" accesskey="n" rel="next">Job Control Variables</a>, Previous: <a href="#Job-Control-Basics" accesskey="p" rel="prev">Job Control Basics</a>, Up: <a href="#Job-Control" accesskey="u" rel="up">Job Control</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">7.2 Job Control Builtins</h3>

<dl compact="compact">
<dt id='index-bg'><code>bg</code><a href='#index-bg' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">bg [<var>jobspec</var> &hellip;]
</pre></div>

Resume each suspended job <var>jobspec</var> in the background, as if it
had been started with &lsquo;<samp>&amp;</samp>&rsquo;.
If <var>jobspec</var> is not supplied, the current job is used.
The return status is zero unless it is run when job control is not
enabled, or, when run with job control enabled, any
<var>jobspec</var> was not found or specifies a job
that was started without job control.

</dd>
<dt id='index-fg'><code>fg</code><a href='#index-fg' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">fg [<var>jobspec</var>]
</pre></div>

Resume the job <var>jobspec</var> in the foreground and make it the current job.
If <var>jobspec</var> is not supplied, the current job is used.
The return status is that of the command placed into the foreground,
or non-zero if run when job control is disabled or, when run with
job control enabled, <var>jobspec</var> does not specify a valid job or
<var>jobspec</var> specifies a job that was started without job control.

</dd>
<dt id='index-jobs'><code>jobs</code><a href='#index-jobs' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">jobs [-lnprs] [<var>jobspec</var>]
jobs -x <var>command</var> [<var>arguments</var>]
</pre></div>

The first form lists the active jobs. The options have the
following meanings:

<dl compact="compact">
<dt><code>-l</code></dt>
<dd>List process IDs in addition to the normal information.

</dd>
<dt><code>-n</code></dt>
<dd>Display information only about jobs that have changed status since
the user was last notified of their status.

</dd>
<dt><code>-p</code></dt>
<dd>List only the process ID of the job&rsquo;s process group leader.

</dd>
<dt><code>-r</code></dt>
<dd>Display only running jobs.

</dd>
<dt><code>-s</code></dt>
<dd>Display only stopped jobs.
</dd>
</dl>

If <var>jobspec</var> is given,
output is restricted to information about that job. 
If <var>jobspec</var> is not supplied, the status of all jobs is
listed.

If the <samp>-x</samp> option is supplied, <code>jobs</code> replaces any
<var>jobspec</var> found in <var>command</var> or <var>arguments</var> with the
corresponding process group ID, and executes <var>command</var>,
passing it <var>argument</var>s, returning its exit status. 

</dd>
<dt id='index-kill'><code>kill</code><a href='#index-kill' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">kill [-s <var>sigspec</var>] [-n <var>signum</var>] [-<var>sigspec</var>] <var>jobspec</var> or <var>pid</var>
kill -l|-L [<var>exit_status</var>]
</pre></div>

Send a signal specified by <var>sigspec</var> or <var>signum</var> to the process
named by job specification <var>jobspec</var> or process ID <var>pid</var>.
<var>sigspec</var> is either a case-insensitive signal name such as
<code>SIGINT</code> (with or without the <code>SIG</code> prefix)
or a signal number; <var>signum</var> is a signal number.
If <var>sigspec</var> and <var>signum</var> are not present, <code>SIGTERM</code> is used.
The <samp>-l</samp> option lists the signal names.
If any arguments are supplied when <samp>-l</samp> is given, the names of the
signals corresponding to the arguments are listed, and the return status
is zero.
<var>exit_status</var> is a number specifying a signal number or the exit
status of a process terminated by a signal.
The <samp>-L</samp> option is equivalent to <samp>-l</samp>.
The return status is zero if at least one signal was successfully sent,
or non-zero if an error occurs or an invalid option is encountered.

</dd>
<dt id='index-wait'><code>wait</code><a href='#index-wait' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">wait [-fn] [-p <var>varname</var>] [<var>jobspec</var> or <var>pid</var> &hellip;]
</pre></div>

Wait until the child process specified by each process ID <var>pid</var>
or job specification <var>jobspec</var> exits and return the exit status of the
last command waited for.
If a job spec is given, all processes in the job are waited for.
If no arguments are given,
<code>wait</code> waits for all running background jobs and
the last-executed process substitution, if its process id is the same as
<var>$!</var>,
and the return status is zero.
If the <samp>-n</samp> option is supplied, <code>wait</code> waits for a single job
from the list of <var>pid</var>s or <var>jobspec</var>s or, if no arguments are
supplied, any job, 
to complete and returns its exit status.
If none of the supplied arguments is a child of the shell, or if no arguments
are supplied and the shell has no unwaited-for children, the exit status
is 127.
If the <samp>-p</samp> option is supplied, the process or job identifier of the job
for which the exit status is returned is assigned to the variable
<var>varname</var> named by the option argument.
The variable will be unset initially, before any assignment.
This is useful only when the <samp>-n</samp> option is supplied.
Supplying the <samp>-f</samp> option, when job control is enabled,
forces <code>wait</code> to wait for each <var>pid</var> or <var>jobspec</var> to
terminate before returning its status, instead of returning when it changes
status.
If neither <var>jobspec</var> nor <var>pid</var> specifies an active child process
of the shell, the return status is 127.
If <code>wait</code> is interrupted by a signal, the return status will be greater
than 128, as described above (see <a href="#Signals">Signals</a>).
Otherwise, the return status is the exit status
of the last process or job waited for.

</dd>
<dt id='index-disown'><code>disown</code><a href='#index-disown' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">disown [-ar] [-h] [<var>jobspec</var> &hellip; | <var>pid</var> &hellip; ]
</pre></div>

Without options, remove each <var>jobspec</var> from the table of
active jobs.
If the <samp>-h</samp> option is given, the job is not removed from the table,
but is marked so that <code>SIGHUP</code> is not sent to the job if the shell
receives a <code>SIGHUP</code>.
If <var>jobspec</var> is not present, and neither the <samp>-a</samp> nor the
<samp>-r</samp> option is supplied, the current job is used.
If no <var>jobspec</var> is supplied, the <samp>-a</samp> option means to remove or
mark all jobs; the <samp>-r</samp> option without a <var>jobspec</var>
argument restricts operation to running jobs.

</dd>
<dt id='index-suspend'><code>suspend</code><a href='#index-suspend' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">suspend [-f]
</pre></div>

Suspend the execution of this shell until it receives a
<code>SIGCONT</code> signal.
A login shell,
or a shell without job control enabled,
cannot be suspended; the <samp>-f</samp>
option can be used to override this and force the suspension.
The return status is 0 unless the shell is a login shell
or job control is not enabled
and
<samp>-f</samp>
is not supplied.

</dd>
</dl>

When job control is not active, the <code>kill</code> and <code>wait</code>
builtins do not accept <var>jobspec</var> arguments. They must be
supplied process IDs.

<hr>
</div>
<div class="section" id="Job-Control-Variables">
<div class="header">

Previous: <a href="#Job-Control-Builtins" accesskey="p" rel="prev">Job Control Builtins</a>, Up: <a href="#Job-Control" accesskey="u" rel="up">Job Control</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">7.3 Job Control Variables</h3>

<dl compact="compact">
<dt id='index-auto_005fresume'><code>auto_resume</code><a href='#index-auto_005fresume' class='copiable-anchor'> &para;</a></dt>
<dd>This variable controls how the shell interacts with the user and
job control. If this variable exists then single word simple
commands without redirections are treated as candidates for resumption
of an existing job. There is no ambiguity allowed; if there is
more than one job beginning with the string typed, then
the most recently accessed job will be selected.
The name of a stopped job, in this context, is the command line
used to start it. If this variable is set to the value &lsquo;<samp>exact</samp>&rsquo;,
the string supplied must match the name of a stopped job exactly;
if set to &lsquo;<samp>substring</samp>&rsquo;,
the string supplied needs to match a substring of the name of a
stopped job. The &lsquo;<samp>substring</samp>&rsquo; value provides functionality
analogous to the &lsquo;<samp>%?</samp>&rsquo; job ID (see <a href="#Job-Control-Basics">Job Control Basics</a>).
If set to any other value, the supplied string must
be a prefix of a stopped job&rsquo;s name; this provides functionality
analogous to the &lsquo;<samp>%</samp>&rsquo; job ID.

</dd>
</dl>

<hr>
</div>
</div>
<div class="chapter" id="Command-Line-Editing">
<div class="header">

Next: <a href="#Using-History-Interactively" accesskey="n" rel="next">Using History Interactively</a>, Previous: <a href="#Job-Control" accesskey="p" rel="prev">Job Control</a>, Up: <a href="#Top" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h2 class="chapter">8 Command Line Editing</h2>

This chapter describes the basic features of the GNU
command line editing interface.
Command line editing is provided by the Readline library, which is
used by several different programs, including Bash.
Command line editing is enabled by default when using an interactive shell,
unless the <samp>--noediting</samp> option is supplied at shell invocation.
Line editing is also used when using the <samp>-e</samp> option to the
<code>read</code> builtin command (see <a href="#Bash-Builtins">Bash Builtin Commands</a>).
By default, the line editing commands are similar to those of Emacs.
A vi-style line editing interface is also available.
Line editing can be enabled at any time using the <samp>-o emacs</samp> or
<samp>-o vi</samp> options to the <code>set</code> builtin command
(see <a href="#The-Set-Builtin">The Set Builtin</a>), or disabled using the <samp>+o emacs</samp> or 
<samp>+o vi</samp> options to <code>set</code>.

<ul class="section-toc">
<li><a href="#Introduction-and-Notation" accesskey="1">Introduction to Line Editing</a></li>
<li><a href="#Readline-Interaction" accesskey="2">Readline Interaction</a></li>
<li><a href="#Readline-Init-File" accesskey="3">Readline Init File</a></li>
<li><a href="#Bindable-Readline-Commands" accesskey="4">Bindable Readline Commands</a></li>
<li><a href="#Readline-vi-Mode" accesskey="5">Readline vi Mode</a></li>
<li><a href="#Programmable-Completion" accesskey="6">Programmable Completion</a></li>
<li><a href="#Programmable-Completion-Builtins" accesskey="7">Programmable Completion Builtins</a></li>
<li><a href="#A-Programmable-Completion-Example" accesskey="8">A Programmable Completion Example</a></li>
</ul>
<hr>
<div class="section" id="Introduction-and-Notation">
<div class="header">

Next: <a href="#Readline-Interaction" accesskey="n" rel="next">Readline Interaction</a>, Up: <a href="#Command-Line-Editing" accesskey="u" rel="up">Command Line Editing</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">8.1 Introduction to Line Editing</h3>

The following paragraphs describe the notation used to represent
keystrokes.

The text <kbd>C-k</kbd> is read as &lsquo;Control-K&rsquo; and describes the character
produced when the <tt class="key">k</tt> key is pressed while the Control key
is depressed.

The text <kbd>M-k</kbd> is read as &lsquo;Meta-K&rsquo; and describes the character
produced when the Meta key (if you have one) is depressed, and the <tt class="key">k</tt>
key is pressed.
The Meta key is labeled <tt class="key">ALT</tt> on many keyboards.
On keyboards with two keys labeled <tt class="key">ALT</tt> (usually to either side of
the space bar), the <tt class="key">ALT</tt> on the left side is generally set to
work as a Meta key.
The <tt class="key">ALT</tt> key on the right may also be configured to work as a
Meta key or may be configured as some other modifier, such as a
Compose key for typing accented characters.

If you do not have a Meta or <tt class="key">ALT</tt> key, or another key working as
a Meta key, the identical keystroke can be generated by typing <tt class="key">ESC</tt>
first, and then typing <tt class="key">k</tt>.
Either process is known as metafying the <tt class="key">k</tt> key.

The text <kbd>M-C-k</kbd> is read as &lsquo;Meta-Control-k&rsquo; and describes the
character produced by metafying <kbd>C-k</kbd>.

In addition, several keys have their own names. Specifically,
<tt class="key">DEL</tt>, <tt class="key">ESC</tt>, <tt class="key">LFD</tt>, <tt class="key">SPC</tt>, <tt class="key">RET</tt>, and <tt class="key">TAB</tt> all
stand for themselves when seen in this text, or in an init file
(see <a href="#Readline-Init-File">Readline Init File</a>).
If your keyboard lacks a <tt class="key">LFD</tt> key, typing <tt class="key">C-j</tt> will
produce the desired character.
The <tt class="key">RET</tt> key may be labeled <tt class="key">Return</tt> or <tt class="key">Enter</tt> on
some keyboards.

<hr>
</div>
<div class="section" id="Readline-Interaction">
<div class="header">

Next: <a href="#Readline-Init-File" accesskey="n" rel="next">Readline Init File</a>, Previous: <a href="#Introduction-and-Notation" accesskey="p" rel="prev">Introduction to Line Editing</a>, Up: <a href="#Command-Line-Editing" accesskey="u" rel="up">Command Line Editing</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">8.2 Readline Interaction</h3>

Often during an interactive session you type in a long line of text,
only to notice that the first word on the line is misspelled. The
Readline library gives you a set of commands for manipulating the text
as you type it in, allowing you to just fix your typo, and not forcing
you to retype the majority of the line. Using these editing commands,
you move the cursor to the place that needs correction, and delete or
insert the text of the corrections. Then, when you are satisfied with
the line, you simply press <tt class="key">RET</tt>. You do not have to be at the
end of the line to press <tt class="key">RET</tt>; the entire line is accepted
regardless of the location of the cursor within the line.

<ul class="section-toc">
<li><a href="#Readline-Bare-Essentials" accesskey="1">Readline Bare Essentials</a></li>
<li><a href="#Readline-Movement-Commands" accesskey="2">Readline Movement Commands</a></li>
<li><a href="#Readline-Killing-Commands" accesskey="3">Readline Killing Commands</a></li>
<li><a href="#Readline-Arguments" accesskey="4">Readline Arguments</a></li>
<li><a href="#Searching" accesskey="5">Searching for Commands in the History</a></li>
</ul>
<hr>
<div class="subsection" id="Readline-Bare-Essentials">
<div class="header">

Next: <a href="#Readline-Movement-Commands" accesskey="n" rel="next">Readline Movement Commands</a>, Up: <a href="#Readline-Interaction" accesskey="u" rel="up">Readline Interaction</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">8.2.1 Readline Bare Essentials</h4>

In order to enter characters into the line, simply type them. The typed
character appears where the cursor was, and then the cursor moves one
space to the right. If you mistype a character, you can use your
erase character to back up and delete the mistyped character.

Sometimes you may mistype a character, and
not notice the error until you have typed several other characters. In
that case, you can type <kbd>C-b</kbd> to move the cursor to the left, and then
correct your mistake. Afterwards, you can move the cursor to the right
with <kbd>C-f</kbd>.

When you add text in the middle of a line, you will notice that characters
to the right of the cursor are &lsquo;pushed over&rsquo; to make room for the text
that you have inserted. Likewise, when you delete text behind the cursor,
characters to the right of the cursor are &lsquo;pulled back&rsquo; to fill in the
blank space created by the removal of the text. A list of the bare
essentials for editing the text of an input line follows.

<dl compact="compact">
<dt><kbd>C-b</kbd></dt>
<dd>Move back one character.
</dd>
<dt><kbd>C-f</kbd></dt>
<dd>Move forward one character.
</dd>
<dt><tt class="key">DEL</tt> or <tt class="key">Backspace</tt></dt>
<dd>Delete the character to the left of the cursor.
</dd>
<dt><kbd>C-d</kbd></dt>
<dd>Delete the character underneath the cursor.
</dd>
<dt>Printing&nbsp;characters</dt>
<dd>Insert the character into the line at the cursor.
</dd>
<dt><kbd>C-_</kbd> or <kbd>C-x C-u</kbd></dt>
<dd>Undo the last editing command. You can undo all the way back to an
empty line.
</dd>
</dl>

(Depending on your configuration, the <tt class="key">Backspace</tt> key might be set to
delete the character to the left of the cursor and the <tt class="key">DEL</tt> key set
to delete the character underneath the cursor, like <kbd>C-d</kbd>, rather
than the character to the left of the cursor.)

<hr>
</div>
<div class="subsection" id="Readline-Movement-Commands">
<div class="header">

Next: <a href="#Readline-Killing-Commands" accesskey="n" rel="next">Readline Killing Commands</a>, Previous: <a href="#Readline-Bare-Essentials" accesskey="p" rel="prev">Readline Bare Essentials</a>, Up: <a href="#Readline-Interaction" accesskey="u" rel="up">Readline Interaction</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">8.2.2 Readline Movement Commands</h4>

The above table describes the most basic keystrokes that you need
in order to do editing of the input line. For your convenience, many
other commands have been added in addition to <kbd>C-b</kbd>, <kbd>C-f</kbd>,
<kbd>C-d</kbd>, and <tt class="key">DEL</tt>. Here are some commands for moving more rapidly
about the line.

<dl compact="compact">
<dt><kbd>C-a</kbd></dt>
<dd>Move to the start of the line.
</dd>
<dt><kbd>C-e</kbd></dt>
<dd>Move to the end of the line.
</dd>
<dt><kbd>M-f</kbd></dt>
<dd>Move forward a word, where a word is composed of letters and digits.
</dd>
<dt><kbd>M-b</kbd></dt>
<dd>Move backward a word.
</dd>
<dt><kbd>C-l</kbd></dt>
<dd>Clear the screen, reprinting the current line at the top.
</dd>
</dl>

Notice how <kbd>C-f</kbd> moves forward a character, while <kbd>M-f</kbd> moves
forward a word. It is a loose convention that control keystrokes
operate on characters while meta keystrokes operate on words.

<hr>
</div>
<div class="subsection" id="Readline-Killing-Commands">
<div class="header">

Next: <a href="#Readline-Arguments" accesskey="n" rel="next">Readline Arguments</a>, Previous: <a href="#Readline-Movement-Commands" accesskey="p" rel="prev">Readline Movement Commands</a>, Up: <a href="#Readline-Interaction" accesskey="u" rel="up">Readline Interaction</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">8.2.3 Readline Killing Commands</h4>

Killing text means to delete the text from the line, but to save
it away for later use, usually by yanking (re-inserting)
it back into the line.
(&lsquo;Cut&rsquo; and &lsquo;paste&rsquo; are more recent jargon for &lsquo;kill&rsquo; and &lsquo;yank&rsquo;.)

If the description for a command says that it &lsquo;kills&rsquo; text, then you can
be sure that you can get the text back in a different (or the same)
place later.

When you use a kill command, the text is saved in a kill-ring.
Any number of consecutive kills save all of the killed text together, so
that when you yank it back, you get it all. The kill
ring is not line specific; the text that you killed on a previously
typed line is available to be yanked back later, when you are typing
another line.


Here is the list of commands for killing text.

<dl compact="compact">
<dt><kbd>C-k</kbd></dt>
<dd>Kill the text from the current cursor position to the end of the line.

</dd>
<dt><kbd>M-d</kbd></dt>
<dd>Kill from the cursor to the end of the current word, or, if between
words, to the end of the next word.
Word boundaries are the same as those used by <kbd>M-f</kbd>.

</dd>
<dt><kbd>M-DEL</kbd></dt>
<dd>Kill from the cursor to the start of the current word, or, if between
words, to the start of the previous word.
Word boundaries are the same as those used by <kbd>M-b</kbd>.

</dd>
<dt><kbd>C-w</kbd></dt>
<dd>Kill from the cursor to the previous whitespace. This is different than
<kbd>M-DEL</kbd> because the word boundaries differ.

</dd>
</dl>

Here is how to yank the text back into the line. Yanking
means to copy the most-recently-killed text from the kill buffer.

<dl compact="compact">
<dt><kbd>C-y</kbd></dt>
<dd>Yank the most recently killed text back into the buffer at the cursor.

</dd>
<dt><kbd>M-y</kbd></dt>
<dd>Rotate the kill-ring, and yank the new top. You can only do this if
the prior command is <kbd>C-y</kbd> or <kbd>M-y</kbd>.
</dd>
</dl>

<hr>
</div>
<div class="subsection" id="Readline-Arguments">
<div class="header">

Next: <a href="#Searching" accesskey="n" rel="next">Searching for Commands in the History</a>, Previous: <a href="#Readline-Killing-Commands" accesskey="p" rel="prev">Readline Killing Commands</a>, Up: <a href="#Readline-Interaction" accesskey="u" rel="up">Readline Interaction</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">8.2.4 Readline Arguments</h4>

You can pass numeric arguments to Readline commands. Sometimes the
argument acts as a repeat count, other times it is the sign of the
argument that is significant. If you pass a negative argument to a
command which normally acts in a forward direction, that command will
act in a backward direction. For example, to kill text back to the
start of the line, you might type &lsquo;<samp>M-- C-k</samp>&rsquo;.

The general way to pass numeric arguments to a command is to type meta
digits before the command. If the first &lsquo;digit&rsquo; typed is a minus
sign (&lsquo;<samp>-</samp>&rsquo;), then the sign of the argument will be negative. Once
you have typed one meta digit to get the argument started, you can type
the remainder of the digits, and then the command. For example, to give
the <kbd>C-d</kbd> command an argument of 10, you could type &lsquo;<samp>M-1 0 C-d</samp>&rsquo;,
which will delete the next ten characters on the input line.

<hr>
</div>
<div class="subsection" id="Searching">
<div class="header">

Previous: <a href="#Readline-Arguments" accesskey="p" rel="prev">Readline Arguments</a>, Up: <a href="#Readline-Interaction" accesskey="u" rel="up">Readline Interaction</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">8.2.5 Searching for Commands in the History</h4>

Readline provides commands for searching through the command history
(see <a href="#Bash-History-Facilities">Bash History Facilities</a>)
for lines containing a specified string.
There are two search modes: incremental and non-incremental.

Incremental searches begin before the user has finished typing the
search string.
As each character of the search string is typed, Readline displays
the next entry from the history matching the string typed so far.
An incremental search requires only as many characters as needed to
find the desired history entry.
To search backward in the history for a particular string, type
<kbd>C-r</kbd>. Typing <kbd>C-s</kbd> searches forward through the history.
The characters present in the value of the <code>isearch-terminators</code> variable
are used to terminate an incremental search.
If that variable has not been assigned a value, the <tt class="key">ESC</tt> and
<kbd>C-J</kbd> characters will terminate an incremental search.
<kbd>C-g</kbd> will abort an incremental search and restore the original line.
When the search is terminated, the history entry containing the
search string becomes the current line.

To find other matching entries in the history list, type <kbd>C-r</kbd> or
<kbd>C-s</kbd> as appropriate.
This will search backward or forward in the history for the next
entry matching the search string typed so far.
Any other key sequence bound to a Readline command will terminate
the search and execute that command.
For instance, a <tt class="key">RET</tt> will terminate the search and accept
the line, thereby executing the command from the history list.
A movement command will terminate the search, make the last line found
the current line, and begin editing.

Readline remembers the last incremental search string. If two
<kbd>C-r</kbd>s are typed without any intervening characters defining a new
search string, any remembered search string is used.

Non-incremental searches read the entire search string before starting
to search for matching history lines. The search string may be
typed by the user or be part of the contents of the current line.

<hr>
</div>
</div>
<div class="section" id="Readline-Init-File">
<div class="header">

Next: <a href="#Bindable-Readline-Commands" accesskey="n" rel="next">Bindable Readline Commands</a>, Previous: <a href="#Readline-Interaction" accesskey="p" rel="prev">Readline Interaction</a>, Up: <a href="#Command-Line-Editing" accesskey="u" rel="up">Command Line Editing</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">8.3 Readline Init File</h3>

Although the Readline library comes with a set of Emacs-like
keybindings installed by default, it is possible to use a different set
of keybindings.
Any user can customize programs that use Readline by putting
commands in an inputrc file,
conventionally in their home directory.
The name of this
file is taken from the value of the shell variable <code>INPUTRC</code>. If
that variable is unset, the default is <samp>~/.inputrc</samp>. If that
file does not exist or cannot be read, the ultimate default is
<samp>/etc/inputrc</samp>.
The <code>bind</code> builtin command can also be used to set Readline
keybindings and variables.
See <a href="#Bash-Builtins">Bash Builtin Commands</a>.

When a program which uses the Readline library starts up, the
init file is read, and the key bindings are set.

In addition, the <code>C-x C-r</code> command re-reads this init file, thus
incorporating any changes that you might have made to it.

<ul class="section-toc">
<li><a href="#Readline-Init-File-Syntax" accesskey="1">Readline Init File Syntax</a></li>
<li><a href="#Conditional-Init-Constructs" accesskey="2">Conditional Init Constructs</a></li>
<li><a href="#Sample-Init-File" accesskey="3">Sample Init File</a></li>
</ul>
<hr>
<div class="subsection" id="Readline-Init-File-Syntax">
<div class="header">

Next: <a href="#Conditional-Init-Constructs" accesskey="n" rel="next">Conditional Init Constructs</a>, Up: <a href="#Readline-Init-File" accesskey="u" rel="up">Readline Init File</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">8.3.1 Readline Init File Syntax</h4>

There are only a few basic constructs allowed in the
Readline init file. Blank lines are ignored.
Lines beginning with a &lsquo;<samp>#</samp>&rsquo; are comments.
Lines beginning with a &lsquo;<samp>$</samp>&rsquo; indicate conditional
constructs (see <a href="#Conditional-Init-Constructs">Conditional Init Constructs</a>). Other lines
denote variable settings and key bindings.

<dl compact="compact">
<dt>Variable Settings</dt>
<dd>You can modify the run-time behavior of Readline by
altering the values of variables in Readline
using the <code>set</code> command within the init file.
The syntax is simple:

<div class="example">
<pre class="example">set <var>variable</var> <var>value</var>
</pre></div>

Here, for example, is how to
change from the default Emacs-like key binding to use
<code>vi</code> line editing commands:

<div class="example">
<pre class="example">set editing-mode vi
</pre></div>

Variable names and values, where appropriate, are recognized without regard
to case. Unrecognized variable names are ignored.

Boolean variables (those that can be set to on or off) are set to on if
the value is null or empty, <var>on</var> (case-insensitive), or 1. Any other
value results in the variable being set to off.

The <code>bind&nbsp;-V</code> command lists the current Readline variable names
and values. See <a href="#Bash-Builtins">Bash Builtin Commands</a>.

A great deal of run-time behavior is changeable with the following
variables.


<dl compact="compact">
<dt id='index-active_002dregion_002dstart_002dcolor'><code>active-region-start-color</code><a href='#index-active_002dregion_002dstart_002dcolor' class='copiable-anchor'> &para;</a></dt>
<dd>A string variable that controls the text color and background when displaying
the text in the active region (see the description of
<code>enable-active-region</code> below).
This string must not take up any physical character positions on the display,
so it should consist only of terminal escape sequences.
It is output to the terminal before displaying the text in the active region.
This variable is reset to the default value whenever the terminal type changes.
The default value is the string that puts the terminal in standout mode,
as obtained from the terminal&rsquo;s terminfo description.
A sample value might be &lsquo;<samp>\e[01;33m</samp>&rsquo;.

</dd>
<dt id='index-active_002dregion_002dend_002dcolor'><code>active-region-end-color</code><a href='#index-active_002dregion_002dend_002dcolor' class='copiable-anchor'> &para;</a></dt>
<dd>A string variable that &quot;undoes&quot; the effects of <code>active-region-start-color</code>
and restores &quot;normal&quot; terminal display appearance after displaying text
in the active region.
This string must not take up any physical character positions on the display,
so it should consist only of terminal escape sequences.
It is output to the terminal after displaying the text in the active region.
This variable is reset to the default value whenever the terminal type changes.
The default value is the string that restores the terminal from standout mode,
as obtained from the terminal&rsquo;s terminfo description.
A sample value might be &lsquo;<samp>\e[0m</samp>&rsquo;.

</dd>
<dt id='index-bell_002dstyle'><code>bell-style</code><a href='#index-bell_002dstyle' class='copiable-anchor'> &para;</a></dt>
<dd>Controls what happens when Readline wants to ring the terminal bell.
If set to &lsquo;<samp>none</samp>&rsquo;, Readline never rings the bell. If set to
&lsquo;<samp>visible</samp>&rsquo;, Readline uses a visible bell if one is available.
If set to &lsquo;<samp>audible</samp>&rsquo; (the default), Readline attempts to ring
the terminal&rsquo;s bell.

</dd>
<dt id='index-bind_002dtty_002dspecial_002dchars'><code>bind-tty-special-chars</code><a href='#index-bind_002dtty_002dspecial_002dchars' class='copiable-anchor'> &para;</a></dt>
<dd>If set to &lsquo;<samp>on</samp>&rsquo; (the default), Readline attempts to bind the control
characters treated specially by the kernel&rsquo;s terminal driver to their
Readline equivalents.

</dd>
<dt id='index-blink_002dmatching_002dparen'><code>blink-matching-paren</code><a href='#index-blink_002dmatching_002dparen' class='copiable-anchor'> &para;</a></dt>
<dd>If set to &lsquo;<samp>on</samp>&rsquo;, Readline attempts to briefly move the cursor to an
opening parenthesis when a closing parenthesis is inserted. The default
is &lsquo;<samp>off</samp>&rsquo;.

</dd>
<dt id='index-colored_002dcompletion_002dprefix'><code>colored-completion-prefix</code><a href='#index-colored_002dcompletion_002dprefix' class='copiable-anchor'> &para;</a></dt>
<dd>If set to &lsquo;<samp>on</samp>&rsquo;, when listing completions, Readline displays the
common prefix of the set of possible completions using a different color.
The color definitions are taken from the value of the <code>LS_COLORS</code>
environment variable.
If there is a color definition in <code>LS_COLORS</code> for the custom suffix
&lsquo;<samp>readline-colored-completion-prefix</samp>&rsquo;, Readline uses this color for
the common prefix instead of its default.
The default is &lsquo;<samp>off</samp>&rsquo;.

</dd>
<dt id='index-colored_002dstats'><code>colored-stats</code><a href='#index-colored_002dstats' class='copiable-anchor'> &para;</a></dt>
<dd>If set to &lsquo;<samp>on</samp>&rsquo;, Readline displays possible completions using different
colors to indicate their file type.
The color definitions are taken from the value of the <code>LS_COLORS</code>
environment variable.
The default is &lsquo;<samp>off</samp>&rsquo;.

</dd>
<dt id='index-comment_002dbegin'><code>comment-begin</code><a href='#index-comment_002dbegin' class='copiable-anchor'> &para;</a></dt>
<dd>The string to insert at the beginning of the line when the
<code>insert-comment</code> command is executed. The default value
is <code>&quot;#&quot;</code>.

</dd>
<dt id='index-completion_002ddisplay_002dwidth'><code>completion-display-width</code><a href='#index-completion_002ddisplay_002dwidth' class='copiable-anchor'> &para;</a></dt>
<dd>The number of screen columns used to display possible matches
when performing completion.
The value is ignored if it is less than 0 or greater than the terminal
screen width.
A value of 0 will cause matches to be displayed one per line.
The default value is -1.

</dd>
<dt id='index-completion_002dignore_002dcase'><code>completion-ignore-case</code><a href='#index-completion_002dignore_002dcase' class='copiable-anchor'> &para;</a></dt>
<dd>If set to &lsquo;<samp>on</samp>&rsquo;, Readline performs filename matching and completion
in a case-insensitive fashion.
The default value is &lsquo;<samp>off</samp>&rsquo;.

</dd>
<dt id='index-completion_002dmap_002dcase'><code>completion-map-case</code><a href='#index-completion_002dmap_002dcase' class='copiable-anchor'> &para;</a></dt>
<dd>If set to &lsquo;<samp>on</samp>&rsquo;, and <var>completion-ignore-case</var> is enabled, Readline
treats hyphens (&lsquo;<samp>-</samp>&rsquo;) and underscores (&lsquo;<samp>_</samp>&rsquo;) as equivalent when
performing case-insensitive filename matching and completion.
The default value is &lsquo;<samp>off</samp>&rsquo;.

</dd>
<dt id='index-completion_002dprefix_002ddisplay_002dlength'><code>completion-prefix-display-length</code><a href='#index-completion_002dprefix_002ddisplay_002dlength' class='copiable-anchor'> &para;</a></dt>
<dd>The length in characters of the common prefix of a list of possible
completions that is displayed without modification. When set to a
value greater than zero, common prefixes longer than this value are
replaced with an ellipsis when displaying possible completions.

</dd>
<dt id='index-completion_002dquery_002ditems'><code>completion-query-items</code><a href='#index-completion_002dquery_002ditems' class='copiable-anchor'> &para;</a></dt>
<dd>The number of possible completions that determines when the user is
asked whether the list of possibilities should be displayed.
If the number of possible completions is greater than or equal to this value,
Readline will ask whether or not the user wishes to view them;
otherwise, they are simply listed.
This variable must be set to an integer value greater than or equal to zero.
A zero value means Readline should never ask; negative values are
treated as zero.
The default limit is <code>100</code>.

</dd>
<dt id='index-convert_002dmeta'><code>convert-meta</code><a href='#index-convert_002dmeta' class='copiable-anchor'> &para;</a></dt>
<dd>If set to &lsquo;<samp>on</samp>&rsquo;, Readline will convert characters with the
eighth bit set to an ASCII key sequence by stripping the eighth
bit and prefixing an <tt class="key">ESC</tt> character, converting them to a
meta-prefixed key sequence.
The default value is &lsquo;<samp>on</samp>&rsquo;, but
will be set to &lsquo;<samp>off</samp>&rsquo; if the locale is one that contains
eight-bit characters.
This variable is dependent on the <code>LC_CTYPE</code> locale category, and
may change if the locale is changed.

</dd>
<dt id='index-disable_002dcompletion'><code>disable-completion</code><a href='#index-disable_002dcompletion' class='copiable-anchor'> &para;</a></dt>
<dd>If set to &lsquo;<samp>On</samp>&rsquo;, Readline will inhibit word completion.
Completion characters will be inserted into the line as if they had
been mapped to <code>self-insert</code>. The default is &lsquo;<samp>off</samp>&rsquo;.

