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<html lang="en">
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<title>Bash Reference Manual</title>
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This text is a brief description of the features that are present in
the Bash shell (version 3.2, 30 December 2006).
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<body>
<h1 class="settitle">Bash Reference Manual</h1>
<div class="contents">
<h2>Table of Contents</h2>
<ul>
<li><a name="toc_Top" href="#Top">Bash Features</a>
<li><a name="toc_Introduction" href="#Introduction">1 Introduction</a>
<ul>
<li><a href="#What-is-Bash_003f">1.1 What is Bash?</a>
<li><a href="#What-is-a-shell_003f">1.2 What is a shell?</a>
</li></ul>
<li><a name="toc_Definitions" href="#Definitions">2 Definitions</a>
<li><a name="toc_Basic-Shell-Features" href="#Basic-Shell-Features">3 Basic Shell Features</a>
<ul>
<li><a href="#Shell-Syntax">3.1 Shell Syntax</a>
<ul>
<li><a href="#Shell-Operation">3.1.1 Shell Operation</a>
<li><a href="#Quoting">3.1.2 Quoting</a>
<ul>
<li><a href="#Escape-Character">3.1.2.1 Escape Character</a>
<li><a href="#Single-Quotes">3.1.2.2 Single Quotes</a>
<li><a href="#Double-Quotes">3.1.2.3 Double Quotes</a>
<li><a href="#ANSI_002dC-Quoting">3.1.2.4 ANSI-C Quoting</a>
<li><a href="#Locale-Translation">3.1.2.5 Locale-Specific Translation</a>
</li></ul>
<li><a href="#Comments">3.1.3 Comments</a>
</li></ul>
<li><a href="#Shell-Commands">3.2 Shell Commands</a>
<ul>
<li><a href="#Simple-Commands">3.2.1 Simple Commands</a>
<li><a href="#Pipelines">3.2.2 Pipelines</a>
<li><a href="#Lists">3.2.3 Lists of Commands</a>
<li><a href="#Compound-Commands">3.2.4 Compound Commands</a>
<ul>
<li><a href="#Looping-Constructs">3.2.4.1 Looping Constructs</a>
<li><a href="#Conditional-Constructs">3.2.4.2 Conditional Constructs</a>
<li><a href="#Command-Grouping">3.2.4.3 Grouping Commands</a>
</li></ul>
</li></ul>
<li><a href="#Shell-Functions">3.3 Shell Functions</a>
<li><a href="#Shell-Parameters">3.4 Shell Parameters</a>
<ul>
<li><a href="#Positional-Parameters">3.4.1 Positional Parameters</a>
<li><a href="#Special-Parameters">3.4.2 Special Parameters</a>
</li></ul>
<li><a href="#Shell-Expansions">3.5 Shell Expansions</a>
<ul>
<li><a href="#Brace-Expansion">3.5.1 Brace Expansion</a>
<li><a href="#Tilde-Expansion">3.5.2 Tilde Expansion</a>
<li><a href="#Shell-Parameter-Expansion">3.5.3 Shell Parameter Expansion</a>
<li><a href="#Command-Substitution">3.5.4 Command Substitution</a>
<li><a href="#Arithmetic-Expansion">3.5.5 Arithmetic Expansion</a>
<li><a href="#Process-Substitution">3.5.6 Process Substitution</a>
<li><a href="#Word-Splitting">3.5.7 Word Splitting</a>
<li><a href="#Filename-Expansion">3.5.8 Filename Expansion</a>
<ul>
<li><a href="#Pattern-Matching">3.5.8.1 Pattern Matching</a>
</li></ul>
<li><a href="#Quote-Removal">3.5.9 Quote Removal</a>
</li></ul>
<li><a href="#Redirections">3.6 Redirections</a>
<ul>
<li><a href="#Redirections">3.6.1 Redirecting Input</a>
<li><a href="#Redirections">3.6.2 Redirecting Output</a>
<li><a href="#Redirections">3.6.3 Appending Redirected Output</a>
<li><a href="#Redirections">3.6.4 Redirecting Standard Output and Standard Error</a>
<li><a href="#Redirections">3.6.5 Here Documents</a>
<li><a href="#Redirections">3.6.6 Here Strings</a>
<li><a href="#Redirections">3.6.7 Duplicating File Descriptors</a>
<li><a href="#Redirections">3.6.8 Moving File Descriptors</a>
<li><a href="#Redirections">3.6.9 Opening File Descriptors for Reading and Writing</a>
</li></ul>
<li><a href="#Executing-Commands">3.7 Executing Commands</a>
<ul>
<li><a href="#Simple-Command-Expansion">3.7.1 Simple Command Expansion</a>
<li><a href="#Command-Search-and-Execution">3.7.2 Command Search and Execution</a>
<li><a href="#Command-Execution-Environment">3.7.3 Command Execution Environment</a>
<li><a href="#Environment">3.7.4 Environment</a>
<li><a href="#Exit-Status">3.7.5 Exit Status</a>
<li><a href="#Signals">3.7.6 Signals</a>
</li></ul>
<li><a href="#Shell-Scripts">3.8 Shell Scripts</a>
</li></ul>
<li><a name="toc_Shell-Builtin-Commands" href="#Shell-Builtin-Commands">4 Shell Builtin Commands</a>
<ul>
<li><a href="#Bourne-Shell-Builtins">4.1 Bourne Shell Builtins</a>
<li><a href="#Bash-Builtins">4.2 Bash Builtin Commands</a>
<li><a href="#Modifying-Shell-Behavior">4.3 Modifying Shell Behavior</a>
<ul>
<li><a href="#The-Set-Builtin">4.3.1 The Set Builtin</a>
<li><a href="#The-Shopt-Builtin">4.3.2 The Shopt Builtin</a>
</li></ul>
<li><a href="#Special-Builtins">4.4 Special Builtins</a>
</li></ul>
<li><a name="toc_Shell-Variables" href="#Shell-Variables">5 Shell Variables</a>
<ul>
<li><a href="#Bourne-Shell-Variables">5.1 Bourne Shell Variables</a>
<li><a href="#Bash-Variables">5.2 Bash Variables</a>
</li></ul>
<li><a name="toc_Bash-Features" href="#Bash-Features">6 Bash Features</a>
<ul>
<li><a href="#Invoking-Bash">6.1 Invoking Bash</a>
<li><a href="#Bash-Startup-Files">6.2 Bash Startup Files</a>
<li><a href="#Interactive-Shells">6.3 Interactive Shells</a>
<ul>
<li><a href="#What-is-an-Interactive-Shell_003f">6.3.1 What is an Interactive Shell?</a>
<li><a href="#Is-this-Shell-Interactive_003f">6.3.2 Is this Shell Interactive?</a>
<li><a href="#Interactive-Shell-Behavior">6.3.3 Interactive Shell Behavior</a>
</li></ul>
<li><a href="#Bash-Conditional-Expressions">6.4 Bash Conditional Expressions</a>
<li><a href="#Shell-Arithmetic">6.5 Shell Arithmetic</a>
<li><a href="#Aliases">6.6 Aliases</a>
<li><a href="#Arrays">6.7 Arrays</a>
<li><a href="#The-Directory-Stack">6.8 The Directory Stack</a>
<ul>
<li><a href="#Directory-Stack-Builtins">6.8.1 Directory Stack Builtins</a>
</li></ul>
<li><a href="#Printing-a-Prompt">6.9 Controlling the Prompt</a>
<li><a href="#The-Restricted-Shell">6.10 The Restricted Shell</a>
<li><a href="#Bash-POSIX-Mode">6.11 Bash POSIX Mode</a>
</li></ul>
<li><a name="toc_Job-Control" href="#Job-Control">7 Job Control</a>
<ul>
<li><a href="#Job-Control-Basics">7.1 Job Control Basics</a>
<li><a href="#Job-Control-Builtins">7.2 Job Control Builtins</a>
<li><a href="#Job-Control-Variables">7.3 Job Control Variables</a>
</li></ul>
<li><a name="toc_Command-Line-Editing" href="#Command-Line-Editing">8 Command Line Editing</a>
<ul>
<li><a href="#Introduction-and-Notation">8.1 Introduction to Line Editing</a>
<li><a href="#Readline-Interaction">8.2 Readline Interaction</a>
<ul>
<li><a href="#Readline-Bare-Essentials">8.2.1 Readline Bare Essentials</a>
<li><a href="#Readline-Movement-Commands">8.2.2 Readline Movement Commands</a>
<li><a href="#Readline-Killing-Commands">8.2.3 Readline Killing Commands</a>
<li><a href="#Readline-Arguments">8.2.4 Readline Arguments</a>
<li><a href="#Searching">8.2.5 Searching for Commands in the History</a>
</li></ul>
<li><a href="#Readline-Init-File">8.3 Readline Init File</a>
<ul>
<li><a href="#Readline-Init-File-Syntax">8.3.1 Readline Init File Syntax</a>
<li><a href="#Conditional-Init-Constructs">8.3.2 Conditional Init Constructs</a>
<li><a href="#Sample-Init-File">8.3.3 Sample Init File</a>
</li></ul>
<li><a href="#Bindable-Readline-Commands">8.4 Bindable Readline Commands</a>
<ul>
<li><a href="#Commands-For-Moving">8.4.1 Commands For Moving</a>
<li><a href="#Commands-For-History">8.4.2 Commands For Manipulating The History</a>
<li><a href="#Commands-For-Text">8.4.3 Commands For Changing Text</a>
<li><a href="#Commands-For-Killing">8.4.4 Killing And Yanking</a>
<li><a href="#Numeric-Arguments">8.4.5 Specifying Numeric Arguments</a>
<li><a href="#Commands-For-Completion">8.4.6 Letting Readline Type For You</a>
<li><a href="#Keyboard-Macros">8.4.7 Keyboard Macros</a>
<li><a href="#Miscellaneous-Commands">8.4.8 Some Miscellaneous Commands</a>
</li></ul>
<li><a href="#Readline-vi-Mode">8.5 Readline vi Mode</a>
<li><a href="#Programmable-Completion">8.6 Programmable Completion</a>
<li><a href="#Programmable-Completion-Builtins">8.7 Programmable Completion Builtins</a>
</li></ul>
<li><a name="toc_Using-History-Interactively" href="#Using-History-Interactively">9 Using History Interactively</a>
<ul>
<li><a href="#Bash-History-Facilities">9.1 Bash History Facilities</a>
<li><a href="#Bash-History-Builtins">9.2 Bash History Builtins</a>
<li><a href="#History-Interaction">9.3 History Expansion</a>
<ul>
<li><a href="#Event-Designators">9.3.1 Event Designators</a>
<li><a href="#Word-Designators">9.3.2 Word Designators</a>
<li><a href="#Modifiers">9.3.3 Modifiers</a>
</li></ul>
</li></ul>
<li><a name="toc_Installing-Bash" href="#Installing-Bash">10 Installing Bash</a>
<ul>
<li><a href="#Basic-Installation">10.1 Basic Installation</a>
<li><a href="#Compilers-and-Options">10.2 Compilers and Options</a>
<li><a href="#Compiling-For-Multiple-Architectures">10.3 Compiling For Multiple Architectures</a>
<li><a href="#Installation-Names">10.4 Installation Names</a>
<li><a href="#Specifying-the-System-Type">10.5 Specifying the System Type</a>
<li><a href="#Sharing-Defaults">10.6 Sharing Defaults</a>
<li><a href="#Operation-Controls">10.7 Operation Controls</a>
<li><a href="#Optional-Features">10.8 Optional Features</a>
</li></ul>
<li><a name="toc_Reporting-Bugs" href="#Reporting-Bugs">Appendix A Reporting Bugs</a>
<li><a name="toc_Major-Differences-From-The-Bourne-Shell" href="#Major-Differences-From-The-Bourne-Shell">Appendix B Major Differences From The Bourne Shell</a>
<ul>
<li><a href="#Major-Differences-From-The-Bourne-Shell">B.1 Implementation Differences From The SVR4.2 Shell</a>
</li></ul>
<li><a name="toc_Copying-This-Manual" href="#Copying-This-Manual">Appendix C Copying This Manual</a>
<ul>
<li><a href="#GNU-Free-Documentation-License">C.1 GNU Free Documentation License</a>
<ul>
<li><a href="#GNU-Free-Documentation-License">C.1.1 ADDENDUM: How to use this License for your documents</a>
</li></ul>
</li></ul>
<li><a name="toc_Builtin-Index" href="#Builtin-Index">Index of Shell Builtin Commands</a>
<li><a name="toc_Reserved-Word-Index" href="#Reserved-Word-Index">Index of Shell Reserved Words</a>
<li><a name="toc_Variable-Index" href="#Variable-Index">Parameter and Variable Index</a>
<li><a name="toc_Function-Index" href="#Function-Index">Function Index</a>
<li><a name="toc_Concept-Index" href="#Concept-Index">Concept Index</a>
</li></ul>
</div>
<div class="node">
<p><hr>
<a name="Top"></a>
Next: <a rel="next" accesskey="n" href="#Introduction">Introduction</a>,
Previous: <a rel="previous" accesskey="p" href="#dir">(dir)</a>,
Up: <a rel="up" accesskey="u" href="#dir">(dir)</a>
</div>
<h2 class="unnumbered">Bash Features</h2>
<p>This text is a brief description of the features that are present in
the Bash shell (version 3.2, 30 December 2006).
<p>This is Edition 3.2, last updated 30 December 2006,
of <cite>The GNU Bash Reference Manual</cite>,
for <code>Bash</code>, Version 3.2.
<p>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><span class="file">sh</span></samp>), the Korn Shell
(<samp><span class="file">ksh</span></samp>), and the C-shell (<samp><span class="file">csh</span></samp> and its successor,
<samp><span class="file">tcsh</span></samp>). The following menu breaks the features up into
categories based upon which one of these other shells inspired the
feature.
<p>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.
<ul class="menu">
<li><a accesskey="1" href="#Introduction">Introduction</a>: An introduction to the shell.
<li><a accesskey="2" href="#Definitions">Definitions</a>: Some definitions used in the rest of this
manual.
<li><a accesskey="3" href="#Basic-Shell-Features">Basic Shell Features</a>: The shell "building blocks".
<li><a accesskey="4" href="#Shell-Builtin-Commands">Shell Builtin Commands</a>: Commands that are a part of the shell.
<li><a accesskey="5" href="#Shell-Variables">Shell Variables</a>: Variables used or set by Bash.
<li><a accesskey="6" href="#Bash-Features">Bash Features</a>: Features found only in Bash.
<li><a accesskey="7" href="#Job-Control">Job Control</a>: What job control is and how Bash allows you
to use it.
<li><a accesskey="8" href="#Using-History-Interactively">Using History Interactively</a>: Command History Expansion
<li><a accesskey="9" href="#Command-Line-Editing">Command Line Editing</a>: Chapter describing the command line
editing features.
<li><a href="#Installing-Bash">Installing Bash</a>: How to build and install Bash on your system.
<li><a href="#Reporting-Bugs">Reporting Bugs</a>: How to report bugs in Bash.
<li><a href="#Major-Differences-From-The-Bourne-Shell">Major Differences From The Bourne Shell</a>: A terse list of the differences
between Bash and historical
versions of /bin/sh.
<li><a href="#Copying-This-Manual">Copying This Manual</a>: Copying this manual.
<li><a href="#Builtin-Index">Builtin Index</a>: Index of Bash builtin commands.
<li><a href="#Reserved-Word-Index">Reserved Word Index</a>: Index of Bash reserved words.
<li><a href="#Variable-Index">Variable Index</a>: Quick reference helps you find the
variable you want.
<li><a href="#Function-Index">Function Index</a>: Index of bindable Readline functions.
<li><a href="#Concept-Index">Concept Index</a>: General index for concepts described in
this manual.
</ul>
<div class="node">
<p><hr>
<a name="Introduction"></a>
Next: <a rel="next" accesskey="n" href="#Definitions">Definitions</a>,
Previous: <a rel="previous" accesskey="p" href="#Top">Top</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="chapter">1 Introduction</h2>
<ul class="menu">
<li><a accesskey="1" href="#What-is-Bash_003f">What is Bash?</a>: A short description of Bash.
<li><a accesskey="2" href="#What-is-a-shell_003f">What is a shell?</a>: A brief introduction to shells.
</ul>
<div class="node">
<p><hr>
<a name="What-is-Bash%3f"></a>
<a name="What-is-Bash_003f"></a>
Next: <a rel="next" accesskey="n" href="#What-is-a-shell_003f">What is a shell?</a>,
Up: <a rel="up" accesskey="u" href="#Introduction">Introduction</a>
</div>
<h3 class="section">1.1 What is Bash?</h3>
<p>Bash is the shell, or command language interpreter,
for the <span class="sc">gnu</span> operating system.
The name is an acronym for the `<samp><span class="samp">Bourne-Again SHell</span></samp>',
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.
<p>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 <span class="sc">ieee</span>
<span class="sc">posix</span> Shell and Tools portion of the <span class="sc">ieee</span> <span class="sc">posix</span>
specification (<span class="sc">ieee</span> Standard 1003.1).
It offers functional improvements over <code>sh</code> for both interactive and
programming use.
<p>While the <span class="sc">gnu</span> operating system provides other shells, including
a version of <code>csh</code>, Bash is the default shell.
Like other <span class="sc">gnu</span> 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 <span class="sc">ms-dos</span>, <span class="sc">os/2</span>,
and Windows platforms.
<div class="node">
<p><hr>
<a name="What-is-a-shell%3f"></a>
<a name="What-is-a-shell_003f"></a>
Previous: <a rel="previous" accesskey="p" href="#What-is-Bash_003f">What is Bash?</a>,
Up: <a rel="up" accesskey="u" href="#Introduction">Introduction</a>
</div>
<h3 class="section">1.2 What is a shell?</h3>
<p>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.
<p>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 <span class="sc">gnu</span> 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><span class="file">/bin</span></samp>, allowing users
or groups to establish custom environments to automate their common
tasks.
<p>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.
<p>A shell allows execution of <span class="sc">gnu</span> 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 <dfn>redirection</dfn> constructs permit
fine-grained control of the input and output of those commands.
Moreover, the shell allows control over the contents of commands'
environments.
<p>Shells also provide a small set of built-in
commands (<dfn>builtins</dfn>) 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.
<p>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.
<p>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.