</dd>
<dt id='index-echo_002dcontrol_002dcharacters'><code>echo-control-characters</code><a href='#index-echo_002dcontrol_002dcharacters' class='copiable-anchor'> &para;</a></dt>
<dd>When set to &lsquo;<samp>on</samp>&rsquo;, on operating systems that indicate they support it,
Readline echoes a character corresponding to a signal generated from the
keyboard. The default is &lsquo;<samp>on</samp>&rsquo;.

</dd>
<dt id='index-editing_002dmode'><code>editing-mode</code><a href='#index-editing_002dmode' class='copiable-anchor'> &para;</a></dt>
<dd>The <code>editing-mode</code> variable controls which default set of
key bindings is used. By default, Readline starts up in Emacs editing
mode, where the keystrokes are most similar to Emacs. This variable can be
set to either &lsquo;<samp>emacs</samp>&rsquo; or &lsquo;<samp>vi</samp>&rsquo;.

</dd>
<dt id='index-emacs_002dmode_002dstring'><code>emacs-mode-string</code><a href='#index-emacs_002dmode_002dstring' class='copiable-anchor'> &para;</a></dt>
<dd>If the <var>show-mode-in-prompt</var> variable is enabled,
this string is displayed immediately before the last line of the primary
prompt when emacs editing mode is active. The value is expanded like a
key binding, so the standard set of meta- and control prefixes and
backslash escape sequences is available.
Use the &lsquo;<samp>\1</samp>&rsquo; and &lsquo;<samp>\2</samp>&rsquo; escapes to begin and end sequences of
non-printing characters, which can be used to embed a terminal control
sequence into the mode string.
The default is &lsquo;<samp>@</samp>&rsquo;.

</dd>
<dt id='index-enable_002dactive_002dregion'><code>enable-active-region</code><a href='#index-enable_002dactive_002dregion' class='copiable-anchor'> &para;</a></dt>
<dd>The point is the current cursor position, and mark refers
to a saved cursor position (see <a href="#Commands-For-Moving">Commands For Moving</a>).
The text between the point and mark is referred to as the region.
When this variable is set to &lsquo;<samp>On</samp>&rsquo;, Readline allows certain commands
to designate the region as active.
When the region is active, Readline highlights the text in the region using
the value of the <code>active-region-start-color</code>, which defaults to the
string that enables
the terminal&rsquo;s standout mode.
The active region shows the text inserted by bracketed-paste and any
matching text found by incremental and non-incremental history searches.
The default is &lsquo;<samp>On</samp>&rsquo;.

</dd>
<dt id='index-enable_002dbracketed_002dpaste'><code>enable-bracketed-paste</code><a href='#index-enable_002dbracketed_002dpaste' class='copiable-anchor'> &para;</a></dt>
<dd>When set to &lsquo;<samp>On</samp>&rsquo;, Readline configures the terminal to insert each
paste into the editing buffer as a single string of characters, instead
of treating each character as if it had been read from the keyboard.
This is called putting the terminal into bracketed paste mode;
it prevents Readline from executing any editing commands bound to key
sequences appearing in the pasted text.
The default is &lsquo;<samp>On</samp>&rsquo;.

</dd>
<dt id='index-enable_002dkeypad'><code>enable-keypad</code><a href='#index-enable_002dkeypad' class='copiable-anchor'> &para;</a></dt>
<dd>When set to &lsquo;<samp>on</samp>&rsquo;, Readline will try to enable the application
keypad when it is called. Some systems need this to enable the
arrow keys. The default is &lsquo;<samp>off</samp>&rsquo;.

</dd>
<dt><code>enable-meta-key</code></dt>
<dd>When set to &lsquo;<samp>on</samp>&rsquo;, Readline will try to enable any meta modifier
key the terminal claims to support when it is called. On many terminals,
the meta key is used to send eight-bit characters.
The default is &lsquo;<samp>on</samp>&rsquo;.

</dd>
<dt id='index-expand_002dtilde'><code>expand-tilde</code><a href='#index-expand_002dtilde' class='copiable-anchor'> &para;</a></dt>
<dd>If set to &lsquo;<samp>on</samp>&rsquo;, tilde expansion is performed when Readline
attempts word completion. The default is &lsquo;<samp>off</samp>&rsquo;.

</dd>
<dt id='index-history_002dpreserve_002dpoint'><code>history-preserve-point</code><a href='#index-history_002dpreserve_002dpoint' class='copiable-anchor'> &para;</a></dt>
<dd>If set to &lsquo;<samp>on</samp>&rsquo;, the history code attempts to place the point (the
current cursor position) at the
same location on each history line retrieved with <code>previous-history</code>
or <code>next-history</code>. The default is &lsquo;<samp>off</samp>&rsquo;.

</dd>
<dt id='index-history_002dsize'><code>history-size</code><a href='#index-history_002dsize' class='copiable-anchor'> &para;</a></dt>
<dd>Set the maximum number of history entries saved in the history list.
If set to zero, any existing history entries are deleted and no new entries
are saved.
If set to a value less than zero, the number of history entries is not
limited.
By default, the number of history entries is not limited.
If an attempt is made to set <var>history-size</var> to a non-numeric value,
the maximum number of history entries will be set to 500.

</dd>
<dt id='index-horizontal_002dscroll_002dmode'><code>horizontal-scroll-mode</code><a href='#index-horizontal_002dscroll_002dmode' class='copiable-anchor'> &para;</a></dt>
<dd>This variable can be set to either &lsquo;<samp>on</samp>&rsquo; or &lsquo;<samp>off</samp>&rsquo;. Setting it
to &lsquo;<samp>on</samp>&rsquo; means that the text of the lines being edited will scroll
horizontally on a single screen line when they are longer than the width
of the screen, instead of wrapping onto a new screen line.
This variable is automatically set to &lsquo;<samp>on</samp>&rsquo; for terminals of height 1.
By default, this variable is set to &lsquo;<samp>off</samp>&rsquo;.

</dd>
<dt id='index-input_002dmeta'><code>input-meta</code><a href='#index-input_002dmeta' class='copiable-anchor'> &para;</a></dt>
<dd>
If set to &lsquo;<samp>on</samp>&rsquo;, Readline will enable eight-bit input (it
will not clear the eighth bit in the characters it reads),
regardless of what the terminal claims it can support. The
default value is &lsquo;<samp>off</samp>&rsquo;, but Readline will set it to &lsquo;<samp>on</samp>&rsquo; if the 
locale contains eight-bit characters.
The name <code>meta-flag</code> is a synonym for this variable.
This variable is dependent on the <code>LC_CTYPE</code> locale category, and
may change if the locale is changed.

</dd>
<dt id='index-isearch_002dterminators'><code>isearch-terminators</code><a href='#index-isearch_002dterminators' class='copiable-anchor'> &para;</a></dt>
<dd>The string of characters that should terminate an incremental search without
subsequently executing the character as a command (see <a href="#Searching">Searching for Commands in the History</a>).
If this variable has not been given a value, the characters <tt class="key">ESC</tt> and
<kbd>C-J</kbd> will terminate an incremental search.

</dd>
<dt id='index-keymap'><code>keymap</code><a href='#index-keymap' class='copiable-anchor'> &para;</a></dt>
<dd>Sets Readline&rsquo;s idea of the current keymap for key binding commands.
Built-in <code>keymap</code> names are
<code>emacs</code>,
<code>emacs-standard</code>,
<code>emacs-meta</code>,
<code>emacs-ctlx</code>,
<code>vi</code>,
<code>vi-move</code>,
<code>vi-command</code>, and
<code>vi-insert</code>.
<code>vi</code> is equivalent to <code>vi-command</code> (<code>vi-move</code> is also a
synonym); <code>emacs</code> is equivalent to <code>emacs-standard</code>.
Applications may add additional names.
The default value is <code>emacs</code>.
The value of the <code>editing-mode</code> variable also affects the
default keymap.

</dd>
<dt><code>keyseq-timeout</code></dt>
<dd>Specifies the duration Readline will wait for a character when reading an
ambiguous key sequence (one that can form a complete key sequence using
the input read so far, or can take additional input to complete a longer
key sequence).
If no input is received within the timeout, Readline will use the shorter
but complete key sequence.
Readline uses this value to determine whether or not input is
available on the current input source (<code>rl_instream</code> by default).
The value is specified in milliseconds, so a value of 1000 means that
Readline will wait one second for additional input.
If this variable is set to a value less than or equal to zero, or to a
non-numeric value, Readline will wait until another key is pressed to
decide which key sequence to complete.
The default value is <code>500</code>.

</dd>
<dt><code>mark-directories</code></dt>
<dd>If set to &lsquo;<samp>on</samp>&rsquo;, completed directory names have a slash
appended. The default is &lsquo;<samp>on</samp>&rsquo;.

</dd>
<dt id='index-mark_002dmodified_002dlines'><code>mark-modified-lines</code><a href='#index-mark_002dmodified_002dlines' class='copiable-anchor'> &para;</a></dt>
<dd>This variable, when set to &lsquo;<samp>on</samp>&rsquo;, causes Readline to display an
asterisk (&lsquo;<samp>*</samp>&rsquo;) at the start of history lines which have been modified.
This variable is &lsquo;<samp>off</samp>&rsquo; by default.

</dd>
<dt id='index-mark_002dsymlinked_002ddirectories'><code>mark-symlinked-directories</code><a href='#index-mark_002dsymlinked_002ddirectories' class='copiable-anchor'> &para;</a></dt>
<dd>If set to &lsquo;<samp>on</samp>&rsquo;, completed names which are symbolic links
to directories have a slash appended (subject to the value of
<code>mark-directories</code>).
The default is &lsquo;<samp>off</samp>&rsquo;.

</dd>
<dt id='index-match_002dhidden_002dfiles'><code>match-hidden-files</code><a href='#index-match_002dhidden_002dfiles' class='copiable-anchor'> &para;</a></dt>
<dd>This variable, when set to &lsquo;<samp>on</samp>&rsquo;, causes Readline to match files whose
names begin with a &lsquo;<samp>.</samp>&rsquo; (hidden files) when performing filename
completion.
If set to &lsquo;<samp>off</samp>&rsquo;, the leading &lsquo;<samp>.</samp>&rsquo; must be
supplied by the user in the filename to be completed.
This variable is &lsquo;<samp>on</samp>&rsquo; by default.

</dd>
<dt id='index-menu_002dcomplete_002ddisplay_002dprefix'><code>menu-complete-display-prefix</code><a href='#index-menu_002dcomplete_002ddisplay_002dprefix' class='copiable-anchor'> &para;</a></dt>
<dd>If set to &lsquo;<samp>on</samp>&rsquo;, menu completion displays the common prefix of the
list of possible completions (which may be empty) before cycling through
the list. The default is &lsquo;<samp>off</samp>&rsquo;.

</dd>
<dt id='index-output_002dmeta'><code>output-meta</code><a href='#index-output_002dmeta' class='copiable-anchor'> &para;</a></dt>
<dd>If set to &lsquo;<samp>on</samp>&rsquo;, Readline will display characters with the
eighth bit set directly rather than as a meta-prefixed escape
sequence.
The default is &lsquo;<samp>off</samp>&rsquo;, but Readline will set it to &lsquo;<samp>on</samp>&rsquo; if the
locale contains eight-bit characters.
This variable is dependent on the <code>LC_CTYPE</code> locale category, and
may change if the locale is changed.

</dd>
<dt id='index-page_002dcompletions'><code>page-completions</code><a href='#index-page_002dcompletions' class='copiable-anchor'> &para;</a></dt>
<dd>If set to &lsquo;<samp>on</samp>&rsquo;, Readline uses an internal <code>more</code>-like pager
to display a screenful of possible completions at a time.
This variable is &lsquo;<samp>on</samp>&rsquo; by default.

</dd>
<dt><code>print-completions-horizontally</code></dt>
<dd>If set to &lsquo;<samp>on</samp>&rsquo;, Readline will display completions with matches
sorted horizontally in alphabetical order, rather than down the screen.
The default is &lsquo;<samp>off</samp>&rsquo;.

</dd>
<dt id='index-revert_002dall_002dat_002dnewline'><code>revert-all-at-newline</code><a href='#index-revert_002dall_002dat_002dnewline' class='copiable-anchor'> &para;</a></dt>
<dd>If set to &lsquo;<samp>on</samp>&rsquo;, Readline will undo all changes to history lines
before returning when <code>accept-line</code> is executed. By default,
history lines may be modified and retain individual undo lists across
calls to <code>readline()</code>. The default is &lsquo;<samp>off</samp>&rsquo;.

</dd>
<dt id='index-show_002dall_002dif_002dambiguous'><code>show-all-if-ambiguous</code><a href='#index-show_002dall_002dif_002dambiguous' class='copiable-anchor'> &para;</a></dt>
<dd>This alters the default behavior of the completion functions. If
set to &lsquo;<samp>on</samp>&rsquo;, 
words which have more than one possible completion cause the
matches to be listed immediately instead of ringing the bell.
The default value is &lsquo;<samp>off</samp>&rsquo;.

</dd>
<dt id='index-show_002dall_002dif_002dunmodified'><code>show-all-if-unmodified</code><a href='#index-show_002dall_002dif_002dunmodified' class='copiable-anchor'> &para;</a></dt>
<dd>This alters the default behavior of the completion functions in
a fashion similar to <var>show-all-if-ambiguous</var>.
If set to &lsquo;<samp>on</samp>&rsquo;, 
words which have more than one possible completion without any
possible partial completion (the possible completions don&rsquo;t share
a common prefix) cause the matches to be listed immediately instead
of ringing the bell.
The default value is &lsquo;<samp>off</samp>&rsquo;.

</dd>
<dt id='index-show_002dmode_002din_002dprompt'><code>show-mode-in-prompt</code><a href='#index-show_002dmode_002din_002dprompt' class='copiable-anchor'> &para;</a></dt>
<dd>If set to &lsquo;<samp>on</samp>&rsquo;, add a string to the beginning of the prompt
indicating the editing mode: emacs, vi command, or vi insertion.
The mode strings are user-settable (e.g., <var>emacs-mode-string</var>).
The default value is &lsquo;<samp>off</samp>&rsquo;.

</dd>
<dt id='index-skip_002dcompleted_002dtext'><code>skip-completed-text</code><a href='#index-skip_002dcompleted_002dtext' class='copiable-anchor'> &para;</a></dt>
<dd>If set to &lsquo;<samp>on</samp>&rsquo;, this alters the default completion behavior when
inserting a single match into the line. It&rsquo;s only active when
performing completion in the middle of a word. If enabled, Readline
does not insert characters from the completion that match characters
after point in the word being completed, so portions of the word
following the cursor are not duplicated.
For instance, if this is enabled, attempting completion when the cursor
is after the &lsquo;<samp>e</samp>&rsquo; in &lsquo;<samp>Makefile</samp>&rsquo; will result in &lsquo;<samp>Makefile</samp>&rsquo;
rather than &lsquo;<samp>Makefilefile</samp>&rsquo;, assuming there is a single possible
completion.
The default value is &lsquo;<samp>off</samp>&rsquo;.

</dd>
<dt id='index-vi_002dcmd_002dmode_002dstring'><code>vi-cmd-mode-string</code><a href='#index-vi_002dcmd_002dmode_002dstring' class='copiable-anchor'> &para;</a></dt>
<dd>If the <var>show-mode-in-prompt</var> variable is enabled,
this string is displayed immediately before the last line of the primary
prompt when vi editing mode is active and in command mode.
The value is expanded like a
key binding, so the standard set of meta- and control prefixes and
backslash escape sequences is available.
Use the &lsquo;<samp>\1</samp>&rsquo; and &lsquo;<samp>\2</samp>&rsquo; escapes to begin and end sequences of
non-printing characters, which can be used to embed a terminal control
sequence into the mode string.
The default is &lsquo;<samp>(cmd)</samp>&rsquo;.

</dd>
<dt id='index-vi_002dins_002dmode_002dstring'><code>vi-ins-mode-string</code><a href='#index-vi_002dins_002dmode_002dstring' class='copiable-anchor'> &para;</a></dt>
<dd>If the <var>show-mode-in-prompt</var> variable is enabled,
this string is displayed immediately before the last line of the primary
prompt when vi editing mode is active and in insertion mode.
The value is expanded like a
key binding, so the standard set of meta- and control prefixes and
backslash escape sequences is available.
Use the &lsquo;<samp>\1</samp>&rsquo; and &lsquo;<samp>\2</samp>&rsquo; escapes to begin and end sequences of
non-printing characters, which can be used to embed a terminal control
sequence into the mode string.
The default is &lsquo;<samp>(ins)</samp>&rsquo;.

</dd>
<dt id='index-visible_002dstats'><code>visible-stats</code><a href='#index-visible_002dstats' class='copiable-anchor'> &para;</a></dt>
<dd>If set to &lsquo;<samp>on</samp>&rsquo;, a character denoting a file&rsquo;s type
is appended to the filename when listing possible
completions. The default is &lsquo;<samp>off</samp>&rsquo;.

</dd>
</dl>

</dd>
<dt>Key Bindings</dt>
<dd>The syntax for controlling key bindings in the init file is
simple. First you need to find the name of the command that you
want to change. The following sections contain tables of the command
name, the default keybinding, if any, and a short description of what
the command does.

Once you know the name of the command, simply place on a line
in the init file the name of the key
you wish to bind the command to, a colon, and then the name of the
command.
There can be no space between the key name and the colon &ndash; that will be
interpreted as part of the key name.
The name of the key can be expressed in different ways, depending on
what you find most comfortable.

In addition to command names, Readline allows keys to be bound
to a string that is inserted when the key is pressed (a <var>macro</var>).

The <code>bind&nbsp;-p</code> command displays Readline function names and
bindings in a format that can be put directly into an initialization file.
See <a href="#Bash-Builtins">Bash Builtin Commands</a>.

<dl compact="compact">
<dt><var>keyname</var>:&nbsp;<var>function-name</var>&nbsp;or&nbsp;<var>macro</var></dt>
<dd><var>keyname</var> is the name of a key spelled out in English. For example:
<div class="example">
<pre class="example">Control-u: universal-argument
Meta-Rubout: backward-kill-word
Control-o: &quot;&gt; output&quot;
</pre></div>

In the example above, <kbd>C-u</kbd> is bound to the function
<code>universal-argument</code>,
<kbd>M-DEL</kbd> is bound to the function <code>backward-kill-word</code>, and
<kbd>C-o</kbd> is bound to run the macro
expressed on the right hand side (that is, to insert the text
&lsquo;<samp>&gt; output</samp>&rsquo; into the line).

A number of symbolic character names are recognized while
processing this key binding syntax:
<var>DEL</var>,
<var>ESC</var>,
<var>ESCAPE</var>,
<var>LFD</var>,
<var>NEWLINE</var>,
<var>RET</var>,
<var>RETURN</var>,
<var>RUBOUT</var>,
<var>SPACE</var>,
<var>SPC</var>,
and
<var>TAB</var>.

</dd>
<dt>&quot;<var>keyseq</var>&quot;:&nbsp;<var>function-name</var>&nbsp;or&nbsp;<var>macro</var></dt>
<dd><var>keyseq</var> differs from <var>keyname</var> above in that strings
denoting an entire key sequence can be specified, by placing
the key sequence in double quotes. Some GNU Emacs style key
escapes can be used, as in the following example, but the
special character names are not recognized.

<div class="example">
<pre class="example">&quot;\C-u&quot;: universal-argument
&quot;\C-x\C-r&quot;: re-read-init-file
&quot;\e[11~&quot;: &quot;Function Key 1&quot;
</pre></div>

In the above example, <kbd>C-u</kbd> is again bound to the function
<code>universal-argument</code> (just as it was in the first example),
&lsquo;<samp><kbd>C-x</kbd> <kbd>C-r</kbd></samp>&rsquo; is bound to the function <code>re-read-init-file</code>,
and &lsquo;<samp>ESC [ 1 1 ~</samp>&rsquo; is bound to insert
the text &lsquo;<samp>Function Key 1</samp>&rsquo;.

</dd>
</dl>

The following GNU Emacs style escape sequences are available when
specifying key sequences:

<dl compact="compact">
<dt><code><kbd>\C-</kbd></code></dt>
<dd>control prefix
</dd>
<dt><code><kbd>\M-</kbd></code></dt>
<dd>meta prefix
</dd>
<dt><code><kbd>\e</kbd></code></dt>
<dd>an escape character
</dd>
<dt><code><kbd>\\</kbd></code></dt>
<dd>backslash
</dd>
<dt><code><kbd>\&quot;</kbd></code></dt>
<dd><tt class="key">&quot;</tt>, a double quotation mark
</dd>
<dt><code><kbd>\'</kbd></code></dt>
<dd><tt class="key">'</tt>, a single quote or apostrophe
</dd>
</dl>

In addition to the GNU Emacs style escape sequences, a second
set of backslash escapes is available:

<dl compact="compact">
<dt><code>\a</code></dt>
<dd>alert (bell)
</dd>
<dt><code>\b</code></dt>
<dd>backspace
</dd>
<dt><code>\d</code></dt>
<dd>delete
</dd>
<dt><code>\f</code></dt>
<dd>form feed
</dd>
<dt><code>\n</code></dt>
<dd>newline
</dd>
<dt><code>\r</code></dt>
<dd>carriage return
</dd>
<dt><code>\t</code></dt>
<dd>horizontal tab
</dd>
<dt><code>\v</code></dt>
<dd>vertical tab
</dd>
<dt><code>\<var>nnn</var></code></dt>
<dd>the eight-bit character whose value is the octal value <var>nnn</var>
(one to three digits)
</dd>
<dt><code>\x<var>HH</var></code></dt>
<dd>the eight-bit character whose value is the hexadecimal value <var>HH</var>
(one or two hex digits)
</dd>
</dl>

When entering the text of a macro, single or double quotes must
be used to indicate a macro definition.
Unquoted text is assumed to be a function name.
In the macro body, the backslash escapes described above are expanded.
Backslash will quote any other character in the macro text,
including &lsquo;<samp>&quot;</samp>&rsquo; and &lsquo;<samp>'</samp>&rsquo;.
For example, the following binding will make &lsquo;<samp><kbd>C-x</kbd> \</samp>&rsquo;
insert a single &lsquo;<samp>\</samp>&rsquo; into the line:
<div class="example">
<pre class="example">&quot;\C-x\\&quot;: &quot;\\&quot;
</pre></div>

</dd>
</dl>

<hr>
</div>
<div class="subsection" id="Conditional-Init-Constructs">
<div class="header">

Next: <a href="#Sample-Init-File" accesskey="n" rel="next">Sample Init File</a>, Previous: <a href="#Readline-Init-File-Syntax" accesskey="p" rel="prev">Readline Init File Syntax</a>, Up: <a href="#Readline-Init-File" accesskey="u" rel="up">Readline Init File</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">8.3.2 Conditional Init Constructs</h4>

Readline implements a facility similar in spirit to the conditional
compilation features of the C preprocessor which allows key
bindings and variable settings to be performed as the result
of tests. There are four parser directives used.

<dl compact="compact">
<dt><code>$if</code></dt>
<dd>The <code>$if</code> construct allows bindings to be made based on the
editing mode, the terminal being used, or the application using
Readline. The text of the test, after any comparison operator,
extends to the end of the line;
unless otherwise noted, no characters are required to isolate it.

<dl compact="compact">
<dt><code>mode</code></dt>
<dd>The <code>mode=</code> form of the <code>$if</code> directive is used to test
whether Readline is in <code>emacs</code> or <code>vi</code> mode.
This may be used in conjunction
with the &lsquo;<samp>set keymap</samp>&rsquo; command, for instance, to set bindings in
the <code>emacs-standard</code> and <code>emacs-ctlx</code> keymaps only if
Readline is starting out in <code>emacs</code> mode.

</dd>
<dt><code>term</code></dt>
<dd>The <code>term=</code> form may be used to include terminal-specific
key bindings, perhaps to bind the key sequences output by the
terminal&rsquo;s function keys. The word on the right side of the
&lsquo;<samp>=</samp>&rsquo; is tested against both the full name of the terminal and
the portion of the terminal name before the first &lsquo;<samp>-</samp>&rsquo;. This
allows <code>sun</code> to match both <code>sun</code> and <code>sun-cmd</code>,
for instance.

</dd>
<dt><code>version</code></dt>
<dd>The <code>version</code> test may be used to perform comparisons against
specific Readline versions.
The <code>version</code> expands to the current Readline version.
The set of comparison operators includes
&lsquo;<samp>=</samp>&rsquo; (and &lsquo;<samp>==</samp>&rsquo;), &lsquo;<samp>!=</samp>&rsquo;, &lsquo;<samp>&lt;=</samp>&rsquo;, &lsquo;<samp>&gt;=</samp>&rsquo;, &lsquo;<samp>&lt;</samp>&rsquo;,
and &lsquo;<samp>&gt;</samp>&rsquo;.
The version number supplied on the right side of the operator consists
of a major version number, an optional decimal point, and an optional
minor version (e.g., &lsquo;<samp>7.1</samp>&rsquo;). If the minor version is omitted, it
is assumed to be &lsquo;<samp>0</samp>&rsquo;.
The operator may be separated from the string <code>version</code> and
from the version number argument by whitespace.
The following example sets a variable if the Readline version being used
is 7.0 or newer:
<div class="example">
<pre class="example">$if version &gt;= 7.0
set show-mode-in-prompt on
$endif
</pre></div>

</dd>
<dt><code>application</code></dt>
<dd>The <var>application</var> construct is used to include
application-specific settings. Each program using the Readline
library sets the <var>application name</var>, and you can test for
a particular value. 
This could be used to bind key sequences to functions useful for
a specific program. For instance, the following command adds a
key sequence that quotes the current or previous word in Bash:
<div class="example">
<pre class="example">$if Bash
# Quote the current or previous word
&quot;\C-xq&quot;: &quot;\eb\&quot;\ef\&quot;&quot;
$endif
</pre></div>

</dd>
<dt><code>variable</code></dt>
<dd>The <var>variable</var> construct provides simple equality tests for Readline
variables and values.
The permitted comparison operators are &lsquo;<samp>=</samp>&rsquo;, &lsquo;<samp>==</samp>&rsquo;, and &lsquo;<samp>!=</samp>&rsquo;.
The variable name must be separated from the comparison operator by
whitespace; the operator may be separated from the value on the right hand
side by whitespace.
Both string and boolean variables may be tested. Boolean variables must be
tested against the values <var>on</var> and <var>off</var>.
The following example is equivalent to the <code>mode=emacs</code> test described
above:
<div class="example">
<pre class="example">$if editing-mode == emacs
set show-mode-in-prompt on
$endif
</pre></div>
</dd>
</dl>

</dd>
<dt><code>$endif</code></dt>
<dd>This command, as seen in the previous example, terminates an
<code>$if</code> command.

</dd>
<dt><code>$else</code></dt>
<dd>Commands in this branch of the <code>$if</code> directive are executed if
the test fails.

</dd>
<dt><code>$include</code></dt>
<dd>This directive takes a single filename as an argument and reads commands
and bindings from that file.
For example, the following directive reads from <samp>/etc/inputrc</samp>:
<div class="example">
<pre class="example">$include /etc/inputrc
</pre></div>
</dd>
</dl>

<hr>
</div>
<div class="subsection" id="Sample-Init-File">
<div class="header">

Previous: <a href="#Conditional-Init-Constructs" accesskey="p" rel="prev">Conditional Init Constructs</a>, Up: <a href="#Readline-Init-File" accesskey="u" rel="up">Readline Init File</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">8.3.3 Sample Init File</h4>

Here is an example of an <var>inputrc</var> file. This illustrates key
binding, variable assignment, and conditional syntax.

<div class="example">
<pre class="example"># This file controls the behaviour of line input editing for
# programs that use the GNU Readline library. Existing
# programs include FTP, Bash, and GDB.
#
# You can re-read the inputrc file with C-x C-r.
# Lines beginning with '#' are comments.
#
# First, include any system-wide bindings and variable
# assignments from /etc/Inputrc
$include /etc/Inputrc

#
# Set various bindings for emacs mode.

set editing-mode emacs

$if mode=emacs

Meta-Control-h:	backward-kill-word	Text after the function name is ignored

#
# Arrow keys in keypad mode
#
#&quot;\M-OD&quot;:        backward-char
#&quot;\M-OC&quot;:        forward-char
#&quot;\M-OA&quot;:        previous-history
#&quot;\M-OB&quot;:        next-history
#
# Arrow keys in ANSI mode
#
&quot;\M-[D&quot;:        backward-char
&quot;\M-[C&quot;:        forward-char
&quot;\M-[A&quot;:        previous-history
&quot;\M-[B&quot;:        next-history
#
# Arrow keys in 8 bit keypad mode
#
#&quot;\M-\C-OD&quot;:       backward-char
#&quot;\M-\C-OC&quot;:       forward-char
#&quot;\M-\C-OA&quot;:       previous-history
#&quot;\M-\C-OB&quot;:       next-history
#
# Arrow keys in 8 bit ANSI mode
#
#&quot;\M-\C-[D&quot;:       backward-char
#&quot;\M-\C-[C&quot;:       forward-char
#&quot;\M-\C-[A&quot;:       previous-history
#&quot;\M-\C-[B&quot;:       next-history

C-q: quoted-insert

$endif

# An old-style binding.  This happens to be the default.
TAB: complete

# Macros that are convenient for shell interaction
$if Bash
# edit the path
&quot;\C-xp&quot;: &quot;PATH=${PATH}\e\C-e\C-a\ef\C-f&quot;
# prepare to type a quoted word --
# insert open and close double quotes
# and move to just after the open quote
&quot;\C-x\&quot;&quot;: &quot;\&quot;\&quot;\C-b&quot;
# insert a backslash (testing backslash escapes
# in sequences and macros)
&quot;\C-x\\&quot;: &quot;\\&quot;
# Quote the current or previous word
&quot;\C-xq&quot;: &quot;\eb\&quot;\ef\&quot;&quot;
# Add a binding to refresh the line, which is unbound
&quot;\C-xr&quot;: redraw-current-line
# Edit variable on current line.
&quot;\M-\C-v&quot;: &quot;\C-a\C-k$\C-y\M-\C-e\C-a\C-y=&quot;
$endif

# use a visible bell if one is available
set bell-style visible

# don't strip characters to 7 bits when reading
set input-meta on

# allow iso-latin1 characters to be inserted rather
# than converted to prefix-meta sequences
set convert-meta off

# display characters with the eighth bit set directly
# rather than as meta-prefixed characters
set output-meta on

# if there are 150 or more possible completions for a word,
# ask whether or not the user wants to see all of them
set completion-query-items 150

# For FTP
$if Ftp
&quot;\C-xg&quot;: &quot;get \M-?&quot;
&quot;\C-xt&quot;: &quot;put \M-?&quot;
&quot;\M-.&quot;: yank-last-arg
$endif
</pre></div>

<hr>
</div>
</div>
<div class="section" id="Bindable-Readline-Commands">
<div class="header">

Next: <a href="#Readline-vi-Mode" accesskey="n" rel="next">Readline vi Mode</a>, Previous: <a href="#Readline-Init-File" accesskey="p" rel="prev">Readline Init File</a>, Up: <a href="#Command-Line-Editing" accesskey="u" rel="up">Command Line Editing</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">8.4 Bindable Readline Commands</h3>

This section describes Readline commands that may be bound to key
sequences.
You can list your key bindings by executing
<code>bind&nbsp;-P</code> or, for a more terse format, suitable for an
<var>inputrc</var> file, <code>bind&nbsp;-p</code>. (See <a href="#Bash-Builtins">Bash Builtin Commands</a>.)
Command names without an accompanying key sequence are unbound by default.

In the following descriptions, point refers to the current cursor
position, and mark refers to a cursor position saved by the
<code>set-mark</code> command.
The text between the point and mark is referred to as the region.

<ul class="section-toc">
<li><a href="#Commands-For-Moving" accesskey="1">Commands For Moving</a></li>
<li><a href="#Commands-For-History" accesskey="2">Commands For Manipulating The History</a></li>
<li><a href="#Commands-For-Text" accesskey="3">Commands For Changing Text</a></li>
<li><a href="#Commands-For-Killing" accesskey="4">Killing And Yanking</a></li>
<li><a href="#Numeric-Arguments" accesskey="5">Specifying Numeric Arguments</a></li>
<li><a href="#Commands-For-Completion" accesskey="6">Letting Readline Type For You</a></li>
<li><a href="#Keyboard-Macros" accesskey="7">Keyboard Macros</a></li>
<li><a href="#Miscellaneous-Commands" accesskey="8">Some Miscellaneous Commands</a></li>
</ul>
<hr>
<div class="subsection" id="Commands-For-Moving">
<div class="header">

Next: <a href="#Commands-For-History" accesskey="n" rel="next">Commands For Manipulating The History</a>, Up: <a href="#Bindable-Readline-Commands" accesskey="u" rel="up">Bindable Readline Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">8.4.1 Commands For Moving</h4>
<dl compact="compact">
<dt id='index-beginning_002dof_002dline-_0028C_002da_0029'><code>beginning-of-line (C-a)</code><a href='#index-beginning_002dof_002dline-_0028C_002da_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Move to the start of the current line.

</dd>
<dt id='index-end_002dof_002dline-_0028C_002de_0029'><code>end-of-line (C-e)</code><a href='#index-end_002dof_002dline-_0028C_002de_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Move to the end of the line.

</dd>
<dt id='index-forward_002dchar-_0028C_002df_0029'><code>forward-char (C-f)</code><a href='#index-forward_002dchar-_0028C_002df_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Move forward a character.

</dd>
<dt id='index-backward_002dchar-_0028C_002db_0029'><code>backward-char (C-b)</code><a href='#index-backward_002dchar-_0028C_002db_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Move back a character.

</dd>
<dt id='index-forward_002dword-_0028M_002df_0029'><code>forward-word (M-f)</code><a href='#index-forward_002dword-_0028M_002df_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Move forward to the end of the next word.
Words are composed of letters and digits.

</dd>
<dt id='index-backward_002dword-_0028M_002db_0029'><code>backward-word (M-b)</code><a href='#index-backward_002dword-_0028M_002db_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Move back to the start of the current or previous word.
Words are composed of letters and digits.

</dd>
<dt id='index-shell_002dforward_002dword-_0028M_002dC_002df_0029'><code>shell-forward-word (M-C-f)</code><a href='#index-shell_002dforward_002dword-_0028M_002dC_002df_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Move forward to the end of the next word.
Words are delimited by non-quoted shell metacharacters.

</dd>
<dt id='index-shell_002dbackward_002dword-_0028M_002dC_002db_0029'><code>shell-backward-word (M-C-b)</code><a href='#index-shell_002dbackward_002dword-_0028M_002dC_002db_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Move back to the start of the current or previous word.
Words are delimited by non-quoted shell metacharacters.

</dd>
<dt id='index-previous_002dscreen_002dline-_0028_0029'><code>previous-screen-line ()</code><a href='#index-previous_002dscreen_002dline-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Attempt to move point to the same physical screen column on the previous
physical screen line. This will not have the desired effect if the current
Readline line does not take up more than one physical line or if point is not
greater than the length of the prompt plus the screen width.

</dd>
<dt id='index-next_002dscreen_002dline-_0028_0029'><code>next-screen-line ()</code><a href='#index-next_002dscreen_002dline-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Attempt to move point to the same physical screen column on the next
physical screen line. This will not have the desired effect if the current
Readline line does not take up more than one physical line or if the length
of the current Readline line is not greater than the length of the prompt
plus the screen width.

</dd>
<dt id='index-clear_002ddisplay-_0028M_002dC_002dl_0029'><code>clear-display (M-C-l)</code><a href='#index-clear_002ddisplay-_0028M_002dC_002dl_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Clear the screen and, if possible, the terminal&rsquo;s scrollback buffer,
then redraw the current line,
leaving the current line at the top of the screen.

</dd>
<dt id='index-clear_002dscreen-_0028C_002dl_0029'><code>clear-screen (C-l)</code><a href='#index-clear_002dscreen-_0028C_002dl_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Clear the screen,
then redraw the current line,
leaving the current line at the top of the screen.

</dd>
<dt id='index-redraw_002dcurrent_002dline-_0028_0029'><code>redraw-current-line ()</code><a href='#index-redraw_002dcurrent_002dline-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Refresh the current line. By default, this is unbound.

</dd>
</dl>

<hr>
</div>
<div class="subsection" id="Commands-For-History">
<div class="header">

Next: <a href="#Commands-For-Text" accesskey="n" rel="next">Commands For Changing Text</a>, Previous: <a href="#Commands-For-Moving" accesskey="p" rel="prev">Commands For Moving</a>, Up: <a href="#Bindable-Readline-Commands" accesskey="u" rel="up">Bindable Readline Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">8.4.2 Commands For Manipulating The History</h4>

<dl compact="compact">
<dt id='index-accept_002dline-_0028Newline-or-Return_0029'><code>accept-line (Newline or Return)</code><a href='#index-accept_002dline-_0028Newline-or-Return_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Accept the line regardless of where the cursor is.
If this line is
non-empty, add it to the history list according to the setting of
the <code>HISTCONTROL</code> and <code>HISTIGNORE</code> variables.
If this line is a modified history line, then restore the history line
to its original state.

</dd>
<dt id='index-previous_002dhistory-_0028C_002dp_0029'><code>previous-history (C-p)</code><a href='#index-previous_002dhistory-_0028C_002dp_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Move &lsquo;back&rsquo; through the history list, fetching the previous command.

</dd>
<dt id='index-next_002dhistory-_0028C_002dn_0029'><code>next-history (C-n)</code><a href='#index-next_002dhistory-_0028C_002dn_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Move &lsquo;forward&rsquo; through the history list, fetching the next command.

</dd>
<dt id='index-beginning_002dof_002dhistory-_0028M_002d_003c_0029'><code>beginning-of-history (M-&lt;)</code><a href='#index-beginning_002dof_002dhistory-_0028M_002d_003c_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Move to the first line in the history.

</dd>
<dt id='index-end_002dof_002dhistory-_0028M_002d_003e_0029'><code>end-of-history (M-&gt;)</code><a href='#index-end_002dof_002dhistory-_0028M_002d_003e_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Move to the end of the input history, i.e., the line currently
being entered.

</dd>
<dt id='index-reverse_002dsearch_002dhistory-_0028C_002dr_0029'><code>reverse-search-history (C-r)</code><a href='#index-reverse_002dsearch_002dhistory-_0028C_002dr_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Search backward starting at the current line and moving &lsquo;up&rsquo; through
the history as necessary. This is an incremental search.
This command sets the region to the matched text and activates the mark.

</dd>
<dt id='index-forward_002dsearch_002dhistory-_0028C_002ds_0029'><code>forward-search-history (C-s)</code><a href='#index-forward_002dsearch_002dhistory-_0028C_002ds_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Search forward starting at the current line and moving &lsquo;down&rsquo; through
the history as necessary. This is an incremental search.
This command sets the region to the matched text and activates the mark.

</dd>
<dt id='index-non_002dincremental_002dreverse_002dsearch_002dhistory-_0028M_002dp_0029'><code>non-incremental-reverse-search-history (M-p)</code><a href='#index-non_002dincremental_002dreverse_002dsearch_002dhistory-_0028M_002dp_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Search backward starting at the current line and moving &lsquo;up&rsquo;
through the history as necessary using a non-incremental search
for a string supplied by the user.
The search string may match anywhere in a history line.

</dd>
<dt id='index-non_002dincremental_002dforward_002dsearch_002dhistory-_0028M_002dn_0029'><code>non-incremental-forward-search-history (M-n)</code><a href='#index-non_002dincremental_002dforward_002dsearch_002dhistory-_0028M_002dn_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Search forward starting at the current line and moving &lsquo;down&rsquo;
through the history as necessary using a non-incremental search
for a string supplied by the user.
The search string may match anywhere in a history line.

</dd>
<dt id='index-history_002dsearch_002dforward-_0028_0029'><code>history-search-forward ()</code><a href='#index-history_002dsearch_002dforward-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Search forward through the history for the string of characters
between the start of the current line and the point.
The search string must match at the beginning of a history line.
This is a non-incremental search.
By default, this command is unbound.

</dd>
<dt id='index-history_002dsearch_002dbackward-_0028_0029'><code>history-search-backward ()</code><a href='#index-history_002dsearch_002dbackward-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Search backward through the history for the string of characters
between the start of the current line and the point.
The search string must match at the beginning of a history line.
This is a non-incremental search.
By default, this command is unbound.

</dd>
<dt id='index-history_002dsubstring_002dsearch_002dforward-_0028_0029'><code>history-substring-search-forward ()</code><a href='#index-history_002dsubstring_002dsearch_002dforward-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Search forward through the history for the string of characters
between the start of the current line and the point.
The search string may match anywhere in a history line.
This is a non-incremental search.
By default, this command is unbound.

</dd>
<dt id='index-history_002dsubstring_002dsearch_002dbackward-_0028_0029'><code>history-substring-search-backward ()</code><a href='#index-history_002dsubstring_002dsearch_002dbackward-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Search backward through the history for the string of characters
between the start of the current line and the point.
The search string may match anywhere in a history line.
This is a non-incremental search.
By default, this command is unbound.

</dd>
<dt id='index-yank_002dnth_002darg-_0028M_002dC_002dy_0029'><code>yank-nth-arg (M-C-y)</code><a href='#index-yank_002dnth_002darg-_0028M_002dC_002dy_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Insert the first argument to the previous command (usually
the second word on the previous line) at point.
With an argument <var>n</var>,
insert the <var>n</var>th word from the previous command (the words
in the previous command begin with word 0). A negative argument
inserts the <var>n</var>th word from the end of the previous command.
Once the argument <var>n</var> is computed, the argument is extracted
as if the &lsquo;<samp>!<var>n</var></samp>&rsquo; history expansion had been specified.

</dd>
<dt id='index-yank_002dlast_002darg-_0028M_002d_002e-or-M_002d_005f_0029'><code>yank-last-arg (M-. or M-_)</code><a href='#index-yank_002dlast_002darg-_0028M_002d_002e-or-M_002d_005f_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Insert last argument to the previous command (the last word of the
previous history entry).
With a numeric argument, behave exactly like <code>yank-nth-arg</code>.
Successive calls to <code>yank-last-arg</code> move back through the history
list, inserting the last word (or the word specified by the argument to
the first call) of each line in turn.
Any numeric argument supplied to these successive calls determines
the direction to move through the history. A negative argument switches
the direction through the history (back or forward).
The history expansion facilities are used to extract the last argument,
as if the &lsquo;<samp>!$</samp>&rsquo; history expansion had been specified.

</dd>
<dt id='index-operate_002dand_002dget_002dnext-_0028C_002do_0029'><code>operate-and-get-next (C-o)</code><a href='#index-operate_002dand_002dget_002dnext-_0028C_002do_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Accept the current line for return to the calling application as if a
newline had been entered,
and fetch the next line relative to the current line from the history
for editing.
A numeric argument, if supplied, specifies the history entry to use instead
of the current line.

</dd>
<dt id='index-fetch_002dhistory-_0028_0029'><code>fetch-history ()</code><a href='#index-fetch_002dhistory-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>With a numeric argument, fetch that entry from the history list
and make it the current line.
Without an argument, move back to the first entry in the history list.

</dd>
</dl>

<hr>
</div>
<div class="subsection" id="Commands-For-Text">
<div class="header">

Next: <a href="#Commands-For-Killing" accesskey="n" rel="next">Killing And Yanking</a>, Previous: <a href="#Commands-For-History" accesskey="p" rel="prev">Commands For Manipulating The History</a>, Up: <a href="#Bindable-Readline-Commands" accesskey="u" rel="up">Bindable Readline Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">8.4.3 Commands For Changing Text</h4>

<dl compact="compact">
<dt id='index-end_002dof_002dfile-_0028usually-C_002dd_0029'><code>end-of-file (usually C-d)</code><a href='#index-end_002dof_002dfile-_0028usually-C_002dd_0029' class='copiable-anchor'> &para;</a></dt>
<dd>The character indicating end-of-file as set, for example, by
<code>stty</code>. If this character is read when there are no characters
on the line, and point is at the beginning of the line, Readline
interprets it as the end of input and returns EOF.

</dd>
<dt id='index-delete_002dchar-_0028C_002dd_0029'><code>delete-char (C-d)</code><a href='#index-delete_002dchar-_0028C_002dd_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Delete the character at point. If this function is bound to the
same character as the tty EOF character, as <kbd>C-d</kbd>
commonly is, see above for the effects.

</dd>
<dt id='index-backward_002ddelete_002dchar-_0028Rubout_0029'><code>backward-delete-char (Rubout)</code><a href='#index-backward_002ddelete_002dchar-_0028Rubout_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Delete the character behind the cursor. A numeric argument means
to kill the characters instead of deleting them.

</dd>
<dt id='index-forward_002dbackward_002ddelete_002dchar-_0028_0029'><code>forward-backward-delete-char ()</code><a href='#index-forward_002dbackward_002ddelete_002dchar-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Delete the character under the cursor, unless the cursor is at the
end of the line, in which case the character behind the cursor is
deleted. By default, this is not bound to a key.

</dd>
<dt id='index-quoted_002dinsert-_0028C_002dq-or-C_002dv_0029'><code>quoted-insert (C-q or C-v)</code><a href='#index-quoted_002dinsert-_0028C_002dq-or-C_002dv_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Add the next character typed to the line verbatim. This is
how to insert key sequences like <kbd>C-q</kbd>, for example.

</dd>
<dt id='index-self_002dinsert-_0028a_002c-b_002c-A_002c-1_002c-_0021_002c-_2026_0029'><code>self-insert (a, b, A, 1, !, &hellip;)</code><a href='#index-self_002dinsert-_0028a_002c-b_002c-A_002c-1_002c-_0021_002c-_2026_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Insert yourself.

</dd>
<dt id='index-bracketed_002dpaste_002dbegin-_0028_0029'><code>bracketed-paste-begin ()</code><a href='#index-bracketed_002dpaste_002dbegin-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>This function is intended to be bound to the &quot;bracketed paste&quot; escape
sequence sent by some terminals, and such a binding is assigned by default.
It allows Readline to insert the pasted text as a single unit without treating
each character as if it had been read from the keyboard. The characters
are inserted as if each one was bound to <code>self-insert</code> instead of
executing any editing commands.

Bracketed paste sets the region (the characters between point and the mark)
to the inserted text. It uses the concept of an active mark: when the
mark is active, Readline redisplay uses the terminal&rsquo;s standout mode to
denote the region.

</dd>
<dt id='index-transpose_002dchars-_0028C_002dt_0029'><code>transpose-chars (C-t)</code><a href='#index-transpose_002dchars-_0028C_002dt_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Drag the character before the cursor forward over
the character at the cursor, moving the
cursor forward as well. If the insertion point
is at the end of the line, then this
transposes the last two characters of the line.
Negative arguments have no effect.

</dd>
<dt id='index-transpose_002dwords-_0028M_002dt_0029'><code>transpose-words (M-t)</code><a href='#index-transpose_002dwords-_0028M_002dt_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Drag the word before point past the word after point,
moving point past that word as well.
If the insertion point is at the end of the line, this transposes
the last two words on the line.

</dd>
<dt id='index-upcase_002dword-_0028M_002du_0029'><code>upcase-word (M-u)</code><a href='#index-upcase_002dword-_0028M_002du_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Uppercase the current (or following) word. With a negative argument,
uppercase the previous word, but do not move the cursor.

</dd>
<dt id='index-downcase_002dword-_0028M_002dl_0029'><code>downcase-word (M-l)</code><a href='#index-downcase_002dword-_0028M_002dl_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Lowercase the current (or following) word. With a negative argument,
lowercase the previous word, but do not move the cursor.

</dd>
<dt id='index-capitalize_002dword-_0028M_002dc_0029'><code>capitalize-word (M-c)</code><a href='#index-capitalize_002dword-_0028M_002dc_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Capitalize the current (or following) word. With a negative argument,
capitalize the previous word, but do not move the cursor.

</dd>
<dt id='index-overwrite_002dmode-_0028_0029'><code>overwrite-mode ()</code><a href='#index-overwrite_002dmode-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Toggle overwrite mode. With an explicit positive numeric argument,
switches to overwrite mode. With an explicit non-positive numeric
argument, switches to insert mode. This command affects only
<code>emacs</code> mode; <code>vi</code> mode does overwrite differently.
Each call to <code>readline()</code> starts in insert mode.

In overwrite mode, characters bound to <code>self-insert</code> replace
the text at point rather than pushing the text to the right.
Characters bound to <code>backward-delete-char</code> replace the character
before point with a space.

By default, this command is unbound.

</dd>
</dl>

<hr>
</div>
<div class="subsection" id="Commands-For-Killing">
<div class="header">

Next: <a href="#Numeric-Arguments" accesskey="n" rel="next">Specifying Numeric Arguments</a>, Previous: <a href="#Commands-For-Text" accesskey="p" rel="prev">Commands For Changing Text</a>, Up: <a href="#Bindable-Readline-Commands" accesskey="u" rel="up">Bindable Readline Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">8.4.4 Killing And Yanking</h4>

<dl compact="compact">
<dt id='index-kill_002dline-_0028C_002dk_0029'><code>kill-line (C-k)</code><a href='#index-kill_002dline-_0028C_002dk_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Kill the text from point to the end of the line.
With a negative numeric argument, kill backward from the cursor to the
beginning of the current line.

</dd>
<dt id='index-backward_002dkill_002dline-_0028C_002dx-Rubout_0029'><code>backward-kill-line (C-x Rubout)</code><a href='#index-backward_002dkill_002dline-_0028C_002dx-Rubout_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Kill backward from the cursor to the beginning of the current line.
With a negative numeric argument, kill forward from the cursor to the
end of the current line.

</dd>
<dt id='index-unix_002dline_002ddiscard-_0028C_002du_0029'><code>unix-line-discard (C-u)</code><a href='#index-unix_002dline_002ddiscard-_0028C_002du_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Kill backward from the cursor to the beginning of the current line.

</dd>
<dt id='index-kill_002dwhole_002dline-_0028_0029'><code>kill-whole-line ()</code><a href='#index-kill_002dwhole_002dline-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Kill all characters on the current line, no matter where point is.
By default, this is unbound.

</dd>
<dt id='index-kill_002dword-_0028M_002dd_0029'><code>kill-word (M-d)</code><a href='#index-kill_002dword-_0028M_002dd_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Kill from point to the end of the current word, or if between
words, to the end of the next word.
Word boundaries are the same as <code>forward-word</code>.

</dd>
<dt id='index-backward_002dkill_002dword-_0028M_002dDEL_0029'><code>backward-kill-word (M-DEL)</code><a href='#index-backward_002dkill_002dword-_0028M_002dDEL_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Kill the word behind point.
Word boundaries are the same as <code>backward-word</code>.

</dd>
<dt id='index-shell_002dkill_002dword-_0028M_002dC_002dd_0029'><code>shell-kill-word (M-C-d)</code><a href='#index-shell_002dkill_002dword-_0028M_002dC_002dd_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Kill from point to the end of the current word, or if between
words, to the end of the next word.
Word boundaries are the same as <code>shell-forward-word</code>.

</dd>
<dt id='index-shell_002dbackward_002dkill_002dword-_0028_0029'><code>shell-backward-kill-word ()</code><a href='#index-shell_002dbackward_002dkill_002dword-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Kill the word behind point.
Word boundaries are the same as <code>shell-backward-word</code>.

</dd>
<dt id='index-shell_002dtranspose_002dwords-_0028M_002dC_002dt_0029'><code>shell-transpose-words (M-C-t)</code><a href='#index-shell_002dtranspose_002dwords-_0028M_002dC_002dt_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Drag the word before point past the word after point,
moving point past that word as well.
If the insertion point is at the end of the line, this transposes
the last two words on the line.
Word boundaries are the same as <code>shell-forward-word</code> and
<code>shell-backward-word</code>.

</dd>
<dt id='index-unix_002dword_002drubout-_0028C_002dw_0029'><code>unix-word-rubout (C-w)</code><a href='#index-unix_002dword_002drubout-_0028C_002dw_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Kill the word behind point, using white space as a word boundary.
The killed text is saved on the kill-ring.

</dd>
<dt id='index-unix_002dfilename_002drubout-_0028_0029'><code>unix-filename-rubout ()</code><a href='#index-unix_002dfilename_002drubout-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Kill the word behind point, using white space and the slash character
as the word boundaries.
The killed text is saved on the kill-ring.

</dd>
<dt id='index-delete_002dhorizontal_002dspace-_0028_0029'><code>delete-horizontal-space ()</code><a href='#index-delete_002dhorizontal_002dspace-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Delete all spaces and tabs around point. By default, this is unbound.

</dd>
<dt id='index-kill_002dregion-_0028_0029'><code>kill-region ()</code><a href='#index-kill_002dregion-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Kill the text in the current region.
By default, this command is unbound.

</dd>
<dt id='index-copy_002dregion_002das_002dkill-_0028_0029'><code>copy-region-as-kill ()</code><a href='#index-copy_002dregion_002das_002dkill-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Copy the text in the region to the kill buffer, so it can be yanked
right away. By default, this command is unbound.

</dd>
<dt id='index-copy_002dbackward_002dword-_0028_0029'><code>copy-backward-word ()</code><a href='#index-copy_002dbackward_002dword-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Copy the word before point to the kill buffer.
The word boundaries are the same as <code>backward-word</code>.
By default, this command is unbound.

</dd>
<dt id='index-copy_002dforward_002dword-_0028_0029'><code>copy-forward-word ()</code><a href='#index-copy_002dforward_002dword-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Copy the word following point to the kill buffer.
The word boundaries are the same as <code>forward-word</code>.
By default, this command is unbound.

</dd>
<dt id='index-yank-_0028C_002dy_0029'><code>yank (C-y)</code><a href='#index-yank-_0028C_002dy_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Yank the top of the kill ring into the buffer at point.

</dd>
<dt id='index-yank_002dpop-_0028M_002dy_0029'><code>yank-pop (M-y)</code><a href='#index-yank_002dpop-_0028M_002dy_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Rotate the kill-ring, and yank the new top. You can only do this if
the prior command is <code>yank</code> or <code>yank-pop</code>.
</dd>
</dl>

<hr>
</div>
<div class="subsection" id="Numeric-Arguments">
<div class="header">

Next: <a href="#Commands-For-Completion" accesskey="n" rel="next">Letting Readline Type For You</a>, Previous: <a href="#Commands-For-Killing" accesskey="p" rel="prev">Killing And Yanking</a>, Up: <a href="#Bindable-Readline-Commands" accesskey="u" rel="up">Bindable Readline Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">8.4.5 Specifying Numeric Arguments</h4>
<dl compact="compact">
<dt id='index-digit_002dargument-_0028M_002d0_002c-M_002d1_002c-_2026-M_002d_002d_0029'><code>digit-argument (<kbd>M-0</kbd>, <kbd>M-1</kbd>, &hellip; <kbd>M--</kbd>)</code><a href='#index-digit_002dargument-_0028M_002d0_002c-M_002d1_002c-_2026-M_002d_002d_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Add this digit to the argument already accumulating, or start a new
argument. <kbd>M--</kbd> starts a negative argument.

</dd>
<dt id='index-universal_002dargument-_0028_0029'><code>universal-argument ()</code><a href='#index-universal_002dargument-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>This is another way to specify an argument.
If this command is followed by one or more digits, optionally with a
leading minus sign, those digits define the argument.
If the command is followed by digits, executing <code>universal-argument</code>
again ends the numeric argument, but is otherwise ignored.
As a special case, if this command is immediately followed by a
character that is neither a digit nor minus sign, the argument count
for the next command is multiplied by four.
The argument count is initially one, so executing this function the
first time makes the argument count four, a second time makes the
argument count sixteen, and so on.
By default, this is not bound to a key.
</dd>
</dl>

<hr>
</div>
<div class="subsection" id="Commands-For-Completion">
<div class="header">

Next: <a href="#Keyboard-Macros" accesskey="n" rel="next">Keyboard Macros</a>, Previous: <a href="#Numeric-Arguments" accesskey="p" rel="prev">Specifying Numeric Arguments</a>, Up: <a href="#Bindable-Readline-Commands" accesskey="u" rel="up">Bindable Readline Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">8.4.6 Letting Readline Type For You</h4>

<dl compact="compact">
<dt id='index-complete-_0028TAB_0029'><code>complete (TAB)</code><a href='#index-complete-_0028TAB_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Attempt to perform completion on the text before point.
The actual completion performed is application-specific.
Bash attempts completion treating the text as a variable (if the
text begins with &lsquo;<samp>$</samp>&rsquo;), username (if the text begins with
&lsquo;<samp>~</samp>&rsquo;), hostname (if the text begins with &lsquo;<samp>@</samp>&rsquo;), or
command (including aliases and functions) in turn. If none 
of these produces a match, filename completion is attempted.

</dd>
<dt id='index-possible_002dcompletions-_0028M_002d_003f_0029'><code>possible-completions (M-?)</code><a href='#index-possible_002dcompletions-_0028M_002d_003f_0029' class='copiable-anchor'> &para;</a></dt>
<dd>List the possible completions of the text before point.
When displaying completions, Readline sets the number of columns used
for display to the value of <code>completion-display-width</code>, the value of
the environment variable <code>COLUMNS</code>, or the screen width, in that order.

</dd>
<dt id='index-insert_002dcompletions-_0028M_002d_002a_0029'><code>insert-completions (M-*)</code><a href='#index-insert_002dcompletions-_0028M_002d_002a_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Insert all completions of the text before point that would have
been generated by <code>possible-completions</code>.

</dd>
<dt id='index-menu_002dcomplete-_0028_0029'><code>menu-complete ()</code><a href='#index-menu_002dcomplete-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Similar to <code>complete</code>, but replaces the word to be completed
with a single match from the list of possible completions.
Repeated execution of <code>menu-complete</code> steps through the list
of possible completions, inserting each match in turn.
At the end of the list of completions, the bell is rung
(subject to the setting of <code>bell-style</code>)
and the original text is restored.
An argument of <var>n</var> moves <var>n</var> positions forward in the list
of matches; a negative argument may be used to move backward
through the list.
This command is intended to be bound to <tt class="key">TAB</tt>, but is unbound
by default.

</dd>
<dt id='index-menu_002dcomplete_002dbackward-_0028_0029'><code>menu-complete-backward ()</code><a href='#index-menu_002dcomplete_002dbackward-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Identical to <code>menu-complete</code>, but moves backward through the list
of possible completions, as if <code>menu-complete</code> had been given a
negative argument.

</dd>
<dt id='index-delete_002dchar_002dor_002dlist-_0028_0029'><code>delete-char-or-list ()</code><a href='#index-delete_002dchar_002dor_002dlist-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Deletes the character under the cursor if not at the beginning or
end of the line (like <code>delete-char</code>).
If at the end of the line, behaves identically to
<code>possible-completions</code>.
This command is unbound by default.

</dd>
<dt id='index-complete_002dfilename-_0028M_002d_002f_0029'><code>complete-filename (M-/)</code><a href='#index-complete_002dfilename-_0028M_002d_002f_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Attempt filename completion on the text before point.

</dd>
<dt id='index-possible_002dfilename_002dcompletions-_0028C_002dx-_002f_0029'><code>possible-filename-completions (C-x /)</code><a href='#index-possible_002dfilename_002dcompletions-_0028C_002dx-_002f_0029' class='copiable-anchor'> &para;</a></dt>
<dd>List the possible completions of the text before point,
treating it as a filename.

</dd>
<dt id='index-complete_002dusername-_0028M_002d_007e_0029'><code>complete-username (M-~)</code><a href='#index-complete_002dusername-_0028M_002d_007e_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Attempt completion on the text before point, treating
it as a username.

</dd>
<dt id='index-possible_002dusername_002dcompletions-_0028C_002dx-_007e_0029'><code>possible-username-completions (C-x ~)</code><a href='#index-possible_002dusername_002dcompletions-_0028C_002dx-_007e_0029' class='copiable-anchor'> &para;</a></dt>
<dd>List the possible completions of the text before point,
treating it as a username.

</dd>
<dt id='index-complete_002dvariable-_0028M_002d_0024_0029'><code>complete-variable (M-$)</code><a href='#index-complete_002dvariable-_0028M_002d_0024_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Attempt completion on the text before point, treating
it as a shell variable.

</dd>
<dt id='index-possible_002dvariable_002dcompletions-_0028C_002dx-_0024_0029'><code>possible-variable-completions (C-x $)</code><a href='#index-possible_002dvariable_002dcompletions-_0028C_002dx-_0024_0029' class='copiable-anchor'> &para;</a></dt>
<dd>List the possible completions of the text before point,
treating it as a shell variable.

</dd>
<dt id='index-complete_002dhostname-_0028M_002d_0040_0029'><code>complete-hostname (M-@)</code><a href='#index-complete_002dhostname-_0028M_002d_0040_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Attempt completion on the text before point, treating
it as a hostname.

</dd>
<dt id='index-possible_002dhostname_002dcompletions-_0028C_002dx-_0040_0029'><code>possible-hostname-completions (C-x @)</code><a href='#index-possible_002dhostname_002dcompletions-_0028C_002dx-_0040_0029' class='copiable-anchor'> &para;</a></dt>
<dd>List the possible completions of the text before point,
treating it as a hostname.

</dd>
<dt id='index-complete_002dcommand-_0028M_002d_0021_0029'><code>complete-command (M-!)</code><a href='#index-complete_002dcommand-_0028M_002d_0021_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Attempt completion on the text before point, treating
it as a command name. Command completion attempts to
match the text against aliases, reserved words, shell
functions, shell builtins, and finally executable filenames,
in that order.

</dd>
<dt id='index-possible_002dcommand_002dcompletions-_0028C_002dx-_0021_0029'><code>possible-command-completions (C-x !)</code><a href='#index-possible_002dcommand_002dcompletions-_0028C_002dx-_0021_0029' class='copiable-anchor'> &para;</a></dt>
<dd>List the possible completions of the text before point,
treating it as a command name.

</dd>
<dt id='index-dynamic_002dcomplete_002dhistory-_0028M_002dTAB_0029'><code>dynamic-complete-history (M-TAB)</code><a href='#index-dynamic_002dcomplete_002dhistory-_0028M_002dTAB_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Attempt completion on the text before point, comparing
the text against lines from the history list for possible
completion matches.

</dd>
<dt id='index-dabbrev_002dexpand-_0028_0029'><code>dabbrev-expand ()</code><a href='#index-dabbrev_002dexpand-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Attempt menu completion on the text before point, comparing
the text against lines from the history list for possible
completion matches.

</dd>
<dt id='index-complete_002dinto_002dbraces-_0028M_002d_007b_0029'><code>complete-into-braces (M-{)</code><a href='#index-complete_002dinto_002dbraces-_0028M_002d_007b_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Perform filename completion and insert the list of possible completions
enclosed within braces so the list is available to the shell
(see <a href="#Brace-Expansion">Brace Expansion</a>).

</dd>
</dl>

<hr>
</div>
<div class="subsection" id="Keyboard-Macros">
<div class="header">

Next: <a href="#Miscellaneous-Commands" accesskey="n" rel="next">Some Miscellaneous Commands</a>, Previous: <a href="#Commands-For-Completion" accesskey="p" rel="prev">Letting Readline Type For You</a>, Up: <a href="#Bindable-Readline-Commands" accesskey="u" rel="up">Bindable Readline Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">8.4.7 Keyboard Macros</h4>
<dl compact="compact">
<dt id='index-start_002dkbd_002dmacro-_0028C_002dx-_0028_0029'><code>start-kbd-macro (C-x ()</code><a href='#index-start_002dkbd_002dmacro-_0028C_002dx-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Begin saving the characters typed into the current keyboard macro.

</dd>
<dt id='index-end_002dkbd_002dmacro-_0028C_002dx-_0029_0029'><code>end-kbd-macro (C-x ))</code><a href='#index-end_002dkbd_002dmacro-_0028C_002dx-_0029_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Stop saving the characters typed into the current keyboard macro
and save the definition.

</dd>
<dt id='index-call_002dlast_002dkbd_002dmacro-_0028C_002dx-e_0029'><code>call-last-kbd-macro (C-x e)</code><a href='#index-call_002dlast_002dkbd_002dmacro-_0028C_002dx-e_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Re-execute the last keyboard macro defined, by making the characters
in the macro appear as if typed at the keyboard.

</dd>
<dt id='index-print_002dlast_002dkbd_002dmacro-_0028_0029'><code>print-last-kbd-macro ()</code><a href='#index-print_002dlast_002dkbd_002dmacro-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Print the last keyboard macro defined in a format suitable for the
<var>inputrc</var> file.

</dd>
</dl>

<hr>
</div>
<div class="subsection" id="Miscellaneous-Commands">
<div class="header">

Previous: <a href="#Keyboard-Macros" accesskey="p" rel="prev">Keyboard Macros</a>, Up: <a href="#Bindable-Readline-Commands" accesskey="u" rel="up">Bindable Readline Commands</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">8.4.8 Some Miscellaneous Commands</h4>
<dl compact="compact">
<dt id='index-re_002dread_002dinit_002dfile-_0028C_002dx-C_002dr_0029'><code>re-read-init-file (C-x C-r)</code><a href='#index-re_002dread_002dinit_002dfile-_0028C_002dx-C_002dr_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Read in the contents of the <var>inputrc</var> file, and incorporate
any bindings or variable assignments found there.

</dd>
<dt id='index-abort-_0028C_002dg_0029'><code>abort (C-g)</code><a href='#index-abort-_0028C_002dg_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Abort the current editing command and
ring the terminal&rsquo;s bell (subject to the setting of
<code>bell-style</code>).

</dd>
<dt id='index-do_002dlowercase_002dversion-_0028M_002dA_002c-M_002dB_002c-M_002dx_002c-_2026_0029'><code>do-lowercase-version (M-A, M-B, M-<var>x</var>, &hellip;)</code><a href='#index-do_002dlowercase_002dversion-_0028M_002dA_002c-M_002dB_002c-M_002dx_002c-_2026_0029' class='copiable-anchor'> &para;</a></dt>
<dd>If the metafied character <var>x</var> is upper case, run the command
that is bound to the corresponding metafied lower case character.
The behavior is undefined if <var>x</var> is already lower case.

</dd>
<dt id='index-prefix_002dmeta-_0028ESC_0029'><code>prefix-meta (ESC)</code><a href='#index-prefix_002dmeta-_0028ESC_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Metafy the next character typed. This is for keyboards
without a meta key. Typing &lsquo;<samp>ESC f</samp>&rsquo; is equivalent to typing
<kbd>M-f</kbd>.

</dd>
<dt id='index-undo-_0028C_002d_005f-or-C_002dx-C_002du_0029'><code>undo (C-_ or C-x C-u)</code><a href='#index-undo-_0028C_002d_005f-or-C_002dx-C_002du_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Incremental undo, separately remembered for each line.

</dd>
<dt id='index-revert_002dline-_0028M_002dr_0029'><code>revert-line (M-r)</code><a href='#index-revert_002dline-_0028M_002dr_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Undo all changes made to this line. This is like executing the <code>undo</code>
command enough times to get back to the beginning.

</dd>
<dt id='index-tilde_002dexpand-_0028M_002d_0026_0029'><code>tilde-expand (M-&amp;)</code><a href='#index-tilde_002dexpand-_0028M_002d_0026_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Perform tilde expansion on the current word.

</dd>
<dt id='index-set_002dmark-_0028C_002d_0040_0029'><code>set-mark (C-@)</code><a href='#index-set_002dmark-_0028C_002d_0040_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Set the mark to the point. If a
numeric argument is supplied, the mark is set to that position.

</dd>
<dt id='index-exchange_002dpoint_002dand_002dmark-_0028C_002dx-C_002dx_0029'><code>exchange-point-and-mark (C-x C-x)</code><a href='#index-exchange_002dpoint_002dand_002dmark-_0028C_002dx-C_002dx_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Swap the point with the mark. The current cursor position is set to
the saved position, and the old cursor position is saved as the mark.

</dd>
<dt id='index-character_002dsearch-_0028C_002d_005d_0029'><code>character-search (C-])</code><a href='#index-character_002dsearch-_0028C_002d_005d_0029' class='copiable-anchor'> &para;</a></dt>
<dd>A character is read and point is moved to the next occurrence of that
character. A negative argument searches for previous occurrences.