<div class="node">
<p><hr>
<a name="Definitions"></a>
Next: <a rel="next" accesskey="n" href="#Basic-Shell-Features">Basic Shell Features</a>,
Previous: <a rel="previous" accesskey="p" href="#Introduction">Introduction</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="chapter">2 Definitions</h2>
<p>These definitions are used throughout the remainder of this manual.
<dl>
<dt><code>POSIX</code><dd><a name="index-POSIX-1"></a>A family of open system standards based on Unix. Bash
is primarily concerned with the Shell and Utilities portion of the
<span class="sc">posix</span> 1003.1 standard.
<br><dt><code>blank</code><dd>A space or tab character.
<br><dt><code>builtin</code><dd><a name="index-builtin-2"></a>A command that is implemented internally by the shell itself, rather
than by an executable program somewhere in the file system.
<br><dt><code>control operator</code><dd><a name="index-control-operator-3"></a>A <code>word</code> that performs a control function. It is a <code>newline</code>
or one of the following:
`<samp><span class="samp">||</span></samp>', `<samp><span class="samp">&&</span></samp>', `<samp><span class="samp">&</span></samp>', `<samp><span class="samp">;</span></samp>', `<samp><span class="samp">;;</span></samp>',
`<samp><span class="samp">|</span></samp>', `<samp><span class="samp">(</span></samp>', or `<samp><span class="samp">)</span></samp>'.
<br><dt><code>exit status</code><dd><a name="index-exit-status-4"></a>The value returned by a command to its caller. The value is restricted
to eight bits, so the maximum value is 255.
<br><dt><code>field</code><dd><a name="index-field-5"></a>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.
<br><dt><code>filename</code><dd><a name="index-filename-6"></a>A string of characters used to identify a file.
<br><dt><code>job</code><dd><a name="index-job-7"></a>A set of processes comprising a pipeline, and any processes descended
from it, that are all in the same process group.
<br><dt><code>job control</code><dd><a name="index-job-control-8"></a>A mechanism by which users can selectively stop (suspend) and restart
(resume) execution of processes.
<br><dt><code>metacharacter</code><dd><a name="index-metacharacter-9"></a>A character that, when unquoted, separates words. A metacharacter is
a <code>blank</code> or one of the following characters:
`<samp><span class="samp">|</span></samp>', `<samp><span class="samp">&</span></samp>', `<samp><span class="samp">;</span></samp>', `<samp><span class="samp">(</span></samp>', `<samp><span class="samp">)</span></samp>', `<samp><span class="samp"><</span></samp>', or
`<samp><span class="samp">></span></samp>'.
<br><dt><code>name</code><dd><a name="index-name-10"></a><a name="index-identifier-11"></a>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>.
<br><dt><code>operator</code><dd><a name="index-operator_002c-shell-12"></a>A <code>control operator</code> or a <code>redirection operator</code>.
See <a href="#Redirections">Redirections</a>, for a list of redirection operators.
<br><dt><code>process group</code><dd><a name="index-process-group-13"></a>A collection of related processes each having the same process
group <span class="sc">id</span>.
<br><dt><code>process group ID</code><dd><a name="index-process-group-ID-14"></a>A unique identifier that represents a <code>process group</code>
during its lifetime.
<br><dt><code>reserved word</code><dd><a name="index-reserved-word-15"></a>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>.
<br><dt><code>return status</code><dd><a name="index-return-status-16"></a>A synonym for <code>exit status</code>.
<br><dt><code>signal</code><dd><a name="index-signal-17"></a>A mechanism by which a process may be notified by the kernel
of an event occurring in the system.
<br><dt><code>special builtin</code><dd><a name="index-special-builtin-18"></a>A shell builtin command that has been classified as special by the
<span class="sc">posix</span> standard.
<br><dt><code>token</code><dd><a name="index-token-19"></a>A sequence of characters considered a single unit by the shell. It is
either a <code>word</code> or an <code>operator</code>.
<br><dt><code>word</code><dd><a name="index-word-20"></a>A <code>token</code> that is not an <code>operator</code>.
</dl>
<div class="node">
<p><hr>
<a name="Basic-Shell-Features"></a>
Next: <a rel="next" accesskey="n" href="#Shell-Builtin-Commands">Shell Builtin Commands</a>,
Previous: <a rel="previous" accesskey="p" href="#Definitions">Definitions</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="chapter">3 Basic Shell Features</h2>
<p><a name="index-Bourne-shell-21"></a>
Bash is an acronym for `<samp><span class="samp">Bourne-Again SHell</span></samp>'.
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 <span class="sc">posix</span>
specification for the `standard' Unix shell.
<p>This chapter briefly summarizes the shell's `building blocks':
commands, control structures, shell functions, shell <i>parameters</i>,
shell expansions,
<i>redirections</i>, which are a way to direct input and output from
and to named files, and how the shell executes commands.
<ul class="menu">
<li><a accesskey="1" href="#Shell-Syntax">Shell Syntax</a>: What your input means to the shell.
<li><a accesskey="2" href="#Shell-Commands">Shell Commands</a>: The types of commands you can use.
<li><a accesskey="3" href="#Shell-Functions">Shell Functions</a>: Grouping commands by name.
<li><a accesskey="4" href="#Shell-Parameters">Shell Parameters</a>: How the shell stores values.
<li><a accesskey="5" href="#Shell-Expansions">Shell Expansions</a>: How Bash expands parameters and the various
expansions available.
<li><a accesskey="6" href="#Redirections">Redirections</a>: A way to control where input and output go.
<li><a accesskey="7" href="#Executing-Commands">Executing Commands</a>: What happens when you run a command.
<li><a accesskey="8" href="#Shell-Scripts">Shell Scripts</a>: Executing files of shell commands.
</ul>
<div class="node">
<p><hr>
<a name="Shell-Syntax"></a>
Next: <a rel="next" accesskey="n" href="#Shell-Commands">Shell Commands</a>,
Up: <a rel="up" accesskey="u" href="#Basic-Shell-Features">Basic Shell Features</a>
</div>
<h3 class="section">3.1 Shell Syntax</h3>
<ul class="menu">
<li><a accesskey="1" href="#Shell-Operation">Shell Operation</a>: The basic operation of the shell.
<li><a accesskey="2" href="#Quoting">Quoting</a>: How to remove the special meaning from characters.
<li><a accesskey="3" href="#Comments">Comments</a>: How to specify comments.
</ul>
<p>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 (`<samp><span class="samp">#</span></samp>'), and the rest
of that line.
<p>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.
<p>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's exit status, and makes that exit status
available for further inspection or processing.
<div class="node">
<p><hr>
<a name="Shell-Operation"></a>
Next: <a rel="next" accesskey="n" href="#Quoting">Quoting</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Syntax">Shell Syntax</a>
</div>
<h4 class="subsection">3.1.1 Shell Operation</h4>
<p>The following is a brief description of the shell's operation when it
reads and executes a command. Basically, the shell does the
following:
<ol type=1 start=1>
<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><span class="option">-c</span></samp> invocation option
(see <a href="#Invoking-Bash">Invoking Bash</a>), or from the user's terminal.
<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>Parses the tokens into simple and compound commands
(see <a href="#Shell-Commands">Shell Commands</a>).
<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>Performs any necessary redirections (see <a href="#Redirections">Redirections</a>) and removes
the redirection operators and their operands from the argument list.
<li>Executes the command (see <a href="#Executing-Commands">Executing Commands</a>).
<li>Optionally waits for the command to complete and collects its exit
status (see <a href="#Exit-Status">Exit Status</a>).
</ol>
<div class="node">
<p><hr>
<a name="Quoting"></a>
Next: <a rel="next" accesskey="n" href="#Comments">Comments</a>,
Previous: <a rel="previous" accesskey="p" href="#Shell-Operation">Shell Operation</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Syntax">Shell Syntax</a>
</div>
<h4 class="subsection">3.1.2 Quoting</h4>
<p><a name="index-quoting-22"></a>
<ul class="menu">
<li><a accesskey="1" href="#Escape-Character">Escape Character</a>: How to remove the special meaning from a single
character.
<li><a accesskey="2" href="#Single-Quotes">Single Quotes</a>: How to inhibit all interpretation of a sequence
of characters.
<li><a accesskey="3" href="#Double-Quotes">Double Quotes</a>: How to suppress most of the interpretation of a
sequence of characters.
<li><a accesskey="4" href="#ANSI_002dC-Quoting">ANSI-C Quoting</a>: How to expand ANSI-C sequences in quoted strings.
<li><a accesskey="5" href="#Locale-Translation">Locale Translation</a>: How to translate strings into different languages.
</ul>
<p>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.
<p>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 Interaction</a>), the
<var>history expansion</var> character, usually `<samp><span class="samp">!</span></samp>', must be quoted
to prevent history expansion. See <a href="#Bash-History-Facilities">Bash History Facilities</a>, for
more details concerning history expansion.
<p>There are three quoting mechanisms: the
<var>escape character</var>, single quotes, and double quotes.
<div class="node">
<p><hr>
<a name="Escape-Character"></a>
Next: <a rel="next" accesskey="n" href="#Single-Quotes">Single Quotes</a>,
Up: <a rel="up" accesskey="u" href="#Quoting">Quoting</a>
</div>
<h5 class="subsubsection">3.1.2.1 Escape Character</h5>
<p>A non-quoted backslash `<samp><span class="samp">\</span></samp>' 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).
<div class="node">
<p><hr>
<a name="Single-Quotes"></a>
Next: <a rel="next" accesskey="n" href="#Double-Quotes">Double Quotes</a>,
Previous: <a rel="previous" accesskey="p" href="#Escape-Character">Escape Character</a>,
Up: <a rel="up" accesskey="u" href="#Quoting">Quoting</a>
</div>
<h5 class="subsubsection">3.1.2.2 Single Quotes</h5>
<p>Enclosing characters in single quotes (`<samp><span class="samp">'</span></samp>') 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.
<div class="node">
<p><hr>
<a name="Double-Quotes"></a>
Next: <a rel="next" accesskey="n" href="#ANSI_002dC-Quoting">ANSI-C Quoting</a>,
Previous: <a rel="previous" accesskey="p" href="#Single-Quotes">Single Quotes</a>,
Up: <a rel="up" accesskey="u" href="#Quoting">Quoting</a>
</div>
<h5 class="subsubsection">3.1.2.3 Double Quotes</h5>
<p>Enclosing characters in double quotes (`<samp><span class="samp">"</span></samp>') preserves the literal value
of all characters within the quotes, with the exception of
`<samp><span class="samp">$</span></samp>', `<samp><span class="samp">`</span></samp>', `<samp><span class="samp">\</span></samp>',
and, when history expansion is enabled, `<samp><span class="samp">!</span></samp>'.
The characters `<samp><span class="samp">$</span></samp>' and `<samp><span class="samp">`</span></samp>'
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:
`<samp><span class="samp">$</span></samp>', `<samp><span class="samp">`</span></samp>', `<samp><span class="samp">"</span></samp>', `<samp><span class="samp">\</span></samp>', or <code>newline</code>.
Within double quotes, backslashes that are followed by one of these
characters are removed. Backslashes preceding characters without a
special meaning are left unmodified.
A double quote may be quoted within double quotes by preceding it with
a backslash.
If enabled, history expansion will be performed unless an `<samp><span class="samp">!</span></samp>'
appearing in double quotes is escaped using a backslash.
The backslash preceding the `<samp><span class="samp">!</span></samp>' is not removed.
<p>The special parameters `<samp><span class="samp">*</span></samp>' and `<samp><span class="samp">@</span></samp>' have special meaning
when in double quotes (see <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>).
<div class="node">
<p><hr>
<a name="ANSI-C-Quoting"></a>
<a name="ANSI_002dC-Quoting"></a>
Next: <a rel="next" accesskey="n" href="#Locale-Translation">Locale Translation</a>,
Previous: <a rel="previous" accesskey="p" href="#Double-Quotes">Double Quotes</a>,
Up: <a rel="up" accesskey="u" href="#Quoting">Quoting</a>
</div>
<h5 class="subsubsection">3.1.2.4 ANSI-C Quoting</h5>
<p><a name="index-quoting_002c-ANSI-23"></a>
Words of the form <code>$'</code><var>string</var><code>'</code> are treated specially. The
word expands to <var>string</var>, with backslash-escaped characters replaced
as specified by the ANSI C standard. Backslash escape sequences, if
present, are decoded as follows:
<dl>
<dt><code>\a</code><dd>alert (bell)
<br><dt><code>\b</code><dd>backspace
<br><dt><code>\e</code><dd>an escape character (not ANSI C)
<br><dt><code>\f</code><dd>form feed
<br><dt><code>\n</code><dd>newline
<br><dt><code>\r</code><dd>carriage return
<br><dt><code>\t</code><dd>horizontal tab
<br><dt><code>\v</code><dd>vertical tab
<br><dt><code>\\</code><dd>backslash
<br><dt><code>\'</code><dd>single quote
<br><dt><code>\</code><var>nnn</var><dd>the eight-bit character whose value is the octal value <var>nnn</var>
(one to three digits)
<br><dt><code>\x</code><var>HH</var><dd>the eight-bit character whose value is the hexadecimal value <var>HH</var>
(one or two hex digits)
<br><dt><code>\c</code><var>x</var><dd>a control-<var>x</var> character
</dl>
<p class="noindent">The expanded result is single-quoted, as if the dollar sign had not
been present.
<div class="node">
<p><hr>
<a name="Locale-Translation"></a>
Previous: <a rel="previous" accesskey="p" href="#ANSI_002dC-Quoting">ANSI-C Quoting</a>,
Up: <a rel="up" accesskey="u" href="#Quoting">Quoting</a>
</div>
<h5 class="subsubsection">3.1.2.5 Locale-Specific Translation</h5>
<p><a name="index-localization-24"></a><a name="index-internationalization-25"></a><a name="index-native-languages-26"></a><a name="index-translation_002c-native-languages-27"></a>
A double-quoted string preceded by a dollar sign (`<samp><span class="samp">$</span></samp>') will cause
the string to be translated according to the current locale.
If the current locale is <code>C</code> or <code>POSIX</code>, the dollar sign
is ignored.
If the string is translated and replaced, the replacement is
double-quoted.
<p><a name="index-LC_005fMESSAGES-28"></a><a name="index-TEXTDOMAIN-29"></a><a name="index-TEXTDOMAINDIR-30"></a>Some systems use the message catalog selected by the <samp><span class="env">LC_MESSAGES</span></samp>
shell variable. Others create the name of the message catalog from the
value of the <samp><span class="env">TEXTDOMAIN</span></samp> shell variable, possibly adding a
suffix of `<samp><span class="samp">.mo</span></samp>'. If you use the <samp><span class="env">TEXTDOMAIN</span></samp> variable, you
may need to set the <samp><span class="env">TEXTDOMAINDIR</span></samp> variable to the location of
the message catalog files. Still others use both variables in this
fashion:
<samp><span class="env">TEXTDOMAINDIR</span></samp>/<samp><span class="env">LC_MESSAGES</span></samp>/LC_MESSAGES/<samp><span class="env">TEXTDOMAIN</span></samp>.mo.
<div class="node">
<p><hr>
<a name="Comments"></a>
Previous: <a rel="previous" accesskey="p" href="#Quoting">Quoting</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Syntax">Shell Syntax</a>
</div>
<h4 class="subsection">3.1.3 Comments</h4>
<p><a name="index-comments_002c-shell-31"></a>
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 `<samp><span class="samp">#</span></samp>'
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.
<div class="node">
<p><hr>
<a name="Shell-Commands"></a>
Next: <a rel="next" accesskey="n" href="#Shell-Functions">Shell Functions</a>,
Previous: <a rel="previous" accesskey="p" href="#Shell-Syntax">Shell Syntax</a>,
Up: <a rel="up" accesskey="u" href="#Basic-Shell-Features">Basic Shell Features</a>
</div>
<h3 class="section">3.2 Shell Commands</h3>
<p><a name="index-commands_002c-shell-32"></a>
A simple shell command such as <code>echo a b c</code> consists of the command
itself followed by arguments, separated by spaces.
<p>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="menu">
<li><a accesskey="1" href="#Simple-Commands">Simple Commands</a>: The most common type of command.
<li><a accesskey="2" href="#Pipelines">Pipelines</a>: Connecting the input and output of several
commands.
<li><a accesskey="3" href="#Lists">Lists</a>: How to execute commands sequentially.
<li><a accesskey="4" href="#Compound-Commands">Compound Commands</a>: Shell commands for control flow.
</ul>
<div class="node">
<p><hr>
<a name="Simple-Commands"></a>
Next: <a rel="next" accesskey="n" href="#Pipelines">Pipelines</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Commands">Shell Commands</a>
</div>
<h4 class="subsection">3.2.1 Simple Commands</h4>
<p><a name="index-commands_002c-simple-33"></a>
A simple command is the kind of command encountered most often.
It's just a sequence of words separated by <code>blank</code>s, terminated
by one of the shell'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's arguments.
<p>The return status (see <a href="#Exit-Status">Exit Status</a>) of a simple command is
its exit status as provided
by the <span class="sc">posix</span> 1003.1 <code>waitpid</code> function, or 128+<var>n</var> if
the command was terminated by signal <var>n</var>.
<div class="node">
<p><hr>
<a name="Pipelines"></a>
Next: <a rel="next" accesskey="n" href="#Lists">Lists</a>,
Previous: <a rel="previous" accesskey="p" href="#Simple-Commands">Simple Commands</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Commands">Shell Commands</a>
</div>
<h4 class="subsection">3.2.2 Pipelines</h4>
<p><a name="index-pipeline-34"></a><a name="index-commands_002c-pipelines-35"></a>
A <code>pipeline</code> is a sequence of simple commands separated by
`<samp><span class="samp">|</span></samp>'.
<p><a name="index-time-36"></a><a name="index-g_t_0021-37"></a><a name="index-command-timing-38"></a>The format for a pipeline is
<pre class="example"> [<code>time</code> [<code>-p</code>]] [<code>!</code>] <var>command1</var> [<code>|</code> <var>command2</var> ...]
</pre>
<p class="noindent">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's output.
<p>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's execution.
The <samp><span class="option">-p</span></samp> option changes the output format to that specified
by <span class="sc">posix</span>.
The <samp><span class="env">TIMEFORMAT</span></samp> 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.