</dd>
<dt id='index-character_002dsearch_002dbackward-_0028M_002dC_002d_005d_0029'><code>character-search-backward (M-C-])</code><a href='#index-character_002dsearch_002dbackward-_0028M_002dC_002d_005d_0029' class='copiable-anchor'> &para;</a></dt>
<dd>A character is read and point is moved to the previous occurrence
of that character. A negative argument searches for subsequent
occurrences.

</dd>
<dt id='index-skip_002dcsi_002dsequence-_0028_0029'><code>skip-csi-sequence ()</code><a href='#index-skip_002dcsi_002dsequence-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Read enough characters to consume a multi-key sequence such as those
defined for keys like Home and End. Such sequences begin with a
Control Sequence Indicator (CSI), usually ESC-[. If this sequence is
bound to &quot;\e[&quot;, keys producing such sequences will have no effect
unless explicitly bound to a Readline command, instead of inserting
stray characters into the editing buffer. This is unbound by default,
but usually bound to ESC-[.

</dd>
<dt id='index-insert_002dcomment-_0028M_002d_0023_0029'><code>insert-comment (M-#)</code><a href='#index-insert_002dcomment-_0028M_002d_0023_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Without a numeric argument, the value of the <code>comment-begin</code>
variable is inserted at the beginning of the current line.
If a numeric argument is supplied, this command acts as a toggle: if
the characters at the beginning of the line do not match the value
of <code>comment-begin</code>, the value is inserted, otherwise
the characters in <code>comment-begin</code> are deleted from the beginning of
the line.
In either case, the line is accepted as if a newline had been typed.
The default value of <code>comment-begin</code> causes this command
to make the current line a shell comment.
If a numeric argument causes the comment character to be removed, the line
will be executed by the shell.

</dd>
<dt id='index-dump_002dfunctions-_0028_0029'><code>dump-functions ()</code><a href='#index-dump_002dfunctions-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Print all of the functions and their key bindings to the
Readline output stream. If a numeric argument is supplied,
the output is formatted in such a way that it can be made part
of an <var>inputrc</var> file. This command is unbound by default.

</dd>
<dt id='index-dump_002dvariables-_0028_0029'><code>dump-variables ()</code><a href='#index-dump_002dvariables-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Print all of the settable variables and their values to the
Readline output stream. If a numeric argument is supplied,
the output is formatted in such a way that it can be made part
of an <var>inputrc</var> file. This command is unbound by default.

</dd>
<dt id='index-dump_002dmacros-_0028_0029'><code>dump-macros ()</code><a href='#index-dump_002dmacros-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Print all of the Readline key sequences bound to macros and the
strings they output. If a numeric argument is supplied,
the output is formatted in such a way that it can be made part
of an <var>inputrc</var> file. This command is unbound by default.

</dd>
<dt id='index-spell_002dcorrect_002dword-_0028C_002dx-s_0029'><code>spell-correct-word (C-x s)</code><a href='#index-spell_002dcorrect_002dword-_0028C_002dx-s_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Perform spelling correction on the current word, treating it as a directory
or filename, in the same way as the <code>cdspell</code> shell option.
Word boundaries are the same as those used by <code>shell-forward-word</code>.

</dd>
<dt id='index-glob_002dcomplete_002dword-_0028M_002dg_0029'><code>glob-complete-word (M-g)</code><a href='#index-glob_002dcomplete_002dword-_0028M_002dg_0029' class='copiable-anchor'> &para;</a></dt>
<dd>The word before point is treated as a pattern for pathname expansion,
with an asterisk implicitly appended. This pattern is used to
generate a list of matching file names for possible completions.

</dd>
<dt id='index-glob_002dexpand_002dword-_0028C_002dx-_002a_0029'><code>glob-expand-word (C-x *)</code><a href='#index-glob_002dexpand_002dword-_0028C_002dx-_002a_0029' class='copiable-anchor'> &para;</a></dt>
<dd>The word before point is treated as a pattern for pathname expansion,
and the list of matching file names is inserted, replacing the word.
If a numeric argument is supplied, a &lsquo;<samp>*</samp>&rsquo; is appended before
pathname expansion.

</dd>
<dt id='index-glob_002dlist_002dexpansions-_0028C_002dx-g_0029'><code>glob-list-expansions (C-x g)</code><a href='#index-glob_002dlist_002dexpansions-_0028C_002dx-g_0029' class='copiable-anchor'> &para;</a></dt>
<dd>The list of expansions that would have been generated by
<code>glob-expand-word</code> is displayed, and the line is redrawn.
If a numeric argument is supplied, a &lsquo;<samp>*</samp>&rsquo; is appended before
pathname expansion.

</dd>
<dt id='index-display_002dshell_002dversion-_0028C_002dx-C_002dv_0029'><code>display-shell-version (C-x C-v)</code><a href='#index-display_002dshell_002dversion-_0028C_002dx-C_002dv_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Display version information about the current instance of Bash.

</dd>
<dt id='index-shell_002dexpand_002dline-_0028M_002dC_002de_0029'><code>shell-expand-line (M-C-e)</code><a href='#index-shell_002dexpand_002dline-_0028M_002dC_002de_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Expand the line as the shell does.
This performs alias and history expansion as well as all of the shell
word expansions (see <a href="#Shell-Expansions">Shell Expansions</a>).

</dd>
<dt id='index-history_002dexpand_002dline-_0028M_002d_005e_0029'><code>history-expand-line (M-^)</code><a href='#index-history_002dexpand_002dline-_0028M_002d_005e_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Perform history expansion on the current line.

</dd>
<dt id='index-magic_002dspace-_0028_0029'><code>magic-space ()</code><a href='#index-magic_002dspace-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Perform history expansion on the current line and insert a space
(see <a href="#History-Interaction">History Expansion</a>).

</dd>
<dt id='index-alias_002dexpand_002dline-_0028_0029'><code>alias-expand-line ()</code><a href='#index-alias_002dexpand_002dline-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Perform alias expansion on the current line (see <a href="#Aliases">Aliases</a>).

</dd>
<dt id='index-history_002dand_002dalias_002dexpand_002dline-_0028_0029'><code>history-and-alias-expand-line ()</code><a href='#index-history_002dand_002dalias_002dexpand_002dline-_0028_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Perform history and alias expansion on the current line.

</dd>
<dt id='index-insert_002dlast_002dargument-_0028M_002d_002e-or-M_002d_005f_0029'><code>insert-last-argument (M-. or M-_)</code><a href='#index-insert_002dlast_002dargument-_0028M_002d_002e-or-M_002d_005f_0029' class='copiable-anchor'> &para;</a></dt>
<dd>A synonym for <code>yank-last-arg</code>.

</dd>
<dt id='index-edit_002dand_002dexecute_002dcommand-_0028C_002dx-C_002de_0029'><code>edit-and-execute-command (C-x C-e)</code><a href='#index-edit_002dand_002dexecute_002dcommand-_0028C_002dx-C_002de_0029' class='copiable-anchor'> &para;</a></dt>
<dd>Invoke an editor on the current command line, and execute the result as shell
commands.
Bash attempts to invoke
<code>$VISUAL</code>, <code>$EDITOR</code>, and <code>emacs</code>
as the editor, in that order.

</dd>
</dl>

<hr>
</div>
</div>
<div class="section" id="Readline-vi-Mode">
<div class="header">

Next: <a href="#Programmable-Completion" accesskey="n" rel="next">Programmable Completion</a>, Previous: <a href="#Bindable-Readline-Commands" accesskey="p" rel="prev">Bindable Readline Commands</a>, Up: <a href="#Command-Line-Editing" accesskey="u" rel="up">Command Line Editing</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">8.5 Readline vi Mode</h3>

While the Readline library does not have a full set of <code>vi</code>
editing functions, it does contain enough to allow simple editing
of the line. The Readline <code>vi</code> mode behaves as specified in
the POSIX standard.

In order to switch interactively between <code>emacs</code> and <code>vi</code>
editing modes, use the &lsquo;<samp>set -o emacs</samp>&rsquo; and &lsquo;<samp>set -o vi</samp>&rsquo;
commands (see <a href="#The-Set-Builtin">The Set Builtin</a>).
The Readline default is <code>emacs</code> mode.

When you enter a line in <code>vi</code> mode, you are already placed in
&lsquo;insertion&rsquo; mode, as if you had typed an &lsquo;<samp>i</samp>&rsquo;. Pressing <tt class="key">ESC</tt>
switches you into &lsquo;command&rsquo; mode, where you can edit the text of the
line with the standard <code>vi</code> movement keys, move to previous
history lines with &lsquo;<samp>k</samp>&rsquo; and subsequent lines with &lsquo;<samp>j</samp>&rsquo;, and
so forth.

<hr>
</div>
<div class="section" id="Programmable-Completion">
<div class="header">

Next: <a href="#Programmable-Completion-Builtins" accesskey="n" rel="next">Programmable Completion Builtins</a>, Previous: <a href="#Readline-vi-Mode" accesskey="p" rel="prev">Readline vi Mode</a>, Up: <a href="#Command-Line-Editing" accesskey="u" rel="up">Command Line Editing</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">8.6 Programmable Completion</h3>

When word completion is attempted for an argument to a command for
which a completion specification (a <var>compspec</var>) has been defined
using the <code>complete</code> builtin (see <a href="#Programmable-Completion-Builtins">Programmable Completion Builtins</a>),
the programmable completion facilities are invoked. 

First, the command name is identified.
If a compspec has been defined for that command, the
compspec is used to generate the list of possible completions for the word.
If the command word is the empty string (completion attempted at the
beginning of an empty line), any compspec defined with
the <samp>-E</samp> option to <code>complete</code> is used.
If the command word is a full pathname, a compspec for the full
pathname is searched for first.
If no compspec is found for the full pathname, an attempt is made to
find a compspec for the portion following the final slash.
If those searches do not result in a compspec, any compspec defined with
the <samp>-D</samp> option to <code>complete</code> is used as the default.
If there is no default compspec, Bash attempts alias expansion
on the command word as a final resort, and attempts to find a compspec
for the command word from any successful expansion 

Once a compspec has been found, it is used to generate the list of
matching words.
If a compspec is not found, the default Bash completion
described above (see <a href="#Commands-For-Completion">Letting Readline Type For You</a>) is performed.

First, the actions specified by the compspec are used.
Only matches which are prefixed by the word being completed are
returned.
When the <samp>-f</samp> or <samp>-d</samp> option is used for filename or
directory name completion, the shell variable <code>FIGNORE</code> is
used to filter the matches.
See <a href="#Bash-Variables">Bash Variables</a>, for a description of <code>FIGNORE</code>.

Any completions specified by a filename expansion pattern to the
<samp>-G</samp> option are generated next.
The words generated by the pattern need not match the word being completed.
The <code>GLOBIGNORE</code> shell variable is not used to filter the matches,
but the <code>FIGNORE</code> shell variable is used.

Next, the string specified as the argument to the <samp>-W</samp> option
is considered.
The string is first split using the characters in the <code>IFS</code>
special variable as delimiters.
Shell quoting is honored within the string, in order to provide a
mechanism for the words to contain shell metacharacters or characters
in the value of <code>IFS</code>.
Each word is then expanded using
brace expansion, tilde expansion, parameter and variable expansion,
command substitution, and arithmetic expansion,
as described above (see <a href="#Shell-Expansions">Shell Expansions</a>).
The results are split using the rules described above
(see <a href="#Word-Splitting">Word Splitting</a>).
The results of the expansion are prefix-matched against the word being
completed, and the matching words become the possible completions.

After these matches have been generated, any shell function or command
specified with the <samp>-F</samp> and <samp>-C</samp> options is invoked.
When the command or function is invoked, the <code>COMP_LINE</code>,
<code>COMP_POINT</code>, <code>COMP_KEY</code>, and <code>COMP_TYPE</code> variables are
assigned values as described above (see <a href="#Bash-Variables">Bash Variables</a>).
If a shell function is being invoked, the <code>COMP_WORDS</code> and
<code>COMP_CWORD</code> variables are also set.
When the function or command is invoked, the first argument ($1) is the
name of the command whose arguments are being completed, the
second argument ($2) is the word being completed, and the third argument
($3) is the word preceding the word being completed on the current command
line.
No filtering of the generated completions against the word being completed
is performed; the function or command has complete freedom in generating
the matches.

Any function specified with <samp>-F</samp> is invoked first.
The function may use any of the shell facilities, including the
<code>compgen</code> and <code>compopt</code> builtins described below
(see <a href="#Programmable-Completion-Builtins">Programmable Completion Builtins</a>), to generate the matches.
It must put the possible completions in the <code>COMPREPLY</code> array
variable, one per array element.

Next, any command specified with the <samp>-C</samp> option is invoked
in an environment equivalent to command substitution.
It should print a list of completions, one per line, to
the standard output.
Backslash may be used to escape a newline, if necessary.

After all of the possible completions are generated, any filter
specified with the <samp>-X</samp> option is applied to the list.
The filter is a pattern as used for pathname expansion; a &lsquo;<samp>&amp;</samp>&rsquo;
in the pattern is replaced with the text of the word being completed.
A literal &lsquo;<samp>&amp;</samp>&rsquo; may be escaped with a backslash; the backslash
is removed before attempting a match.
Any completion that matches the pattern will be removed from the list.
A leading &lsquo;<samp>!</samp>&rsquo; negates the pattern; in this case any completion
not matching the pattern will be removed.
If the <code>nocasematch</code> shell option
(see the description of <code>shopt</code> in <a href="#The-Shopt-Builtin">The Shopt Builtin</a>)
is enabled, the match is performed without regard to the case
of alphabetic characters.

Finally, any prefix and suffix specified with the <samp>-P</samp> and <samp>-S</samp>
options are added to each member of the completion list, and the result is
returned to the Readline completion code as the list of possible
completions.

If the previously-applied actions do not generate any matches, and the
<samp>-o dirnames</samp> option was supplied to <code>complete</code> when the
compspec was defined, directory name completion is attempted. 

If the <samp>-o plusdirs</samp> option was supplied to <code>complete</code> when
the compspec was defined, directory name completion is attempted and any
matches are added to the results of the other actions.

By default, if a compspec is found, whatever it generates is returned to
the completion code as the full set of possible completions.
The default Bash completions are not attempted, and the Readline default
of filename completion is disabled.
If the <samp>-o bashdefault</samp> option was supplied to <code>complete</code> when
the compspec was defined, the default Bash completions are attempted
if the compspec generates no matches.
If the <samp>-o default</samp> option was supplied to <code>complete</code> when the
compspec was defined, Readline&rsquo;s default completion will be performed
if the compspec (and, if attempted, the default Bash completions)
generate no matches.

When a compspec indicates that directory name completion is desired,
the programmable completion functions force Readline to append a slash
to completed names which are symbolic links to directories, subject to
the value of the <var>mark-directories</var> Readline variable, regardless
of the setting of the <var>mark-symlinked-directories</var> Readline variable.

There is some support for dynamically modifying completions. This is
most useful when used in combination with a default completion specified
with <samp>-D</samp>. It&rsquo;s possible for shell functions executed as completion
handlers to indicate that completion should be retried by returning an
exit status of 124. If a shell function returns 124, and changes
the compspec associated with the command on which completion is being
attempted (supplied as the first argument when the function is executed),
programmable completion restarts from the beginning, with an
attempt to find a new compspec for that command. This allows a set of
completions to be built dynamically as completion is attempted, rather than
being loaded all at once.

For instance, assuming that there is a library of compspecs, each kept in a
file corresponding to the name of the command, the following default
completion function would load completions dynamically:

<div class="example">
<pre class="example">_completion_loader()
{
 . &quot;/etc/bash_completion.d/$1.sh&quot; &gt;/dev/null 2&gt;&amp;1 &amp;&amp; return 124
}
complete -D -F _completion_loader -o bashdefault -o default
</pre></div>

<hr>
</div>
<div class="section" id="Programmable-Completion-Builtins">
<div class="header">

Next: <a href="#A-Programmable-Completion-Example" accesskey="n" rel="next">A Programmable Completion Example</a>, Previous: <a href="#Programmable-Completion" accesskey="p" rel="prev">Programmable Completion</a>, Up: <a href="#Command-Line-Editing" accesskey="u" rel="up">Command Line Editing</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">8.7 Programmable Completion Builtins</h3>

Three builtin commands are available to manipulate the programmable completion
facilities: one to specify how the arguments to a particular command are to
be completed, and two to modify the completion as it is happening.

<dl compact="compact">
<dt id='index-compgen'><code>compgen</code><a href='#index-compgen' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example"><code>compgen [<var>option</var>] [<var>word</var>]</code>
</pre></div>

Generate possible completion matches for <var>word</var> according to
the <var>option</var>s, which may be any option accepted by the
<code>complete</code>
builtin with the exception of <samp>-p</samp> and <samp>-r</samp>, and write
the matches to the standard output.
When using the <samp>-F</samp> or <samp>-C</samp> options, the various shell variables
set by the programmable completion facilities, while available, will not
have useful values.

The matches will be generated in the same way as if the programmable
completion code had generated them directly from a completion specification
with the same flags.
If <var>word</var> is specified, only those completions matching <var>word</var>
will be displayed.

The return value is true unless an invalid option is supplied, or no
matches were generated.

</dd>
<dt id='index-complete'><code>complete</code><a href='#index-complete' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example"><code>complete [-abcdefgjksuv] [-o <var>comp-option</var>] [-DEI] [-A <var>action</var>] [-G <var>globpat</var>]
[-W <var>wordlist</var>] [-F <var>function</var>] [-C <var>command</var>] [-X <var>filterpat</var>]
[-P <var>prefix</var>] [-S <var>suffix</var>] <var>name</var> [<var>name</var> &hellip;]</code>
<code>complete -pr [-DEI] [<var>name</var> &hellip;]</code>
</pre></div>

Specify how arguments to each <var>name</var> should be completed.
If the <samp>-p</samp> option is supplied, or if no options are supplied, existing
completion specifications are printed in a way that allows them to be
reused as input.
The <samp>-r</samp> option removes a completion specification for
each <var>name</var>, or, if no <var>name</var>s are supplied, all
completion specifications.
The <samp>-D</samp> option indicates that other supplied options and actions should
apply to the &ldquo;default&rdquo; command completion; that is, completion attempted
on a command for which no completion has previously been defined.
The <samp>-E</samp> option indicates that other supplied options and actions should
apply to &ldquo;empty&rdquo; command completion; that is, completion attempted on a 
blank line.
The <samp>-I</samp> option indicates that other supplied options and actions should
apply to completion on the initial non-assignment word on the line, or after a
command delimiter such as &lsquo;<samp>;</samp>&rsquo; or &lsquo;<samp>|</samp>&rsquo;, which is usually command
name completion.
If multiple options are supplied, the <samp>-D</samp> option takes precedence
over <samp>-E</samp>, and both take precedence over <samp>-I</samp>.
If any of <samp>-D</samp>, <samp>-E</samp>, or <samp>-I</samp> are supplied, any other
<var>name</var> arguments are ignored; these completions only apply to the case
specified by the option.

The process of applying these completion specifications when word completion
is attempted is described above (see <a href="#Programmable-Completion">Programmable Completion</a>).

Other options, if specified, have the following meanings.
The arguments to the <samp>-G</samp>, <samp>-W</samp>, and <samp>-X</samp> options
(and, if necessary, the <samp>-P</samp> and <samp>-S</samp> options)
should be quoted to protect them from expansion before the
<code>complete</code> builtin is invoked.

<dl compact="compact">
<dt><code>-o <var>comp-option</var></code></dt>
<dd>The <var>comp-option</var> controls several aspects of the compspec&rsquo;s behavior
beyond the simple generation of completions.
<var>comp-option</var> may be one of: 

<dl compact="compact">
<dt><code>bashdefault</code></dt>
<dd>Perform the rest of the default Bash completions if the compspec
generates no matches.

</dd>
<dt><code>default</code></dt>
<dd>Use Readline&rsquo;s default filename completion if the compspec generates
no matches.

</dd>
<dt><code>dirnames</code></dt>
<dd>Perform directory name completion if the compspec generates no matches.

</dd>
<dt><code>filenames</code></dt>
<dd>Tell Readline that the compspec generates filenames, so it can perform any
filename-specific processing (like adding a slash to directory names,
quoting special characters, or suppressing trailing spaces).
This option is intended to be used with shell functions specified
with <samp>-F</samp>.

</dd>
<dt><code>noquote</code></dt>
<dd>Tell Readline not to quote the completed words if they are filenames
(quoting filenames is the default).

</dd>
<dt><code>nosort</code></dt>
<dd>Tell Readline not to sort the list of possible completions alphabetically.

</dd>
<dt><code>nospace</code></dt>
<dd>Tell Readline not to append a space (the default) to words completed at
the end of the line.

</dd>
<dt><code>plusdirs</code></dt>
<dd>After any matches defined by the compspec are generated, 
directory name completion is attempted and any
matches are added to the results of the other actions.

</dd>
</dl>

</dd>
<dt><code>-A <var>action</var></code></dt>
<dd>The <var>action</var> may be one of the following to generate a list of possible
completions:

<dl compact="compact">
<dt><code>alias</code></dt>
<dd>Alias names. May also be specified as <samp>-a</samp>.

</dd>
<dt><code>arrayvar</code></dt>
<dd>Array variable names.

</dd>
<dt><code>binding</code></dt>
<dd>Readline key binding names (see <a href="#Bindable-Readline-Commands">Bindable Readline Commands</a>).

</dd>
<dt><code>builtin</code></dt>
<dd>Names of shell builtin commands. May also be specified as <samp>-b</samp>.

</dd>
<dt><code>command</code></dt>
<dd>Command names. May also be specified as <samp>-c</samp>.

</dd>
<dt><code>directory</code></dt>
<dd>Directory names. May also be specified as <samp>-d</samp>.

</dd>
<dt><code>disabled</code></dt>
<dd>Names of disabled shell builtins.

</dd>
<dt><code>enabled</code></dt>
<dd>Names of enabled shell builtins.

</dd>
<dt><code>export</code></dt>
<dd>Names of exported shell variables. May also be specified as <samp>-e</samp>.

</dd>
<dt><code>file</code></dt>
<dd>File names. May also be specified as <samp>-f</samp>.

</dd>
<dt><code>function</code></dt>
<dd>Names of shell functions.

</dd>
<dt><code>group</code></dt>
<dd>Group names. May also be specified as <samp>-g</samp>.

</dd>
<dt><code>helptopic</code></dt>
<dd>Help topics as accepted by the <code>help</code> builtin (see <a href="#Bash-Builtins">Bash Builtin Commands</a>).

</dd>
<dt><code>hostname</code></dt>
<dd>Hostnames, as taken from the file specified by the
<code>HOSTFILE</code> shell variable (see <a href="#Bash-Variables">Bash Variables</a>).

</dd>
<dt><code>job</code></dt>
<dd>Job names, if job control is active. May also be specified as <samp>-j</samp>.

</dd>
<dt><code>keyword</code></dt>
<dd>Shell reserved words. May also be specified as <samp>-k</samp>.

</dd>
<dt><code>running</code></dt>
<dd>Names of running jobs, if job control is active.

</dd>
<dt><code>service</code></dt>
<dd>Service names. May also be specified as <samp>-s</samp>.

</dd>
<dt><code>setopt</code></dt>
<dd>Valid arguments for the <samp>-o</samp> option to the <code>set</code> builtin
(see <a href="#The-Set-Builtin">The Set Builtin</a>).

</dd>
<dt><code>shopt</code></dt>
<dd>Shell option names as accepted by the <code>shopt</code> builtin
(see <a href="#Bash-Builtins">Bash Builtin Commands</a>).

</dd>
<dt><code>signal</code></dt>
<dd>Signal names.

</dd>
<dt><code>stopped</code></dt>
<dd>Names of stopped jobs, if job control is active.

</dd>
<dt><code>user</code></dt>
<dd>User names. May also be specified as <samp>-u</samp>.

</dd>
<dt><code>variable</code></dt>
<dd>Names of all shell variables. May also be specified as <samp>-v</samp>.
</dd>
</dl>

</dd>
<dt><code>-C <var>command</var></code></dt>
<dd><var>command</var> is executed in a subshell environment, and its output is
used as the possible completions.
Arguments are passed as with the <samp>-F</samp> option.

</dd>
<dt><code>-F <var>function</var></code></dt>
<dd>The shell function <var>function</var> is executed in the current shell
environment.
When it is executed, $1 is the name of the command whose arguments are
being completed, $2 is the word being completed, and $3 is the word
preceding the word being completed, as described above
(see <a href="#Programmable-Completion">Programmable Completion</a>).
When it finishes, the possible completions are retrieved from the value
of the <code>COMPREPLY</code> array variable.

</dd>
<dt><code>-G <var>globpat</var></code></dt>
<dd>The filename expansion pattern <var>globpat</var> is expanded to generate
the possible completions.

</dd>
<dt><code>-P <var>prefix</var></code></dt>
<dd><var>prefix</var> is added at the beginning of each possible completion
after all other options have been applied.

</dd>
<dt><code>-S <var>suffix</var></code></dt>
<dd><var>suffix</var> is appended to each possible completion
after all other options have been applied.

</dd>
<dt><code>-W <var>wordlist</var></code></dt>
<dd>The <var>wordlist</var> is split using the characters in the
<code>IFS</code> special variable as delimiters, and each resultant word
is expanded.
The possible completions are the members of the resultant list which
match the word being completed.

</dd>
<dt><code>-X <var>filterpat</var></code></dt>
<dd><var>filterpat</var> is a pattern as used for filename expansion.
It is applied to the list of possible completions generated by the
preceding options and arguments, and each completion matching
<var>filterpat</var> is removed from the list.
A leading &lsquo;<samp>!</samp>&rsquo; in <var>filterpat</var> negates the pattern; in this
case, any completion not matching <var>filterpat</var> is removed.
</dd>
</dl>

The return value is true unless an invalid option is supplied, an option
other than <samp>-p</samp> or <samp>-r</samp> is supplied without a <var>name</var>
argument, an attempt is made to remove a completion specification for
a <var>name</var> for which no specification exists, or
an error occurs adding a completion specification.

</dd>
<dt id='index-compopt'><code>compopt</code><a href='#index-compopt' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example"><code>compopt</code> [-o <var>option</var>] [-DEI] [+o <var>option</var>] [<var>name</var>]
</pre></div>
Modify completion options for each <var>name</var> according to the
<var>option</var>s, or for the currently-executing completion if no <var>name</var>s
are supplied.
If no <var>option</var>s are given, display the completion options for each
<var>name</var> or the current completion.
The possible values of <var>option</var> are those valid for the <code>complete</code>
builtin described above.
The <samp>-D</samp> option indicates that other supplied options should
apply to the &ldquo;default&rdquo; command completion; that is, completion attempted
on a command for which no completion has previously been defined.
The <samp>-E</samp> option indicates that other supplied options should
apply to &ldquo;empty&rdquo; command completion; that is, completion attempted on a 
blank line.
The <samp>-I</samp> option indicates that other supplied options should
apply to completion on the initial non-assignment word on the line, or after a
command delimiter such as &lsquo;<samp>;</samp>&rsquo; or &lsquo;<samp>|</samp>&rsquo;, which is usually command
name completion.

If multiple options are supplied, the <samp>-D</samp> option takes precedence
over <samp>-E</samp>, and both take precedence over <samp>-I</samp>

The return value is true unless an invalid option is supplied, an attempt
is made to modify the options for a <var>name</var> for which no completion
specification exists, or an output error occurs.

</dd>
</dl>

<hr>
</div>
<div class="section" id="A-Programmable-Completion-Example">
<div class="header">

Previous: <a href="#Programmable-Completion-Builtins" accesskey="p" rel="prev">Programmable Completion Builtins</a>, Up: <a href="#Command-Line-Editing" accesskey="u" rel="up">Command Line Editing</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">8.8 A Programmable Completion Example</h3>

The most common way to obtain additional completion functionality beyond
the default actions <code>complete</code> and <code>compgen</code> provide is to use
a shell function and bind it to a particular command using <code>complete -F</code>.

The following function provides completions for the <code>cd</code> builtin.
It is a reasonably good example of what shell functions must do when
used for completion. This function uses the word passed as <code>$2</code>
to determine the directory name to complete. You can also use the
<code>COMP_WORDS</code> array variable; the current word is indexed by the
<code>COMP_CWORD</code> variable.

The function relies on the <code>complete</code> and <code>compgen</code> builtins
to do much of the work, adding only the things that the Bash <code>cd</code>
does beyond accepting basic directory names:
tilde expansion (see <a href="#Tilde-Expansion">Tilde Expansion</a>),
searching directories in <var>$CDPATH</var>, which is described above
(see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>),
and basic support for the <code>cdable_vars</code> shell option
(see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>).
<code>_comp_cd</code> modifies the value of <var>IFS</var> so that it contains only
a newline to accommodate file names containing spaces and tabs &ndash;
<code>compgen</code> prints the possible completions it generates one per line.

Possible completions go into the <var>COMPREPLY</var> array variable, one
completion per array element. The programmable completion system retrieves
the completions from there when the function returns.

<div class="example">
<pre class="example"># A completion function for the cd builtin
# based on the cd completion function from the bash_completion package
_comp_cd()
{
 local IFS=$' \t\n' # normalize IFS
 local cur _skipdot _cdpath
 local i j k

# Tilde expansion, which also expands tilde to full pathname
    case &quot;$2&quot; in
    \~*)    eval cur=&quot;$2&quot; ;;
    *)      cur=$2 ;;
    esac

# no cdpath or absolute pathname -- straight directory completion
    if [[ -z &quot;${CDPATH:-}&quot; ]] || [[ &quot;$cur&quot; == @(./*|../*|/*) ]]; then
        # compgen prints paths one per line; could also use while loop
        IFS=$'\n'
        COMPREPLY=( $(compgen -d -- &quot;$cur&quot;) )
        IFS=$' \t\n'
    # CDPATH+directories in the current directory if not in CDPATH
    else
        IFS=$'\n'
        _skipdot=false
        # preprocess CDPATH to convert null directory names to .
        _cdpath=${CDPATH/#:/.:}
        _cdpath=${_cdpath//::/:.:}
        _cdpath=${_cdpath/%:/:.}
        for i in ${_cdpath//:/$'\n'}; do
            if [[ $i -ef . ]]; then _skipdot=true; fi
            k=&quot;${#COMPREPLY[@]}&quot;
            for j in $( compgen -d -- &quot;$i/$cur&quot; ); do
                COMPREPLY[k++]=${j#$i/}        # cut off directory
            done
        done
        $_skipdot || COMPREPLY+=( $(compgen -d -- &quot;$cur&quot;) )
        IFS=$' \t\n'
    fi

# variable names if appropriate shell option set and no completions
    if shopt -q cdable_vars &amp;&amp; [[ ${#COMPREPLY[@]} -eq 0 ]]; then
        COMPREPLY=( $(compgen -v -- &quot;$cur&quot;) )
    fi

return 0
}
</pre></div>

We install the completion function using the <samp>-F</samp> option to
<code>complete</code>:

<div class="example">
<pre class="example"># Tell readline to quote appropriate and append slashes to directories;
# use the bash default completion for other arguments
complete -o filenames -o nospace -o bashdefault -F _comp_cd cd
</pre></div>

Since we&rsquo;d like Bash and Readline to take care of some
of the other details for us, we use several other options to tell Bash
and Readline what to do. The <samp>-o filenames</samp> option tells Readline
that the possible completions should be treated as filenames, and quoted
appropriately. That option will also cause Readline to append a slash to
filenames it can determine are directories (which is why we might want to
extend <code>_comp_cd</code> to append a slash if we&rsquo;re using directories found
via <var>CDPATH</var>: Readline can&rsquo;t tell those completions are directories).
The <samp>-o nospace</samp> option tells Readline to not append a space
character to the directory name, in case we want to append to it.
The <samp>-o bashdefault</samp> option brings in the rest of the &quot;Bash default&quot;
completions &ndash; possible completions that Bash adds to the default Readline
set. These include things like command name completion, variable completion
for words beginning with &lsquo;<samp>$</samp>&rsquo; or &lsquo;<samp>${</samp>&rsquo;, completions containing pathname
expansion patterns (see <a href="#Filename-Expansion">Filename Expansion</a>), and so on.

Once installed using <code>complete</code>, <code>_comp_cd</code> will be called every
time we attempt word completion for a <code>cd</code> command.

Many more examples &ndash; an extensive collection of completions for most of
the common GNU, Unix, and Linux commands &ndash; are available as part of the
bash_completion project. This is installed by default on many GNU/Linux
distributions. Originally written by Ian Macdonald, the project now lives
at <a href="https://github.com/scop/bash-completion/">https://github.com/scop/bash-completion/</a>. There are ports for
other systems such as Solaris and Mac OS X.

An older version of the bash_completion package is distributed with bash
in the <samp>examples/complete</samp> subdirectory.

<hr>
</div>
</div>
<div class="chapter" id="Using-History-Interactively">
<div class="header">

Next: <a href="#Installing-Bash" accesskey="n" rel="next">Installing Bash</a>, Previous: <a href="#Command-Line-Editing" accesskey="p" rel="prev">Command Line Editing</a>, Up: <a href="#Top" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h2 class="chapter">9 Using History Interactively</h2>

This chapter describes how to use the GNU History Library
interactively, from a user&rsquo;s standpoint.
It should be considered a user&rsquo;s guide.
For information on using the GNU History Library in other programs,
see the GNU Readline Library Manual.

<ul class="section-toc">
<li><a href="#Bash-History-Facilities" accesskey="1">Bash History Facilities</a></li>
<li><a href="#Bash-History-Builtins" accesskey="2">Bash History Builtins</a></li>
<li><a href="#History-Interaction" accesskey="3">History Expansion</a></li>
</ul>
<hr>
<div class="section" id="Bash-History-Facilities">
<div class="header">

Next: <a href="#Bash-History-Builtins" accesskey="n" rel="next">Bash History Builtins</a>, Up: <a href="#Using-History-Interactively" accesskey="u" rel="up">Using History Interactively</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">9.1 Bash History Facilities</h3>

When the <samp>-o history</samp> option to the <code>set</code> builtin
is enabled (see <a href="#The-Set-Builtin">The Set Builtin</a>),
the shell provides access to the command history,
the list of commands previously typed.
The value of the <code>HISTSIZE</code> shell variable is used as the
number of commands to save in a history list.
The text of the last <code>$HISTSIZE</code>
commands (default 500) is saved.
The shell stores each command in the history list prior to
parameter and variable expansion
but after history expansion is performed, subject to the
values of the shell variables
<code>HISTIGNORE</code> and <code>HISTCONTROL</code>.