<p>If the pipeline is not executed asynchronously (see <a href="#Lists">Lists</a>), the
shell waits for all commands in the pipeline to complete.
<p>Each command in a pipeline is executed in its own subshell
(see <a href="#Command-Execution-Environment">Command Execution Environment</a>). 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'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 `<samp><span class="samp">!</span></samp>' 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.
<div class="node">
<p><hr>
<a name="Lists"></a>
Next: <a rel="next" accesskey="n" href="#Compound-Commands">Compound Commands</a>,
Previous: <a rel="previous" accesskey="p" href="#Pipelines">Pipelines</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Commands">Shell Commands</a>
</div>
<h4 class="subsection">3.2.3 Lists of Commands</h4>
<p><a name="index-commands_002c-lists-39"></a>
A <code>list</code> is a sequence of one or more pipelines separated by one
of the operators `<samp><span class="samp">;</span></samp>', `<samp><span class="samp">&</span></samp>', `<samp><span class="samp">&&</span></samp>', or `<samp><span class="samp">||</span></samp>',
and optionally terminated by one of `<samp><span class="samp">;</span></samp>', `<samp><span class="samp">&</span></samp>', or a
<code>newline</code>.
<p>Of these list operators, `<samp><span class="samp">&&</span></samp>' and `<samp><span class="samp">||</span></samp>'
have equal precedence, followed by `<samp><span class="samp">;</span></samp>' and `<samp><span class="samp">&</span></samp>',
which have equal precedence.
<p>A sequence of one or more newlines may appear in a <code>list</code>
to delimit commands, equivalent to a semicolon.
<p>If a command is terminated by the control operator `<samp><span class="samp">&</span></samp>',
the shell executes the command asynchronously in a subshell.
This is known as executing the command in the <var>background</var>.
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>.
<p>Commands separated by a `<samp><span class="samp">;</span></samp>' 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.
<p>The control operators `<samp><span class="samp">&&</span></samp>' and `<samp><span class="samp">||</span></samp>'
denote <span class="sc">and</span> lists and <span class="sc">or</span> lists, respectively.
An <span class="sc">and</span> list has the form
<pre class="example"> <var>command1</var> && <var>command2</var>
</pre>
<p class="noindent"><var>command2</var> is executed if, and only if, <var>command1</var>
returns an exit status of zero.
<p>An <span class="sc">or</span> list has the form
<pre class="example"> <var>command1</var> || <var>command2</var>
</pre>
<p class="noindent"><var>command2</var> is executed if, and only if, <var>command1</var>
returns a non-zero exit status.
<p>The return status of
<span class="sc">and</span> and <span class="sc">or</span> lists is the exit status of the last command
executed in the list.
<div class="node">
<p><hr>
<a name="Compound-Commands"></a>
Previous: <a rel="previous" accesskey="p" href="#Lists">Lists</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Commands">Shell Commands</a>
</div>
<h4 class="subsection">3.2.4 Compound Commands</h4>
<p><a name="index-commands_002c-compound-40"></a>
<ul class="menu">
<li><a accesskey="1" href="#Looping-Constructs">Looping Constructs</a>: Shell commands for iterative action.
<li><a accesskey="2" href="#Conditional-Constructs">Conditional Constructs</a>: Shell commands for conditional execution.
<li><a accesskey="3" href="#Command-Grouping">Command Grouping</a>: Ways to group commands.
</ul>
<p>Compound commands are the shell programming 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.
<p>Bash provides looping constructs, conditional commands, and mechanisms
to group commands and execute them as a unit.
<div class="node">
<p><hr>
<a name="Looping-Constructs"></a>
Next: <a rel="next" accesskey="n" href="#Conditional-Constructs">Conditional Constructs</a>,
Up: <a rel="up" accesskey="u" href="#Compound-Commands">Compound Commands</a>
</div>
<h5 class="subsubsection">3.2.4.1 Looping Constructs</h5>
<p><a name="index-commands_002c-looping-41"></a>
Bash supports the following looping constructs.
<p>Note that wherever a `<samp><span class="samp">;</span></samp>' appears in the description of a
command's syntax, it may be replaced with one or more newlines.
<dl>
<dt><code>until</code><dd><a name="index-until-42"></a><a name="index-do-43"></a><a name="index-done-44"></a>The syntax of the <code>until</code> command is:
<pre class="example"> until <var>test-commands</var>; do <var>consequent-commands</var>; done
</pre>
<p>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.
<br><dt><code>while</code><dd><a name="index-while-45"></a>The syntax of the <code>while</code> command is:
<pre class="example"> while <var>test-commands</var>; do <var>consequent-commands</var>; done
</pre>
<p>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.
<br><dt><code>for</code><dd><a name="index-for-46"></a>The syntax of the <code>for</code> command is:
<pre class="example"> for <var>name</var> [in <var>words</var> ...]; do <var>commands</var>; done
</pre>
<p>Expand <var>words</var>, and execute <var>commands</var> once for each member
in the resultant list, with <var>name</var> bound to the current member.
If `<samp><span class="samp">in </span><var>words</var></samp>' is not present, the <code>for</code> command
executes the <var>commands</var> once for each positional parameter that is
set, as if `<samp><span class="samp">in "$@"</span></samp>' 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.
<p>An alternate form of the <code>for</code> command is also supported:
<pre class="example"> for (( <var>expr1</var> ; <var>expr2</var> ; <var>expr3</var> )) ; do <var>commands</var> ; done
</pre>
<p>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>list</var>
that is executed, or false if any of the expressions is invalid.
</dl>
<p>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.
<div class="node">
<p><hr>
<a name="Conditional-Constructs"></a>
Next: <a rel="next" accesskey="n" href="#Command-Grouping">Command Grouping</a>,
Previous: <a rel="previous" accesskey="p" href="#Looping-Constructs">Looping Constructs</a>,
Up: <a rel="up" accesskey="u" href="#Compound-Commands">Compound Commands</a>
</div>
<h5 class="subsubsection">3.2.4.2 Conditional Constructs</h5>
<p><a name="index-commands_002c-conditional-47"></a>
<dl>
<dt><code>if</code><dd><a name="index-if-48"></a><a name="index-then-49"></a><a name="index-else-50"></a><a name="index-elif-51"></a><a name="index-fi-52"></a>The syntax of the <code>if</code> command is:
<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>
<p>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 `<samp><span class="samp">else </span><var>alternate-consequents</var></samp>' 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.
<br><dt><code>case</code><dd><a name="index-case-53"></a><a name="index-in-54"></a><a name="index-esac-55"></a>The syntax of the <code>case</code> command is:
<pre class="example"> <code>case </code><var>word</var><code> in [ [(] </code><var>pattern</var><code> [| </code><var>pattern</var><code>]...) </code><var>command-list</var><code> ;;]... esac</code>
</pre>
<p><code>case</code> will selectively execute the <var>command-list</var> corresponding to
the first <var>pattern</var> that matches <var>word</var>.
If the shell option <code>nocasematch</code>
(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 `<samp><span class="samp">|</span></samp>' is used to separate multiple patterns, and the `<samp><span class="samp">)</span></samp>'
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 `<samp><span class="samp">;;</span></samp>'.
The <var>word</var> undergoes tilde expansion, parameter expansion, command
substitution, arithmetic expansion, and quote removal before matching is
attempted. Each <var>pattern</var> undergoes tilde expansion, parameter
expansion, command substitution, and arithmetic expansion.
<p>There may be an arbitrary number of <code>case</code> clauses, each terminated
by a `<samp><span class="samp">;;</span></samp>'. The first pattern that matches determines the
command-list that is executed.
<p>Here is an example using <code>case</code> in a script that could be used to
describe one interesting feature of an animal:
<pre class="example"> echo -n "Enter the name of an animal: "
read ANIMAL
echo -n "The $ANIMAL has "
case $ANIMAL in
horse | dog | cat) echo -n "four";;
man | kangaroo ) echo -n "two";;
*) echo -n "an unknown number of";;
esac
echo " legs."
</pre>
<p class="noindent">The return status is zero if no <var>pattern</var> is matched. Otherwise, the
return status is the exit status of the <var>command-list</var> executed.
<br><dt><code>select</code><dd><a name="index-select-56"></a>
The <code>select</code> construct allows the easy generation of menus.
It has almost the same syntax as the <code>for</code> command:
<pre class="example"> select <var>name</var> [in <var>words</var> ...]; do <var>commands</var>; done
</pre>
<p>The list of words following <code>in</code> is expanded, generating a list
of items. The set of expanded words is printed on the standard
error output stream, each preceded by a number. If the
`<samp><span class="samp">in </span><var>words</var></samp>' is omitted, the positional parameters are printed,
as if `<samp><span class="samp">in "$@"</span></samp>' had been specified.
The <samp><span class="env">PS3</span></samp> prompt is then displayed and a line is read 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.
Any other value read causes <var>name</var> to be set to null.
The line read is saved in the variable <samp><span class="env">REPLY</span></samp>.
<p>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.
<p>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.
<pre class="example"> select fname in *;
do
echo you picked $fname \($REPLY\)
break;
done
</pre>
<br><dt><code>((...))</code><dd>
<pre class="example"> (( <var>expression</var> ))
</pre>
<p>The arithmetic <var>expression</var> is evaluated according to the rules
described below (see <a href="#Shell-Arithmetic">Shell Arithmetic</a>).
If the value of the expression is non-zero, the return status is 0;
otherwise the return status is 1. This is exactly equivalent to
<pre class="example"> let "<var>expression</var>"
</pre>
<p class="noindent">See <a href="#Bash-Builtins">Bash Builtins</a>, for a full description of the <code>let</code> builtin.
<br><dt><code>[[...]]</code><dd><a name="index-g_t_005b_005b-57"></a><a name="index-g_t_005d_005d-58"></a>
<pre class="example"> [[ <var>expression</var> ]]
</pre>
<p>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>.
Word splitting and filename expansion are not performed on the words
between the `<samp><span class="samp">[[</span></samp>' and `<samp><span class="samp">]]</span></samp>'; tilde expansion, parameter and
variable expansion, arithmetic expansion, command substitution, process
substitution, and quote removal are performed.
Conditional operators such as `<samp><span class="samp">-f</span></samp>' must be unquoted to be recognized
as primaries.
<p>When the `<samp><span class="samp">==</span></samp>' and `<samp><span class="samp">!=</span></samp>' 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>.
If the shell option <code>nocasematch</code>
(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 (`<samp><span class="samp">==</span></samp>') or does not
match (`<samp><span class="samp">!=</span></samp>')the pattern, and 1 otherwise.
Any part of the pattern may be quoted to force it to be matched as a
string.
<p>An additional binary operator, `<samp><span class="samp">=~</span></samp>', is available, with the same
precedence as `<samp><span class="samp">==</span></samp>' and `<samp><span class="samp">!=</span></samp>'.
When it is used, the string to the right of the operator is considered
an extended regular expression and matched accordingly (as in <i>regex</i>3)).
The return value is 0 if the string matches
the pattern, and 1 otherwise.
If the regular expression is syntactically incorrect, the conditional
expression's return value is 2.
If the shell option <code>nocasematch</code>
(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.
Substrings matched by parenthesized subexpressions within the regular
expression are saved in the array variable <code>BASH_REMATCH</code>.
The element of <code>BASH_REMATCH</code> with index 0 is the portion of the string
matching the entire regular expression.
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.
<p>Expressions may be combined using the following operators, listed
in decreasing order of precedence:
<dl>
<dt><code>( </code><var>expression</var><code> )</code><dd>Returns the value of <var>expression</var>.
This may be used to override the normal precedence of operators.
<br><dt><code>! </code><var>expression</var><dd>True if <var>expression</var> is false.
<br><dt><var>expression1</var><code> && </code><var>expression2</var><dd>True if both <var>expression1</var> and <var>expression2</var> are true.
<br><dt><var>expression1</var><code> || </code><var>expression2</var><dd>True if either <var>expression1</var> or <var>expression2</var> is true.
</dl>
The <code>&&</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.
</dl>
<div class="node">
<p><hr>
<a name="Command-Grouping"></a>
Previous: <a rel="previous" accesskey="p" href="#Conditional-Constructs">Conditional Constructs</a>,
Up: <a rel="up" accesskey="u" href="#Compound-Commands">Compound Commands</a>
</div>
<h5 class="subsubsection">3.2.4.3 Grouping Commands</h5>
<p><a name="index-commands_002c-grouping-59"></a>
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>
<dt><code>()</code><dd>
<pre class="example"> ( <var>list</var> )
</pre>
<p>Placing a list of commands between parentheses causes a subshell
environment to be created (see <a href="#Command-Execution-Environment">Command Execution Environment</a>), and each
of the commands in <var>list</var> to be executed in that subshell. Since the
<var>list</var> is executed in a subshell, variable assignments do not remain in
effect after the subshell completes.
<br><dt><code>{}</code><dd><a name="index-g_t_0040_007b-60"></a><a name="index-g_t_0040_007d-61"></a>
<pre class="example"> { <var>list</var>; }
</pre>
<p>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.
</dl>
<p>In addition to the creation of a subshell, there is a subtle difference
between these two constructs due to historical reasons. The braces
are <code>reserved words</code>, so they must be separated from the <var>list</var>
by <code>blank</code>s. The parentheses are <code>operators</code>, and are
recognized as separate tokens by the shell even if they are not separated
from the <var>list</var> by whitespace.
<p>The exit status of both of these constructs is the exit status of
<var>list</var>.
<div class="node">
<p><hr>
<a name="Shell-Functions"></a>
Next: <a rel="next" accesskey="n" href="#Shell-Parameters">Shell Parameters</a>,
Previous: <a rel="previous" accesskey="p" href="#Shell-Commands">Shell Commands</a>,
Up: <a rel="up" accesskey="u" href="#Basic-Shell-Features">Basic Shell Features</a>
</div>
<h3 class="section">3.3 Shell Functions</h3>
<p><a name="index-shell-function-62"></a><a name="index-functions_002c-shell-63"></a>
Shell functions are a way to group commands for later execution
using a single name for the group. They are executed just like
a "regular" 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.
<p>Functions are declared using this syntax:
<a name="index-function-64"></a>
<pre class="example"> [ <code>function</code> ] <var>name</var> () <var>compound-command</var> [ <var>redirections</var> ]
</pre>
<p>This defines a shell function named <var>name</var>. The reserved
word <code>function</code> is optional.
If the <code>function</code> reserved
word is supplied, the parentheses are optional.
The <var>body</var> 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.
<var>compound-command</var> is executed whenever <var>name</var> is specified as the
name of a command.
Any redirections (see <a href="#Redirections">Redirections</a>) associated with the shell function
are performed when the function is executed.
<p>A function definition may be deleted using the <samp><span class="option">-f</span></samp> option to the
<code>unset</code> builtin (see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>).
<p>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.
<p>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 by whitespace.
Also, when using the braces, the <var>list</var> must be terminated by a semicolon,
a `<samp><span class="samp">&</span></samp>', or a newline.
<p>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 `<samp><span class="samp">#</span></samp>' 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 <samp><span class="env">FUNCNAME</span></samp> 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 the exception that the <samp><span class="env">DEBUG</span></samp> and <samp><span class="env">RETURN</span></samp> 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 <samp><span class="env">DEBUG</span></samp> and <samp><span class="env">RETURN</span></samp> traps).
See <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>, for the description of the
<code>trap</code> builtin.
<p>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 `<samp><span class="samp">#</span></samp>'
are restored to the values they had prior to the function's
execution. If a numeric argument is given to <code>return</code>,
that is the function's return status; otherwise the function's
return status is the exit status of the last command executed
before the <code>return</code>.
<p>Variables local to the function may be declared with the
<code>local</code> builtin. These variables are visible only to
the function and the commands it invokes.
<p>Function names and definitions may be listed with the
<samp><span class="option">-f</span></samp> option to the <code>declare</code> or <code>typeset</code>
builtin commands (see <a href="#Bash-Builtins">Bash Builtins</a>).
The <samp><span class="option">-F</span></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 subshells
automatically have them defined with the
<samp><span class="option">-f</span></samp> option to the <code>export</code> builtin
(see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>).
Note that shell functions and variables with the same name may result
in multiple identically-named entries in the environment passed to the
shell's children.
Care should be taken in cases where this may cause a problem.
<p>Functions may be recursive. No limit is placed on the number of
recursive calls.
<div class="node">
<p><hr>
<a name="Shell-Parameters"></a>
Next: <a rel="next" accesskey="n" href="#Shell-Expansions">Shell Expansions</a>,
Previous: <a rel="previous" accesskey="p" href="#Shell-Functions">Shell Functions</a>,
Up: <a rel="up" accesskey="u" href="#Basic-Shell-Features">Basic Shell Features</a>
</div>
<h3 class="section">3.4 Shell Parameters</h3>
<p><a name="index-parameters-65"></a><a name="index-variable_002c-shell-66"></a><a name="index-shell-variable-67"></a>
<ul class="menu">
<li><a accesskey="1" href="#Positional-Parameters">Positional Parameters</a>: The shell's command-line arguments.
<li><a accesskey="2" href="#Special-Parameters">Special Parameters</a>: Parameters denoted by special characters.
</ul>
<p>A <var>parameter</var> is an entity that stores values.
It can be a <code>name</code>, a number, or one of the special characters
listed below.
A <var>variable</var> is a parameter denoted by a <code>name</code>.
A variable has a <var>value</var> and zero or more <var>attributes</var>.
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 Builtins</a>).
<p>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.
<p>A variable may be assigned to by a statement of the form
<pre class="example"> <var>name</var>=[<var>value</var>]
</pre>
<p class="noindent">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 (detailed below). If the variable has its <code>integer</code>
attribute set, then <var>value</var>
is evaluated as an arithmetic expression even if the <code>$((...))</code>
expansion is not used (see <a href="#Arithmetic-Expansion">Arithmetic Expansion</a>).
Word splitting is not performed, with the exception
of <code>"$@"</code> as explained below.
Filename expansion is 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.
<p>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 `<samp><span class="samp">+=</span></samp>'
operator can be used to
append to or add to the variable's previous value.
When `<samp><span class="samp">+=</span></samp>' is applied to a variable for which the integer attribute
has been set, <var>value</var> is evaluated as an arithmetic expression and
added to the variable's current value, which is also evaluated.