When the shell starts up, the history is initialized from the
file named by the <code>HISTFILE</code> variable (default <samp>~/.bash_history</samp>).
The file named by the value of <code>HISTFILE</code> is truncated, if
necessary, to contain no more than the number of lines specified by
the value of the <code>HISTFILESIZE</code> variable.
When a shell with history enabled exits, the last
<code>$HISTSIZE</code> lines are copied from the history list to the file
named by <code>$HISTFILE</code>.
If the <code>histappend</code> shell option is set (see <a href="#Bash-Builtins">Bash Builtin Commands</a>),
the lines are appended to the history file,
otherwise the history file is overwritten.
If <code>HISTFILE</code>
is unset, or if the history file is unwritable, the history is not saved.
After saving the history, the history file is truncated
to contain no more than <code>$HISTFILESIZE</code> lines.
If <code>HISTFILESIZE</code> is unset, or set to null, a non-numeric value, or
a numeric value less than zero, the history file is not truncated.

If the <code>HISTTIMEFORMAT</code> is set, the time stamp information
associated with each history entry is written to the history file,
marked with the history comment character.
When the history file is read, lines beginning with the history
comment character followed immediately by a digit are interpreted
as timestamps for the following history entry.

The builtin command <code>fc</code> may be used to list or edit and re-execute
a portion of the history list.
The <code>history</code> builtin may be used to display or modify the history
list and manipulate the history file.
When using command-line editing, search commands
are available in each editing mode that provide access to the
history list (see <a href="#Commands-For-History">Commands For Manipulating The History</a>).

The shell allows control over which commands are saved on the history
list. The <code>HISTCONTROL</code> and <code>HISTIGNORE</code>
variables may be set to cause the shell to save only a subset of the
commands entered.
The <code>cmdhist</code>
shell option, if enabled, causes the shell to attempt to save each
line of a multi-line command in the same history entry, adding
semicolons where necessary to preserve syntactic correctness.
The <code>lithist</code>
shell option causes the shell to save the command with embedded newlines
instead of semicolons.
The <code>shopt</code> builtin is used to set these options.
See <a href="#The-Shopt-Builtin">The Shopt Builtin</a>, for a description of <code>shopt</code>.

<hr>
</div>
<div class="section" id="Bash-History-Builtins">
<div class="header">

Next: <a href="#History-Interaction" accesskey="n" rel="next">History Expansion</a>, Previous: <a href="#Bash-History-Facilities" accesskey="p" rel="prev">Bash History Facilities</a>, Up: <a href="#Using-History-Interactively" accesskey="u" rel="up">Using History Interactively</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">9.2 Bash History Builtins</h3>

Bash provides two builtin commands which manipulate the
history list and history file.

<dl compact="compact">
<dt id='index-fc'><code>fc</code><a href='#index-fc' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example"><code>fc [-e <var>ename</var>] [-lnr] [<var>first</var>] [<var>last</var>]</code>
<code>fc -s [<var>pat</var>=<var>rep</var>] [<var>command</var>]</code>
</pre></div>

The first form selects a range of commands from <var>first</var> to
<var>last</var> from the history list and displays or edits and re-executes
them.
Both <var>first</var> and
<var>last</var> may be specified as a string (to locate the most recent
command beginning with that string) or as a number (an index into the
history list, where a negative number is used as an offset from the
current command number).

When listing, a <var>first</var> or <var>last</var> of 0 is equivalent to -1
and -0 is equivalent to the current command (usually the <code>fc</code>
command);
otherwise 0 is equivalent to -1 and -0 is invalid.

If <var>last</var> is not specified, it is set to
<var>first</var>. If <var>first</var> is not specified, it is set to the previous
command for editing and -16 for listing. If the <samp>-l</samp> flag is
given, the commands are listed on standard output. The <samp>-n</samp> flag
suppresses the command numbers when listing. The <samp>-r</samp> flag
reverses the order of the listing. Otherwise, the editor given by
<var>ename</var> is invoked on a file containing those commands. If
<var>ename</var> is not given, the value of the following variable expansion
is used: <code>${FCEDIT:-${EDITOR:-vi}}</code>. This says to use the
value of the <code>FCEDIT</code> variable if set, or the value of the
<code>EDITOR</code> variable if that is set, or <code>vi</code> if neither is set.
When editing is complete, the edited commands are echoed and executed.

In the second form, <var>command</var> is re-executed after each instance
of <var>pat</var> in the selected command is replaced by <var>rep</var>.
<var>command</var> is interpreted the same as <var>first</var> above.

A useful alias to use with the <code>fc</code> command is <code>r='fc -s'</code>, so
that typing &lsquo;<samp>r cc</samp>&rsquo; runs the last command beginning with <code>cc</code>
and typing &lsquo;<samp>r</samp>&rsquo; re-executes the last command (see <a href="#Aliases">Aliases</a>).

</dd>
<dt id='index-history'><code>history</code><a href='#index-history' class='copiable-anchor'> &para;</a></dt>
<dd><div class="example">
<pre class="example">history [<var>n</var>]
history -c
history -d <var>offset</var>
history -d <var>start</var>-<var>end</var>
history [-anrw] [<var>filename</var>]
history -ps <var>arg</var>
</pre></div>

With no options, display the history list with line numbers.
Lines prefixed with a &lsquo;<samp>*</samp>&rsquo; have been modified.
An argument of <var>n</var> lists only the last <var>n</var> lines.
If the shell variable <code>HISTTIMEFORMAT</code> is set and not null,
it is used as a format string for <var>strftime</var> to display
the time stamp associated with each displayed history entry.
No intervening blank is printed between the formatted time stamp
and the history line.

Options, if supplied, have the following meanings:

<dl compact="compact">
<dt><code>-c</code></dt>
<dd>Clear the history list. This may be combined
with the other options to replace the history list completely.

</dd>
<dt><code>-d <var>offset</var></code></dt>
<dd>Delete the history entry at position <var>offset</var>.
If <var>offset</var> is positive, it should be specified as it appears when
the history is displayed.
If <var>offset</var> is negative, it is interpreted as relative to one greater
than the last history position, so negative indices count back from the
end of the history, and an index of &lsquo;<samp>-1</samp>&rsquo; refers to the current
<code>history -d</code> command.

</dd>
<dt><code>-d <var>start</var>-<var>end</var></code></dt>
<dd>Delete the range of history entries between positions <var>start</var> and
<var>end</var>, inclusive.
Positive and negative values for <var>start</var> and <var>end</var>
are interpreted as described above.

</dd>
<dt><code>-a</code></dt>
<dd>Append the new history lines to the history file.
These are history lines entered since the beginning of the current
Bash session, but not already appended to the history file.

</dd>
<dt><code>-n</code></dt>
<dd>Append the history lines not already read from the history file
to the current history list. These are lines appended to the history
file since the beginning of the current Bash session.

</dd>
<dt><code>-r</code></dt>
<dd>Read the history file and append its contents to
the history list.

</dd>
<dt><code>-w</code></dt>
<dd>Write out the current history list to the history file.

</dd>
<dt><code>-p</code></dt>
<dd>Perform history substitution on the <var>arg</var>s and display the result
on the standard output, without storing the results in the history list.

</dd>
<dt><code>-s</code></dt>
<dd>The <var>arg</var>s are added to the end of
the history list as a single entry.

</dd>
</dl>

If a <var>filename</var> argument is supplied
when any of the <samp>-w</samp>, <samp>-r</samp>, <samp>-a</samp>, or <samp>-n</samp> options
is used, Bash uses <var>filename</var> as the history file.
If not, then the value of the <code>HISTFILE</code> variable is used.

The return value is 0 unless an invalid option is encountered, an
error occurs while reading or writing the history file, an invalid
<var>offset</var> or range is supplied as an argument to <samp>-d</samp>, or the
history expansion supplied as an argument to <samp>-p</samp> fails.

</dd>
</dl>

<hr>
</div>
<div class="section" id="History-Interaction">
<div class="header">

Previous: <a href="#Bash-History-Builtins" accesskey="p" rel="prev">Bash History Builtins</a>, Up: <a href="#Using-History-Interactively" accesskey="u" rel="up">Using History Interactively</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">9.3 History Expansion</h3>

The History library provides a history expansion feature that is similar
to the history expansion provided by <code>csh</code>. This section
describes the syntax used to manipulate the history information.

History expansions introduce words from the history list into
the input stream, making it easy to repeat commands, insert the
arguments to a previous command into the current input line, or
fix errors in previous commands quickly.

History expansion is performed immediately after a complete line
is read, before the shell breaks it into words, and is performed
on each line individually. Bash attempts to inform the history
expansion functions about quoting still in effect from previous lines.

History expansion takes place in two parts. The first is to determine
which line from the history list should be used during substitution.
The second is to select portions of that line for inclusion into the
current one. The line selected from the history is called the
event, and the portions of that line that are acted upon are
called words. Various modifiers are available to manipulate
the selected words. The line is broken into words in the same fashion
that Bash does, so that several words
surrounded by quotes are considered one word.
History expansions are introduced by the appearance of the
history expansion character, which is &lsquo;<samp>!</samp>&rsquo; by default.

History expansion implements shell-like quoting conventions:
a backslash can be used to remove the special handling for the next character;
single quotes enclose verbatim sequences of characters, and can be used to
inhibit history expansion;
and characters enclosed within double quotes may be subject to history
expansion, since backslash can escape the history expansion character,
but single quotes may not, since they are not treated specially within
double quotes.

When using the shell, only &lsquo;<samp>\</samp>&rsquo; and &lsquo;<samp>'</samp>&rsquo; may be used to escape the
history expansion character, but the history expansion character is
also treated as quoted if it immediately precedes the closing double quote
in a double-quoted string. 

Several shell options settable with the <code>shopt</code>
builtin (see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>) may be used to tailor
the behavior of history expansion. If the
<code>histverify</code> shell option is enabled, and Readline
is being used, history substitutions are not immediately passed to
the shell parser.
Instead, the expanded line is reloaded into the Readline
editing buffer for further modification.
If Readline is being used, and the <code>histreedit</code>
shell option is enabled, a failed history expansion will be
reloaded into the Readline editing buffer for correction.
The <samp>-p</samp> option to the <code>history</code> builtin command
may be used to see what a history expansion will do before using it.
The <samp>-s</samp> option to the <code>history</code> builtin may be used to
add commands to the end of the history list without actually executing
them, so that they are available for subsequent recall.
This is most useful in conjunction with Readline.

The shell allows control of the various characters used by the
history expansion mechanism with the <code>histchars</code> variable,
as explained above (see <a href="#Bash-Variables">Bash Variables</a>). The shell uses
the history comment character to mark history timestamps when
writing the history file.

<ul class="section-toc">
<li><a href="#Event-Designators" accesskey="1">Event Designators</a></li>
<li><a href="#Word-Designators" accesskey="2">Word Designators</a></li>
<li><a href="#Modifiers" accesskey="3">Modifiers</a></li>
</ul>
<hr>
<div class="subsection" id="Event-Designators">
<div class="header">

Next: <a href="#Word-Designators" accesskey="n" rel="next">Word Designators</a>, Up: <a href="#History-Interaction" accesskey="u" rel="up">History Expansion</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">9.3.1 Event Designators</h4>

An event designator is a reference to a command line entry in the
history list.
Unless the reference is absolute, events are relative to the current
position in the history list.


<dl compact="compact">
<dt><code>!</code></dt>
<dd>Start a history substitution, except when followed by a space, tab,
the end of the line, &lsquo;<samp>=</samp>&rsquo; or &lsquo;<samp>(</samp>&rsquo; (when the
<code>extglob</code> shell option is enabled using the <code>shopt</code> builtin).

</dd>
<dt><code>!<var>n</var></code></dt>
<dd>Refer to command line <var>n</var>.

</dd>
<dt><code>!-<var>n</var></code></dt>
<dd>Refer to the command <var>n</var> lines back.

</dd>
<dt><code>!!</code></dt>
<dd>Refer to the previous command. This is a synonym for &lsquo;<samp>!-1</samp>&rsquo;.

</dd>
<dt><code>!<var>string</var></code></dt>
<dd>Refer to the most recent command
preceding the current position in the history list
starting with <var>string</var>.

</dd>
<dt><code>!?<var>string</var>[?]</code></dt>
<dd>Refer to the most recent command
preceding the current position in the history list
containing <var>string</var>.
The trailing
&lsquo;<samp>?</samp>&rsquo; may be omitted if the <var>string</var> is followed immediately by
a newline.
If <var>string</var> is missing, the string from the most recent search is used;
it is an error if there is no previous search string.

</dd>
<dt><code>^<var>string1</var>^<var>string2</var>^</code></dt>
<dd>Quick Substitution. Repeat the last command, replacing <var>string1</var>
with <var>string2</var>. Equivalent to
<code>!!:s^<var>string1</var>^<var>string2</var>^</code>.

</dd>
<dt><code>!#</code></dt>
<dd>The entire command line typed so far.

</dd>
</dl>

<hr>
</div>
<div class="subsection" id="Word-Designators">
<div class="header">

Next: <a href="#Modifiers" accesskey="n" rel="next">Modifiers</a>, Previous: <a href="#Event-Designators" accesskey="p" rel="prev">Event Designators</a>, Up: <a href="#History-Interaction" accesskey="u" rel="up">History Expansion</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">9.3.2 Word Designators</h4>

Word designators are used to select desired words from the event.
A &lsquo;<samp>:</samp>&rsquo; separates the event specification from the word designator. It
may be omitted if the word designator begins with a &lsquo;<samp>^</samp>&rsquo;, &lsquo;<samp>$</samp>&rsquo;,
&lsquo;<samp>*</samp>&rsquo;, &lsquo;<samp>-</samp>&rsquo;, or &lsquo;<samp>%</samp>&rsquo;. Words are numbered from the beginning
of the line, with the first word being denoted by 0 (zero). Words are
inserted into the current line separated by single spaces.

For example,

<dl compact="compact">
<dt><code>!!</code></dt>
<dd>designates the preceding command. When you type this, the preceding
command is repeated in toto.

</dd>
<dt><code>!!:$</code></dt>
<dd>designates the last argument of the preceding command. This may be
shortened to <code>!$</code>.

</dd>
<dt><code>!fi:2</code></dt>
<dd>designates the second argument of the most recent command starting with
the letters <code>fi</code>.
</dd>
</dl>

Here are the word designators:
 
<dl compact="compact">
<dt><code>0 (zero)</code></dt>
<dd>The <code>0</code>th word. For many applications, this is the command word.

</dd>
<dt><code><var>n</var></code></dt>
<dd>The <var>n</var>th word.

</dd>
<dt><code>^</code></dt>
<dd>The first argument; that is, word 1.

</dd>
<dt><code>$</code></dt>
<dd>The last argument.

</dd>
<dt><code>%</code></dt>
<dd>The first word matched by the most recent &lsquo;<samp>?<var>string</var>?</samp>&rsquo; search,
if the search string begins with a character that is part of a word.

</dd>
<dt><code><var>x</var>-<var>y</var></code></dt>
<dd>A range of words; &lsquo;<samp>-<var>y</var></samp>&rsquo; abbreviates &lsquo;<samp>0-<var>y</var></samp>&rsquo;.

</dd>
<dt><code>*</code></dt>
<dd>All of the words, except the <code>0</code>th. This is a synonym for &lsquo;<samp>1-$</samp>&rsquo;.
It is not an error to use &lsquo;<samp>*</samp>&rsquo; if there is just one word in the event;
the empty string is returned in that case.

</dd>
<dt><code><var>x</var>*</code></dt>
<dd>Abbreviates &lsquo;<samp><var>x</var>-$</samp>&rsquo;

</dd>
<dt><code><var>x</var>-</code></dt>
<dd>Abbreviates &lsquo;<samp><var>x</var>-$</samp>&rsquo; like &lsquo;<samp><var>x</var>*</samp>&rsquo;, but omits the last word.
If &lsquo;<samp>x</samp>&rsquo; is missing, it defaults to 0.

</dd>
</dl>

If a word designator is supplied without an event specification, the
previous command is used as the event.

<hr>
</div>
<div class="subsection" id="Modifiers">
<div class="header">

Previous: <a href="#Word-Designators" accesskey="p" rel="prev">Word Designators</a>, Up: <a href="#History-Interaction" accesskey="u" rel="up">History Expansion</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h4 class="subsection">9.3.3 Modifiers</h4>

After the optional word designator, you can add a sequence of one or more
of the following modifiers, each preceded by a &lsquo;<samp>:</samp>&rsquo;.
These modify, or edit, the word or words selected from the history event.

<dl compact="compact">
<dt><code>h</code></dt>
<dd>Remove a trailing pathname component, leaving only the head.

</dd>
<dt><code>t</code></dt>
<dd>Remove all leading pathname components, leaving the tail.

</dd>
<dt><code>r</code></dt>
<dd>Remove a trailing suffix of the form &lsquo;<samp>.<var>suffix</var></samp>&rsquo;, leaving
the basename.

</dd>
<dt><code>e</code></dt>
<dd>Remove all but the trailing suffix.

</dd>
<dt><code>p</code></dt>
<dd>Print the new command but do not execute it.

</dd>
<dt><code>q</code></dt>
<dd>Quote the substituted words, escaping further substitutions.

</dd>
<dt><code>x</code></dt>
<dd>Quote the substituted words as with &lsquo;<samp>q</samp>&rsquo;,
but break into words at spaces, tabs, and newlines.
The &lsquo;<samp>q</samp>&rsquo; and &lsquo;<samp>x</samp>&rsquo; modifiers are mutually exclusive; the last one
supplied is used.

</dd>
<dt><code>s/<var>old</var>/<var>new</var>/</code></dt>
<dd>Substitute <var>new</var> for the first occurrence of <var>old</var> in the
event line.
Any character may be used as the delimiter in place of &lsquo;<samp>/</samp>&rsquo;.
The delimiter may be quoted in <var>old</var> and <var>new</var>
with a single backslash. If &lsquo;<samp>&amp;</samp>&rsquo; appears in <var>new</var>,
it is replaced by <var>old</var>. A single backslash will quote
the &lsquo;<samp>&amp;</samp>&rsquo;.
If <var>old</var> is null, it is set to the last <var>old</var>
substituted, or, if no previous history substitutions took place,
the last <var>string</var>
in a !?<var>string</var><code>[?]</code>
search.
If <var>new</var> is null, each matching <var>old</var> is deleted.
The final delimiter is optional if it is the last
character on the input line.

</dd>
<dt><code>&amp;</code></dt>
<dd>Repeat the previous substitution.

</dd>
<dt><code>g</code></dt>
<dt><code>a</code></dt>
<dd>Cause changes to be applied over the entire event line. Used in
conjunction with &lsquo;<samp>s</samp>&rsquo;, as in <code>gs/<var>old</var>/<var>new</var>/</code>,
or with &lsquo;<samp>&amp;</samp>&rsquo;.

</dd>
<dt><code>G</code></dt>
<dd>Apply the following &lsquo;<samp>s</samp>&rsquo; or &lsquo;<samp>&amp;</samp>&rsquo; modifier once to each word
in the event.

</dd>
</dl>

<hr>
</div>
</div>
</div>
<div class="chapter" id="Installing-Bash">
<div class="header">

Next: <a href="#Reporting-Bugs" accesskey="n" rel="next">Reporting Bugs</a>, Previous: <a href="#Using-History-Interactively" accesskey="p" rel="prev">Using History Interactively</a>, Up: <a href="#Top" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h2 class="chapter">10 Installing Bash</h2>

This chapter provides basic instructions for installing Bash on
the various supported platforms. The distribution supports the
GNU operating systems, nearly every version of Unix, and several
non-Unix systems such as BeOS and Interix.
Other independent ports exist for
MS-DOS, OS/2, and Windows platforms.

<ul class="section-toc">
<li><a href="#Basic-Installation" accesskey="1">Basic Installation</a></li>
<li><a href="#Compilers-and-Options" accesskey="2">Compilers and Options</a></li>
<li><a href="#Compiling-For-Multiple-Architectures" accesskey="3">Compiling For Multiple Architectures</a></li>
<li><a href="#Installation-Names" accesskey="4">Installation Names</a></li>
<li><a href="#Specifying-the-System-Type" accesskey="5">Specifying the System Type</a></li>
<li><a href="#Sharing-Defaults" accesskey="6">Sharing Defaults</a></li>
<li><a href="#Operation-Controls" accesskey="7">Operation Controls</a></li>
<li><a href="#Optional-Features" accesskey="8">Optional Features</a></li>
</ul>
<hr>
<div class="section" id="Basic-Installation">
<div class="header">

Next: <a href="#Compilers-and-Options" accesskey="n" rel="next">Compilers and Options</a>, Up: <a href="#Installing-Bash" accesskey="u" rel="up">Installing Bash</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">10.1 Basic Installation</h3>

These are installation instructions for Bash.

The simplest way to compile Bash is:

<ol>
<li> <code>cd</code> to the directory containing the source code and type
&lsquo;<samp>./configure</samp>&rsquo; to configure Bash for your system. If you&rsquo;re
using <code>csh</code> on an old version of System V, you might need to
type &lsquo;<samp>sh ./configure</samp>&rsquo; instead to prevent <code>csh</code> from trying
to execute <code>configure</code> itself.

Running <code>configure</code> takes some time.
While running, it prints messages telling which features it is
checking for.

</li><li> Type &lsquo;<samp>make</samp>&rsquo; to compile Bash and build the <code>bashbug</code> bug
reporting script.

</li><li> Optionally, type &lsquo;<samp>make tests</samp>&rsquo; to run the Bash test suite.

</li><li> Type &lsquo;<samp>make install</samp>&rsquo; to install <code>bash</code> and <code>bashbug</code>.
This will also install the manual pages and Info file, message translation
files, some supplemental documentation, a number of example loadable
builtin commands, and a set of header files for developing loadable
builtins.
You may need additional privileges to install <code>bash</code> to your
desired destination, so &lsquo;<samp>sudo make install</samp>&rsquo; might be required.
More information about controlling the locations where <code>bash</code> and
other files are installed is below (see <a href="#Installation-Names">Installation Names</a>).

</li></ol>

The <code>configure</code> shell script attempts to guess correct
values for various system-dependent variables used during
compilation. It uses those values to create a <samp>Makefile</samp> in
each directory of the package (the top directory, the
<samp>builtins</samp>, <samp>doc</samp>, <samp>po</samp>, and <samp>support</samp> directories,
each directory under <samp>lib</samp>, and several others). It also creates a
<samp>config.h</samp> file containing system-dependent definitions. 
Finally, it creates a shell script named <code>config.status</code> that you
can run in the future to recreate the current configuration, a
file <samp>config.cache</samp> that saves the results of its tests to
speed up reconfiguring, and a file <samp>config.log</samp> containing
compiler output (useful mainly for debugging <code>configure</code>). 
If at some point
<samp>config.cache</samp> contains results you don&rsquo;t want to keep, you
may remove or edit it. 

To find out more about the options and arguments that the
<code>configure</code> script understands, type 

<div class="example">
<pre class="example">bash-4.2$ ./configure --help
</pre></div>

at the Bash prompt in your Bash source directory.

If you want to build Bash in a directory separate from the source
directory &ndash; to build for multiple architectures, for example &ndash;
just use the full path to the configure script. The following commands
will build bash in a directory under <samp>/usr/local/build</samp> from
the source code in <samp>/usr/local/src/bash-4.4</samp>:

<div class="example">
<pre class="example">mkdir /usr/local/build/bash-4.4
cd /usr/local/build/bash-4.4
bash /usr/local/src/bash-4.4/configure
make
</pre></div>

See <a href="#Compiling-For-Multiple-Architectures">Compiling For Multiple Architectures</a> for more information
about building in a directory separate from the source.

If you need to do unusual things to compile Bash, please
try to figure out how <code>configure</code> could check whether or not
to do them, and mail diffs or instructions to
<a href="mailto:bash-maintainers@gnu.org">bash-maintainers@gnu.org</a> so they can be
considered for the next release.

The file <samp>configure.ac</samp> is used to create <code>configure</code>
by a program called Autoconf.
You only need <samp>configure.ac</samp> if you want to change it or regenerate
<code>configure</code> using a newer version of Autoconf.
If you do this, make sure you are using Autoconf version 2.69 or
newer.

You can remove the program binaries and object files from the
source code directory by typing &lsquo;<samp>make clean</samp>&rsquo;. To also remove the
files that <code>configure</code> created (so you can compile Bash for
a different kind of computer), type &lsquo;<samp>make distclean</samp>&rsquo;.

<hr>
</div>
<div class="section" id="Compilers-and-Options">
<div class="header">

Next: <a href="#Compiling-For-Multiple-Architectures" accesskey="n" rel="next">Compiling For Multiple Architectures</a>, Previous: <a href="#Basic-Installation" accesskey="p" rel="prev">Basic Installation</a>, Up: <a href="#Installing-Bash" accesskey="u" rel="up">Installing Bash</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">10.2 Compilers and Options</h3>

Some systems require unusual options for compilation or linking
that the <code>configure</code> script does not know about. You can
give <code>configure</code> initial values for variables by setting
them in the environment. Using a Bourne-compatible shell, you
can do that on the command line like this:

<div class="example">
<pre class="example">CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure
</pre></div>

On systems that have the <code>env</code> program, you can do it like this:

<div class="example">
<pre class="example">env CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure
</pre></div>

The configuration process uses GCC to build Bash if it
is available.

<hr>
</div>
<div class="section" id="Compiling-For-Multiple-Architectures">
<div class="header">

Next: <a href="#Installation-Names" accesskey="n" rel="next">Installation Names</a>, Previous: <a href="#Compilers-and-Options" accesskey="p" rel="prev">Compilers and Options</a>, Up: <a href="#Installing-Bash" accesskey="u" rel="up">Installing Bash</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">10.3 Compiling For Multiple Architectures</h3>

You can compile Bash for more than one kind of computer at the
same time, by placing the object files for each architecture in their
own directory. To do this, you must use a version of <code>make</code> that
supports the <code>VPATH</code> variable, such as GNU <code>make</code>.
<code>cd</code> to the
directory where you want the object files and executables to go and run
the <code>configure</code> script from the source directory
(see <a href="#Basic-Installation">Basic Installation</a>).
You may need to
supply the <samp>--srcdir=PATH</samp> argument to tell <code>configure</code> where the
source files are. <code>configure</code> automatically checks for the
source code in the directory that <code>configure</code> is in and in &lsquo;..&rsquo;.

If you have to use a <code>make</code> that does not support the <code>VPATH</code>
variable, you can compile Bash for one architecture at a
time in the source code directory. After you have installed
Bash for one architecture, use &lsquo;<samp>make distclean</samp>&rsquo; before
reconfiguring for another architecture.

Alternatively, if your system supports symbolic links, you can use the
<samp>support/mkclone</samp> script to create a build tree which has
symbolic links back to each file in the source directory. Here&rsquo;s an
example that creates a build directory in the current directory from a
source directory <samp>/usr/gnu/src/bash-2.0</samp>:

<div class="example">
<pre class="example">bash /usr/gnu/src/bash-2.0/support/mkclone -s /usr/gnu/src/bash-2.0 .
</pre></div>

The <code>mkclone</code> script requires Bash, so you must have already built
Bash for at least one architecture before you can create build
directories for other architectures.

<hr>
</div>
<div class="section" id="Installation-Names">
<div class="header">

Next: <a href="#Specifying-the-System-Type" accesskey="n" rel="next">Specifying the System Type</a>, Previous: <a href="#Compiling-For-Multiple-Architectures" accesskey="p" rel="prev">Compiling For Multiple Architectures</a>, Up: <a href="#Installing-Bash" accesskey="u" rel="up">Installing Bash</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">10.4 Installation Names</h3>

By default, &lsquo;<samp>make install</samp>&rsquo; will install into
<samp>/usr/local/bin</samp>, <samp>/usr/local/man</samp>, etc.;
that is, the installation prefix defaults to <samp>/usr/local</samp>.
You can specify an installation prefix other than <samp>/usr/local</samp> by
giving <code>configure</code> the option <samp>--prefix=<var>PATH</var></samp>,
or by specifying a value for the <code>prefix</code> &lsquo;<samp>make</samp>&rsquo;
variable when running &lsquo;<samp>make install</samp>&rsquo;
(e.g., &lsquo;<samp>make install prefix=<var>PATH</var></samp>&rsquo;).
The <code>prefix</code> variable provides a default for <code>exec_prefix</code> and
other variables used when installing bash.

You can specify separate installation prefixes for
architecture-specific files and architecture-independent files. 
If you give <code>configure</code> the option
<samp>--exec-prefix=<var>PATH</var></samp>, &lsquo;<samp>make install</samp>&rsquo; will use
<var>PATH</var> as the prefix for installing programs and libraries.
Documentation and other data files will still use the regular prefix.

If you would like to change the installation locations for a single run,
you can specify these variables as arguments to <code>make</code>:
&lsquo;<samp>make install exec_prefix=/</samp>&rsquo; will install <code>bash</code> and
<code>bashbug</code> into <samp>/bin</samp> instead of the default <samp>/usr/local/bin</samp>.

If you want to see the files bash will install and where it will install
them without changing anything on your system, specify the variable
<code>DESTDIR</code> as an argument to <code>make</code>. Its value should be the
absolute directory path you&rsquo;d like to use as the root of your sample
installation tree. For example,

<div class="example">
<pre class="example">mkdir /fs1/bash-install
make install DESTDIR=/fs1/bash-install
</pre></div>

will install <code>bash</code> into <samp>/fs1/bash-install/usr/local/bin/bash</samp>,
the documentation into directories within
<samp>/fs1/bash-install/usr/local/share</samp>, the example loadable builtins into
<samp>/fs1/bash-install/usr/local/lib/bash</samp>, and so on.
You can use the usual <code>exec_prefix</code> and <code>prefix</code> variables to alter
the directory paths beneath the value of <code>DESTDIR</code>.

The GNU Makefile standards provide a more complete description of these
variables and their effects.

<hr>
</div>
<div class="section" id="Specifying-the-System-Type">
<div class="header">

Next: <a href="#Sharing-Defaults" accesskey="n" rel="next">Sharing Defaults</a>, Previous: <a href="#Installation-Names" accesskey="p" rel="prev">Installation Names</a>, Up: <a href="#Installing-Bash" accesskey="u" rel="up">Installing Bash</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">10.5 Specifying the System Type</h3>

There may be some features <code>configure</code> can not figure out
automatically, but needs to determine by the type of host Bash
will run on. Usually <code>configure</code> can figure that
out, but if it prints a message saying it can not guess the host
type, give it the <samp>--host=TYPE</samp> option. &lsquo;<samp>TYPE</samp>&rsquo; can
either be a short name for the system type, such as &lsquo;<samp>sun4</samp>&rsquo;,
or a canonical name with three fields: &lsquo;<samp>CPU-COMPANY-SYSTEM</samp>&rsquo;
(e.g., &lsquo;<samp>i386-unknown-freebsd4.2</samp>&rsquo;).

See the file <samp>support/config.sub</samp> for the possible
values of each field. 

<hr>
</div>
<div class="section" id="Sharing-Defaults">
<div class="header">

Next: <a href="#Operation-Controls" accesskey="n" rel="next">Operation Controls</a>, Previous: <a href="#Specifying-the-System-Type" accesskey="p" rel="prev">Specifying the System Type</a>, Up: <a href="#Installing-Bash" accesskey="u" rel="up">Installing Bash</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">10.6 Sharing Defaults</h3>

If you want to set default values for <code>configure</code> scripts to
share, you can create a site shell script called
<code>config.site</code> that gives default values for variables like
<code>CC</code>, <code>cache_file</code>, and <code>prefix</code>. <code>configure</code>
looks for <samp>PREFIX/share/config.site</samp> if it exists, then
<samp>PREFIX/etc/config.site</samp> if it exists. Or, you can set the
<code>CONFIG_SITE</code> environment variable to the location of the site
script. A warning: the Bash <code>configure</code> looks for a site script,
but not all <code>configure</code> scripts do.

<hr>
</div>
<div class="section" id="Operation-Controls">
<div class="header">

Next: <a href="#Optional-Features" accesskey="n" rel="next">Optional Features</a>, Previous: <a href="#Sharing-Defaults" accesskey="p" rel="prev">Sharing Defaults</a>, Up: <a href="#Installing-Bash" accesskey="u" rel="up">Installing Bash</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">10.7 Operation Controls</h3>

<code>configure</code> recognizes the following options to control how it
operates.

<dl compact="compact">
<dt><code>--cache-file=<var>file</var></code></dt>
<dd>Use and save the results of the tests in
<var>file</var> instead of <samp>./config.cache</samp>. Set <var>file</var> to
<samp>/dev/null</samp> to disable caching, for debugging
<code>configure</code>. 

</dd>
<dt><code>--help</code></dt>
<dd>Print a summary of the options to <code>configure</code>, and exit.

</dd>
<dt><code>--quiet</code></dt>
<dt><code>--silent</code></dt>
<dt><code>-q</code></dt>
<dd>Do not print messages saying which checks are being made.

</dd>
<dt><code>--srcdir=<var>dir</var></code></dt>
<dd>Look for the Bash source code in directory <var>dir</var>. Usually
<code>configure</code> can determine that directory automatically.

</dd>
<dt><code>--version</code></dt>
<dd>Print the version of Autoconf used to generate the <code>configure</code>
script, and exit.
</dd>
</dl>

<code>configure</code> also accepts some other, not widely used, boilerplate
options. &lsquo;<samp>configure --help</samp>&rsquo; prints the complete list.

<hr>
</div>
<div class="section" id="Optional-Features">
<div class="header">

Previous: <a href="#Operation-Controls" accesskey="p" rel="prev">Operation Controls</a>, Up: <a href="#Installing-Bash" accesskey="u" rel="up">Installing Bash</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="section">10.8 Optional Features</h3>

The Bash <code>configure</code> has a number of <samp>--enable-<var>feature</var></samp>
options, where <var>feature</var> indicates an optional part of Bash.
There are also several <samp>--with-<var>package</var></samp> options,
where <var>package</var> is something like &lsquo;<samp>bash-malloc</samp>&rsquo; or &lsquo;<samp>purify</samp>&rsquo;.
To turn off the default use of a package, use
<samp>--without-<var>package</var></samp>. To configure Bash without a feature
that is enabled by default, use <samp>--disable-<var>feature</var></samp>.

Here is a complete list of the <samp>--enable-</samp> and
<samp>--with-</samp> options that the Bash <code>configure</code> recognizes. 

<dl compact="compact">
<dt><code>--with-afs</code></dt>
<dd>Define if you are using the Andrew File System from Transarc.

</dd>
<dt><code>--with-bash-malloc</code></dt>
<dd>Use the Bash version of
<code>malloc</code> in the directory <samp>lib/malloc</samp>. This is not the same
<code>malloc</code> that appears in GNU libc, but an older version
originally derived from the 4.2 BSD <code>malloc</code>. This <code>malloc</code>
is very fast, but wastes some space on each allocation.
This option is enabled by default.
The <samp>NOTES</samp> file contains a list of systems for
which this should be turned off, and <code>configure</code> disables this
option automatically for a number of systems.

</dd>
<dt><code>--with-curses</code></dt>
<dd>Use the curses library instead of the termcap library. This should
be supplied if your system has an inadequate or incomplete termcap
database.

</dd>
<dt><code>--with-gnu-malloc</code></dt>
<dd>A synonym for <code>--with-bash-malloc</code>.

</dd>
<dt><code>--with-installed-readline[=<var>PREFIX</var>]</code></dt>
<dd>Define this to make Bash link with a locally-installed version of Readline
rather than the version in <samp>lib/readline</samp>. This works only with
Readline 5.0 and later versions. If <var>PREFIX</var> is <code>yes</code> or not
supplied, <code>configure</code> uses the values of the make variables
<code>includedir</code> and <code>libdir</code>, which are subdirectories of <code>prefix</code>
by default, to find the installed version of Readline if it is not in
the standard system include and library directories.
If <var>PREFIX</var> is <code>no</code>, Bash links with the version in
<samp>lib/readline</samp>.
If <var>PREFIX</var> is set to any other value, <code>configure</code> treats it as
a directory pathname and looks for
the installed version of Readline in subdirectories of that directory
(include files in <var>PREFIX</var>/<code>include</code> and the library in
<var>PREFIX</var>/<code>lib</code>).

</dd>
<dt><code>--with-libintl-prefix[=<var>PREFIX</var>]</code></dt>
<dd>Define this to make Bash link with a locally-installed version of the
libintl library instead of the version in <samp>lib/intl</samp>.

</dd>
<dt><code>--with-libiconv-prefix[=<var>PREFIX</var>]</code></dt>
<dd>Define this to make Bash look for libiconv in <var>PREFIX</var> instead of the
standard system locations. There is no version included with Bash.

</dd>
<dt><code>--enable-minimal-config</code></dt>
<dd>This produces a shell with minimal features, close to the historical
Bourne shell.
</dd>
</dl>

There are several <samp>--enable-</samp> options that alter how Bash is
compiled, linked, and installed, rather than changing run-time features.

<dl compact="compact">
<dt><code>--enable-largefile</code></dt>
<dd>Enable support for <a href="http://www.unix.org/version2/whatsnew/lfs20mar.html">large files</a> if the operating system requires special compiler options
to build programs which can access large files. This is enabled by
default, if the operating system provides large file support.

</dd>
<dt><code>--enable-profiling</code></dt>
<dd>This builds a Bash binary that produces profiling information to be
processed by <code>gprof</code> each time it is executed.

</dd>
<dt><code>--enable-separate-helpfiles</code></dt>
<dd>Use external files for the documentation displayed by the <code>help</code> builtin
instead of storing the text internally.

</dd>
<dt><code>--enable-static-link</code></dt>
<dd>This causes Bash to be linked statically, if <code>gcc</code> is being used.
This could be used to build a version to use as root&rsquo;s shell.

</dd>
</dl>

The &lsquo;<samp>minimal-config</samp>&rsquo; option can be used to disable all of
the following options, but it is processed first, so individual
options may be enabled using &lsquo;<samp>enable-<var>feature</var></samp>&rsquo;. 

All of the following options except for
&lsquo;<samp>alt-array-implementation</samp>&rsquo;,
&lsquo;<samp>disabled-builtins</samp>&rsquo;,
&lsquo;<samp>direxpand-default</samp>&rsquo;,
&lsquo;<samp>strict-posix-default</samp>&rsquo;,
and
&lsquo;<samp>xpg-echo-default</samp>&rsquo; are
enabled by default, unless the operating system does not provide the
necessary support.

<dl compact="compact">
<dt><code>--enable-alias</code></dt>
<dd>Allow alias expansion and include the <code>alias</code> and <code>unalias</code>
builtins (see <a href="#Aliases">Aliases</a>).

</dd>
<dt><code>--enable-alt-array-implementation</code></dt>
<dd>This builds bash using an alternate implementation of arrays
(see <a href="#Arrays">Arrays</a>) that provides faster access at the expense of using
more memory (sometimes many times more, depending on how sparse an array is).

</dd>
<dt><code>--enable-arith-for-command</code></dt>
<dd>Include support for the alternate form of the <code>for</code> command
that behaves like the C language <code>for</code> statement
(see <a href="#Looping-Constructs">Looping Constructs</a>).

</dd>
<dt><code>--enable-array-variables</code></dt>
<dd>Include support for one-dimensional array shell variables
(see <a href="#Arrays">Arrays</a>).

</dd>
<dt><code>--enable-bang-history</code></dt>
<dd>Include support for <code>csh</code>-like history substitution
(see <a href="#History-Interaction">History Expansion</a>).

</dd>
<dt><code>--enable-brace-expansion</code></dt>
<dd>Include <code>csh</code>-like brace expansion
( <code>b{a,b}c</code> &rarr; <code>bac bbc</code> ).
See <a href="#Brace-Expansion">Brace Expansion</a>, for a complete description.

</dd>
<dt><code>--enable-casemod-attributes</code></dt>
<dd>Include support for case-modifying attributes in the <code>declare</code> builtin
and assignment statements. Variables with the <code>uppercase</code> attribute,
for example, will have their values converted to uppercase upon assignment.

</dd>
<dt><code>--enable-casemod-expansion</code></dt>
<dd>Include support for case-modifying word expansions.

</dd>
<dt><code>--enable-command-timing</code></dt>
<dd>Include support for recognizing <code>time</code> as a reserved word and for
displaying timing statistics for the pipeline following <code>time</code>
(see <a href="#Pipelines">Pipelines</a>).
This allows pipelines as well as shell builtins and functions to be timed.

</dd>
<dt><code>--enable-cond-command</code></dt>
<dd>Include support for the <code>[[</code> conditional command.
(see <a href="#Conditional-Constructs">Conditional Constructs</a>).

</dd>
<dt><code>--enable-cond-regexp</code></dt>
<dd>Include support for matching POSIX regular expressions using the
&lsquo;<samp>=~</samp>&rsquo; binary operator in the <code>[[</code> conditional command.
(see <a href="#Conditional-Constructs">Conditional Constructs</a>).

</dd>
<dt><code>--enable-coprocesses</code></dt>
<dd>Include support for coprocesses and the <code>coproc</code> reserved word
(see <a href="#Pipelines">Pipelines</a>).

</dd>
<dt><code>--enable-debugger</code></dt>
<dd>Include support for the bash debugger (distributed separately).

</dd>
<dt><code>--enable-dev-fd-stat-broken</code></dt>
<dd>If calling <code>stat</code> on /dev/fd/<var>N</var> returns different results than
calling <code>fstat</code> on file descriptor <var>N</var>, supply this option to
enable a workaround.
This has implications for conditional commands that test file attributes.

</dd>
<dt><code>--enable-direxpand-default</code></dt>
<dd>Cause the <code>direxpand</code> shell option (see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>)
to be enabled by default when the shell starts.
It is normally disabled by default.

</dd>
<dt><code>--enable-directory-stack</code></dt>
<dd>Include support for a <code>csh</code>-like directory stack and the
<code>pushd</code>, <code>popd</code>, and <code>dirs</code> builtins
(see <a href="#The-Directory-Stack">The Directory Stack</a>).

</dd>
<dt><code>--enable-disabled-builtins</code></dt>
<dd>Allow builtin commands to be invoked via &lsquo;<samp>builtin xxx</samp>&rsquo;
even after <code>xxx</code> has been disabled using &lsquo;<samp>enable -n xxx</samp>&rsquo;.
See <a href="#Bash-Builtins">Bash Builtin Commands</a>, for details of the <code>builtin</code> and
<code>enable</code> builtin commands.

</dd>
<dt><code>--enable-dparen-arithmetic</code></dt>
<dd>Include support for the <code>((&hellip;))</code> command
(see <a href="#Conditional-Constructs">Conditional Constructs</a>).

</dd>
<dt><code>--enable-extended-glob</code></dt>
<dd>Include support for the extended pattern matching features described
above under <a href="#Pattern-Matching">Pattern Matching</a>.

</dd>
<dt><code>--enable-extended-glob-default</code></dt>
<dd>Set the default value of the <code>extglob</code> shell option described
above under <a href="#The-Shopt-Builtin">The Shopt Builtin</a> to be enabled.

</dd>
<dt><code>--enable-function-import</code></dt>
<dd>Include support for importing function definitions exported by another
instance of the shell from the environment. This option is enabled by
default.

</dd>
<dt><code>--enable-glob-asciirange-default</code></dt>
<dd>Set the default value of the <code>globasciiranges</code> shell option described
above under <a href="#The-Shopt-Builtin">The Shopt Builtin</a> to be enabled.
This controls the behavior of character ranges when used in pattern matching
bracket expressions.

</dd>
<dt><code>--enable-help-builtin</code></dt>
<dd>Include the <code>help</code> builtin, which displays help on shell builtins and
variables (see <a href="#Bash-Builtins">Bash Builtin Commands</a>).

</dd>
<dt><code>--enable-history</code></dt>
<dd>Include command history and the <code>fc</code> and <code>history</code>
builtin commands (see <a href="#Bash-History-Facilities">Bash History Facilities</a>).

</dd>
<dt><code>--enable-job-control</code></dt>
<dd>This enables the job control features (see <a href="#Job-Control">Job Control</a>),
if the operating system supports them.

</dd>
<dt><code>--enable-multibyte</code></dt>
<dd>This enables support for multibyte characters if the operating
system provides the necessary support.

</dd>
<dt><code>--enable-net-redirections</code></dt>
<dd>This enables the special handling of filenames of the form
<code>/dev/tcp/<var>host</var>/<var>port</var></code> and
<code>/dev/udp/<var>host</var>/<var>port</var></code>
when used in redirections (see <a href="#Redirections">Redirections</a>).

</dd>
<dt><code>--enable-process-substitution</code></dt>
<dd>This enables process substitution (see <a href="#Process-Substitution">Process Substitution</a>) if
the operating system provides the necessary support.

</dd>
<dt><code>--enable-progcomp</code></dt>
<dd>Enable the programmable completion facilities
(see <a href="#Programmable-Completion">Programmable Completion</a>).
If Readline is not enabled, this option has no effect.

</dd>
<dt><code>--enable-prompt-string-decoding</code></dt>
<dd>Turn on the interpretation of a number of backslash-escaped characters
in the <code>$PS0</code>, <code>$PS1</code>, <code>$PS2</code>, and <code>$PS4</code> prompt
strings. See <a href="#Controlling-the-Prompt">Controlling the Prompt</a>, for a complete list of prompt
string escape sequences.

</dd>
<dt><code>--enable-readline</code></dt>
<dd>Include support for command-line editing and history with the Bash
version of the Readline library (see <a href="#Command-Line-Editing">Command Line Editing</a>).

</dd>
<dt><code>--enable-restricted</code></dt>
<dd>Include support for a restricted shell. If this is enabled, Bash,
when called as <code>rbash</code>, enters a restricted mode. See
<a href="#The-Restricted-Shell">The Restricted Shell</a>, for a description of restricted mode.

</dd>
<dt><code>--enable-select</code></dt>
<dd>Include the <code>select</code> compound command, which allows the generation of
simple menus (see <a href="#Conditional-Constructs">Conditional Constructs</a>).

</dd>
<dt><code>--enable-single-help-strings</code></dt>
<dd>Store the text displayed by the <code>help</code> builtin as a single string for
each help topic. This aids in translating the text to different languages.
You may need to disable this if your compiler cannot handle very long string
literals.

</dd>
<dt><code>--enable-strict-posix-default</code></dt>
<dd>Make Bash POSIX-conformant by default (see <a href="#Bash-POSIX-Mode">Bash POSIX Mode</a>).

</dd>
<dt><code>--enable-translatable-strings</code></dt>
<dd>Enable support for <code>$&quot;<var>string</var>&quot;</code> translatable strings
(see <a href="#Locale-Translation">Locale-Specific Translation</a>).

</dd>
<dt><code>--enable-usg-echo-default</code></dt>
<dd>A synonym for <code>--enable-xpg-echo-default</code>.

</dd>
<dt><code>--enable-xpg-echo-default</code></dt>
<dd>Make the <code>echo</code> builtin expand backslash-escaped characters by default,
without requiring the <samp>-e</samp> option.
This sets the default value of the <code>xpg_echo</code> shell option to <code>on</code>,
which makes the Bash <code>echo</code> behave more like the version specified in
the Single Unix Specification, version 3.
See <a href="#Bash-Builtins">Bash Builtin Commands</a>, for a description of the escape sequences that
<code>echo</code> recognizes.
</dd>
</dl>

The file <samp>config-top.h</samp> contains C Preprocessor
&lsquo;<samp>#define</samp>&rsquo; statements for options which are not settable from
<code>configure</code>.
Some of these are not meant to be changed; beware of the consequences if
you do.
Read the comments associated with each definition for more
information about its effect.

<hr>
</div>
</div>
<div class="appendix" id="Reporting-Bugs">
<div class="header">

Next: <a href="#Major-Differences-From-The-Bourne-Shell" accesskey="n" rel="next">Major Differences From The Bourne Shell</a>, Previous: <a href="#Installing-Bash" accesskey="p" rel="prev">Installing Bash</a>, Up: <a href="#Top" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h2 class="appendix">Appendix A Reporting Bugs</h2>

Please report all bugs you find in Bash.
But first, you should
make sure that it really is a bug, and that it appears in the latest
version of Bash.
The latest version of Bash is always available for FTP from
<a href="ftp://ftp.gnu.org/pub/gnu/bash/">ftp://ftp.gnu.org/pub/gnu/bash/</a> and from
<a href="http://git.savannah.gnu.org/cgit/bash.git/snapshot/bash-master.tar.gz">http://git.savannah.gnu.org/cgit/bash.git/snapshot/bash-master.tar.gz</a>.

Once you have determined that a bug actually exists, use the
<code>bashbug</code> command to submit a bug report.
If you have a fix, you are encouraged to mail that as well!
Suggestions and &lsquo;philosophical&rsquo; bug reports may be mailed
to <a href="mailto:bug-bash@gnu.org">bug-bash@gnu.org</a> or posted to the Usenet
newsgroup <code>gnu.bash.bug</code>.

All bug reports should include:
<ul>
<li> The version number of Bash.
</li><li> The hardware and operating system.
</li><li> The compiler used to compile Bash.
</li><li> A description of the bug behaviour.
</li><li> A short script or &lsquo;recipe&rsquo; which exercises the bug and may be used
to reproduce it.
</li></ul>

<code>bashbug</code> inserts the first three items automatically into
the template it provides for filing a bug report.

Please send all reports concerning this manual to
<a href="mailto:bug-bash@gnu.org">bug-bash@gnu.org</a>.

<hr>
</div>
<div class="appendix" id="Major-Differences-From-The-Bourne-Shell">
<div class="header">

Next: <a href="#GNU-Free-Documentation-License" accesskey="n" rel="next">GNU Free Documentation License</a>, Previous: <a href="#Reporting-Bugs" accesskey="p" rel="prev">Reporting Bugs</a>, Up: <a href="#Top" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h2 class="appendix">Appendix B Major Differences From The Bourne Shell</h2>

Bash implements essentially the same grammar, parameter and
variable expansion, redirection, and quoting as the Bourne Shell. 
Bash uses the POSIX standard as the specification of
how these features are to be implemented. There are some
differences between the traditional Bourne shell and Bash; this
section quickly details the differences of significance. A
number of these differences are explained in greater depth in
previous sections.
This section uses the version of <code>sh</code> included in SVR4.2 (the
last version of the historical Bourne shell) as the baseline reference.

<ul>
<li> Bash is POSIX-conformant, even where the POSIX specification
differs from traditional <code>sh</code> behavior (see <a href="#Bash-POSIX-Mode">Bash POSIX Mode</a>).

</li><li> Bash has multi-character invocation options (see <a href="#Invoking-Bash">Invoking Bash</a>).

</li><li> Bash has command-line editing (see <a href="#Command-Line-Editing">Command Line Editing</a>) and
the <code>bind</code> builtin.

</li><li> Bash provides a programmable word completion mechanism
(see <a href="#Programmable-Completion">Programmable Completion</a>), and builtin commands
<code>complete</code>, <code>compgen</code>, and <code>compopt</code>, to
manipulate it.

</li><li> Bash has command history (see <a href="#Bash-History-Facilities">Bash History Facilities</a>) and the
<code>history</code> and <code>fc</code> builtins to manipulate it.
The Bash history list maintains timestamp information and uses the
value of the <code>HISTTIMEFORMAT</code> variable to display it.

</li><li> Bash implements <code>csh</code>-like history expansion
(see <a href="#History-Interaction">History Expansion</a>).

</li><li> Bash has one-dimensional array variables (see <a href="#Arrays">Arrays</a>), and the
appropriate variable expansions and assignment syntax to use them.
Several of the Bash builtins take options to act on arrays.
Bash provides a number of built-in array variables.

</li><li> The <code>$'&hellip;'</code> quoting syntax, which expands ANSI-C
backslash-escaped characters in the text between the single quotes,
is supported (see <a href="#ANSI_002dC-Quoting">ANSI-C Quoting</a>).

</li><li> Bash supports the <code>$&quot;&hellip;&quot;</code> quoting syntax to do
locale-specific translation of the characters between the double
quotes. The <samp>-D</samp>, <samp>--dump-strings</samp>, and <samp>--dump-po-strings</samp>
invocation options list the translatable strings found in a script
(see <a href="#Locale-Translation">Locale-Specific Translation</a>).

</li><li> Bash implements the <code>!</code> keyword to negate the return value of
a pipeline (see <a href="#Pipelines">Pipelines</a>).
Very useful when an <code>if</code> statement needs to act only if a test fails.
The Bash &lsquo;<samp>-o pipefail</samp>&rsquo; option to <code>set</code> will cause a pipeline to
return a failure status if any command fails.

</li><li> Bash has the <code>time</code> reserved word and command timing (see <a href="#Pipelines">Pipelines</a>).
The display of the timing statistics may be controlled with the
<code>TIMEFORMAT</code> variable.

</li><li> Bash implements the <code>for (( <var>expr1</var> ; <var>expr2</var> ; <var>expr3</var> ))</code>
arithmetic for command, similar to the C language (see <a href="#Looping-Constructs">Looping Constructs</a>).

</li><li> Bash includes the <code>select</code> compound command, which allows the
generation of simple menus (see <a href="#Conditional-Constructs">Conditional Constructs</a>).

</li><li> Bash includes the <code>[[</code> compound command, which makes conditional
testing part of the shell grammar (see <a href="#Conditional-Constructs">Conditional Constructs</a>), including
optional regular expression matching.

</li><li> Bash provides optional case-insensitive matching for the <code>case</code> and
<code>[[</code> constructs.

</li><li> Bash includes brace expansion (see <a href="#Brace-Expansion">Brace Expansion</a>) and tilde
expansion (see <a href="#Tilde-Expansion">Tilde Expansion</a>).

</li><li> Bash implements command aliases and the <code>alias</code> and <code>unalias</code>
builtins (see <a href="#Aliases">Aliases</a>).

</li><li> Bash provides shell arithmetic, the <code>((</code> compound command
(see <a href="#Conditional-Constructs">Conditional Constructs</a>),
and arithmetic expansion (see <a href="#Shell-Arithmetic">Shell Arithmetic</a>).

</li><li> Variables present in the shell&rsquo;s initial environment are automatically
exported to child processes. The Bourne shell does not normally do
this unless the variables are explicitly marked using the <code>export</code>
command.

</li><li> Bash supports the &lsquo;<samp>+=</samp>&rsquo; assignment operator, which appends to the value
of the variable named on the left hand side.

</li><li> Bash includes the POSIX pattern removal &lsquo;<samp>%</samp>&rsquo;, &lsquo;<samp>#</samp>&rsquo;, &lsquo;<samp>%%</samp>&rsquo;
and &lsquo;<samp>##</samp>&rsquo; expansions to remove leading or trailing substrings from
variable values (see <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>).

</li><li> The expansion <code>${#xx}</code>, which returns the length of <code>${xx}</code>,
is supported (see <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>).

</li><li> The expansion <code>${var:</code><var>offset</var><code>[:</code><var>length</var><code>]}</code>,
which expands to the substring of <code>var</code>&rsquo;s value of length
<var>length</var>, beginning at <var>offset</var>, is present
(see <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>).

</li><li> The expansion
<code>${<var>var</var>/[/]</code><var>pattern</var><code>[/</code><var>replacement</var><code>]}</code>,
which matches <var>pattern</var> and replaces it with <var>replacement</var> in
the value of <var>var</var>, is available (see <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>).

</li><li> The expansion <code>${!<var>prefix</var>*}</code> expansion, which expands to
the names of all shell variables whose names begin with <var>prefix</var>,
is available (see <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>).

</li><li> Bash has indirect variable expansion using <code>${!word}</code>
(see <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>).

</li><li> Bash can expand positional parameters beyond <code>$9</code> using
<code>${<var>num</var>}</code>.

</li><li> The POSIX <code>$()</code> form of command substitution
is implemented (see <a href="#Command-Substitution">Command Substitution</a>),
and preferred to the Bourne shell&rsquo;s <code>``</code> (which
is also implemented for backwards compatibility).

</li><li> Bash has process substitution (see <a href="#Process-Substitution">Process Substitution</a>).

</li><li> Bash automatically assigns variables that provide information about the
current user (<code>UID</code>, <code>EUID</code>, and <code>GROUPS</code>), the current host
(<code>HOSTTYPE</code>, <code>OSTYPE</code>, <code>MACHTYPE</code>, and <code>HOSTNAME</code>),
and the instance of Bash that is running (<code>BASH</code>,
<code>BASH_VERSION</code>, and <code>BASH_VERSINFO</code>). See <a href="#Bash-Variables">Bash Variables</a>,
for details.

</li><li> The <code>IFS</code> variable is used to split only the results of expansion,
not all words (see <a href="#Word-Splitting">Word Splitting</a>).
This closes a longstanding shell security hole.

</li><li> The filename expansion bracket expression code uses &lsquo;<samp>!</samp>&rsquo; and &lsquo;<samp>^</samp>&rsquo;
to negate the set of characters between the brackets.
The Bourne shell uses only &lsquo;<samp>!</samp>&rsquo;.

</li><li> Bash implements the full set of POSIX filename expansion operators,
including character classes, equivalence classes, and
collating symbols (see <a href="#Filename-Expansion">Filename Expansion</a>).

</li><li> Bash implements extended pattern matching features when the <code>extglob</code>
shell option is enabled (see <a href="#Pattern-Matching">Pattern Matching</a>).

</li><li> It is possible to have a variable and a function with the same name;
<code>sh</code> does not separate the two name spaces.

</li><li> Bash functions are permitted to have local variables using the
<code>local</code> builtin, and thus useful recursive functions may be written
(see <a href="#Bash-Builtins">Bash Builtin Commands</a>).

</li><li> Variable assignments preceding commands affect only that command, even
builtins and functions (see <a href="#Environment">Environment</a>).
In <code>sh</code>, all variable assignments 
preceding commands are global unless the command is executed from the
file system.

</li><li> Bash performs filename expansion on filenames specified as operands
to input and output redirection operators (see <a href="#Redirections">Redirections</a>).

</li><li> Bash contains the &lsquo;<samp>&lt;&gt;</samp>&rsquo; redirection operator, allowing a file to be
opened for both reading and writing, and the &lsquo;<samp>&amp;&gt;</samp>&rsquo; redirection
operator, for directing standard output and standard error to the same
file (see <a href="#Redirections">Redirections</a>).

</li><li> Bash includes the &lsquo;<samp>&lt;&lt;&lt;</samp>&rsquo; redirection operator, allowing a string to
be used as the standard input to a command.

</li><li> Bash implements the &lsquo;<samp>[n]&lt;&amp;<var>word</var></samp>&rsquo; and &lsquo;<samp>[n]&gt;&amp;<var>word</var></samp>&rsquo;
redirection operators, which move one file descriptor to another.

</li><li> Bash treats a number of filenames specially when they are
used in redirection operators (see <a href="#Redirections">Redirections</a>).

</li><li> Bash can open network connections to arbitrary machines and services
with the redirection operators (see <a href="#Redirections">Redirections</a>).

</li><li> The <code>noclobber</code> option is available to avoid overwriting existing
files with output redirection (see <a href="#The-Set-Builtin">The Set Builtin</a>).
The &lsquo;<samp>&gt;|</samp>&rsquo; redirection operator may be used to override <code>noclobber</code>.

</li><li> The Bash <code>cd</code> and <code>pwd</code> builtins (see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>)
each take <samp>-L</samp> and <samp>-P</samp> options to switch between logical and
physical modes.

</li><li> Bash allows a function to override a builtin with the same name, and provides
access to that builtin&rsquo;s functionality within the function via the
<code>builtin</code> and <code>command</code> builtins (see <a href="#Bash-Builtins">Bash Builtin Commands</a>).

</li><li> The <code>command</code> builtin allows selective disabling of functions
when command lookup is performed (see <a href="#Bash-Builtins">Bash Builtin Commands</a>).

</li><li> Individual builtins may be enabled or disabled using the <code>enable</code>
builtin (see <a href="#Bash-Builtins">Bash Builtin Commands</a>).

</li><li> The Bash <code>exec</code> builtin takes additional options that allow users
to control the contents of the environment passed to the executed
command, and what the zeroth argument to the command is to be
(see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>).

</li><li> Shell functions may be exported to children via the environment
using <code>export -f</code> (see <a href="#Shell-Functions">Shell Functions</a>).

</li><li> The Bash <code>export</code>, <code>readonly</code>, and <code>declare</code> builtins can
take a <samp>-f</samp> option to act on shell functions, a <samp>-p</samp> option to
display variables with various attributes set in a format that can be
used as shell input, a <samp>-n</samp> option to remove various variable
attributes, and &lsquo;<samp>name=value</samp>&rsquo; arguments to set variable attributes
and values simultaneously.

</li><li> The Bash <code>hash</code> builtin allows a name to be associated with
an arbitrary filename, even when that filename cannot be found by
searching the <code>$PATH</code>, using &lsquo;<samp>hash -p</samp>&rsquo;
(see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>).

</li><li> Bash includes a <code>help</code> builtin for quick reference to shell
facilities (see <a href="#Bash-Builtins">Bash Builtin Commands</a>).

</li><li> The <code>printf</code> builtin is available to display formatted output
(see <a href="#Bash-Builtins">Bash Builtin Commands</a>).

</li><li> The Bash <code>read</code> builtin (see <a href="#Bash-Builtins">Bash Builtin Commands</a>)
will read a line ending in &lsquo;<samp>\</samp>&rsquo; with
the <samp>-r</samp> option, and will use the <code>REPLY</code> variable as a
default if no non-option arguments are supplied.
The Bash <code>read</code> builtin
also accepts a prompt string with the <samp>-p</samp> option and will use
Readline to obtain the line when given the <samp>-e</samp> option.
The <code>read</code> builtin also has additional options to control input:
the <samp>-s</samp> option will turn off echoing of input characters as
they are read, the <samp>-t</samp> option will allow <code>read</code> to time out
if input does not arrive within a specified number of seconds, the
<samp>-n</samp> option will allow reading only a specified number of
characters rather than a full line, and the <samp>-d</samp> option will read
until a particular character rather than newline.

</li><li> The <code>return</code> builtin may be used to abort execution of scripts
executed with the <code>.</code> or <code>source</code> builtins
(see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>).

</li><li> Bash includes the <code>shopt</code> builtin, for finer control of shell
optional capabilities (see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>), and allows these options
to be set and unset at shell invocation (see <a href="#Invoking-Bash">Invoking Bash</a>).

</li><li> Bash has much more optional behavior controllable with the <code>set</code>
builtin (see <a href="#The-Set-Builtin">The Set Builtin</a>).

</li><li> The &lsquo;<samp>-x</samp>&rsquo; (<samp>xtrace</samp>) option displays commands other than
simple commands when performing an execution trace
(see <a href="#The-Set-Builtin">The Set Builtin</a>).

</li><li> The <code>test</code> builtin (see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>)
is slightly different, as it implements the POSIX algorithm,
which specifies the behavior based on the number of arguments.

</li><li> Bash includes the <code>caller</code> builtin, which displays the context of
any active subroutine call (a shell function or a script executed with
the <code>.</code> or <code>source</code> builtins). This supports the Bash
debugger.

</li><li> The <code>trap</code> builtin (see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>) allows a
<code>DEBUG</code> pseudo-signal specification, similar to <code>EXIT</code>.
Commands specified with a <code>DEBUG</code> trap are executed before every
simple command, <code>for</code> command, <code>case</code> command,
<code>select</code> command, every arithmetic <code>for</code> command, and before
the first command executes in a shell function.
The <code>DEBUG</code> trap is not inherited by shell functions unless the
function has been given the <code>trace</code> attribute or the
<code>functrace</code> option has been enabled using the <code>shopt</code> builtin.
The <code>extdebug</code> shell option has additional effects on the
<code>DEBUG</code> trap.

The <code>trap</code> builtin (see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>) allows an
<code>ERR</code> pseudo-signal specification, similar to <code>EXIT</code> and <code>DEBUG</code>.
Commands specified with an <code>ERR</code> trap are executed after a simple
command fails, with a few exceptions.
The <code>ERR</code> trap is not inherited by shell functions unless the
<code>-o errtrace</code> option to the <code>set</code> builtin is enabled.

The <code>trap</code> builtin (see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>) allows a
<code>RETURN</code> pseudo-signal specification, similar to
<code>EXIT</code> and <code>DEBUG</code>.
Commands specified with a <code>RETURN</code> trap are executed before
execution resumes after a shell function or a shell script executed with
<code>.</code> or <code>source</code> returns.
The <code>RETURN</code> trap is not inherited by shell functions unless the
function has been given the <code>trace</code> attribute or the
<code>functrace</code> option has been enabled using the <code>shopt</code> builtin.

</li><li> The Bash <code>type</code> builtin is more extensive and gives more information
about the names it finds (see <a href="#Bash-Builtins">Bash Builtin Commands</a>).

</li><li> The Bash <code>umask</code> builtin permits a <samp>-p</samp> option to cause
the output to be displayed in the form of a <code>umask</code> command
that may be reused as input (see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>).

</li><li> Bash implements a <code>csh</code>-like directory stack, and provides the
<code>pushd</code>, <code>popd</code>, and <code>dirs</code> builtins to manipulate it
(see <a href="#The-Directory-Stack">The Directory Stack</a>).
Bash also makes the directory stack visible as the value of the
<code>DIRSTACK</code> shell variable.

</li><li> Bash interprets special backslash-escaped characters in the prompt
strings when interactive (see <a href="#Controlling-the-Prompt">Controlling the Prompt</a>).

</li><li> The Bash restricted mode is more useful (see <a href="#The-Restricted-Shell">The Restricted Shell</a>);
the SVR4.2 shell restricted mode is too limited.

</li><li> The <code>disown</code> builtin can remove a job from the internal shell
job table (see <a href="#Job-Control-Builtins">Job Control Builtins</a>) or suppress the sending
of <code>SIGHUP</code> to a job when the shell exits as the result of a
<code>SIGHUP</code>.

</li><li> Bash includes a number of features to support a separate debugger for
shell scripts.

</li><li> The SVR4.2 shell has two privilege-related builtins
(<code>mldmode</code> and <code>priv</code>) not present in Bash.

</li><li> Bash does not have the <code>stop</code> or <code>newgrp</code> builtins.

</li><li> Bash does not use the <code>SHACCT</code> variable or perform shell accounting.

</li><li> The SVR4.2 <code>sh</code> uses a <code>TIMEOUT</code> variable like Bash uses
<code>TMOUT</code>.

</li></ul>

More features unique to Bash may be found in <a href="#Bash-Features">Bash Features</a>.

<ul class="section-toc">
<li><a href="#Implementation-Differences-From-The-SVR4_002e2-Shell" accesskey="1">Implementation Differences From The SVR4.2 Shell</a></li>
</ul>
<div class="appendixsec" id="Implementation-Differences-From-The-SVR4_002e2-Shell">
<h3 class="appendixsec">B.1 Implementation Differences From The SVR4.2 Shell</h3>

Since Bash is a completely new implementation, it does not suffer from
many of the limitations of the SVR4.2 shell. For instance:

<ul>
<li> Bash does not fork a subshell when redirecting into or out of
a shell control structure such as an <code>if</code> or <code>while</code>
statement.

</li><li> Bash does not allow unbalanced quotes. The SVR4.2 shell will silently
insert a needed closing quote at <code>EOF</code> under certain circumstances.
This can be the cause of some hard-to-find errors.

</li><li> The SVR4.2 shell uses a baroque memory management scheme based on
trapping <code>SIGSEGV</code>. If the shell is started from a process with
<code>SIGSEGV</code> blocked (e.g., by using the <code>system()</code> C library
function call), it misbehaves badly.

</li><li> In a questionable attempt at security, the SVR4.2 shell,
when invoked without the <samp>-p</samp> option, will alter its real
and effective UID and GID if they are less than some
magic threshold value, commonly 100.
This can lead to unexpected results.