When `<samp><span class="samp">+=</span></samp>' is applied to an array variable using compound assignment
(see <a href="#Arrays">Arrays</a>), the
variable's value is not unset (as it is when using `<samp><span class="samp">=</span></samp>'), and new
values are appended to the array beginning at one greater than the array's
maximum index.
When applied to a string-valued variable, <var>value</var> is expanded and
appended to the variable's value.
<div class="node">
<p><hr>
<a name="Positional-Parameters"></a>
Next: <a rel="next" accesskey="n" href="#Special-Parameters">Special Parameters</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Parameters">Shell Parameters</a>
</div>
<h4 class="subsection">3.4.1 Positional Parameters</h4>
<p><a name="index-parameters_002c-positional-68"></a>
A <var>positional parameter</var> is a parameter denoted by one or more
digits, other than the single digit <code>0</code>. Positional parameters are
assigned from the shell'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>).
<p>When a positional parameter consisting of more than a single
digit is expanded, it must be enclosed in braces.
<div class="node">
<p><hr>
<a name="Special-Parameters"></a>
Previous: <a rel="previous" accesskey="p" href="#Positional-Parameters">Positional Parameters</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Parameters">Shell Parameters</a>
</div>
<h4 class="subsection">3.4.2 Special Parameters</h4>
<p><a name="index-parameters_002c-special-69"></a>
The shell treats several parameters specially. These parameters may
only be referenced; assignment to them is not allowed.
<dl>
<dt><code>*</code><a name="index-g_t_002a-70"></a><dd>Expands to the positional parameters, starting from one. 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 <samp><span class="env">IFS</span></samp>
special variable. That is, <code>"$*"</code> is equivalent
to <code>"$1</code><var>c</var><code>$2</code><var>c</var><code>..."</code>, where <var>c</var>
is the first character of the value of the <code>IFS</code>
variable.
If <samp><span class="env">IFS</span></samp> is unset, the parameters are separated by spaces.
If <samp><span class="env">IFS</span></samp> is null, the parameters are joined without intervening
separators.
<br><dt><code>@</code><a name="index-g_t_0040_0040-71"></a><dd>Expands to the positional parameters, starting from one. When the
expansion occurs within double quotes, each parameter expands to a
separate word. That is, <code>"$@"</code> is equivalent to
<code>"$1" "$2" ...</code>.
If the double-quoted expansion occurs within a word, the expansion of
the first parameter is joined with the beginning part of the original
word, and the expansion of the last parameter is joined with the last
part of the original word.
When there are no positional parameters, <code>"$@"</code> and
<code>$@</code>
expand to nothing (i.e., they are removed).
<br><dt><code>#</code><a name="index-g_t_0023-72"></a><dd>Expands to the number of positional parameters in decimal.
<br><dt><code>?</code><a name="index-g_t_003f-73"></a><dd>Expands to the exit status of the most recently executed foreground
pipeline.
<br><dt><code>-</code><a name="index-g_t_002d-74"></a><dd>(A hyphen.) Expands to the current option flags as specified upon
invocation, by the <code>set</code>
builtin command, or those set by the shell itself
(such as the <samp><span class="option">-i</span></samp> option).
<br><dt><code>$</code><a name="index-g_t_0024-75"></a><dd>Expands to the process <span class="sc">id</span> of the shell. In a <code>()</code> subshell, it
expands to the process <span class="sc">id</span> of the invoking shell, not the subshell.
<br><dt><code>!</code><a name="index-g_t_0021-76"></a><dd>Expands to the process <span class="sc">id</span> of the most recently executed background
(asynchronous) command.
<br><dt><code>0</code><a name="index-g_t0-77"></a><dd>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><span class="option">-c</span></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.
<br><dt><code>_</code><a name="index-g_t_005f-78"></a><dd>(An underscore.)
At shell startup, set to the absolute 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 command,
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.
</dl>
<div class="node">
<p><hr>
<a name="Shell-Expansions"></a>
Next: <a rel="next" accesskey="n" href="#Redirections">Redirections</a>,
Previous: <a rel="previous" accesskey="p" href="#Shell-Parameters">Shell Parameters</a>,
Up: <a rel="up" accesskey="u" href="#Basic-Shell-Features">Basic Shell Features</a>
</div>
<h3 class="section">3.5 Shell Expansions</h3>
<p><a name="index-expansion-79"></a>
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>tilde expansion
<li>parameter and variable expansion
<li>command substitution
<li>arithmetic expansion
<li>word splitting
<li>filename expansion
</ul>
<ul class="menu">
<li><a accesskey="1" href="#Brace-Expansion">Brace Expansion</a>: Expansion of expressions within braces.
<li><a accesskey="2" href="#Tilde-Expansion">Tilde Expansion</a>: Expansion of the ~ character.
<li><a accesskey="3" href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>: How Bash expands variables to their values.
<li><a accesskey="4" href="#Command-Substitution">Command Substitution</a>: Using the output of a command as an argument.
<li><a accesskey="5" href="#Arithmetic-Expansion">Arithmetic Expansion</a>: How to use arithmetic in shell expansions.
<li><a accesskey="6" href="#Process-Substitution">Process Substitution</a>: A way to write and read to and from a
command.
<li><a accesskey="7" href="#Word-Splitting">Word Splitting</a>: How the results of expansion are split into separate
arguments.
<li><a accesskey="8" href="#Filename-Expansion">Filename Expansion</a>: A shorthand for specifying filenames matching patterns.
<li><a accesskey="9" href="#Quote-Removal">Quote Removal</a>: How and when quote characters are removed from
words.
</ul>
<p>The order of expansions is: brace expansion, tilde expansion,
parameter, variable, and arithmetic expansion and
command substitution
(done in a left-to-right fashion), word splitting, and filename
expansion.
<p>On systems that can support it, there is an additional expansion
available: <var>process substitution</var>. This is performed at the
same time as parameter, variable, and arithmetic expansion and
command substitution.
<p>Only brace expansion, word splitting, and filename expansion
can change 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>"$@"</code> (see <a href="#Special-Parameters">Special Parameters</a>) and <code>"${</code><var>name</var><code>[@]}"</code>
(see <a href="#Arrays">Arrays</a>).
<p>After all expansions, <code>quote removal</code> (see <a href="#Quote-Removal">Quote Removal</a>)
is performed.
<div class="node">
<p><hr>
<a name="Brace-Expansion"></a>
Next: <a rel="next" accesskey="n" href="#Tilde-Expansion">Tilde Expansion</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Expansions">Shell Expansions</a>
</div>
<h4 class="subsection">3.5.1 Brace Expansion</h4>
<p><a name="index-brace-expansion-80"></a><a name="index-expansion_002c-brace-81"></a>
Brace expansion is a mechanism by which arbitrary strings may be generated.
This mechanism is similar to
<var>filename expansion</var> (see <a href="#Filename-Expansion">Filename Expansion</a>),
but the file names generated need not exist.
Patterns to be brace expanded take the form of an optional <var>preamble</var>,
followed by either a series of comma-separated strings or a seqeunce expression
between a pair of braces,
followed by an optional <var>postscript</var>.
The preamble is prefixed to each string contained within the braces, and
the postscript is then appended to each resulting string, expanding left
to right.
<p>Brace expansions may be nested.
The results of each expanded string are not sorted; left to right order
is preserved.
For example,
<pre class="example"> bash$ echo a{d,c,b}e
ade ace abe
</pre>
<p>A sequence expression takes the form <code>{</code><var>x</var><code>..</code><var>y</var><code>}</code>,
where <var>x</var> and <var>y</var> are either integers or single characters.
When integers are supplied, the expression expands to each number between
<var>x</var> and <var>y</var>, inclusive.
When characters are supplied, the expression expands to each character
lexicographically between <var>x</var> and <var>y</var>, inclusive. Note that
both <var>x</var> and <var>y</var> must be of the same type.
<p>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.
To avoid conflicts with parameter expansion, the string `<samp><span class="samp">${</span></samp>'
is not considered eligible for brace expansion.
<p>A correctly-formed brace expansion must contain unquoted opening
and closing braces, and at least one unquoted comma or a valid
sequence expression.
Any incorrectly formed brace expansion is left unchanged.
<p>A { or `<samp><span class="samp">,</span></samp>' may be quoted with a backslash to prevent its
being considered part of a brace expression.
To avoid conflicts with parameter expansion, the string `<samp><span class="samp">${</span></samp>'
is not considered eligible for brace expansion.
<p>This construct is typically used as shorthand when the common
prefix of the strings to be generated is longer than in the
above example:
<pre class="example"> mkdir /usr/local/src/bash/{old,new,dist,bugs}
</pre>
<p>or
<pre class="example"> chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}
</pre>
<div class="node">
<p><hr>
<a name="Tilde-Expansion"></a>
Next: <a rel="next" accesskey="n" href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>,
Previous: <a rel="previous" accesskey="p" href="#Brace-Expansion">Brace Expansion</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Expansions">Shell Expansions</a>
</div>
<h4 class="subsection">3.5.2 Tilde Expansion</h4>
<p><a name="index-tilde-expansion-82"></a><a name="index-expansion_002c-tilde-83"></a>
If a word begins with an unquoted tilde character (`<samp><span class="samp">~</span></samp>'), all of the
characters up to the first unquoted slash (or all characters,
if there is no unquoted slash) are considered a <var>tilde-prefix</var>.
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 <var>login name</var>.
If this login name is the null string, the tilde is replaced with the
value of the <samp><span class="env">HOME</span></samp> shell variable.
If <samp><span class="env">HOME</span></samp> 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.
<p>If the tilde-prefix is `<samp><span class="samp">~+</span></samp>', the value of
the shell variable <samp><span class="env">PWD</span></samp> replaces the tilde-prefix.
If the tilde-prefix is `<samp><span class="samp">~-</span></samp>', the value of the shell variable
<samp><span class="env">OLDPWD</span></samp>, if it is set, is substituted.
<p>If the characters following the tilde in the tilde-prefix consist of a
number <var>N</var>, optionally prefixed by a `<samp><span class="samp">+</span></samp>' or a `<samp><span class="samp">-</span></samp>',
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 `<samp><span class="samp">+</span></samp>' or `<samp><span class="samp">-</span></samp>', `<samp><span class="samp">+</span></samp>' is assumed.
<p>If the login name is invalid, or the tilde expansion fails, the word is
left unchanged.
<p>Each variable assignment is checked for unquoted tilde-prefixes immediately
following a `<samp><span class="samp">:</span></samp>' or the first `<samp><span class="samp">=</span></samp>'.
In these cases, tilde expansion is also performed.
Consequently, one may use file names with tildes in assignments to
<samp><span class="env">PATH</span></samp>, <samp><span class="env">MAILPATH</span></samp>, and <samp><span class="env">CDPATH</span></samp>,
and the shell assigns the expanded value.
<p>The following table shows how Bash treats unquoted tilde-prefixes:
<dl>
<dt><code>~</code><dd>The value of <code>$HOME</code>
<br><dt><code>~/foo</code><dd><samp><span class="file">$HOME/foo</span></samp>
<br><dt><code>~fred/foo</code><dd>The subdirectory <code>foo</code> of the home directory of the user
<code>fred</code>
<br><dt><code>~+/foo</code><dd><samp><span class="file">$PWD/foo</span></samp>
<br><dt><code>~-/foo</code><dd><samp><span class="file">${OLDPWD-'~-'}/foo</span></samp>
<br><dt><code>~</code><var>N</var><dd>The string that would be displayed by `<samp><span class="samp">dirs +</span><var>N</var></samp>'
<br><dt><code>~+</code><var>N</var><dd>The string that would be displayed by `<samp><span class="samp">dirs +</span><var>N</var></samp>'
<br><dt><code>~-</code><var>N</var><dd>The string that would be displayed by `<samp><span class="samp">dirs -</span><var>N</var></samp>'
</dl>
<div class="node">
<p><hr>
<a name="Shell-Parameter-Expansion"></a>
Next: <a rel="next" accesskey="n" href="#Command-Substitution">Command Substitution</a>,
Previous: <a rel="previous" accesskey="p" href="#Tilde-Expansion">Tilde Expansion</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Expansions">Shell Expansions</a>
</div>
<h4 class="subsection">3.5.3 Shell Parameter Expansion</h4>
<p><a name="index-parameter-expansion-84"></a><a name="index-expansion_002c-parameter-85"></a>
The `<samp><span class="samp">$</span></samp>' 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.
<p>When braces are used, the matching ending brace is the first `<samp><span class="samp">}</span></samp>'
not escaped by a backslash or within a quoted string, and not within an
embedded arithmetic expansion, command substitution, or parameter
expansion.
<p>The basic form of parameter expansion is ${<var>parameter</var>}.
The value of <var>parameter</var> is substituted. 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.
<p>If the first character of <var>parameter</var> is an exclamation point,
a level of variable indirection is introduced.
Bash uses the value of the variable formed from the rest of
<var>parameter</var> as the name of the variable; this variable is then
expanded and that value is used in the rest of the substitution, rather
than the value of <var>parameter</var> itself.
This is known as <code>indirect expansion</code>.
The exceptions to this are the expansions of ${!<var>prefix*</var>}
and ${!<var>name</var>[@]}
described below.
The exclamation point must immediately follow the left brace in order to
introduce indirection.
<p>In each of the cases below, <var>word</var> is subject to tilde expansion,
parameter expansion, command substitution, and arithmetic expansion.
<p>When not performing substring expansion, Bash tests for a parameter
that is unset or null; omitting the colon results in a test only for a
parameter that is unset. Put another way, if the colon is included,
the operator tests for both existence and that the value is not null;
if the colon is omitted, the operator tests only for existence.
<dl>
<dt><code>${</code><var>parameter</var><code>:−</code><var>word</var><code>}</code><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.
<br><dt><code>${</code><var>parameter</var><code>:=</code><var>word</var><code>}</code><dd>If <var>parameter</var>
is unset or null, the expansion of <var>word</var>
is assigned to <var>parameter</var>.
The value of <var>parameter</var> is then substituted.
Positional parameters and special parameters may not be assigned to
in this way.
<br><dt><code>${</code><var>parameter</var><code>:?</code><var>word</var><code>}</code><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.
<br><dt><code>${</code><var>parameter</var><code>:+</code><var>word</var><code>}</code><dd>If <var>parameter</var>
is null or unset, nothing is substituted, otherwise the expansion of
<var>word</var> is substituted.
<br><dt><code>${</code><var>parameter</var><code>:</code><var>offset</var><code>}</code><dt><code>${</code><var>parameter</var><code>:</code><var>offset</var><code>:</code><var>length</var><code>}</code><dd>Expands to up to <var>length</var> characters of <var>parameter</var>
starting at the character specified by <var>offset</var>.
If <var>length</var> is omitted, expands to the substring of
<var>parameter</var> starting at the character specified by <var>offset</var>.
<var>length</var> and <var>offset</var> are arithmetic expressions
(see <a href="#Shell-Arithmetic">Shell Arithmetic</a>).
This is referred to as Substring Expansion.
<p><var>length</var> must evaluate to a number greater than or equal to zero.
If <var>offset</var> evaluates to a number less than zero, the value
is used as an offset from the end of the value of <var>parameter</var>.
If <var>parameter</var> is `<samp><span class="samp">@</span></samp>', the result is <var>length</var> positional
parameters beginning at <var>offset</var>.
If <var>parameter</var> is an array name indexed by `<samp><span class="samp">@</span></samp>' or `<samp><span class="samp">*</span></samp>',
the result is the <var>length</var>
members of the array beginning with <code>${</code><var>parameter</var><code>[</code><var>offset</var><code>]}</code>.
A negative <var>offset</var> is taken relative to one greater than the maximum
index of the specified array.
Note that a negative offset must be separated from the colon by at least
one space to avoid being confused with the `<samp><span class="samp">:-</span></samp>' expansion.
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>$@</code> is
prefixed to the list.
<br><dt><code>${!</code><var>prefix</var><code>*}</code><dt><code>${!</code><var>prefix</var><code>@}</code><dd>Expands to the names of variables whose names begin with <var>prefix</var>,
separated by the first character of the <samp><span class="env">IFS</span></samp> special variable.
When `<samp><span class="samp">@</span></samp>' is used and the expansion appears within double quotes, each
variable name expands to a separate word.
<br><dt><code>${!</code><var>name</var><code>[@]}</code><dt><code>${!</code><var>name</var><code>[*]}</code><dd>If <var>name</var> is an array variable, expands to the list of array indices
(keys) assigned in <var>name</var>.
If <var>name</var> is not an array, expands to 0 if <var>name</var> is set and null
otherwise.
When `<samp><span class="samp">@</span></samp>' is used and the expansion appears within double quotes, each
key expands to a separate word.
<br><dt><code>${#</code><var>parameter</var><code>}</code><dd>The length in characters of the expanded value of <var>parameter</var> is
substituted.
If <var>parameter</var> is `<samp><span class="samp">*</span></samp>' or `<samp><span class="samp">@</span></samp>', the value substituted
is the number of positional parameters.
If <var>parameter</var> is an array name subscripted by `<samp><span class="samp">*</span></samp>' or `<samp><span class="samp">@</span></samp>',
the value substituted is the number of elements in the array.
<br><dt><code>${</code><var>parameter</var><code>#</code><var>word</var><code>}</code><dt><code>${</code><var>parameter</var><code>##</code><var>word</var><code>}</code><dd>The <var>word</var>
is expanded to produce a pattern just as in filename
expansion (see <a href="#Filename-Expansion">Filename Expansion</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 `<samp><span class="samp">#</span></samp>' case) or the
longest matching pattern (the `<samp><span class="samp">##</span></samp>' case) deleted.
If <var>parameter</var> is `<samp><span class="samp">@</span></samp>' or `<samp><span class="samp">*</span></samp>',
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
`<samp><span class="samp">@</span></samp>' or `<samp><span class="samp">*</span></samp>',
the pattern removal operation is applied to each member of the
array in turn, and the expansion is the resultant list.
<br><dt><code>${</code><var>parameter</var><code>%</code><var>word</var><code>}</code><dt><code>${</code><var>parameter</var><code>%%</code><var>word</var><code>}</code><dd>The <var>word</var> is expanded to produce a pattern just as in
filename expansion.
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 `<samp><span class="samp">%</span></samp>' case)
or the longest matching pattern (the `<samp><span class="samp">%%</span></samp>' case) deleted.
If <var>parameter</var> is `<samp><span class="samp">@</span></samp>' or `<samp><span class="samp">*</span></samp>',
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 `<samp><span class="samp">@</span></samp>' or `<samp><span class="samp">*</span></samp>',
the pattern removal operation is applied to each member of the
array in turn, and the expansion is the resultant list.
<br><dt><code>${</code><var>parameter</var><code>/</code><var>pattern</var><code>/</code><var>string</var><code>}</code><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>.
If <var>pattern</var> begins with `<samp><span class="samp">/</span></samp>', all matches of <var>pattern</var> are
replaced with <var>string</var>. Normally only the first match is replaced.
If <var>pattern</var> begins with `<samp><span class="samp">#</span></samp>', it must match at the beginning
of the expanded value of <var>parameter</var>.
If <var>pattern</var> begins with `<samp><span class="samp">%</span></samp>', it must match at the end
of the expanded value of <var>parameter</var>.
If <var>string</var> is null, matches of <var>pattern</var> are deleted
and the <code>/</code> following <var>pattern</var> may be omitted.
If <var>parameter</var> is `<samp><span class="samp">@</span></samp>' or `<samp><span class="samp">*</span></samp>',
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 `<samp><span class="samp">@</span></samp>' or `<samp><span class="samp">*</span></samp>',
the substitution operation is applied to each member of the
array in turn, and the expansion is the resultant list.
</dl>
<div class="node">
<p><hr>
<a name="Command-Substitution"></a>
Next: <a rel="next" accesskey="n" href="#Arithmetic-Expansion">Arithmetic Expansion</a>,
Previous: <a rel="previous" accesskey="p" href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Expansions">Shell Expansions</a>
</div>
<h4 class="subsection">3.5.4 Command Substitution</h4>
<p><a name="index-command-substitution-86"></a>
Command substitution allows the output of a command to replace
the command itself.
Command substitution occurs when a command is enclosed as follows:
<pre class="example"> $(<var>command</var>)
</pre>
<p class="noindent">or
<pre class="example"> `<var>command</var>`
</pre>
<p class="noindent">Bash performs the expansion by executing <var>command</var> and
replacing the command substitution with the standard output of the
command, with any trailing newlines deleted.
Embedded newlines are not deleted, but they may be removed during
word splitting.
The command substitution <code>$(cat </code><var>file</var><code>)</code> can be
replaced by the equivalent but faster <code>$(< </code><var>file</var><code>)</code>.
<p>When the old-style backquote form of substitution is used,
backslash retains its literal meaning except when followed by
`<samp><span class="samp">$</span></samp>', `<samp><span class="samp">`</span></samp>', or `<samp><span class="samp">\</span></samp>'.
The first backquote not preceded by a backslash terminates the
command substitution.
When using the <code>$(</code><var>command</var><code>)</code> form, all characters between
the parentheses make up the command; none are treated specially.
<p>Command substitutions may be nested. To nest when using the backquoted
form, escape the inner backquotes with backslashes.
<p>If the substitution appears within double quotes, word splitting and
filename expansion are not performed on the results.
<div class="node">
<p><hr>
<a name="Arithmetic-Expansion"></a>
Next: <a rel="next" accesskey="n" href="#Process-Substitution">Process Substitution</a>,
Previous: <a rel="previous" accesskey="p" href="#Command-Substitution">Command Substitution</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Expansions">Shell Expansions</a>
</div>
<h4 class="subsection">3.5.5 Arithmetic Expansion</h4>
<p><a name="index-expansion_002c-arithmetic-87"></a><a name="index-arithmetic-expansion-88"></a>
Arithmetic expansion allows the evaluation of an arithmetic expression
and the substitution of the result. The format for arithmetic expansion is:
<pre class="example"> $(( <var>expression</var> ))
</pre>
<p>The expression is treated as if it were within double quotes, but
a double quote inside the parentheses is not treated specially.
All tokens in the expression undergo parameter expansion, command
substitution, and quote removal.
Arithmetic expansions may be nested.
<p>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.
<div class="node">
<p><hr>
<a name="Process-Substitution"></a>
Next: <a rel="next" accesskey="n" href="#Word-Splitting">Word Splitting</a>,
Previous: <a rel="previous" accesskey="p" href="#Arithmetic-Expansion">Arithmetic Expansion</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Expansions">Shell Expansions</a>
</div>
<h4 class="subsection">3.5.6 Process Substitution</h4>
<p><a name="index-process-substitution-89"></a>
Process substitution is supported on systems that support named
pipes (<span class="sc">fifo</span>s) or the <samp><span class="file">/dev/fd</span></samp> method of naming open files.
It takes the form of
<pre class="example"> <(<var>list</var>)
</pre>
<p class="noindent">or
<pre class="example"> >(<var>list</var>)
</pre>
<p class="noindent">The process <var>list</var> is run with its input or output connected to a
<span class="sc">fifo</span> or some file in <samp><span class="file">/dev/fd</span></samp>. The name of this file is
passed as an argument to the current command as the result of the
expansion. If the <code>>(</code><var>list</var><code>)</code> form is used, writing to
the file will provide input for <var>list</var>. If the
<code><(</code><var>list</var><code>)</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><</code> or <code>></code>
and the left parenthesis, otherwise the construct would be interpreted
as a redirection.
<p>When available, process substitution is performed simultaneously with
parameter and variable expansion, command substitution, and arithmetic
expansion.
<div class="node">
<p><hr>
<a name="Word-Splitting"></a>
Next: <a rel="next" accesskey="n" href="#Filename-Expansion">Filename Expansion</a>,
Previous: <a rel="previous" accesskey="p" href="#Process-Substitution">Process Substitution</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Expansions">Shell Expansions</a>
</div>
<h4 class="subsection">3.5.7 Word Splitting</h4>
<p><a name="index-word-splitting-90"></a>
The shell scans the results of parameter expansion, command substitution,
and arithmetic expansion that did not occur within double quotes for
word splitting.
<p>The shell treats each character of <samp><span class="env">$IFS</span></samp> as a delimiter, and splits
the results of the other expansions into words on these characters.
If <samp><span class="env">IFS</span></samp> is unset, or its value is exactly <code><space><tab><newline></code>,
the default, then sequences of
<code> <space></code>, <code><tab></code>, and <code><newline></code>
at the beginning and end of the results of the previous
expansions are ignored, and any sequence of <samp><span class="env">IFS</span></samp>
characters not at the beginning or end serves to delimit words.
If <samp><span class="env">IFS</span></samp> has a value other than the default, then sequences of
the whitespace characters <code>space</code> and <code>tab</code>
are ignored at the beginning and end of the
word, as long as the whitespace character is in the
value of <samp><span class="env">IFS</span></samp> (an <samp><span class="env">IFS</span></samp> whitespace character).
Any character in <samp><span class="env">IFS</span></samp> that is not <samp><span class="env">IFS</span></samp>
whitespace, along with any adjacent <samp><span class="env">IFS</span></samp>
whitespace characters, delimits a field. A sequence of <samp><span class="env">IFS</span></samp>
whitespace characters is also treated as a delimiter.
If the value of <samp><span class="env">IFS</span></samp> is null, no word splitting occurs.
<p>Explicit null arguments (<code>""</code> or <code>''</code>) are retained.
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.
<p>Note that if no expansion occurs, no splitting
is performed.
<div class="node">
<p><hr>
<a name="Filename-Expansion"></a>
Next: <a rel="next" accesskey="n" href="#Quote-Removal">Quote Removal</a>,
Previous: <a rel="previous" accesskey="p" href="#Word-Splitting">Word Splitting</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Expansions">Shell Expansions</a>
</div>
<h4 class="subsection">3.5.8 Filename Expansion</h4>
<ul class="menu">
<li><a accesskey="1" href="#Pattern-Matching">Pattern Matching</a>: How the shell matches patterns.
</ul>
<a name="index-expansion_002c-filename-91"></a><a name="index-expansion_002c-pathname-92"></a><a name="index-filename-expansion-93"></a><a name="index-pathname-expansion-94"></a>
After word splitting, unless the <samp><span class="option">-f</span></samp> option has been set
(see <a href="#The-Set-Builtin">The Set Builtin</a>), Bash scans each word for the characters
`<samp><span class="samp">*</span></samp>', `<samp><span class="samp">?</span></samp>', and `<samp><span class="samp">[</span></samp>'.
If one of these characters appears, then the word is
regarded as a <var>pattern</var>,
and replaced with an alphabetically sorted list of
file names matching the pattern. If no matching file names 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.
<p>When a pattern is used for filename generation, the character `<samp><span class="samp">.</span></samp>'
at the start of a filename or immediately following a slash
must be matched explicitly, unless the shell option <code>dotglob</code> is set.
When matching a file name, the slash character must always be
matched explicitly.
In other cases, the `<samp><span class="samp">.</span></samp>' character is not treated specially.
<p>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>failglob</code>, and <code>dotglob</code> options.
<p>The <samp><span class="env">GLOBIGNORE</span></samp>
shell variable may be used to restrict the set of filenames matching a
pattern. If <samp><span class="env">GLOBIGNORE</span></samp>
is set, each matching filename that also matches one of the patterns in
<samp><span class="env">GLOBIGNORE</span></samp> is removed from the list of matches. The filenames
<samp><span class="file">.</span></samp> and <samp><span class="file">..</span></samp>
are always ignored when <samp><span class="env">GLOBIGNORE</span></samp>
is set and not null.
However, setting <samp><span class="env">GLOBIGNORE</span></samp> to a non-null value has the effect of
enabling the <code>dotglob</code>
shell option, so all other filenames beginning with a
`<samp><span class="samp">.</span></samp>' will match.
To get the old behavior of ignoring filenames beginning with a
`<samp><span class="samp">.</span></samp>', make `<samp><span class="samp">.*</span></samp>' one of the patterns in <samp><span class="env">GLOBIGNORE</span></samp>.
The <code>dotglob</code> option is disabled when <samp><span class="env">GLOBIGNORE</span></samp>
is unset.
<div class="node">
<p><hr>
<a name="Pattern-Matching"></a>
Up: <a rel="up" accesskey="u" href="#Filename-Expansion">Filename Expansion</a>
</div>
<h5 class="subsubsection">3.5.8.1 Pattern Matching</h5>
<p><a name="index-pattern-matching-95"></a><a name="index-matching_002c-pattern-96"></a>
Any character that appears in a pattern, other than the special pattern
characters described below, matches itself.
The <span class="sc">nul</span> 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.
<p>The special pattern characters have the following meanings:
<dl>
<dt><code>*</code><dd>Matches any string, including the null string.
<br><dt><code>?</code><dd>Matches any single character.
<br><dt><code>[...]</code><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 sorts between those two characters, inclusive,
using the current locale's collating sequence and character set,
is matched. If the first character following the
`<samp><span class="samp">[</span></samp>' is a `<samp><span class="samp">!</span></samp>' or a `<samp><span class="samp">^</span></samp>'
then any character not enclosed is matched. A `<samp><span class="samp">−</span></samp>'
may be matched by including it as the first or last character
in the set. A `<samp><span class="samp">]</span></samp>' may be matched by including it as the first
character in the set.
The sorting order of characters in range expressions is determined by
the current locale and the value of the <samp><span class="env">LC_COLLATE</span></samp> shell variable,
if set.
<p>For example, in the default C locale, `<samp><span class="samp">[a-dx-z]</span></samp>' is equivalent to
`<samp><span class="samp">[abcdxyz]</span></samp>'. Many locales sort characters in dictionary order, and in
these locales `<samp><span class="samp">[a-dx-z]</span></samp>' is typically not equivalent to `<samp><span class="samp">[abcdxyz]</span></samp>';
it might be equivalent to `<samp><span class="samp">[aBbCcDdxXyYz]</span></samp>', for example. To obtain
the traditional interpretation of ranges in bracket expressions, you can
force the use of the C locale by setting the <samp><span class="env">LC_COLLATE</span></samp> or
<samp><span class="env">LC_ALL</span></samp> environment variable to the value `<samp><span class="samp">C</span></samp>'.
<p>Within `<samp><span class="samp">[</span></samp>' and `<samp><span class="samp">]</span></samp>', <var>character classes</var> 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 <span class="sc">posix</span> standard:
<pre class="example"> alnum alpha ascii blank cntrl digit graph lower
print punct space upper word xdigit
</pre>
<p class="noindent">A character class matches any character belonging to that class.
The <code>word</code> character class matches letters, digits, and the character
`<samp><span class="samp">_</span></samp>'.
<p>Within `<samp><span class="samp">[</span></samp>' and `<samp><span class="samp">]</span></samp>', an <var>equivalence class</var> 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>.
<p>Within `<samp><span class="samp">[</span></samp>' and `<samp><span class="samp">]</span></samp>', the syntax <code>[.</code><var>symbol</var><code>.]</code>
matches the collating symbol <var>symbol</var>.
</dl>
<p>If the <code>extglob</code> shell option is enabled using the <code>shopt</code>
builtin, several extended pattern matching operators are recognized.
In the following description, a <var>pattern-list</var> is a list of one
or more patterns separated by a `<samp><span class="samp">|</span></samp>'.
Composite patterns may be formed using one or more of the following
sub-patterns:
<dl>
<dt><code>?(</code><var>pattern-list</var><code>)</code><dd>Matches zero or one occurrence of the given patterns.
<br><dt><code>*(</code><var>pattern-list</var><code>)</code><dd>Matches zero or more occurrences of the given patterns.
<br><dt><code>+(</code><var>pattern-list</var><code>)</code><dd>Matches one or more occurrences of the given patterns.
<br><dt><code>@(</code><var>pattern-list</var><code>)</code><dd>Matches one of the given patterns.
<br><dt><code>!(</code><var>pattern-list</var><code>)</code><dd>Matches anything except one of the given patterns.
</dl>
<div class="node">
<p><hr>
<a name="Quote-Removal"></a>
Previous: <a rel="previous" accesskey="p" href="#Filename-Expansion">Filename Expansion</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Expansions">Shell Expansions</a>
</div>
<h4 class="subsection">3.5.9 Quote Removal</h4>
<p>After the preceding expansions, all unquoted occurrences of the
characters `<samp><span class="samp">\</span></samp>', `<samp><span class="samp">'</span></samp>', and `<samp><span class="samp">"</span></samp>' that did not
result from one of the above expansions are removed.
<div class="node">
<p><hr>
<a name="Redirections"></a>
Next: <a rel="next" accesskey="n" href="#Executing-Commands">Executing Commands</a>,
Previous: <a rel="previous" accesskey="p" href="#Shell-Expansions">Shell Expansions</a>,
Up: <a rel="up" accesskey="u" href="#Basic-Shell-Features">Basic Shell Features</a>
</div>
<h3 class="section">3.6 Redirections</h3>
<p><a name="index-redirection-97"></a>
Before a command is executed, its input and output
may be <var>redirected</var>
using a special notation interpreted by the shell.
Redirection may also be used to open and close files for 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.
<p>In the following descriptions, if the file descriptor number is
omitted, and the first character of the redirection operator is
`<samp><span class="samp"><</span></samp>', the redirection refers to the standard input (file
descriptor 0). If the first character of the redirection operator
is `<samp><span class="samp">></span></samp>', the redirection refers to the standard output (file
descriptor 1).
<p>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.
<p>Note that the order of redirections is significant. For example,
the command
<pre class="example"> ls > <var>dirlist</var> 2>&1
</pre>
<p class="noindent">directs both standard output (file descriptor 1) and standard error
(file descriptor 2) to the file <var>dirlist</var>, while the command
<pre class="example"> ls 2>&1 > <var>dirlist</var>
</pre>
<p class="noindent">directs only the standard output to file <var>dirlist</var>,
because the standard error was duplicated as standard output
before the standard output was redirected to <var>dirlist</var>.
<p>Bash handles several filenames specially when they are used in
redirections, as described in the following table:
<dl>
<dt><code>/dev/fd/</code><var>fd</var><dd>If <var>fd</var> is a valid integer, file descriptor <var>fd</var> is duplicated.
<br><dt><code>/dev/stdin</code><dd>File descriptor 0 is duplicated.
<br><dt><code>/dev/stdout</code><dd>File descriptor 1 is duplicated.
<br><dt><code>/dev/stderr</code><dd>File descriptor 2 is duplicated.
<br><dt><code>/dev/tcp/</code><var>host</var><code>/</code><var>port</var><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 a TCP
connection to the corresponding socket.
<br><dt><code>/dev/udp/</code><var>host</var><code>/</code><var>port</var><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 a UDP
connection to the corresponding socket.
</dl>
<p>A failure to open or create a file causes the redirection to fail.
<p>Redirections using file descriptors greater than 9 should be used with
care, as they may conflict with file descriptors the shell uses
internally.
<h4 class="subsection">3.6.1 Redirecting Input</h4>
<p>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.
<p>The general format for redirecting input is:
<pre class="example"> [<var>n</var>]<<var>word</var>
</pre>
<h4 class="subsection">3.6.2 Redirecting Output</h4>
<p>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.
<p>The general format for redirecting output is:
<pre class="example"> [<var>n</var>]>[|]<var>word</var>
</pre>
<p>If the redirection operator is `<samp><span class="samp">></span></samp>', 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 `<samp><span class="samp">>|</span></samp>', or the redirection operator is
`<samp><span class="samp">></span></samp>' and the <code>noclobber</code> option is not enabled, the redirection
is attempted even if the file named by <var>word</var> exists.
<h4 class="subsection">3.6.3 Appending Redirected Output</h4>
<p>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.
<p>The general format for appending output is:
<pre class="example"> [<var>n</var>]>><var>word</var>
</pre>
<h4 class="subsection">3.6.4 Redirecting Standard Output and Standard Error</h4>
<p>Bash 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> with this construct.
<p>There are two formats for redirecting standard output and
standard error:
<pre class="example"> &><var>word</var>
</pre>
<p class="noindent">and
<pre class="example"> >&<var>word</var>
</pre>
<p class="noindent">Of the two forms, the first is preferred.
This is semantically equivalent to
<pre class="example"> ><var>word</var> 2>&1
</pre>
<h4 class="subsection">3.6.5 Here Documents</h4>
<p>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 for a command.