</li><li> The SVR4.2 shell does not allow users to trap <code>SIGSEGV</code>,
<code>SIGALRM</code>, or <code>SIGCHLD</code>.

</li><li> The SVR4.2 shell does not allow the <code>IFS</code>, <code>MAILCHECK</code>,
<code>PATH</code>, <code>PS1</code>, or <code>PS2</code> variables to be unset.

</li><li> The SVR4.2 shell treats &lsquo;<samp>^</samp>&rsquo; as the undocumented equivalent of
&lsquo;<samp>|</samp>&rsquo;.

</li><li> Bash allows multiple option arguments when it is invoked (<code>-x -v</code>);
the SVR4.2 shell allows only one option argument (<code>-xv</code>). In
fact, some versions of the shell dump core if the second argument begins
with a &lsquo;<samp>-</samp>&rsquo;.

</li><li> The SVR4.2 shell exits a script if any builtin fails; Bash exits
a script only if one of the POSIX special builtins fails, and
only for certain failures, as enumerated in the POSIX standard.

</li><li> The SVR4.2 shell behaves differently when invoked as <code>jsh</code>
(it turns on job control).
</li></ul>

<hr>
</div>
</div>
<div class="appendix" id="GNU-Free-Documentation-License">
<div class="header">

Next: <a href="#Indexes" accesskey="n" rel="next">Indexes</a>, Previous: <a href="#Major-Differences-From-The-Bourne-Shell" accesskey="p" rel="prev">Major Differences From The Bourne Shell</a>, Up: <a href="#Top" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h2 class="appendix">Appendix C GNU Free Documentation License</h2>

<div align="center">Version 1.3, 3 November 2008
</div>

Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
</pre></div>

<ol start="0">
<li> PREAMBLE

The purpose of this License is to make a manual, textbook, or other
functional and useful document free in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or noncommercially.
Secondarily, this License preserves for the author and publisher a way
to get credit for their work, while not being considered responsible
for modifications made by others.

This License is a kind of &ldquo;copyleft&rdquo;, which means that derivative
works of the document must themselves be free in the same sense. It
complements the GNU General Public License, which is a copyleft
license designed for free software.

We have designed this License in order to use it for manuals for free
software, because free software needs free documentation: a free
program should come with manuals providing the same freedoms that the
software does. But this License is not limited to software manuals;
it can be used for any textual work, regardless of subject matter or
whether it is published as a printed book. We recommend this License
principally for works whose purpose is instruction or reference.

</li><li> APPLICABILITY AND DEFINITIONS

This License applies to any manual or other work, in any medium, that
contains a notice placed by the copyright holder saying it can be
distributed under the terms of this License. Such a notice grants a
world-wide, royalty-free license, unlimited in duration, to use that
work under the conditions stated herein. The &ldquo;Document&rdquo;, below,
refers to any such manual or work. Any member of the public is a
licensee, and is addressed as &ldquo;you&rdquo;. You accept the license if you
copy, modify or distribute the work in a way requiring permission
under copyright law.

A &ldquo;Modified Version&rdquo; of the Document means any work containing the
Document or a portion of it, either copied verbatim, or with
modifications and/or translated into another language.

A &ldquo;Secondary Section&rdquo; is a named appendix or a front-matter section
of the Document that deals exclusively with the relationship of the
publishers or authors of the Document to the Document&rsquo;s overall
subject (or to related matters) and contains nothing that could fall
directly within that overall subject. (Thus, if the Document is in
part a textbook of mathematics, a Secondary Section may not explain
any mathematics.) The relationship could be a matter of historical
connection with the subject or with related matters, or of legal,
commercial, philosophical, ethical or political position regarding
them.

The &ldquo;Invariant Sections&rdquo; are certain Secondary Sections whose titles
are designated, as being those of Invariant Sections, in the notice
that says that the Document is released under this License. If a
section does not fit the above definition of Secondary then it is not
allowed to be designated as Invariant. The Document may contain zero
Invariant Sections. If the Document does not identify any Invariant
Sections then there are none.

The &ldquo;Cover Texts&rdquo; are certain short passages of text that are listed,
as Front-Cover Texts or Back-Cover Texts, in the notice that says that
the Document is released under this License. A Front-Cover Text may
be at most 5 words, and a Back-Cover Text may be at most 25 words.

A &ldquo;Transparent&rdquo; copy of the Document means a machine-readable copy,
represented in a format whose specification is available to the
general public, that is suitable for revising the document
straightforwardly with generic text editors or (for images composed of
pixels) generic paint programs or (for drawings) some widely available
drawing editor, and that is suitable for input to text formatters or
for automatic translation to a variety of formats suitable for input
to text formatters. A copy made in an otherwise Transparent file
format whose markup, or absence of markup, has been arranged to thwart
or discourage subsequent modification by readers is not Transparent.
An image format is not Transparent if used for any substantial amount
of text. A copy that is not &ldquo;Transparent&rdquo; is called &ldquo;Opaque&rdquo;.

Examples of suitable formats for Transparent copies include plain
ASCII without markup, Texinfo input format, LaTeX input
format, <acronym>SGML</acronym> or <acronym>XML</acronym> using a publicly available
<acronym>DTD</acronym>, and standard-conforming simple <acronym>HTML</acronym>,
PostScript or <acronym>PDF</acronym> designed for human modification. Examples
of transparent image formats include <acronym>PNG</acronym>, <acronym>XCF</acronym> and
<acronym>JPG</acronym>. Opaque formats include proprietary formats that can be
read and edited only by proprietary word processors, <acronym>SGML</acronym> or
<acronym>XML</acronym> for which the <acronym>DTD</acronym> and/or processing tools are
not generally available, and the machine-generated <acronym>HTML</acronym>,
PostScript or <acronym>PDF</acronym> produced by some word processors for
output purposes only.

The &ldquo;Title Page&rdquo; means, for a printed book, the title page itself,
plus such following pages as are needed to hold, legibly, the material
this License requires to appear in the title page. For works in
formats which do not have any title page as such, &ldquo;Title Page&rdquo; means
the text near the most prominent appearance of the work&rsquo;s title,
preceding the beginning of the body of the text.

The &ldquo;publisher&rdquo; means any person or entity that distributes copies
of the Document to the public.

A section &ldquo;Entitled XYZ&rdquo; means a named subunit of the Document whose
title either is precisely XYZ or contains XYZ in parentheses following
text that translates XYZ in another language. (Here XYZ stands for a
specific section name mentioned below, such as &ldquo;Acknowledgements&rdquo;,
&ldquo;Dedications&rdquo;, &ldquo;Endorsements&rdquo;, or &ldquo;History&rdquo;.) To &ldquo;Preserve the Title&rdquo;
of such a section when you modify the Document means that it remains a
section &ldquo;Entitled XYZ&rdquo; according to this definition.

The Document may include Warranty Disclaimers next to the notice which
states that this License applies to the Document. These Warranty
Disclaimers are considered to be included by reference in this
License, but only as regards disclaiming warranties: any other
implication that these Warranty Disclaimers may have is void and has
no effect on the meaning of this License.

</li><li> VERBATIM COPYING

You may copy and distribute the Document in any medium, either
commercially or noncommercially, provided that this License, the
copyright notices, and the license notice saying this License applies
to the Document are reproduced in all copies, and that you add no other
conditions whatsoever to those of this License. You may not use
technical measures to obstruct or control the reading or further
copying of the copies you make or distribute. However, you may accept
compensation in exchange for copies. If you distribute a large enough
number of copies you must also follow the conditions in section 3.

You may also lend copies, under the same conditions stated above, and
you may publicly display copies.

</li><li> COPYING IN QUANTITY

If you publish printed copies (or copies in media that commonly have
printed covers) of the Document, numbering more than 100, and the
Document&rsquo;s license notice requires Cover Texts, you must enclose the
copies in covers that carry, clearly and legibly, all these Cover
Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on
the back cover. Both covers must also clearly and legibly identify
you as the publisher of these copies. The front cover must present
the full title with all words of the title equally prominent and
visible. You may add other material on the covers in addition.
Copying with changes limited to the covers, as long as they preserve
the title of the Document and satisfy these conditions, can be treated
as verbatim copying in other respects.

If the required texts for either cover are too voluminous to fit
legibly, you should put the first ones listed (as many as fit
reasonably) on the actual cover, and continue the rest onto adjacent
pages.

If you publish or distribute Opaque copies of the Document numbering
more than 100, you must either include a machine-readable Transparent
copy along with each Opaque copy, or state in or with each Opaque copy
a computer-network location from which the general network-using
public has access to download using public-standard network protocols
a complete Transparent copy of the Document, free of added material.
If you use the latter option, you must take reasonably prudent steps,
when you begin distribution of Opaque copies in quantity, to ensure
that this Transparent copy will remain thus accessible at the stated
location until at least one year after the last time you distribute an
Opaque copy (directly or through your agents or retailers) of that
edition to the public.

It is requested, but not required, that you contact the authors of the
Document well before redistributing any large number of copies, to give
them a chance to provide you with an updated version of the Document.

</li><li> MODIFICATIONS

You may copy and distribute a Modified Version of the Document under
the conditions of sections 2 and 3 above, provided that you release
the Modified Version under precisely this License, with the Modified
Version filling the role of the Document, thus licensing distribution
and modification of the Modified Version to whoever possesses a copy
of it. In addition, you must do these things in the Modified Version:

<ol type="A" start="1">
<li> Use in the Title Page (and on the covers, if any) a title distinct
from that of the Document, and from those of previous versions
(which should, if there were any, be listed in the History section
of the Document). You may use the same title as a previous version
if the original publisher of that version gives permission.

</li><li> List on the Title Page, as authors, one or more persons or entities
responsible for authorship of the modifications in the Modified
Version, together with at least five of the principal authors of the
Document (all of its principal authors, if it has fewer than five),
unless they release you from this requirement.

</li><li> State on the Title page the name of the publisher of the
Modified Version, as the publisher.

</li><li> Preserve all the copyright notices of the Document.

</li><li> Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.

</li><li> Include, immediately after the copyright notices, a license notice
giving the public permission to use the Modified Version under the
terms of this License, in the form shown in the Addendum below.

</li><li> Preserve in that license notice the full lists of Invariant Sections
and required Cover Texts given in the Document&rsquo;s license notice.

</li><li> Include an unaltered copy of this License.

</li><li> Preserve the section Entitled &ldquo;History&rdquo;, Preserve its Title, and add
to it an item stating at least the title, year, new authors, and
publisher of the Modified Version as given on the Title Page. If
there is no section Entitled &ldquo;History&rdquo; in the Document, create one
stating the title, year, authors, and publisher of the Document as
given on its Title Page, then add an item describing the Modified
Version as stated in the previous sentence.

</li><li> Preserve the network location, if any, given in the Document for
public access to a Transparent copy of the Document, and likewise
the network locations given in the Document for previous versions
it was based on. These may be placed in the &ldquo;History&rdquo; section.
You may omit a network location for a work that was published at
least four years before the Document itself, or if the original
publisher of the version it refers to gives permission.

</li><li> For any section Entitled &ldquo;Acknowledgements&rdquo; or &ldquo;Dedications&rdquo;, Preserve
the Title of the section, and preserve in the section all the
substance and tone of each of the contributor acknowledgements and/or
dedications given therein.

</li><li> Preserve all the Invariant Sections of the Document,
unaltered in their text and in their titles. Section numbers
or the equivalent are not considered part of the section titles.

</li><li> Delete any section Entitled &ldquo;Endorsements&rdquo;. Such a section
may not be included in the Modified Version.

</li><li> Do not retitle any existing section to be Entitled &ldquo;Endorsements&rdquo; or
to conflict in title with any Invariant Section.

</li><li> Preserve any Warranty Disclaimers.
</li></ol>

If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no material
copied from the Document, you may at your option designate some or all
of these sections as invariant. To do this, add their titles to the
list of Invariant Sections in the Modified Version&rsquo;s license notice.
These titles must be distinct from any other section titles.

You may add a section Entitled &ldquo;Endorsements&rdquo;, provided it contains
nothing but endorsements of your Modified Version by various
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You may add a passage of up to five words as a Front-Cover Text, and a
passage of up to 25 words as a Back-Cover Text, to the end of the list
of Cover Texts in the Modified Version. Only one passage of
Front-Cover Text and one of Back-Cover Text may be added by (or
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you may not add another; but you may replace the old one, on explicit
permission from the previous publisher that added the old one.

The author(s) and publisher(s) of the Document do not by this License
give permission to use their names for publicity for or to assert or
imply endorsement of any Modified Version.

</li><li> COMBINING DOCUMENTS

You may combine the Document with other documents released under this
License, under the terms defined in section 4 above for modified
versions, provided that you include in the combination all of the
Invariant Sections of all of the original documents, unmodified, and
list them all as Invariant Sections of your combined work in its
license notice, and that you preserve all their Warranty Disclaimers.

The combined work need only contain one copy of this License, and
multiple identical Invariant Sections may be replaced with a single
copy. If there are multiple Invariant Sections with the same name but
different contents, make the title of each such section unique by
adding at the end of it, in parentheses, the name of the original
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Make the same adjustment to the section titles in the list of
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In the combination, you must combine any sections Entitled &ldquo;History&rdquo;
in the various original documents, forming one section Entitled
&ldquo;History&rdquo;; likewise combine any sections Entitled &ldquo;Acknowledgements&rdquo;,
and any sections Entitled &ldquo;Dedications&rdquo;. You must delete all
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</li><li> COLLECTIONS OF DOCUMENTS

You may make a collection consisting of the Document and other documents
released under this License, and replace the individual copies of this
License in the various documents with a single copy that is included in
the collection, provided that you follow the rules of this License for
verbatim copying of each of the documents in all other respects.

You may extract a single document from such a collection, and distribute
it individually under this License, provided you insert a copy of this
License into the extracted document, and follow this License in all
other respects regarding verbatim copying of that document.

</li><li> AGGREGATION WITH INDEPENDENT WORKS

A compilation of the Document or its derivatives with other separate
and independent documents or works, in or on a volume of a storage or
distribution medium, is called an &ldquo;aggregate&rdquo; if the copyright
resulting from the compilation is not used to limit the legal rights
of the compilation&rsquo;s users beyond what the individual works permit.
When the Document is included in an aggregate, this License does not
apply to the other works in the aggregate which are not themselves
derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one half of
the entire aggregate, the Document&rsquo;s Cover Texts may be placed on
covers that bracket the Document within the aggregate, or the
electronic equivalent of covers if the Document is in electronic form.
Otherwise they must appear on printed covers that bracket the whole
aggregate.

</li><li> TRANSLATION

Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section 4.
Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections. You may include a
translation of this License, and all the license notices in the
Document, and any Warranty Disclaimers, provided that you also include
the original English version of this License and the original versions
of those notices and disclaimers. In case of a disagreement between
the translation and the original version of this License or a notice
or disclaimer, the original version will prevail.

If a section in the Document is Entitled &ldquo;Acknowledgements&rdquo;,
&ldquo;Dedications&rdquo;, or &ldquo;History&rdquo;, the requirement (section 4) to Preserve
its Title (section 1) will typically require changing the actual
title.

</li><li> TERMINATION

You may not copy, modify, sublicense, or distribute the Document
except as expressly provided under this License. Any attempt
otherwise to copy, modify, sublicense, or distribute it is void, and
will automatically terminate your rights under this License.

However, if you cease all violation of this License, then your license
from a particular copyright holder is reinstated (a) provisionally,
unless and until the copyright holder explicitly and finally
terminates your license, and (b) permanently, if the copyright holder
fails to notify you of the violation by some reasonable means prior to
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Moreover, your license from a particular copyright holder is
reinstated permanently if the copyright holder notifies you of the
violation by some reasonable means, this is the first time you have
received notice of violation of this License (for any work) from that
copyright holder, and you cure the violation prior to 30 days after
your receipt of the notice.

Termination of your rights under this section does not terminate the
licenses of parties who have received copies or rights from you under
this License. If your rights have been terminated and not permanently
reinstated, receipt of a copy of some or all of the same material does
not give you any rights to use it.

</li><li> FUTURE REVISIONS OF THIS LICENSE

The Free Software Foundation may publish new, revised versions
of the GNU Free Documentation License from time to time. Such new
versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns. See
<a href="http://www.gnu.org/copyleft/">http://www.gnu.org/copyleft/</a>.

Each version of the License is given a distinguishing version number.
If the Document specifies that a particular numbered version of this
License &ldquo;or any later version&rdquo; applies to it, you have the option of
following the terms and conditions either of that specified version or
of any later version that has been published (not as a draft) by the
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specifies that a proxy can decide which future versions of this
License can be used, that proxy&rsquo;s public statement of acceptance of a
version permanently authorizes you to choose that version for the
Document.

</li><li> RELICENSING

&ldquo;Massive Multiauthor Collaboration Site&rdquo; (or &ldquo;MMC Site&rdquo;) means any
World Wide Web server that publishes copyrightable works and also
provides prominent facilities for anybody to edit those works. A
public wiki that anybody can edit is an example of such a server. A
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site means any set of copyrightable works thus published on the MMC
site.

&ldquo;CC-BY-SA&rdquo; means the Creative Commons Attribution-Share Alike 3.0
license published by Creative Commons Corporation, a not-for-profit
corporation with a principal place of business in San Francisco,
California, as well as future copyleft versions of that license
published by that same organization.

&ldquo;Incorporate&rdquo; means to publish or republish a Document, in whole or
in part, as part of another Document.

An MMC is &ldquo;eligible for relicensing&rdquo; if it is licensed under this
License, and if all works that were first published under this License
somewhere other than this MMC, and subsequently incorporated in whole
or in part into the MMC, (1) had no cover texts or invariant sections,
and (2) were thus incorporated prior to November 1, 2008.

The operator of an MMC Site may republish an MMC contained in the site
under CC-BY-SA on the same site at any time before August 1, 2009,
provided the MMC is eligible for relicensing.

</li></ol>

<h3 class="heading">ADDENDUM: How to use this License for your documents</h3>

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and
license notices just after the title page:

<div class="example">
<pre class="example"> Copyright (C) <var>year</var> <var>your name</var>.
 Permission is granted to copy, distribute and/or modify this document
 under the terms of the GNU Free Documentation License, Version 1.3
 or any later version published by the Free Software Foundation;
 with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
 Texts. A copy of the license is included in the section entitled ``GNU
 Free Documentation License''.
</pre></div>

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the &ldquo;with&hellip;Texts.&rdquo; line with this:

<div class="example">
<pre class="example"> with the Invariant Sections being <var>list their titles</var>, with
 the Front-Cover Texts being <var>list</var>, and with the Back-Cover Texts
 being <var>list</var>.
</pre></div>

If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.

If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License,
to permit their use in free software.

<hr>
</div>
<div class="appendix" id="Indexes">
<div class="header">

Previous: <a href="#GNU-Free-Documentation-License" accesskey="p" rel="prev">GNU Free Documentation License</a>, Up: <a href="#Top" accesskey="u" rel="up">Bash Features</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h2 class="appendix">Appendix D Indexes</h2>

<ul class="section-toc">
<li><a href="#Builtin-Index" accesskey="1">Index of Shell Builtin Commands</a></li>
<li><a href="#Reserved-Word-Index" accesskey="2">Index of Shell Reserved Words</a></li>
<li><a href="#Variable-Index" accesskey="3">Parameter and Variable Index</a></li>
<li><a href="#Function-Index" accesskey="4">Function Index</a></li>
<li><a href="#Concept-Index" accesskey="5">Concept Index</a></li>
</ul>
<hr>
<div class="appendixsec" id="Builtin-Index">
<div class="header">

Next: <a href="#Reserved-Word-Index" accesskey="n" rel="next">Index of Shell Reserved Words</a>, Up: <a href="#Indexes" accesskey="u" rel="up">Indexes</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="appendixsec">D.1 Index of Shell Builtin Commands</h3>
<table><tr><th valign="top">Jump to: &nbsp; </th><td><a class="summary-letter" href="#Builtin-Index_bt_symbol-1">.</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_symbol-2">:</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_symbol-3">[</a>
 &nbsp; 
 
<a class="summary-letter" href="#Builtin-Index_bt_letter-A">A</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-B">B</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-C">C</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-D">D</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-E">E</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-F">F</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-G">G</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-H">H</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-J">J</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-K">K</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-L">L</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-M">M</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-P">P</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-R">R</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-S">S</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-T">T</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-U">U</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-W">W</a>
 &nbsp; 
</td></tr></table>
<table class="index-bt" border="0">
<tr><td></td><th align="left">Index Entry</th><td>&nbsp;</td><th align="left"> Section</th></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_symbol-1">.</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-_002e"><code>.</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_symbol-2">:</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-_003a"><code>:</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_symbol-3">[</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-_005b"><code>[</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_letter-A">A</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-alias"><code>alias</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_letter-B">B</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-bg"><code>bg</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Job-Control-Builtins">Job Control Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-bind"><code>bind</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-break"><code>break</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-builtin"><code>builtin</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_letter-C">C</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-caller"><code>caller</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-cd"><code>cd</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-command"><code>command</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-compgen"><code>compgen</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Programmable-Completion-Builtins">Programmable Completion Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-complete"><code>complete</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Programmable-Completion-Builtins">Programmable Completion Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-compopt"><code>compopt</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Programmable-Completion-Builtins">Programmable Completion Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-continue"><code>continue</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_letter-D">D</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-declare"><code>declare</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-dirs"><code>dirs</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Directory-Stack-Builtins">Directory Stack Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-disown"><code>disown</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Job-Control-Builtins">Job Control Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_letter-E">E</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-echo"><code>echo</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-enable"><code>enable</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-eval"><code>eval</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-exec"><code>exec</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-exit"><code>exit</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-export"><code>export</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_letter-F">F</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-fc"><code>fc</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-History-Builtins">Bash History Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-fg"><code>fg</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Job-Control-Builtins">Job Control Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_letter-G">G</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-getopts"><code>getopts</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_letter-H">H</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-hash"><code>hash</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-help"><code>help</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-history"><code>history</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-History-Builtins">Bash History Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_letter-J">J</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-jobs"><code>jobs</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Job-Control-Builtins">Job Control Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_letter-K">K</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-kill"><code>kill</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Job-Control-Builtins">Job Control Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_letter-L">L</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-let"><code>let</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-local"><code>local</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-logout"><code>logout</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_letter-M">M</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-mapfile"><code>mapfile</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_letter-P">P</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-popd"><code>popd</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Directory-Stack-Builtins">Directory Stack Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-printf"><code>printf</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-pushd"><code>pushd</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Directory-Stack-Builtins">Directory Stack Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-pwd"><code>pwd</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_letter-R">R</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-read"><code>read</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-readarray"><code>readarray</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-readonly"><code>readonly</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-return"><code>return</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_letter-S">S</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-set"><code>set</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#The-Set-Builtin">The Set Builtin</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-shift"><code>shift</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-shopt"><code>shopt</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#The-Shopt-Builtin">The Shopt Builtin</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-source"><code>source</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-suspend"><code>suspend</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Job-Control-Builtins">Job Control Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_letter-T">T</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-test"><code>test</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-times"><code>times</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-trap"><code>trap</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-type"><code>type</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-typeset"><code>typeset</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_letter-U">U</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-ulimit"><code>ulimit</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-umask"><code>umask</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-unalias"><code>unalias</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Builtins">Bash Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-unset"><code>unset</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Builtin-Index_bt_letter-W">W</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-wait"><code>wait</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Job-Control-Builtins">Job Control Builtins</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
</table>
<table><tr><th valign="top">Jump to: &nbsp; </th><td><a class="summary-letter" href="#Builtin-Index_bt_symbol-1">.</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_symbol-2">:</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_symbol-3">[</a>
 &nbsp; 
 
<a class="summary-letter" href="#Builtin-Index_bt_letter-A">A</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-B">B</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-C">C</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-D">D</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-E">E</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-F">F</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-G">G</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-H">H</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-J">J</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-K">K</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-L">L</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-M">M</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-P">P</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-R">R</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-S">S</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-T">T</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-U">U</a>
 &nbsp; 
<a class="summary-letter" href="#Builtin-Index_bt_letter-W">W</a>
 &nbsp; 
</td></tr></table>

<hr>
</div>
<div class="appendixsec" id="Reserved-Word-Index">
<div class="header">

Next: <a href="#Variable-Index" accesskey="n" rel="next">Parameter and Variable Index</a>, Previous: <a href="#Builtin-Index" accesskey="p" rel="prev">Index of Shell Builtin Commands</a>, Up: <a href="#Indexes" accesskey="u" rel="up">Indexes</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="appendixsec">D.2 Index of Shell Reserved Words</h3>
<table><tr><th valign="top">Jump to: &nbsp; </th><td><a class="summary-letter" href="#Reserved-Word-Index_rw_symbol-1">!</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_symbol-2">[</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_symbol-3">]</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_symbol-4">{</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_symbol-5">}</a>
 &nbsp; 
 
<a class="summary-letter" href="#Reserved-Word-Index_rw_letter-C">C</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_letter-D">D</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_letter-E">E</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_letter-F">F</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_letter-I">I</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_letter-S">S</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_letter-T">T</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_letter-U">U</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_letter-W">W</a>
 &nbsp; 
</td></tr></table>
<table class="index-rw" border="0">
<tr><td></td><th align="left">Index Entry</th><td>&nbsp;</td><th align="left"> Section</th></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Reserved-Word-Index_rw_symbol-1">!</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-_0021"><code>!</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Pipelines">Pipelines</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Reserved-Word-Index_rw_symbol-2">[</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-_005b_005b"><code>[[</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Conditional-Constructs">Conditional Constructs</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Reserved-Word-Index_rw_symbol-3">]</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-_005d_005d"><code>]]</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Conditional-Constructs">Conditional Constructs</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Reserved-Word-Index_rw_symbol-4">{</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-_007b"><code>{</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Command-Grouping">Command Grouping</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Reserved-Word-Index_rw_symbol-5">}</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-_007d"><code>}</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Command-Grouping">Command Grouping</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Reserved-Word-Index_rw_letter-C">C</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-case"><code>case</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Conditional-Constructs">Conditional Constructs</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Reserved-Word-Index_rw_letter-D">D</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-do"><code>do</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Looping-Constructs">Looping Constructs</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-done"><code>done</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Looping-Constructs">Looping Constructs</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Reserved-Word-Index_rw_letter-E">E</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-elif"><code>elif</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Conditional-Constructs">Conditional Constructs</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-else"><code>else</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Conditional-Constructs">Conditional Constructs</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-esac"><code>esac</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Conditional-Constructs">Conditional Constructs</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Reserved-Word-Index_rw_letter-F">F</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-fi"><code>fi</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Conditional-Constructs">Conditional Constructs</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-for"><code>for</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Looping-Constructs">Looping Constructs</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-function"><code>function</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Shell-Functions">Shell Functions</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Reserved-Word-Index_rw_letter-I">I</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-if"><code>if</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Conditional-Constructs">Conditional Constructs</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-in"><code>in</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Conditional-Constructs">Conditional Constructs</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Reserved-Word-Index_rw_letter-S">S</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-select"><code>select</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Conditional-Constructs">Conditional Constructs</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Reserved-Word-Index_rw_letter-T">T</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-then"><code>then</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Conditional-Constructs">Conditional Constructs</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-time"><code>time</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Pipelines">Pipelines</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Reserved-Word-Index_rw_letter-U">U</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-until"><code>until</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Looping-Constructs">Looping Constructs</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Reserved-Word-Index_rw_letter-W">W</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-while"><code>while</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Looping-Constructs">Looping Constructs</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
</table>
<table><tr><th valign="top">Jump to: &nbsp; </th><td><a class="summary-letter" href="#Reserved-Word-Index_rw_symbol-1">!</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_symbol-2">[</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_symbol-3">]</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_symbol-4">{</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_symbol-5">}</a>
 &nbsp; 
 
<a class="summary-letter" href="#Reserved-Word-Index_rw_letter-C">C</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_letter-D">D</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_letter-E">E</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_letter-F">F</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_letter-I">I</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_letter-S">S</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_letter-T">T</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_letter-U">U</a>
 &nbsp; 
<a class="summary-letter" href="#Reserved-Word-Index_rw_letter-W">W</a>
 &nbsp; 
</td></tr></table>

<hr>
</div>
<div class="appendixsec" id="Variable-Index">
<div class="header">

Next: <a href="#Function-Index" accesskey="n" rel="next">Function Index</a>, Previous: <a href="#Reserved-Word-Index" accesskey="p" rel="prev">Index of Shell Reserved Words</a>, Up: <a href="#Indexes" accesskey="u" rel="up">Indexes</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="appendixsec">D.3 Parameter and Variable Index</h3>
<table><tr><th valign="top">Jump to: &nbsp; </th><td><a class="summary-letter" href="#Variable-Index_vr_symbol-1">!</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_symbol-2">#</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_symbol-3">$</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_symbol-4">*</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_symbol-5">-</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_symbol-6">0</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_symbol-7">?</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_symbol-8">@</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_symbol-9">_</a>
 &nbsp; 
 