<p>The format of here-documents is:
<pre class="example"> <<[−]<var>word</var>
<var>here-document</var>
<var>delimiter</var>
</pre>
<p>No parameter expansion, command substitution, arithmetic expansion,
or filename expansion is performed on
<var>word</var>. If any characters in <var>word</var> are 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. In the latter
case, the character sequence <code>\newline</code> is ignored, and `<samp><span class="samp">\</span></samp>'
must be used to quote the characters
`<samp><span class="samp">\</span></samp>', `<samp><span class="samp">$</span></samp>', and `<samp><span class="samp">`</span></samp>'.
<p>If the redirection operator is `<samp><span class="samp"><<-</span></samp>',
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.
<h4 class="subsection">3.6.6 Here Strings</h4>
<p>A variant of here documents, the format is:
<pre class="example"> <<< <var>word</var>
</pre>
<p>The <var>word</var> is expanded and supplied to the command on its standard
input.
<h4 class="subsection">3.6.7 Duplicating File Descriptors</h4>
<p>The redirection operator
<pre class="example"> [<var>n</var>]<&<var>word</var>
</pre>
<p class="noindent">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 `<samp><span class="samp">-</span></samp>', file descriptor <var>n</var> is closed. If
<var>n</var> is not specified, the standard input (file descriptor 0) is used.
<p>The operator
<pre class="example"> [<var>n</var>]>&<var>word</var>
</pre>
<p class="noindent">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.
As a special case, if <var>n</var> is omitted, and <var>word</var> does not
expand to one or more digits, the standard output and standard
error are redirected as described previously.
<h4 class="subsection">3.6.8 Moving File Descriptors</h4>
<p>The redirection operator
<pre class="example"> [<var>n</var>]<&<var>digit</var>-
</pre>
<p class="noindent">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>.
<p>Similarly, the redirection operator
<pre class="example"> [<var>n</var>]>&<var>digit</var>-
</pre>
<p class="noindent">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.
<h4 class="subsection">3.6.9 Opening File Descriptors for Reading and Writing</h4>
<p>The redirection operator
<pre class="example"> [<var>n</var>]<><var>word</var>
</pre>
<p class="noindent">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.
<div class="node">
<p><hr>
<a name="Executing-Commands"></a>
Next: <a rel="next" accesskey="n" href="#Shell-Scripts">Shell Scripts</a>,
Previous: <a rel="previous" accesskey="p" href="#Redirections">Redirections</a>,
Up: <a rel="up" accesskey="u" href="#Basic-Shell-Features">Basic Shell Features</a>
</div>
<h3 class="section">3.7 Executing Commands</h3>
<ul class="menu">
<li><a accesskey="1" href="#Simple-Command-Expansion">Simple Command Expansion</a>: How Bash expands simple commands before
executing them.
<li><a accesskey="2" href="#Command-Search-and-Execution">Command Search and Execution</a>: How Bash finds commands and runs them.
<li><a accesskey="3" href="#Command-Execution-Environment">Command Execution Environment</a>: The environment in which Bash
executes commands that are not
shell builtins.
<li><a accesskey="4" href="#Environment">Environment</a>: The environment given to a command.
<li><a accesskey="5" href="#Exit-Status">Exit Status</a>: The status returned by commands and how Bash
interprets it.
<li><a accesskey="6" href="#Signals">Signals</a>: What happens when Bash or a command it runs
receives a signal.
</ul>
<div class="node">
<p><hr>
<a name="Simple-Command-Expansion"></a>
Next: <a rel="next" accesskey="n" href="#Command-Search-and-Execution">Command Search and Execution</a>,
Up: <a rel="up" accesskey="u" href="#Executing-Commands">Executing Commands</a>
</div>
<h4 class="subsection">3.7.1 Simple Command Expansion</h4>
<p><a name="index-command-expansion-98"></a>
When a simple command is executed, the shell performs the following
expansions, assignments, and redirections, from left to right.
<ol type=1 start=1>
<li>The words that the parser has marked as variable assignments (those
preceding the command name) and redirections are saved for later
processing.
<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>Redirections are performed as described above (see <a href="#Redirections">Redirections</a>).
<li>The text after the `<samp><span class="samp">=</span></samp>' in each variable assignment undergoes tilde
expansion, parameter expansion, command substitution, arithmetic expansion,
and quote removal before being assigned to the variable.
</ol>
<p>If no command name results, the variable assignments affect the current
shell environment. 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.
<p>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.
<p>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.
<div class="node">
<p><hr>
<a name="Command-Search-and-Execution"></a>
Next: <a rel="next" accesskey="n" href="#Command-Execution-Environment">Command Execution Environment</a>,
Previous: <a rel="previous" accesskey="p" href="#Simple-Command-Expansion">Simple Command Expansion</a>,
Up: <a rel="up" accesskey="u" href="#Executing-Commands">Executing Commands</a>
</div>
<h4 class="subsection">3.7.2 Command Search and Execution</h4>
<p><a name="index-command-execution-99"></a><a name="index-command-search-100"></a>
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 type=1 start=1>
<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>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>If the name is neither a shell function nor a builtin,
and contains no slashes, Bash searches each element of
<samp><span class="env">$PATH</span></samp> 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 <samp><span class="env">PATH</span></samp> 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 <samp><span class="env">$PATH</span></samp>
is performed only if the command is not found in the hash table.
If the search is unsuccessful, the shell prints an error
message and returns an exit status of 127.
<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>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
<var>shell script</var> and the shell executes it as described in
<a href="#Shell-Scripts">Shell Scripts</a>.
<li>If the command was not begun asynchronously, the shell waits for
the command to complete and collects its exit status.
</ol>
<div class="node">
<p><hr>
<a name="Command-Execution-Environment"></a>
Next: <a rel="next" accesskey="n" href="#Environment">Environment</a>,
Previous: <a rel="previous" accesskey="p" href="#Command-Search-and-Execution">Command Search and Execution</a>,
Up: <a rel="up" accesskey="u" href="#Executing-Commands">Executing Commands</a>
</div>
<h4 class="subsection">3.7.3 Command Execution Environment</h4>
<p><a name="index-execution-environment-101"></a>
The shell has an <var>execution environment</var>, 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>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>the file creation mode mask as set by <code>umask</code> or inherited from
the shell's parent
<li>current traps set by <code>trap</code>
<li>shell parameters that are set by variable assignment or with <code>set</code>
or inherited from the shell's parent in the environment
<li>shell functions defined during execution or inherited from the shell's
parent in the environment
<li>options enabled at invocation (either by default or with command-line
arguments) or by <code>set</code>
<li>options enabled by <code>shopt</code> (see <a href="#The-Shopt-Builtin">The Shopt Builtin</a>)
<li>shell aliases defined with <code>alias</code> (see <a href="#Aliases">Aliases</a>)
<li>various process <span class="sc">id</span>s, including those of background jobs
(see <a href="#Lists">Lists</a>), the value of <code>$$</code>, and the value of
<samp><span class="env">$PPID</span></samp>
</ul>
<p>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's open files, plus any modifications and additions specified
by redirections to the command
<li>the current working directory
<li>the file creation mode mask
<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>traps caught by the shell are reset to the values inherited from the
shell's parent, and traps ignored by the shell are ignored
</ul>
<p>A command invoked in this separate environment cannot affect the
shell's execution environment.
<p>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's execution environment.
<p>If a command is followed by a `<samp><span class="samp">&</span></samp>' and job control is not active, the
default standard input for the command is the empty file <samp><span class="file">/dev/null</span></samp>.
Otherwise, the invoked command inherits the file descriptors of the calling
shell as modified by redirections.
<div class="node">
<p><hr>
<a name="Environment"></a>
Next: <a rel="next" accesskey="n" href="#Exit-Status">Exit Status</a>,
Previous: <a rel="previous" accesskey="p" href="#Command-Execution-Environment">Command Execution Environment</a>,
Up: <a rel="up" accesskey="u" href="#Executing-Commands">Executing Commands</a>
</div>
<h4 class="subsection">3.7.4 Environment</h4>
<p><a name="index-environment-102"></a>
When a program is invoked it is given an array of strings
called the <var>environment</var>.
This is a list of name-value pairs, of the form <code>name=value</code>.
<p>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 <var>export</var>
to child processes. Executed commands inherit the environment.
The <code>export</code> and `<samp><span class="samp">declare -x</span></samp>'
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's
initial environment, whose values may be modified in the shell,
less any pairs removed by the <code>unset</code> and `<samp><span class="samp">export -n</span></samp>'
commands, plus any additions via the <code>export</code> and
`<samp><span class="samp">declare -x</span></samp>' commands.
<p>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.
<p>If the <samp><span class="option">-k</span></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.
<p>When Bash invokes an external command, the variable `<samp><span class="samp">$_</span></samp>'
is set to the full path name of the command and passed to that
command in its environment.
<div class="node">
<p><hr>
<a name="Exit-Status"></a>
Next: <a rel="next" accesskey="n" href="#Signals">Signals</a>,
Previous: <a rel="previous" accesskey="p" href="#Environment">Environment</a>,
Up: <a rel="up" accesskey="u" href="#Executing-Commands">Executing Commands</a>
</div>
<h4 class="subsection">3.7.5 Exit Status</h4>
<p><a name="index-exit-status-103"></a>
For the shell'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.
<p>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.
<p>If a command fails because of an error during expansion or redirection,
the exit status is greater than zero.
<p>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</a>).
<p>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.
<div class="node">
<p><hr>
<a name="Signals"></a>
Previous: <a rel="previous" accesskey="p" href="#Exit-Status">Exit Status</a>,
Up: <a rel="up" accesskey="u" href="#Executing-Commands">Executing Commands</a>
</div>
<h4 class="subsection">3.7.6 Signals</h4>
<p><a name="index-signal-handling-104"></a>
When Bash is interactive, in the absence of any traps, it ignores
<code>SIGTERM</code> (so that `<samp><span class="samp">kill 0</span></samp>' 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>.
<p>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>.
<p>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>.
<p>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.
<p>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.
<div class="node">
<p><hr>
<a name="Shell-Scripts"></a>
Previous: <a rel="previous" accesskey="p" href="#Executing-Commands">Executing Commands</a>,
Up: <a rel="up" accesskey="u" href="#Basic-Shell-Features">Basic Shell Features</a>
</div>
<h3 class="section">3.8 Shell Scripts</h3>
<p><a name="index-shell-script-105"></a>
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><span class="option">-c</span></samp> nor <samp><span class="option">-s</span></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 <samp><span class="env">$PATH</span></samp> if not found there.
<p>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.
<p>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 <samp><span class="env">$PATH</span></samp> for a command, it spawns a subshell to
execute it. In other words, executing
<pre class="example"> filename <var>arguments</var>
</pre>
<p class="noindent">is equivalent to executing
<pre class="example"> bash filename <var>arguments</var>
</pre>
<p class="noindent">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.
<p>Most versions of Unix make this a part of the operating system's command
execution mechanism. If the first line of a script begins with
the two characters `<samp><span class="samp">#!</span></samp>', the remainder of the line specifies
an interpreter for the program.
Thus, you can specify Bash, <code>awk</code>, Perl, or some other
interpreter and write the rest of the script file in that language.
<p>The arguments to the interpreter
consist of a single optional argument 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. 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 argument to a maximum of 32 characters.
<p>Bash scripts often begin with <code>#! /bin/bash</code> (assuming that
Bash has been installed in <samp><span class="file">/bin</span></samp>), since this ensures that
Bash will be used to interpret the script, even if it is executed
under another shell.
<div class="node">
<p><hr>
<a name="Shell-Builtin-Commands"></a>
Next: <a rel="next" accesskey="n" href="#Shell-Variables">Shell Variables</a>,
Previous: <a rel="previous" accesskey="p" href="#Basic-Shell-Features">Basic Shell Features</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="chapter">4 Shell Builtin Commands</h2>
<ul class="menu">
<li><a accesskey="1" href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>: Builtin commands inherited from the Bourne
Shell.
<li><a accesskey="2" href="#Bash-Builtins">Bash Builtins</a>: Table of builtins specific to Bash.
<li><a accesskey="3" href="#Modifying-Shell-Behavior">Modifying Shell Behavior</a>: Builtins to modify shell attributes and
optional behavior.
<li><a accesskey="4" href="#Special-Builtins">Special Builtins</a>: Builtin commands classified specially by
POSIX.
</ul>
<p>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.
<p>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.
<p>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>).
<p>Many of the builtins have been extended by <span class="sc">posix</span> or Bash.
<p>Unless otherwise noted, each builtin command documented as accepting
options preceded by `<samp><span class="samp">-</span></samp>' accepts `<samp><span class="samp">--</span></samp>'
to signify the end of the options.
For example, the <code>:</code>, <code>true</code>, <code>false</code>, and <code>test</code>
builtins do not accept options.
<div class="node">
<p><hr>
<a name="Bourne-Shell-Builtins"></a>
Next: <a rel="next" accesskey="n" href="#Bash-Builtins">Bash Builtins</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Builtin-Commands">Shell Builtin Commands</a>
</div>
<h3 class="section">4.1 Bourne Shell Builtins</h3>
<p>The following shell builtin commands are inherited from the Bourne Shell.
These commands are implemented as specified by the <span class="sc">posix</span> standard.
<dl>
<dt><code>: </code><span class="roman">(a colon)</span><dd><a name="index-g_t_003a-106"></a>
<pre class="example"> : [<var>arguments</var>]
</pre>
<p>Do nothing beyond expanding <var>arguments</var> and performing redirections.
The return status is zero.
<br><dt><code>. </code><span class="roman">(a period)</span><dd><a name="index-g_t_002e-107"></a>
<pre class="example"> . <var>filename</var> [<var>arguments</var>]
</pre>
<p>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 <samp><span class="env">PATH</span></samp> variable is used to find <var>filename</var>.
When Bash is not in <span class="sc">posix</span> mode, the current directory is searched
if <var>filename</var> is not found in <samp><span class="env">$PATH</span></samp>.
If any <var>arguments</var> are supplied, they become the positional
parameters when <var>filename</var> is executed. Otherwise the positional
parameters are unchanged.
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>.
<br><dt><code>break</code><dd><a name="index-break-108"></a>
<pre class="example"> break [<var>n</var>]
</pre>
<p>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.
<br><dt><code>cd</code><dd><a name="index-cd-109"></a>
<pre class="example"> cd [-L|-P] [<var>directory</var>]
</pre>
<p>Change the current working directory to <var>directory</var>.
If <var>directory</var> is not given, the value of the <samp><span class="env">HOME</span></samp> shell
variable is used.
If the shell variable <samp><span class="env">CDPATH</span></samp> exists, it is used as a search path.
If <var>directory</var> begins with a slash, <samp><span class="env">CDPATH</span></samp> is not used.
<p>The <samp><span class="option">-P</span></samp> option means to not follow symbolic links; symbolic
links are followed by default or with the <samp><span class="option">-L</span></samp> option.
If <var>directory</var> is `<samp><span class="samp">-</span></samp>', it is equivalent to <samp><span class="env">$OLDPWD</span></samp>.
<p>If a non-empty directory name from <samp><span class="env">CDPATH</span></samp> is used, or if
`<samp><span class="samp">-</span></samp>' is the first argument, and the directory change is
successful, the absolute pathname of the new working directory is
written to the standard output.
<p>The return status is zero if the directory is successfully changed,
non-zero otherwise.
<br><dt><code>continue</code><dd><a name="index-continue-110"></a>
<pre class="example"> continue [<var>n</var>]
</pre>
<p>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.
<br><dt><code>eval</code><dd><a name="index-eval-111"></a>
<pre class="example"> eval [<var>arguments</var>]
</pre>
<p>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.
<br><dt><code>exec</code><dd><a name="index-exec-112"></a>
<pre class="example"> exec [-cl] [-a <var>name</var>] [<var>command</var> [<var>arguments</var>]]
</pre>
<p>If <var>command</var>
is supplied, it replaces the shell without creating a new process.
If the <samp><span class="option">-l</span></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><span class="option">-c</span></samp> option causes <var>command</var> to be executed with an empty
environment.
If <samp><span class="option">-a</span></samp> is supplied, the shell passes <var>name</var> as the zeroth
argument to <var>command</var>.
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.
<br><dt><code>exit</code><dd><a name="index-exit-113"></a>
<pre class="example"> exit [<var>n</var>]
</pre>
<p>Exit the shell, returning a status of <var>n</var> to the shell'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.
<br><dt><code>export</code><dd><a name="index-export-114"></a>
<pre class="example"> export [-fn] [-p] [<var>name</var>[=<var>value</var>]]
</pre>
<p>Mark each <var>name</var> to be passed to child processes
in the environment. If the <samp><span class="option">-f</span></samp> option is supplied, the <var>name</var>s
refer to shell functions; otherwise the names refer to shell variables.
The <samp><span class="option">-n</span></samp> option means to no longer mark each <var>name</var> for export.
If no <var>names</var> are supplied, or if the <samp><span class="option">-p</span></samp> option is given, a
list of exported names is displayed.
The <samp><span class="option">-p</span></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>.
<p>The return status is zero unless an invalid option is supplied, one of
the names is not a valid shell variable name, or <samp><span class="option">-f</span></samp> is supplied
with a name that is not a shell function.
<br><dt><code>getopts</code><dd><a name="index-getopts-115"></a>
<pre class="example"> getopts <var>optstring</var> <var>name</var> [<var>args</var>]
</pre>
<p><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 white space.
The colon (`<samp><span class="samp">:</span></samp>') and question mark (`<samp><span class="samp">?</span></samp>') 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 <samp><span class="env">OPTIND</span></samp>.
<samp><span class="env">OPTIND</span></samp> 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 <samp><span class="env">OPTARG</span></samp>.
The shell does not reset <samp><span class="env">OPTIND</span></samp> 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.
<p>When the end of options is encountered, <code>getopts</code> exits with a
return value greater than zero.
<samp><span class="env">OPTIND</span></samp> is set to the index of the first non-option argument,
and <code>name</code> is set to `<samp><span class="samp">?</span></samp>'.
<p><code>getopts</code>
normally parses the positional parameters, but if more arguments are
given in <var>args</var>, <code>getopts</code> parses those instead.
<p><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 <samp><span class="env">OPTERR</span></samp>
is set to 0, no error messages will be displayed, even if the first
character of <code>optstring</code> is not a colon.
<p>If an invalid option is seen,
<code>getopts</code> places `<samp><span class="samp">?</span></samp>' into <var>name</var> and, if not silent,
prints an error message and unsets <samp><span class="env">OPTARG</span></samp>.
If <code>getopts</code> is silent, the option character found is placed in
<samp><span class="env">OPTARG</span></samp> and no diagnostic message is printed.
<p>If a required argument is not found, and <code>getopts</code>
is not silent, a question mark (`<samp><span class="samp">?</span></samp>') 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 (`<samp><span class="samp">:</span></samp>') is placed in
<var>name</var> and <samp><span class="env">OPTARG</span></samp> is set to the option character found.
<br><dt><code>hash</code><dd><a name="index-hash-116"></a>
<pre class="example"> hash [-r] [-p <var>filename</var>] [-dt] [<var>name</var>]
</pre>
<p>Remember the full pathnames of 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
<samp><span class="env">$PATH</span></samp>.
The <samp><span class="option">-p</span></samp> option inhibits the path search, and <var>filename</var> is
used as the location of <var>name</var>.
The <samp><span class="option">-r</span></samp> option causes the shell to forget all remembered locations.
The <samp><span class="option">-d</span></samp> option causes the shell to forget the remembered location
of each <var>name</var>.
If the <samp><span class="option">-t</span></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><span class="option">-t</span></samp> the <var>name</var> is printed before the hashed
full pathname.
The <samp><span class="option">-l</span></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><span class="option">-l</span></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.
<br><dt><code>pwd</code><dd><a name="index-pwd-117"></a>
<pre class="example"> pwd [-LP]
</pre>
<p>Print the absolute pathname of the current working directory.
If the <samp><span class="option">-P</span></samp> option is supplied, the pathname printed will not
contain symbolic links.
If the <samp><span class="option">-L</span></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.
<br><dt><code>readonly</code><dd><a name="index-readonly-118"></a>
<pre class="example"> readonly [-apf] [<var>name</var>[=<var>value</var>]] ...
</pre>
<p>Mark each <var>name</var> as readonly.
The values of these names may not be changed by subsequent assignment.
If the <samp><span class="option">-f</span></samp> option is supplied, each <var>name</var> refers to a shell
function.
The <samp><span class="option">-a</span></samp> option means each <var>name</var> refers to an array variable.
If no <var>name</var> arguments are given, or if the <samp><span class="option">-p</span></samp>
option is supplied, a list of all readonly names is printed.
The <samp><span class="option">-p</span></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><span class="option">-f</span></samp> option is supplied with a name that is not a shell function.
<br><dt><code>return</code><dd><a name="index-return-119"></a>
<pre class="example"> return [<var>n</var>]
</pre>
<p>Cause a shell function to exit with the return value <var>n</var>.
If <var>n</var> is not supplied, the return value is the exit status of the
last command executed in the function.
This may also be used to terminate execution of a script being executed
with the <code>.</code> (or <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.
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 used outside a function
and not during the execution of a script by <code>.</code> or <code>source</code>.
<br><dt><code>shift</code><dd><a name="index-shift-120"></a>
<pre class="example"> shift [<var>n</var>]
</pre>
<p>Shift the positional parameters to the left by <var>n</var>.
The positional parameters from <var>n</var>+1 <small class="dots">...</small> <code>$#</code> are
renamed to <code>$1</code> <small class="dots">...</small> <code>$#</code>-<var>n</var>.
Parameters represented by the numbers <code>$#</code> 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.
<br><dt><code>test</code><dt><code>[</code><dd><a name="index-test-121"></a><a name="index-g_t_005b-122"></a>Evaluate a conditional expression <var>expr</var>.
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><span class="option">--</span></samp> as signifying the end of options.
<p>When the <code>[</code> form is used, the last argument to the command must
be a <code>]</code>.
<p>Expressions may be combined using the following operators, listed in
decreasing order of precedence.
<dl>
<dt><code>! </code><var>expr</var><dd>True if <var>expr</var> is false.
<br><dt><code>( </code><var>expr</var><code> )</code><dd>Returns the value of <var>expr</var>.
This may be used to override the normal precedence of operators.
<br><dt><var>expr1</var><code> -a </code><var>expr2</var><dd>True if both <var>expr1</var> and <var>expr2</var> are true.
<br><dt><var>expr1</var><code> -o </code><var>expr2</var><dd>True if either <var>expr1</var> or <var>expr2</var> is true.
</dl>
<p>The <code>test</code> and <code>[</code> builtins evaluate conditional
expressions using a set of rules based on the number of arguments.
<dl>
<dt>0 arguments<dd>The expression is false.
<br><dt>1 argument<dd>The expression is true if and only if the argument is not null.
<br><dt>2 arguments<dd>If the first argument is `<samp><span class="samp">!</span></samp>', 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.
<br><dt>3 arguments<dd>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.
If the first argument is `<samp><span class="samp">!</span></samp>', the value is the negation of
the two-argument test using the second and third arguments.
If the first argument is exactly `<samp><span class="samp">(</span></samp>' and the third argument is
exactly `<samp><span class="samp">)</span></samp>', the result is the one-argument test of the second
argument.
Otherwise, the expression is false.
The `<samp><span class="samp">-a</span></samp>' and `<samp><span class="samp">-o</span></samp>' operators are considered binary operators
in this case.
<br><dt>4 arguments<dd>If the first argument is `<samp><span class="samp">!</span></samp>', the result is the negation of
the three-argument expression composed of the remaining arguments.
Otherwise, the expression is parsed and evaluated according to
precedence using the rules listed above.
<br><dt>5 or more arguments<dd>The expression is parsed and evaluated according to precedence
using the rules listed above.
</dl>
<br><dt><code>times</code><dd><a name="index-times-123"></a>
<pre class="example"> times
</pre>
<p>Print out the user and system times used by the shell and its children.
The return status is zero.
<br><dt><code>trap</code><dd><a name="index-trap-124"></a>
<pre class="example"> trap [-lp] [<var>arg</var>] [<var>sigspec</var> ...]
</pre>
<p>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 `<samp><span class="samp">-</span></samp>', each specified signal'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><span class="option">-p</span></samp> has been supplied,
the shell displays the trap commands associated with each <var>sigspec</var>.
If no arguments are supplied, or
only <samp><span class="option">-p</span></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><span class="option">-l</span></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>extglob</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>ERR</code>, the command <var>arg</var>
is executed whenever a simple command has 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 in an <code>if</code> statement,
part of a <code>&&</code> or <code>||</code> list, or if the command's return
status is being inverted using <code>!</code>.
These are the same conditions obeyed by the <code>errexit</code> option.
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.
<p>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 child process when it is created.
<p>The return status is zero unless a <var>sigspec</var> does not specify a
valid signal.
<br><dt><code>umask</code><dd><a name="index-umask-125"></a>
<pre class="example"> umask [-p] [-S] [<var>mode</var>]
</pre>
<p>Set the shell process'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><span class="option">-S</span></samp>
option is supplied without a <var>mode</var> argument, the mask is printed
in a symbolic format.
If the <samp><span class="option">-p</span></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.
<p>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>.
<br><dt><code>unset</code><dd><a name="index-unset-126"></a>
<pre class="example"> unset [-fv] [<var>name</var>]
</pre>
<p>Each variable or function <var>name</var> is removed.
If no options are supplied, or the <samp><span class="option">-v</span></samp> option is given, each
<var>name</var> refers to a shell variable.
If the <samp><span class="option">-f</span></samp> option is given, the <var>name</var>s refer to shell
functions, and the function definition is removed.
Readonly variables and functions may not be unset.
The return status is zero unless a <var>name</var> is readonly.
</dl>
<div class="node">
<p><hr>
<a name="Bash-Builtins"></a>
Next: <a rel="next" accesskey="n" href="#Modifying-Shell-Behavior">Modifying Shell Behavior</a>,
Previous: <a rel="previous" accesskey="p" href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Builtin-Commands">Shell Builtin Commands</a>
</div>
<h3 class="section">4.2 Bash Builtin Commands</h3>
<p>This section describes builtin commands which are unique to
or have been extended in Bash.
Some of these commands are specified in the <span class="sc">posix</span> standard.
<dl>
<dt><code>alias</code><dd><a name="index-alias-127"></a>
<pre class="example"> alias [<code>-p</code>] [<var>name</var>[=<var>value</var>] ...]
</pre>
<p>Without arguments or with the <samp><span class="option">-p</span></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>.
<br><dt><code>bind</code><dd><a name="index-bind-128"></a>
<pre class="example"> bind [-m <var>keymap</var>] [-lpsvPSV]
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 <var>readline-command</var>
</pre>
<p>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.,
`<samp><span class="samp">"\C-x\C-r":re-read-init-file</span></samp>'.
Options, if supplied, have the following meanings:
<dl>
<dt><code>-m </code><var>keymap</var><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>emacs</code> is equivalent to <code>emacs-standard</code>.
<br><dt><code>-l</code><dd>List the names of all Readline functions.
<br><dt><code>-p</code><dd>Display Readline function names and bindings in such a way that they
can be used as input or in a Readline initialization file.
<br><dt><code>-P</code><dd>List current Readline function names and bindings.
<br><dt><code>-v</code><dd>Display Readline variable names and values in such a way that they
can be used as input or in a Readline initialization file.
<br><dt><code>-V</code><dd>List current Readline variable names and values.
<br><dt><code>-s</code><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.
<br><dt><code>-S</code><dd>Display Readline key sequences bound to macros and the strings they output.
<br><dt><code>-f </code><var>filename</var><dd>Read key bindings from <var>filename</var>.
<br><dt><code>-q </code><var>function</var><dd>Query about which keys invoke the named <var>function</var>.
<br><dt><code>-u </code><var>function</var><dd>Unbind all keys bound to the named <var>function</var>.
<br><dt><code>-r </code><var>keyseq</var><dd>Remove any current binding for <var>keyseq</var>.
<br><dt><code>-x </code><var>keyseq:shell-command</var><dd>Cause <var>shell-command</var> to be executed whenever <var>keyseq</var> is
entered.
</dl>
<p class="noindent">The return status is zero unless an invalid option is supplied or an
error occurs.
<br><dt><code>builtin</code><dd><a name="index-builtin-129"></a>
<pre class="example"> builtin [<var>shell-builtin</var> [<var>args</var>]]
</pre>
<p>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.
<br><dt><code>caller</code><dd><a name="index-caller-130"></a>
<pre class="example"> caller [<var>expr</var>]
</pre>
<p>Returns the context of any active subroutine call (a shell function or
a script executed with the <code>.</code> or <code>source</code> builtins).
<p>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.
<p>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.
<br><dt><code>command</code><dd><a name="index-command-131"></a>
<pre class="example"> command [-pVv] <var>command</var> [<var>arguments</var> ...]
</pre>
<p>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
<samp><span class="env">PATH</span></samp> are executed.
If there is a shell function named <code>ls</code>, running `<samp><span class="samp">command ls</span></samp>'
within the function will execute the external command <code>ls</code>
instead of calling the function recursively.
The <samp><span class="option">-p</span></samp> option means to use a default value for <samp><span class="env">PATH</span></samp>
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.
<p>If either the <samp><span class="option">-V</span></samp> or <samp><span class="option">-v</span></samp> option is supplied, a
description of <var>command</var> is printed. The <samp><span class="option">-v</span></samp> option
causes a single word indicating the command or file name used to
invoke <var>command</var> to be displayed; the <samp><span class="option">-V</span></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.
<br><dt><code>declare</code><dd><a name="index-declare-132"></a>
<pre class="example"> declare [-afFirtx] [-p] [<var>name</var>[=<var>value</var>] ...]
</pre>
<p>Declare variables and give them attributes. If no <var>name</var>s
are given, then display the values of variables instead.
<p>The <samp><span class="option">-p</span></samp> option will display the attributes and values of each
<var>name</var>.
When <samp><span class="option">-p</span></samp> is used, additional options are ignored.
The <samp><span class="option">-F</span></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
the function is defined are displayed as well.
<samp><span class="option">-F</span></samp> implies <samp><span class="option">-f</span></samp>.
The following options can be used to restrict output to variables with
the specified attributes or to give variables attributes:
<dl>
<dt><code>-a</code><dd>Each <var>name</var> is an array variable (see <a href="#Arrays">Arrays</a>).
<br><dt><code>-f</code><dd>Use function names only.
<br><dt><code>-i</code><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.
<br><dt><code>-r</code><dd>Make <var>name</var>s readonly. These names cannot then be assigned values
by subsequent assignment statements or unset.
<br><dt><code>-t</code><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.
<br><dt><code>-x</code><dd>Mark each <var>name</var> for export to subsequent commands via
the environment.
</dl>
<p>Using `<samp><span class="samp">+</span></samp>' instead of `<samp><span class="samp">-</span></samp>' turns off the attribute instead,
with the exceptions that `<samp><span class="samp">+a</span></samp>'
may not be used to destroy an array variable and `<samp><span class="samp">+r</span></samp>' 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. If a variable name is followed by
=<var>value</var>, the value of the variable is set to <var>value</var>.
<p>The return status is zero unless an invalid option is encountered,
an attempt is made to define a function using `<samp><span class="samp">-f foo=bar</span></samp>',
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>names</var> 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><span class="option">-f</span></samp>.
<br><dt><code>echo</code><dd><a name="index-echo-133"></a>
<pre class="example"> echo [-neE] [<var>arg</var> ...]
</pre>
<p>Output the <var>arg</var>s, separated by spaces, terminated with a
newline.
The return status is always 0.
If <samp><span class="option">-n</span></samp> is specified, the trailing newline is suppressed.
If the <samp><span class="option">-e</span></samp> option is given, interpretation of the following
backslash-escaped characters is enabled.
The <samp><span class="option">-E</span></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><span class="option">--</span></samp> to mean the end of options.
<p><code>echo</code> interprets the following escape sequences:
<dl>
<dt><code>\a</code><dd>alert (bell)
<br><dt><code>\b</code><dd>backspace
<br><dt><code>\c</code><dd>suppress trailing newline
<br><dt><code>\e</code><dd>escape
<br><dt><code>\f</code><dd>form feed
<br><dt><code>\n</code><dd>new line
<br><dt><code>\r</code><dd>carriage return
<br><dt><code>\t</code><dd>horizontal tab
<br><dt><code>\v</code><dd>vertical tab
<br><dt><code>\\</code><dd>backslash
<br><dt><code>\0</code><var>nnn</var><dd>the eight-bit character whose value is the octal value <var>nnn</var>
(zero to three octal digits)
<br><dt><code>\x</code><var>HH</var><dd>the eight-bit character whose value is the hexadecimal value <var>HH</var>
(one or two hex digits)
</dl>
<br><dt><code>enable</code><dd><a name="index-enable-134"></a>
<pre class="example"> enable [-a] [-dnps] [-f <var>filename</var>] [<var>name</var> ...]
</pre>
<p>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><span class="option">-n</span></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 <samp><span class="env">$PATH</span></samp> instead of the shell builtin version, type
`<samp><span class="samp">enable -n test</span></samp>'.
<p>If the <samp><span class="option">-p</span></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><span class="option">-a</span></samp> option means to list
each builtin with an indication of whether or not it is enabled.
<p>The <samp><span class="option">-f</span></samp> option means to load the new builtin command <var>name</var>
from shared object <var>filename</var>, on systems that support dynamic loading.
The <samp><span class="option">-d</span></samp> option will delete a builtin loaded with <samp><span class="option">-f</span></samp>.
<p>If there are no options, a list of the shell builtins is displayed.
The <samp><span class="option">-s</span></samp> option restricts <code>enable</code> to the <span class="sc">posix</span> special
builtins. If <samp><span class="option">-s</span></samp> is used with <samp><span class="option">-f</span></samp>, the new builtin becomes
a special builtin (see <a href="#Special-Builtins">Special Builtins</a>).
<p>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.
<br><dt><code>help</code><dd><a name="index-help-135"></a>
<pre class="example"> help [-s] [<var>pattern</var>]
</pre>
<p>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.
The <samp><span class="option">-s</span></samp> option restricts the information displayed to a short
usage synopsis.
The return status is zero unless no command matches <var>pattern</var>.
<br><dt><code>let</code><dd><a name="index-let-136"></a>
<pre class="example"> let <var>expression</var> [<var>expression</var>]
</pre>
<p>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.
<br><dt><code>local</code><dd><a name="index-local-137"></a>
<pre class="example"> local [<var>option</var>] <var>name</var>[=<var>value</var>] ...
</pre>
<p>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. 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.
<br><dt><code>logout</code><dd><a name="index-logout-138"></a>
<pre class="example"> logout [<var>n</var>]
</pre>
<p>Exit a login shell, returning a status of <var>n</var> to the shell's
parent.
<br><dt><code>printf</code><dd><a name="index-printf-139"></a>
<pre class="example"> <code>printf</code> [-v <var>var</var>] <var>format</var> [<var>arguments</var>]
</pre>
<p>Write the formatted <var>arguments</var> to the standard output under the
control of the <var>format</var>.
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, `<samp><span class="samp">%b</span></samp>' causes
<code>printf</code> to expand backslash escape sequences in the corresponding
<var>argument</var>,
(except that `<samp><span class="samp">\c</span></samp>' terminates output, backslashes in
`<samp><span class="samp">\'</span></samp>', `<samp><span class="samp">\"</span></samp>', and `<samp><span class="samp">\?</span></samp>' are not removed, and octal escapes
beginning with `<samp><span class="samp">\0</span></samp>' may contain up to four digits),
and `<samp><span class="samp">%q</span></samp>' causes <code>printf</code> to output the
corresponding <var>argument</var> in a format that can be reused as shell input.
<p>The <samp><span class="option">-v</span></samp> option causes the output to be assigned to the variable
<var>var</var> rather than being printed to the standard output.
<p>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.
<br><dt><code>read</code><dd><a name="index-read-140"></a>
<pre class="example"> read [-ers] [-a <var>aname</var>] [-d <var>delim</var>] [-n <var>nchars</var>] [-p <var>prompt</var>] [-t <var>timeout</var>] [-u <var>fd</var>] [<var>name</var> ...]
</pre>
<p>One line is read from the standard input, or from the file descriptor
<var>fd</var> supplied as an argument to the <samp><span class="option">-u</span></samp> option, and the first word
is assigned to the first <var>name</var>, the second word to the second <var>name</var>,
and so on, with leftover words and their intervening separators 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 <samp><span class="env">IFS</span></samp> variable
are used to split the line into words.