<a class="summary-letter" href="#Variable-Index_vr_letter-A">A</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-B">B</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-C">C</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-D">D</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-E">E</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-F">F</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-G">G</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-H">H</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-I">I</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-K">K</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-L">L</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-M">M</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-O">O</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-P">P</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-R">R</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-S">S</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-T">T</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-U">U</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-V">V</a>
 &nbsp; 
</td></tr></table>
<table class="index-vr" border="0">
<tr><td></td><th align="left">Index Entry</th><td>&nbsp;</td><th align="left"> Section</th></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_symbol-1">!</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-_0021-1"><code>!</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Special-Parameters">Special Parameters</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_symbol-2">#</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-_0023"><code>#</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Special-Parameters">Special Parameters</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_symbol-3">$</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-_0024"><code>$</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Special-Parameters">Special Parameters</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-_0024_0021"><code>$!</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Special-Parameters">Special Parameters</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-_0024_0023"><code>$#</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Special-Parameters">Special Parameters</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-_0024_0024"><code>$$</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Special-Parameters">Special Parameters</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-_0024_002a"><code>$*</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Special-Parameters">Special Parameters</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-_0024_002d"><code>$-</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Special-Parameters">Special Parameters</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-_00240"><code>$0</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Special-Parameters">Special Parameters</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-_0024_003f"><code>$?</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Special-Parameters">Special Parameters</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-_0024_0040"><code>$@</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Special-Parameters">Special Parameters</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-_0024_005f"><code>$_</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_symbol-4">*</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-_002a"><code>*</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Special-Parameters">Special Parameters</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_symbol-5">-</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-_002d"><code>-</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Special-Parameters">Special Parameters</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_symbol-6">0</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-0"><code>0</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Special-Parameters">Special Parameters</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_symbol-7">?</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-_003f"><code>?</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Special-Parameters">Special Parameters</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_symbol-8">@</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-_0040"><code>@</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Special-Parameters">Special Parameters</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_symbol-9">_</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-_005f"><code>_</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_letter-A">A</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-active_002dregion_002dend_002dcolor"><code>active-region-end-color</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-active_002dregion_002dstart_002dcolor"><code>active-region-start-color</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-auto_005fresume"><code>auto_resume</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Job-Control-Variables">Job Control Variables</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_letter-B">B</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASH"><code>BASH</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASHOPTS"><code>BASHOPTS</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASHPID"><code>BASHPID</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASH_005fALIASES"><code>BASH_ALIASES</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASH_005fARGC"><code>BASH_ARGC</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASH_005fARGV"><code>BASH_ARGV</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASH_005fARGV0"><code>BASH_ARGV0</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASH_005fCMDS"><code>BASH_CMDS</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASH_005fCOMMAND"><code>BASH_COMMAND</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASH_005fCOMPAT"><code>BASH_COMPAT</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASH_005fENV"><code>BASH_ENV</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASH_005fEXECUTION_005fSTRING"><code>BASH_EXECUTION_STRING</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASH_005fLINENO"><code>BASH_LINENO</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASH_005fLOADABLES_005fPATH"><code>BASH_LOADABLES_PATH</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASH_005fREMATCH"><code>BASH_REMATCH</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASH_005fSOURCE"><code>BASH_SOURCE</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASH_005fSUBSHELL"><code>BASH_SUBSHELL</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASH_005fVERSINFO"><code>BASH_VERSINFO</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASH_005fVERSION"><code>BASH_VERSION</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-BASH_005fXTRACEFD"><code>BASH_XTRACEFD</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-bell_002dstyle"><code>bell-style</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-bind_002dtty_002dspecial_002dchars"><code>bind-tty-special-chars</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-blink_002dmatching_002dparen"><code>blink-matching-paren</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_letter-C">C</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-CDPATH"><code>CDPATH</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-CHILD_005fMAX"><code>CHILD_MAX</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-colored_002dcompletion_002dprefix"><code>colored-completion-prefix</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-colored_002dstats"><code>colored-stats</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-COLUMNS"><code>COLUMNS</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-comment_002dbegin"><code>comment-begin</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-completion_002ddisplay_002dwidth"><code>completion-display-width</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-completion_002dignore_002dcase"><code>completion-ignore-case</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-completion_002dmap_002dcase"><code>completion-map-case</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-completion_002dprefix_002ddisplay_002dlength"><code>completion-prefix-display-length</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-completion_002dquery_002ditems"><code>completion-query-items</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-COMPREPLY"><code>COMPREPLY</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-COMP_005fCWORD"><code>COMP_CWORD</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-COMP_005fKEY"><code>COMP_KEY</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-COMP_005fLINE"><code>COMP_LINE</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-COMP_005fPOINT"><code>COMP_POINT</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-COMP_005fTYPE"><code>COMP_TYPE</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-COMP_005fWORDBREAKS"><code>COMP_WORDBREAKS</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-COMP_005fWORDS"><code>COMP_WORDS</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-convert_002dmeta"><code>convert-meta</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-COPROC"><code>COPROC</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_letter-D">D</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-DIRSTACK"><code>DIRSTACK</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-disable_002dcompletion"><code>disable-completion</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_letter-E">E</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-echo_002dcontrol_002dcharacters"><code>echo-control-characters</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-editing_002dmode"><code>editing-mode</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-EMACS"><code>EMACS</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-emacs_002dmode_002dstring"><code>emacs-mode-string</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-enable_002dactive_002dregion"><code>enable-active-region</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-enable_002dbracketed_002dpaste"><code>enable-bracketed-paste</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-enable_002dkeypad"><code>enable-keypad</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-ENV"><code>ENV</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-EPOCHREALTIME"><code>EPOCHREALTIME</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-EPOCHSECONDS"><code>EPOCHSECONDS</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-EUID"><code>EUID</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-EXECIGNORE"><code>EXECIGNORE</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-expand_002dtilde"><code>expand-tilde</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_letter-F">F</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-FCEDIT"><code>FCEDIT</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-FIGNORE"><code>FIGNORE</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-FUNCNAME"><code>FUNCNAME</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-FUNCNEST"><code>FUNCNEST</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_letter-G">G</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-GLOBIGNORE"><code>GLOBIGNORE</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-GROUPS"><code>GROUPS</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_letter-H">H</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-histchars"><code>histchars</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-HISTCMD"><code>HISTCMD</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-HISTCONTROL"><code>HISTCONTROL</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-HISTFILE"><code>HISTFILE</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-HISTFILESIZE"><code>HISTFILESIZE</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-HISTIGNORE"><code>HISTIGNORE</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-history_002dpreserve_002dpoint"><code>history-preserve-point</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-history_002dsize"><code>history-size</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-HISTSIZE"><code>HISTSIZE</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-HISTTIMEFORMAT"><code>HISTTIMEFORMAT</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-HOME"><code>HOME</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-horizontal_002dscroll_002dmode"><code>horizontal-scroll-mode</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-HOSTFILE"><code>HOSTFILE</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-HOSTNAME"><code>HOSTNAME</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-HOSTTYPE"><code>HOSTTYPE</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_letter-I">I</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-IFS"><code>IFS</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-IGNOREEOF"><code>IGNOREEOF</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-input_002dmeta"><code>input-meta</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-INPUTRC"><code>INPUTRC</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-INSIDE_005fEMACS"><code>INSIDE_EMACS</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-isearch_002dterminators"><code>isearch-terminators</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_letter-K">K</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-keymap"><code>keymap</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_letter-L">L</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-LANG"><code>LANG</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Creating-Internationalized-Scripts">Creating Internationalized Scripts</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-LANG-1"><code>LANG</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-LC_005fALL"><code>LC_ALL</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-LC_005fCOLLATE"><code>LC_COLLATE</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-LC_005fCTYPE"><code>LC_CTYPE</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-LC_005fMESSAGES"><code>LC_MESSAGES</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Creating-Internationalized-Scripts">Creating Internationalized Scripts</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-LC_005fMESSAGES-1"><code>LC_MESSAGES</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-LC_005fNUMERIC"><code>LC_NUMERIC</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-LC_005fTIME"><code>LC_TIME</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-LINENO"><code>LINENO</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-LINES"><code>LINES</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_letter-M">M</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-MACHTYPE"><code>MACHTYPE</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-MAIL"><code>MAIL</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-MAILCHECK"><code>MAILCHECK</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-MAILPATH"><code>MAILPATH</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-MAPFILE"><code>MAPFILE</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-mark_002dmodified_002dlines"><code>mark-modified-lines</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-mark_002dsymlinked_002ddirectories"><code>mark-symlinked-directories</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-match_002dhidden_002dfiles"><code>match-hidden-files</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-menu_002dcomplete_002ddisplay_002dprefix"><code>menu-complete-display-prefix</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-meta_002dflag"><code>meta-flag</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_letter-O">O</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-OLDPWD"><code>OLDPWD</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-OPTARG"><code>OPTARG</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-OPTERR"><code>OPTERR</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-OPTIND"><code>OPTIND</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-OSTYPE"><code>OSTYPE</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-output_002dmeta"><code>output-meta</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_letter-P">P</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-page_002dcompletions"><code>page-completions</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-PATH"><code>PATH</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-PIPESTATUS"><code>PIPESTATUS</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-POSIXLY_005fCORRECT"><code>POSIXLY_CORRECT</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-PPID"><code>PPID</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-PROMPT_005fCOMMAND"><code>PROMPT_COMMAND</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-PROMPT_005fDIRTRIM"><code>PROMPT_DIRTRIM</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-PS0"><code>PS0</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-PS1"><code>PS1</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-PS2"><code>PS2</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-PS3"><code>PS3</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-PS4"><code>PS4</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-PWD"><code>PWD</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_letter-R">R</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-RANDOM"><code>RANDOM</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-READLINE_005fARGUMENT"><code>READLINE_ARGUMENT</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-READLINE_005fLINE"><code>READLINE_LINE</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-READLINE_005fMARK"><code>READLINE_MARK</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-READLINE_005fPOINT"><code>READLINE_POINT</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-REPLY"><code>REPLY</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-revert_002dall_002dat_002dnewline"><code>revert-all-at-newline</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_letter-S">S</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-SECONDS"><code>SECONDS</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-SHELL"><code>SHELL</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-SHELLOPTS"><code>SHELLOPTS</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-SHLVL"><code>SHLVL</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-show_002dall_002dif_002dambiguous"><code>show-all-if-ambiguous</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-show_002dall_002dif_002dunmodified"><code>show-all-if-unmodified</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-show_002dmode_002din_002dprompt"><code>show-mode-in-prompt</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-skip_002dcompleted_002dtext"><code>skip-completed-text</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-SRANDOM"><code>SRANDOM</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_letter-T">T</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-TEXTDOMAIN"><code>TEXTDOMAIN</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Creating-Internationalized-Scripts">Creating Internationalized Scripts</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-TEXTDOMAINDIR"><code>TEXTDOMAINDIR</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Creating-Internationalized-Scripts">Creating Internationalized Scripts</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-TIMEFORMAT"><code>TIMEFORMAT</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-TMOUT"><code>TMOUT</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-TMPDIR"><code>TMPDIR</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_letter-U">U</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-UID"><code>UID</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Variables">Bash Variables</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Variable-Index_vr_letter-V">V</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-vi_002dcmd_002dmode_002dstring"><code>vi-cmd-mode-string</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-vi_002dins_002dmode_002dstring"><code>vi-ins-mode-string</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-visible_002dstats"><code>visible-stats</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
</table>
<table><tr><th valign="top">Jump to: &nbsp; </th><td><a class="summary-letter" href="#Variable-Index_vr_symbol-1">!</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_symbol-2">#</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_symbol-3">$</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_symbol-4">*</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_symbol-5">-</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_symbol-6">0</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_symbol-7">?</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_symbol-8">@</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_symbol-9">_</a>
 &nbsp; 
 
<a class="summary-letter" href="#Variable-Index_vr_letter-A">A</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-B">B</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-C">C</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-D">D</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-E">E</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-F">F</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-G">G</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-H">H</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-I">I</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-K">K</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-L">L</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-M">M</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-O">O</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-P">P</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-R">R</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-S">S</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-T">T</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-U">U</a>
 &nbsp; 
<a class="summary-letter" href="#Variable-Index_vr_letter-V">V</a>
 &nbsp; 
</td></tr></table>

<hr>
</div>
<div class="appendixsec" id="Function-Index">
<div class="header">

Next: <a href="#Concept-Index" accesskey="n" rel="next">Concept Index</a>, Previous: <a href="#Variable-Index" accesskey="p" rel="prev">Parameter and Variable Index</a>, Up: <a href="#Indexes" accesskey="u" rel="up">Indexes</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="appendixsec">D.4 Function Index</h3>
<table><tr><th valign="top">Jump to: &nbsp; </th><td><a class="summary-letter" href="#Function-Index_fn_letter-A">A</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-B">B</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-C">C</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-D">D</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-E">E</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-F">F</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-G">G</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-H">H</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-I">I</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-K">K</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-M">M</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-N">N</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-O">O</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-P">P</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-Q">Q</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-R">R</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-S">S</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-T">T</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-U">U</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-Y">Y</a>
 &nbsp; 
</td></tr></table>
<table class="index-fn" border="0">
<tr><td></td><th align="left">Index Entry</th><td>&nbsp;</td><th align="left"> Section</th></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-A">A</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-abort-_0028C_002dg_0029"><code>abort (C-g)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-accept_002dline-_0028Newline-or-Return_0029"><code>accept-line (Newline or Return)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-History">Commands For History</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-alias_002dexpand_002dline-_0028_0029"><code>alias-expand-line ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-B">B</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-backward_002dchar-_0028C_002db_0029"><code>backward-char (C-b)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Moving">Commands For Moving</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-backward_002ddelete_002dchar-_0028Rubout_0029"><code>backward-delete-char (Rubout)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Text">Commands For Text</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-backward_002dkill_002dline-_0028C_002dx-Rubout_0029"><code>backward-kill-line (C-x Rubout)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Killing">Commands For Killing</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-backward_002dkill_002dword-_0028M_002dDEL_0029"><code>backward-kill-word (M-DEL)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Killing">Commands For Killing</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-backward_002dword-_0028M_002db_0029"><code>backward-word (M-b)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Moving">Commands For Moving</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-beginning_002dof_002dhistory-_0028M_002d_003c_0029"><code>beginning-of-history (M-&lt;)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-History">Commands For History</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-beginning_002dof_002dline-_0028C_002da_0029"><code>beginning-of-line (C-a)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Moving">Commands For Moving</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-bracketed_002dpaste_002dbegin-_0028_0029"><code>bracketed-paste-begin ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Text">Commands For Text</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-C">C</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-call_002dlast_002dkbd_002dmacro-_0028C_002dx-e_0029"><code>call-last-kbd-macro (C-x e)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Keyboard-Macros">Keyboard Macros</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-capitalize_002dword-_0028M_002dc_0029"><code>capitalize-word (M-c)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Text">Commands For Text</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-character_002dsearch-_0028C_002d_005d_0029"><code>character-search (C-])</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-character_002dsearch_002dbackward-_0028M_002dC_002d_005d_0029"><code>character-search-backward (M-C-])</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-clear_002ddisplay-_0028M_002dC_002dl_0029"><code>clear-display (M-C-l)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Moving">Commands For Moving</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-clear_002dscreen-_0028C_002dl_0029"><code>clear-screen (C-l)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Moving">Commands For Moving</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-complete-_0028TAB_0029"><code>complete (TAB)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Completion">Commands For Completion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-complete_002dcommand-_0028M_002d_0021_0029"><code>complete-command (M-!)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Completion">Commands For Completion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-complete_002dfilename-_0028M_002d_002f_0029"><code>complete-filename (M-/)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Completion">Commands For Completion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-complete_002dhostname-_0028M_002d_0040_0029"><code>complete-hostname (M-@)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Completion">Commands For Completion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-complete_002dinto_002dbraces-_0028M_002d_007b_0029"><code>complete-into-braces (M-{)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Completion">Commands For Completion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-complete_002dusername-_0028M_002d_007e_0029"><code>complete-username (M-~)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Completion">Commands For Completion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-complete_002dvariable-_0028M_002d_0024_0029"><code>complete-variable (M-$)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Completion">Commands For Completion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-copy_002dbackward_002dword-_0028_0029"><code>copy-backward-word ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Killing">Commands For Killing</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-copy_002dforward_002dword-_0028_0029"><code>copy-forward-word ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Killing">Commands For Killing</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-copy_002dregion_002das_002dkill-_0028_0029"><code>copy-region-as-kill ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Killing">Commands For Killing</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-D">D</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-dabbrev_002dexpand-_0028_0029"><code>dabbrev-expand ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Completion">Commands For Completion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-delete_002dchar-_0028C_002dd_0029"><code>delete-char (C-d)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Text">Commands For Text</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-delete_002dchar_002dor_002dlist-_0028_0029"><code>delete-char-or-list ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Completion">Commands For Completion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-delete_002dhorizontal_002dspace-_0028_0029"><code>delete-horizontal-space ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Killing">Commands For Killing</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-digit_002dargument-_0028M_002d0_002c-M_002d1_002c-_2026-M_002d_002d_0029"><code>digit-argument (<kbd>M-0</kbd>, <kbd>M-1</kbd>, &hellip; <kbd>M--</kbd>)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Numeric-Arguments">Numeric Arguments</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-display_002dshell_002dversion-_0028C_002dx-C_002dv_0029"><code>display-shell-version (C-x C-v)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-do_002dlowercase_002dversion-_0028M_002dA_002c-M_002dB_002c-M_002dx_002c-_2026_0029"><code>do-lowercase-version (M-A, M-B, M-<var>x</var>, &hellip;)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-downcase_002dword-_0028M_002dl_0029"><code>downcase-word (M-l)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Text">Commands For Text</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-dump_002dfunctions-_0028_0029"><code>dump-functions ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-dump_002dmacros-_0028_0029"><code>dump-macros ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-dump_002dvariables-_0028_0029"><code>dump-variables ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-dynamic_002dcomplete_002dhistory-_0028M_002dTAB_0029"><code>dynamic-complete-history (M-TAB)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Completion">Commands For Completion</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-E">E</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-edit_002dand_002dexecute_002dcommand-_0028C_002dx-C_002de_0029"><code>edit-and-execute-command (C-x C-e)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-end_002dkbd_002dmacro-_0028C_002dx-_0029_0029"><code>end-kbd-macro (C-x ))</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Keyboard-Macros">Keyboard Macros</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-end_002dof_002dfile-_0028usually-C_002dd_0029"><code>end-of-file (usually C-d)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Text">Commands For Text</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-end_002dof_002dhistory-_0028M_002d_003e_0029"><code>end-of-history (M-&gt;)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-History">Commands For History</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-end_002dof_002dline-_0028C_002de_0029"><code>end-of-line (C-e)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Moving">Commands For Moving</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-exchange_002dpoint_002dand_002dmark-_0028C_002dx-C_002dx_0029"><code>exchange-point-and-mark (C-x C-x)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-F">F</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-fetch_002dhistory-_0028_0029"><code>fetch-history ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-History">Commands For History</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-forward_002dbackward_002ddelete_002dchar-_0028_0029"><code>forward-backward-delete-char ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Text">Commands For Text</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-forward_002dchar-_0028C_002df_0029"><code>forward-char (C-f)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Moving">Commands For Moving</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-forward_002dsearch_002dhistory-_0028C_002ds_0029"><code>forward-search-history (C-s)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-History">Commands For History</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-forward_002dword-_0028M_002df_0029"><code>forward-word (M-f)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Moving">Commands For Moving</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-G">G</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-glob_002dcomplete_002dword-_0028M_002dg_0029"><code>glob-complete-word (M-g)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-glob_002dexpand_002dword-_0028C_002dx-_002a_0029"><code>glob-expand-word (C-x *)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-glob_002dlist_002dexpansions-_0028C_002dx-g_0029"><code>glob-list-expansions (C-x g)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-H">H</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-history_002dand_002dalias_002dexpand_002dline-_0028_0029"><code>history-and-alias-expand-line ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-history_002dexpand_002dline-_0028M_002d_005e_0029"><code>history-expand-line (M-^)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-history_002dsearch_002dbackward-_0028_0029"><code>history-search-backward ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-History">Commands For History</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-history_002dsearch_002dforward-_0028_0029"><code>history-search-forward ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-History">Commands For History</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-history_002dsubstring_002dsearch_002dbackward-_0028_0029"><code>history-substring-search-backward ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-History">Commands For History</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-history_002dsubstring_002dsearch_002dforward-_0028_0029"><code>history-substring-search-forward ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-History">Commands For History</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-I">I</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-insert_002dcomment-_0028M_002d_0023_0029"><code>insert-comment (M-#)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-insert_002dcompletions-_0028M_002d_002a_0029"><code>insert-completions (M-*)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Completion">Commands For Completion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-insert_002dlast_002dargument-_0028M_002d_002e-or-M_002d_005f_0029"><code>insert-last-argument (M-. or M-_)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-K">K</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-kill_002dline-_0028C_002dk_0029"><code>kill-line (C-k)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Killing">Commands For Killing</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-kill_002dregion-_0028_0029"><code>kill-region ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Killing">Commands For Killing</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-kill_002dwhole_002dline-_0028_0029"><code>kill-whole-line ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Killing">Commands For Killing</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-kill_002dword-_0028M_002dd_0029"><code>kill-word (M-d)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Killing">Commands For Killing</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-M">M</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-magic_002dspace-_0028_0029"><code>magic-space ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-menu_002dcomplete-_0028_0029"><code>menu-complete ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Completion">Commands For Completion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-menu_002dcomplete_002dbackward-_0028_0029"><code>menu-complete-backward ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Completion">Commands For Completion</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-N">N</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-next_002dhistory-_0028C_002dn_0029"><code>next-history (C-n)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-History">Commands For History</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-next_002dscreen_002dline-_0028_0029"><code>next-screen-line ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Moving">Commands For Moving</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-non_002dincremental_002dforward_002dsearch_002dhistory-_0028M_002dn_0029"><code>non-incremental-forward-search-history (M-n)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-History">Commands For History</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-non_002dincremental_002dreverse_002dsearch_002dhistory-_0028M_002dp_0029"><code>non-incremental-reverse-search-history (M-p)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-History">Commands For History</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-O">O</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-operate_002dand_002dget_002dnext-_0028C_002do_0029"><code>operate-and-get-next (C-o)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-History">Commands For History</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-overwrite_002dmode-_0028_0029"><code>overwrite-mode ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Text">Commands For Text</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-P">P</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-possible_002dcommand_002dcompletions-_0028C_002dx-_0021_0029"><code>possible-command-completions (C-x !)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Completion">Commands For Completion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-possible_002dcompletions-_0028M_002d_003f_0029"><code>possible-completions (M-?)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Completion">Commands For Completion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-possible_002dfilename_002dcompletions-_0028C_002dx-_002f_0029"><code>possible-filename-completions (C-x /)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Completion">Commands For Completion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-possible_002dhostname_002dcompletions-_0028C_002dx-_0040_0029"><code>possible-hostname-completions (C-x @)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Completion">Commands For Completion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-possible_002dusername_002dcompletions-_0028C_002dx-_007e_0029"><code>possible-username-completions (C-x ~)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Completion">Commands For Completion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-possible_002dvariable_002dcompletions-_0028C_002dx-_0024_0029"><code>possible-variable-completions (C-x $)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Completion">Commands For Completion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-prefix_002dmeta-_0028ESC_0029"><code>prefix-meta (ESC)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-previous_002dhistory-_0028C_002dp_0029"><code>previous-history (C-p)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-History">Commands For History</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-previous_002dscreen_002dline-_0028_0029"><code>previous-screen-line ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Moving">Commands For Moving</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-print_002dlast_002dkbd_002dmacro-_0028_0029"><code>print-last-kbd-macro ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Keyboard-Macros">Keyboard Macros</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-Q">Q</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-quoted_002dinsert-_0028C_002dq-or-C_002dv_0029"><code>quoted-insert (C-q or C-v)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Text">Commands For Text</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-R">R</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-re_002dread_002dinit_002dfile-_0028C_002dx-C_002dr_0029"><code>re-read-init-file (C-x C-r)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-redraw_002dcurrent_002dline-_0028_0029"><code>redraw-current-line ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Moving">Commands For Moving</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-reverse_002dsearch_002dhistory-_0028C_002dr_0029"><code>reverse-search-history (C-r)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-History">Commands For History</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-revert_002dline-_0028M_002dr_0029"><code>revert-line (M-r)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-S">S</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-self_002dinsert-_0028a_002c-b_002c-A_002c-1_002c-_0021_002c-_2026_0029"><code>self-insert (a, b, A, 1, !, &hellip;)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Text">Commands For Text</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-set_002dmark-_0028C_002d_0040_0029"><code>set-mark (C-@)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-shell_002dbackward_002dkill_002dword-_0028_0029"><code>shell-backward-kill-word ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Killing">Commands For Killing</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-shell_002dbackward_002dword-_0028M_002dC_002db_0029"><code>shell-backward-word (M-C-b)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Moving">Commands For Moving</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-shell_002dexpand_002dline-_0028M_002dC_002de_0029"><code>shell-expand-line (M-C-e)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-shell_002dforward_002dword-_0028M_002dC_002df_0029"><code>shell-forward-word (M-C-f)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Moving">Commands For Moving</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-shell_002dkill_002dword-_0028M_002dC_002dd_0029"><code>shell-kill-word (M-C-d)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Killing">Commands For Killing</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-shell_002dtranspose_002dwords-_0028M_002dC_002dt_0029"><code>shell-transpose-words (M-C-t)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Killing">Commands For Killing</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-skip_002dcsi_002dsequence-_0028_0029"><code>skip-csi-sequence ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-spell_002dcorrect_002dword-_0028C_002dx-s_0029"><code>spell-correct-word (C-x s)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-start_002dkbd_002dmacro-_0028C_002dx-_0028_0029"><code>start-kbd-macro (C-x ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Keyboard-Macros">Keyboard Macros</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-T">T</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-tilde_002dexpand-_0028M_002d_0026_0029"><code>tilde-expand (M-&amp;)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-transpose_002dchars-_0028C_002dt_0029"><code>transpose-chars (C-t)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Text">Commands For Text</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-transpose_002dwords-_0028M_002dt_0029"><code>transpose-words (M-t)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Text">Commands For Text</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-U">U</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-undo-_0028C_002d_005f-or-C_002dx-C_002du_0029"><code>undo (C-_ or C-x C-u)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Miscellaneous-Commands">Miscellaneous Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-universal_002dargument-_0028_0029"><code>universal-argument ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Numeric-Arguments">Numeric Arguments</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-unix_002dfilename_002drubout-_0028_0029"><code>unix-filename-rubout ()</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Killing">Commands For Killing</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-unix_002dline_002ddiscard-_0028C_002du_0029"><code>unix-line-discard (C-u)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Killing">Commands For Killing</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-unix_002dword_002drubout-_0028C_002dw_0029"><code>unix-word-rubout (C-w)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Killing">Commands For Killing</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-upcase_002dword-_0028M_002du_0029"><code>upcase-word (M-u)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Text">Commands For Text</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Function-Index_fn_letter-Y">Y</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-yank-_0028C_002dy_0029"><code>yank (C-y)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Killing">Commands For Killing</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-yank_002dlast_002darg-_0028M_002d_002e-or-M_002d_005f_0029"><code>yank-last-arg (M-. or M-_)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-History">Commands For History</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-yank_002dnth_002darg-_0028M_002dC_002dy_0029"><code>yank-nth-arg (M-C-y)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-History">Commands For History</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-yank_002dpop-_0028M_002dy_0029"><code>yank-pop (M-y)</code></a>:</td><td>&nbsp;</td><td valign="top"><a href="#Commands-For-Killing">Commands For Killing</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
</table>
<table><tr><th valign="top">Jump to: &nbsp; </th><td><a class="summary-letter" href="#Function-Index_fn_letter-A">A</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-B">B</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-C">C</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-D">D</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-E">E</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-F">F</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-G">G</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-H">H</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-I">I</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-K">K</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-M">M</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-N">N</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-O">O</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-P">P</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-Q">Q</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-R">R</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-S">S</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-T">T</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-U">U</a>
 &nbsp; 
<a class="summary-letter" href="#Function-Index_fn_letter-Y">Y</a>
 &nbsp; 
</td></tr></table>

<hr>
</div>
<div class="appendixsec" id="Concept-Index">
<div class="header">

Previous: <a href="#Function-Index" accesskey="p" rel="prev">Function Index</a>, Up: <a href="#Indexes" accesskey="u" rel="up">Indexes</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="#Indexes" title="Index" rel="index">Index</a>]
</div>
<h3 class="appendixsec">D.5 Concept Index</h3>
<table><tr><th valign="top">Jump to: &nbsp; </th><td><a class="summary-letter" href="#Concept-Index_cp_letter-A">A</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-B">B</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-C">C</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-D">D</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-E">E</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-F">F</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-H">H</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-I">I</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-J">J</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-K">K</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-L">L</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-M">M</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-N">N</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-O">O</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-P">P</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-Q">Q</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-R">R</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-S">S</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-T">T</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-V">V</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-W">W</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-Y">Y</a>
 &nbsp; 
</td></tr></table>
<table class="index-cp" border="0">
<tr><td></td><th align="left">Index Entry</th><td>&nbsp;</td><th align="left"> Section</th></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-A">A</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-alias-expansion">alias expansion</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Aliases">Aliases</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-arithmetic-evaluation">arithmetic evaluation</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Shell-Arithmetic">Shell Arithmetic</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-arithmetic-expansion">arithmetic expansion</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Arithmetic-Expansion">Arithmetic Expansion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-arithmetic_002c-shell">arithmetic, shell</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Shell-Arithmetic">Shell Arithmetic</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-arrays">arrays</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Arrays">Arrays</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-B">B</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-background">background</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Job-Control-Basics">Job Control Basics</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-Bash-configuration">Bash configuration</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Basic-Installation">Basic Installation</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-Bash-installation">Bash installation</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Basic-Installation">Basic Installation</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-Bourne-shell">Bourne shell</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Basic-Shell-Features">Basic Shell Features</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-brace-expansion">brace expansion</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Brace-Expansion">Brace Expansion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-builtin-1">builtin</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-C">C</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-command-editing">command editing</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Bare-Essentials">Readline Bare Essentials</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-command-execution">command execution</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Command-Search-and-Execution">Command Search and Execution</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-command-expansion">command expansion</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Simple-Command-Expansion">Simple Command Expansion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-command-history">command history</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-History-Facilities">Bash History Facilities</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-command-search">command search</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Command-Search-and-Execution">Command Search and Execution</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-command-substitution">command substitution</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Command-Substitution">Command Substitution</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-command-timing">command timing</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Pipelines">Pipelines</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-commands_002c-compound">commands, compound</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Compound-Commands">Compound Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-commands_002c-conditional">commands, conditional</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Conditional-Constructs">Conditional Constructs</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-commands_002c-grouping">commands, grouping</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Command-Grouping">Command Grouping</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-commands_002c-lists">commands, lists</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Lists">Lists</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-commands_002c-looping">commands, looping</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Looping-Constructs">Looping Constructs</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-commands_002c-pipelines">commands, pipelines</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Pipelines">Pipelines</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-commands_002c-shell">commands, shell</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Shell-Commands">Shell Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-commands_002c-simple">commands, simple</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Simple-Commands">Simple Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-comments_002c-shell">comments, shell</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Comments">Comments</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-Compatibility-Level">Compatibility Level</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Shell-Compatibility-Mode">Shell Compatibility Mode</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-Compatibility-Mode">Compatibility Mode</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Shell-Compatibility-Mode">Shell Compatibility Mode</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-completion-builtins">completion builtins</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Programmable-Completion-Builtins">Programmable Completion Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-configuration">configuration</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Basic-Installation">Basic Installation</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-control-operator">control operator</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-coprocess">coprocess</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Coprocesses">Coprocesses</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-D">D</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-directory-stack">directory stack</a>:</td><td>&nbsp;</td><td valign="top"><a href="#The-Directory-Stack">The Directory Stack</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-E">E</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-editing-command-lines">editing command lines</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Bare-Essentials">Readline Bare Essentials</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-environment">environment</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Environment">Environment</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-evaluation_002c-arithmetic">evaluation, arithmetic</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Shell-Arithmetic">Shell Arithmetic</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-event-designators">event designators</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Event-Designators">Event Designators</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-execution-environment">execution environment</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Command-Execution-Environment">Command Execution Environment</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-exit-status">exit status</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-exit-status-1">exit status</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Exit-Status">Exit Status</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-expansion">expansion</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Shell-Expansions">Shell Expansions</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-expansion_002c-arithmetic">expansion, arithmetic</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Arithmetic-Expansion">Arithmetic Expansion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-expansion_002c-brace">expansion, brace</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Brace-Expansion">Brace Expansion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-expansion_002c-filename">expansion, filename</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Filename-Expansion">Filename Expansion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-expansion_002c-parameter">expansion, parameter</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-expansion_002c-pathname">expansion, pathname</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Filename-Expansion">Filename Expansion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-expansion_002c-tilde">expansion, tilde</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Tilde-Expansion">Tilde Expansion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-expressions_002c-arithmetic">expressions, arithmetic</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Shell-Arithmetic">Shell Arithmetic</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-expressions_002c-conditional">expressions, conditional</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Conditional-Expressions">Bash Conditional Expressions</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-F">F</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-field">field</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-filename">filename</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-filename-expansion">filename expansion</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Filename-Expansion">Filename Expansion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-foreground">foreground</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Job-Control-Basics">Job Control Basics</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-functions_002c-shell">functions, shell</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Shell-Functions">Shell Functions</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-H">H</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-history-builtins">history builtins</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-History-Builtins">Bash History Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-history-events">history events</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Event-Designators">Event Designators</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-history-expansion">history expansion</a>:</td><td>&nbsp;</td><td valign="top"><a href="#History-Interaction">History Interaction</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-history-list">history list</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-History-Facilities">Bash History Facilities</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-History_002c-how-to-use">History, how to use</a>:</td><td>&nbsp;</td><td valign="top"><a href="#A-Programmable-Completion-Example">A Programmable Completion Example</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-I">I</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-identifier">identifier</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-initialization-file_002c-readline">initialization file, readline</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File">Readline Init File</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-installation">installation</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Basic-Installation">Basic Installation</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-interaction_002c-readline">interaction, readline</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Interaction">Readline Interaction</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-interactive-shell">interactive shell</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Invoking-Bash">Invoking Bash</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-interactive-shell-1">interactive shell</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Interactive-Shells">Interactive Shells</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-internationalization">internationalization</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Locale-Translation">Locale Translation</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-internationalized-scripts">internationalized scripts</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Creating-Internationalized-Scripts">Creating Internationalized Scripts</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-J">J</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-job">job</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-job-control">job control</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-job-control-1">job control</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Job-Control-Basics">Job Control Basics</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-K">K</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-kill-ring">kill ring</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Killing-Commands">Readline Killing Commands</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-killing-text">killing text</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Killing-Commands">Readline Killing Commands</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-L">L</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-localization">localization</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Locale-Translation">Locale Translation</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-login-shell">login shell</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Invoking-Bash">Invoking Bash</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-M">M</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-matching_002c-pattern">matching, pattern</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Pattern-Matching">Pattern Matching</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-metacharacter">metacharacter</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-N">N</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-name">name</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-native-languages">native languages</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Locale-Translation">Locale Translation</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-notation_002c-readline">notation, readline</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Bare-Essentials">Readline Bare Essentials</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-O">O</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-operator_002c-shell">operator, shell</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-P">P</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-parameter-expansion">parameter expansion</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-parameters">parameters</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Shell-Parameters">Shell Parameters</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-parameters_002c-positional">parameters, positional</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Positional-Parameters">Positional Parameters</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-parameters_002c-special">parameters, special</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Special-Parameters">Special Parameters</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-pathname-expansion">pathname expansion</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Filename-Expansion">Filename Expansion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-pattern-matching">pattern matching</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Pattern-Matching">Pattern Matching</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-pipeline">pipeline</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Pipelines">Pipelines</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-POSIX">POSIX</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-POSIX-Mode">POSIX Mode</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-POSIX-Mode">Bash POSIX Mode</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-process-group">process group</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-process-group-ID">process group ID</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-process-substitution">process substitution</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Process-Substitution">Process Substitution</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-programmable-completion">programmable completion</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Programmable-Completion">Programmable Completion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-prompting">prompting</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Controlling-the-Prompt">Controlling the Prompt</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-Q">Q</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-quoting">quoting</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Quoting">Quoting</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-quoting_002c-ANSI">quoting, ANSI</a>:</td><td>&nbsp;</td><td valign="top"><a href="#ANSI_002dC-Quoting">ANSI-C Quoting</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-R">R</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-Readline_002c-how-to-use">Readline, how to use</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Job-Control-Variables">Job Control Variables</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-redirection">redirection</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Redirections">Redirections</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-reserved-word">reserved word</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-reserved-words">reserved words</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Reserved-Words">Reserved Words</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-restricted-shell">restricted shell</a>:</td><td>&nbsp;</td><td valign="top"><a href="#The-Restricted-Shell">The Restricted Shell</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-return-status">return status</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-S">S</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-shell-arithmetic">shell arithmetic</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Shell-Arithmetic">Shell Arithmetic</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-shell-function">shell function</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Shell-Functions">Shell Functions</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-shell-script">shell script</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Shell-Scripts">Shell Scripts</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-shell-variable">shell variable</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Shell-Parameters">Shell Parameters</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-shell_002c-interactive">shell, interactive</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Interactive-Shells">Interactive Shells</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-signal">signal</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-signal-handling">signal handling</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Signals">Signals</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-special-builtin">special builtin</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-special-builtin-1">special builtin</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Special-Builtins">Special Builtins</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-startup-files">startup files</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Bash-Startup-Files">Bash Startup Files</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-string-translations">string translations</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Creating-Internationalized-Scripts">Creating Internationalized Scripts</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-suspending-jobs">suspending jobs</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Job-Control-Basics">Job Control Basics</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-T">T</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-tilde-expansion">tilde expansion</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Tilde-Expansion">Tilde Expansion</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-token">token</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-translation_002c-native-languages">translation, native languages</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Locale-Translation">Locale Translation</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-V">V</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-variable_002c-shell">variable, shell</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Shell-Parameters">Shell Parameters</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-variables_002c-readline">variables, readline</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-W">W</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-word">word</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Definitions">Definitions</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-word-splitting">word splitting</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Word-Splitting">Word Splitting</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th id="Concept-Index_cp_letter-Y">Y</th><td></td><td></td></tr>
<tr><td></td><td valign="top"><a href="#index-yanking-text">yanking text</a>:</td><td>&nbsp;</td><td valign="top"><a href="#Readline-Killing-Commands">Readline Killing Commands</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
</table>
<table><tr><th valign="top">Jump to: &nbsp; </th><td><a class="summary-letter" href="#Concept-Index_cp_letter-A">A</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-B">B</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-C">C</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-D">D</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-E">E</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-F">F</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-H">H</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-I">I</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-J">J</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-K">K</a>
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<a class="summary-letter" href="#Concept-Index_cp_letter-L">L</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-M">M</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-N">N</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-O">O</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-P">P</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-Q">Q</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-R">R</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-S">S</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-T">T</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-V">V</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-W">W</a>
 &nbsp; 
<a class="summary-letter" href="#Concept-Index_cp_letter-Y">Y</a>
 &nbsp; 
</td></tr></table>

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