The backslash character `<samp><span class="samp">\</span></samp>' may be used to remove any special
meaning for the next character read and for line continuation.
If no names are supplied, the line read is assigned to the
variable <samp><span class="env">REPLY</span></samp>.
The return code is zero, unless end-of-file is encountered, <code>read</code>
times out, or an invalid file descriptor is supplied as the argument to
<samp><span class="option">-u</span></samp>.
Options, if supplied, have the following meanings:
<dl>
<dt><code>-a </code><var>aname</var><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.
<br><dt><code>-d </code><var>delim</var><dd>The first character of <var>delim</var> is used to terminate the input line,
rather than newline.
<br><dt><code>-e</code><dd>Readline (see <a href="#Command-Line-Editing">Command Line Editing</a>) is used to obtain the line.
<br><dt><code>-n </code><var>nchars</var><dd><code>read</code> returns after reading <var>nchars</var> characters rather than
waiting for a complete line of input.
<br><dt><code>-p </code><var>prompt</var><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.
<br><dt><code>-r</code><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 be used as a line
continuation.
<br><dt><code>-s</code><dd>Silent mode. If input is coming from a terminal, characters are
not echoed.
<br><dt><code>-t </code><var>timeout</var><dd>Cause <code>read</code> to time out and return failure if a complete line of
input is not read within <var>timeout</var> seconds.
This option has no effect if <code>read</code> is not reading input from the
terminal or a pipe.
<br><dt><code>-u </code><var>fd</var><dd>Read input from file descriptor <var>fd</var>.
</dl>
<br><dt><code>source</code><dd><a name="index-source-141"></a>
<pre class="example"> source <var>filename</var>
</pre>
<p>A synonym for <code>.</code> (see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>).
<br><dt><code>type</code><dd><a name="index-type-142"></a>
<pre class="example"> type [-afptP] [<var>name</var> ...]
</pre>
<p>For each <var>name</var>, indicate how it would be interpreted if used as a
command name.
<p>If the <samp><span class="option">-t</span></samp> option is used, <code>type</code> prints a single word
which is one of `<samp><span class="samp">alias</span></samp>', `<samp><span class="samp">function</span></samp>', `<samp><span class="samp">builtin</span></samp>',
`<samp><span class="samp">file</span></samp>' or `<samp><span class="samp">keyword</span></samp>',
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.
<p>If the <samp><span class="option">-p</span></samp> option is used, <code>type</code> either returns the name
of the disk file that would be executed, or nothing if <samp><span class="option">-t</span></samp>
would not return `<samp><span class="samp">file</span></samp>'.
<p>The <samp><span class="option">-P</span></samp> option forces a path search for each <var>name</var>, even if
<samp><span class="option">-t</span></samp> would not return `<samp><span class="samp">file</span></samp>'.
<p>If a command is hashed, <samp><span class="option">-p</span></samp> and <samp><span class="option">-P</span></samp> print the hashed value,
not necessarily the file that appears first in <code>$PATH</code>.
<p>If the <samp><span class="option">-a</span></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><span class="option">-p</span></samp> option
is not also used.
<p>If the <samp><span class="option">-f</span></samp> option is used, <code>type</code> does not attempt to find
shell functions, as with the <code>command</code> builtin.
<p>The return status is zero if any of the <var>names</var> are found, non-zero
if none are found.
<br><dt><code>typeset</code><dd><a name="index-typeset-143"></a>
<pre class="example"> typeset [-afFrxi] [-p] [<var>name</var>[=<var>value</var>] ...]
</pre>
<p>The <code>typeset</code> command is supplied for compatibility with the Korn
shell; however, it has been deprecated in favor of the <code>declare</code>
builtin command.
<br><dt><code>ulimit</code><dd><a name="index-ulimit-144"></a>
<pre class="example"> ulimit [-acdefilmnpqrstuvxSH] [<var>limit</var>]
</pre>
<p><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>
<dt><code>-S</code><dd>Change and report the soft limit associated with a resource.
<br><dt><code>-H</code><dd>Change and report the hard limit associated with a resource.
<br><dt><code>-a</code><dd>All current limits are reported.
<br><dt><code>-c</code><dd>The maximum size of core files created.
<br><dt><code>-d</code><dd>The maximum size of a process's data segment.
<br><dt><code>-e</code><dd>The maximum scheduling priority ("nice").
<br><dt><code>-f</code><dd>The maximum size of files written by the shell and its children.
<br><dt><code>-i</code><dd>The maximum number of pending signals.
<br><dt><code>-l</code><dd>The maximum size that may be locked into memory.
<br><dt><code>-m</code><dd>The maximum resident set size.
<br><dt><code>-n</code><dd>The maximum number of open file descriptors.
<br><dt><code>-p</code><dd>The pipe buffer size.
<br><dt><code>-q</code><dd>The maximum number of bytes in POSIX message queues.
<br><dt><code>-r</code><dd>The maximum real-time scheduling priority.
<br><dt><code>-s</code><dd>The maximum stack size.
<br><dt><code>-t</code><dd>The maximum amount of cpu time in seconds.
<br><dt><code>-u</code><dd>The maximum number of processes available to a single user.
<br><dt><code>-v</code><dd>The maximum amount of virtual memory available to the process.
<br><dt><code>-x</code><dd>The maximum number of file locks.
</dl>
<p>If <var>limit</var> is given, it 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.
Otherwise, the current value of the soft limit for the specified resource
is printed, unless the <samp><span class="option">-H</span></samp> option is supplied.
When setting new limits, if neither <samp><span class="option">-H</span></samp> nor <samp><span class="option">-S</span></samp> is supplied,
both the hard and soft limits are set.
If no option is given, then <samp><span class="option">-f</span></samp> is assumed. Values are in 1024-byte
increments, except for <samp><span class="option">-t</span></samp>, which is in seconds, <samp><span class="option">-p</span></samp>,
which is in units of 512-byte blocks, and <samp><span class="option">-n</span></samp> and <samp><span class="option">-u</span></samp>, which
are unscaled values.
<p>The return status is zero unless an invalid option or argument is supplied,
or an error occurs while setting a new limit.
<br><dt><code>unalias</code><dd><a name="index-unalias-145"></a>
<pre class="example"> unalias [-a] [<var>name</var> ... ]
</pre>
<p>Remove each <var>name</var> from the list of aliases. If <samp><span class="option">-a</span></samp> is
supplied, all aliases are removed.
Aliases are described in <a href="#Aliases">Aliases</a>.
</dl>
<div class="node">
<p><hr>
<a name="Modifying-Shell-Behavior"></a>
Next: <a rel="next" accesskey="n" href="#Special-Builtins">Special Builtins</a>,
Previous: <a rel="previous" accesskey="p" href="#Bash-Builtins">Bash Builtins</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Builtin-Commands">Shell Builtin Commands</a>
</div>
<h3 class="section">4.3 Modifying Shell Behavior</h3>
<ul class="menu">
<li><a accesskey="1" href="#The-Set-Builtin">The Set Builtin</a>: Change the values of shell attributes and
positional parameters.
<li><a accesskey="2" href="#The-Shopt-Builtin">The Shopt Builtin</a>: Modify shell optional behavior.
</ul>
<div class="node">
<p><hr>
<a name="The-Set-Builtin"></a>
Next: <a rel="next" accesskey="n" href="#The-Shopt-Builtin">The Shopt Builtin</a>,
Up: <a rel="up" accesskey="u" href="#Modifying-Shell-Behavior">Modifying Shell Behavior</a>
</div>
<h4 class="subsection">4.3.1 The Set Builtin</h4>
<p>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>
<dt><code>set</code><dd><a name="index-set-146"></a>
<pre class="example"> set [--abefhkmnptuvxBCEHPT] [-o <var>option</var>] [<var>argument</var> ...]
set [+abefhkmnptuvxBCEHPT] [+o <var>option</var>] [<var>argument</var> ...]
</pre>
<p>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 <span class="sc">posix</span> mode, only shell variables are listed.
<p>When options are supplied, they set or unset shell attributes.
Options, if specified, have the following meanings:
<dl>
<dt><code>-a</code><dd>Mark variables and function which are modified or created for export
to the environment of subsequent commands.
<br><dt><code>-b</code><dd>Cause the status of terminated background jobs to be reported
immediately, rather than before printing the next primary prompt.
<br><dt><code>-e</code><dd>Exit immediately if a simple command (see <a href="#Simple-Commands">Simple Commands</a>) exits
with a non-zero status, unless 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 a <code>&&</code> or <code>||</code> list,
any command in a pipeline but the last,
or if the command's return status is being inverted using <code>!</code>.
A trap on <code>ERR</code>, if set, is executed before the shell exits.
<br><dt><code>-f</code><dd>Disable file name generation (globbing).
<br><dt><code>-h</code><dd>Locate and remember (hash) commands as they are looked up for execution.
This option is enabled by default.
<br><dt><code>-k</code><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.
<br><dt><code>-m</code><dd>Job control is enabled (see <a href="#Job-Control">Job Control</a>).
<br><dt><code>-n</code><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.
<br><dt><code>-o </code><var>option-name</var><dd>
Set the option corresponding to <var>option-name</var>:
<dl>
<dt><code>allexport</code><dd>Same as <code>-a</code>.
<br><dt><code>braceexpand</code><dd>Same as <code>-B</code>.
<br><dt><code>emacs</code><dd>Use an <code>emacs</code>-style line editing interface (see <a href="#Command-Line-Editing">Command Line Editing</a>).
<br><dt><code>errexit</code><dd>Same as <code>-e</code>.
<br><dt><code>errtrace</code><dd>Same as <code>-E</code>.
<br><dt><code>functrace</code><dd>Same as <code>-T</code>.
<br><dt><code>hashall</code><dd>Same as <code>-h</code>.
<br><dt><code>histexpand</code><dd>Same as <code>-H</code>.
<br><dt><code>history</code><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.
<br><dt><code>ignoreeof</code><dd>An interactive shell will not exit upon reading EOF.
<br><dt><code>keyword</code><dd>Same as <code>-k</code>.
<br><dt><code>monitor</code><dd>Same as <code>-m</code>.
<br><dt><code>noclobber</code><dd>Same as <code>-C</code>.
<br><dt><code>noexec</code><dd>Same as <code>-n</code>.
<br><dt><code>noglob</code><dd>Same as <code>-f</code>.
<br><dt><code>nolog</code><dd>Currently ignored.
<br><dt><code>notify</code><dd>Same as <code>-b</code>.
<br><dt><code>nounset</code><dd>Same as <code>-u</code>.
<br><dt><code>onecmd</code><dd>Same as <code>-t</code>.
<br><dt><code>physical</code><dd>Same as <code>-P</code>.
<br><dt><code>pipefail</code><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.
<br><dt><code>posix</code><dd>Change the behavior of Bash where the default operation differs
from the <span class="sc">posix</span> 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.
<br><dt><code>privileged</code><dd>Same as <code>-p</code>.
<br><dt><code>verbose</code><dd>Same as <code>-v</code>.
<br><dt><code>vi</code><dd>Use a <code>vi</code>-style line editing interface.
<br><dt><code>xtrace</code><dd>Same as <code>-x</code>.
</dl>
<br><dt><code>-p</code><dd>Turn on privileged mode.
In this mode, the <samp><span class="env">$BASH_ENV</span></samp> and <samp><span class="env">$ENV</span></samp> files are not
processed, shell functions are not inherited from the environment,
and the <samp><span class="env">SHELLOPTS</span></samp> variable, if it appears in the environment,
is ignored.
If the shell is started with the effective user (group) id not equal to the
real user (group) id, and the <code>-p</code> option is not supplied, these actions
are taken and the effective user id is set to the real user id.
If the <code>-p</code> 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.
<br><dt><code>-t</code><dd>Exit after reading and executing one command.
<br><dt><code>-u</code><dd>Treat unset variables as an error when performing parameter expansion.
An error message will be written to the standard error, and a non-interactive
shell will exit.
<br><dt><code>-v</code><dd>Print shell input lines as they are read.
<br><dt><code>-x</code><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 <samp><span class="env">PS4</span></samp>
variable is expanded and the resultant value is printed before
the command and its expanded arguments.
<br><dt><code>-B</code><dd>The shell will perform brace expansion (see <a href="#Brace-Expansion">Brace Expansion</a>).
This option is on by default.
<br><dt><code>-C</code><dd>Prevent output redirection using `<samp><span class="samp">></span></samp>', `<samp><span class="samp">>&</span></samp>', and `<samp><span class="samp"><></span></samp>'
from overwriting existing files.
<br><dt><code>-E</code><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.
<br><dt><code>-H</code><dd>Enable `<samp><span class="samp">!</span></samp>' style history substitution (see <a href="#History-Interaction">History Interaction</a>).
This option is on by default for interactive shells.
<br><dt><code>-P</code><dd>If set, do not follow 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.
<p>For example, if <samp><span class="file">/usr/sys</span></samp> is a symbolic link to <samp><span class="file">/usr/local/sys</span></samp>
then:
<pre class="example"> $ cd /usr/sys; echo $PWD
/usr/sys
$ cd ..; pwd
/usr
</pre>
<p class="noindent">If <code>set -P</code> is on, then:
<pre class="example"> $ cd /usr/sys; echo $PWD
/usr/local/sys
$ cd ..; pwd
/usr/local
</pre>
<br><dt><code>-T</code><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.
<br><dt><code>--</code><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 `<samp><span class="samp">-</span></samp>'.
<br><dt><code>-</code><dd>Signal the end of options, cause all remaining <var>arguments</var>
to be assigned to the positional parameters. The <samp><span class="option">-x</span></samp>
and <samp><span class="option">-v</span></samp> options are turned off.
If there are no arguments, the positional parameters remain unchanged.
</dl>
<p>Using `<samp><span class="samp">+</span></samp>' rather than `<samp><span class="samp">-</span></samp>' 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>.
<p>The remaining N <var>arguments</var> are positional parameters and are
assigned, in order, to <code>$1</code>, <code>$2</code>, <small class="dots">...</small> <code>$N</code>.
The special parameter <code>#</code> is set to N.
<p>The return status is always zero unless an invalid option is supplied.
</dl>
<div class="node">
<p><hr>
<a name="The-Shopt-Builtin"></a>
Previous: <a rel="previous" accesskey="p" href="#The-Set-Builtin">The Set Builtin</a>,
Up: <a rel="up" accesskey="u" href="#Modifying-Shell-Behavior">Modifying Shell Behavior</a>
</div>
<h4 class="subsection">4.3.2 The Shopt Builtin</h4>
<p>This builtin allows you to change additional shell optional behavior.
<dl>
<dt><code>shopt</code><dd><a name="index-shopt-147"></a>
<pre class="example"> shopt [-pqsu] [-o] [<var>optname</var> ...]
</pre>
<p>Toggle the values of variables controlling optional shell behavior.
With no options, or with the <samp><span class="option">-p</span></samp> option, a list of all settable
options is displayed, with an indication of whether or not each is set.
The <samp><span class="option">-p</span></samp> option causes output to be displayed in a form that
may be reused as input.
Other options have the following meanings:
<dl>
<dt><code>-s</code><dd>Enable (set) each <var>optname</var>.
<br><dt><code>-u</code><dd>Disable (unset) each <var>optname</var>.
<br><dt><code>-q</code><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><span class="option">-q</span></samp>,
the return status is zero if all <var>optnames</var> are enabled;
non-zero otherwise.
<br><dt><code>-o</code><dd>Restricts the values of
<var>optname</var> to be those defined for the <samp><span class="option">-o</span></samp> option to the
<code>set</code> builtin (see <a href="#The-Set-Builtin">The Set Builtin</a>).
</dl>
<p>If either <samp><span class="option">-s</span></samp> or <samp><span class="option">-u</span></samp>
is used with no <var>optname</var> arguments, the display is limited to
those options which are set or unset, respectively.
<p>Unless otherwise noted, the <code>shopt</code> options are disabled (off)
by default.
<p>The return status when listing options is zero if all <var>optnames</var>
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.
<p>The list of <code>shopt</code> options is:
<dl>
<dt><code>autocd</code><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.
<br><dt><code>cdable_vars</code><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.
<br><dt><code>cdspell</code><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.
<br><dt><code>checkhash</code><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.
<br><dt><code>checkjobs</code><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.
<br><dt><code>checkwinsize</code><dd>If set, Bash checks the window size after each command
and, if necessary, updates the values of
<samp><span class="env">LINES</span></samp> and <samp><span class="env">COLUMNS</span></samp>.
<br><dt><code>cmdhist</code><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.
<br><dt><code>dotglob</code><dd>If set, Bash includes filenames beginning with a `.' in
the results of filename expansion.
<br><dt><code>execfail</code><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.
<br><dt><code>expand_aliases</code><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.
<br><dt><code>extdebug</code><dd>If set, behavior intended for use by debuggers is enabled:
<ol type=1 start=1>
<li>The <samp><span class="option">-F</span></samp> option to the <code>declare</code> builtin (see <a href="#Bash-Builtins">Bash Builtins</a>)
displays the source file name and line number corresponding to each function
name supplied as an argument.
<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>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), a call to
<code>return</code> is simulated.
<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>Function tracing is enabled: command substitution, shell functions, and
subshells invoked with <code>( </code><var>command</var><code> )</code> inherit the
<code>DEBUG</code> and <code>RETURN</code> traps.
<li>Error tracing is enabled: command substitution, shell functions, and
subshells invoked with <code>( </code><var>command</var><code> )</code> inherit the
<code>ERROR</code> trap.
</ol>
<br><dt><code>extglob</code><dd>If set, the extended pattern matching features described above
(see <a href="#Pattern-Matching">Pattern Matching</a>) are enabled.
<br><dt><code>extquote</code><dd>If set, <code>$'</code><var>string</var><code>'</code> and <code>$"</code><var>string</var><code>"</code> quoting is
performed within <code>${</code><var>parameter</var><code>}</code> expansions
enclosed in double quotes. This option is enabled by default.
<br><dt><code>failglob</code><dd>If set, patterns which fail to match filenames during pathname expansion
result in an expansion error.
<br><dt><code>force_fignore</code><dd>If set, the suffixes specified by the <samp><span class="env">FIGNORE</span></samp> 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 <samp><span class="env">FIGNORE</span></samp>.
This option is enabled by default.
<br><dt><code>gnu_errfmt</code><dd>If set, shell error messages are written in the standard <span class="sc">gnu</span> error
message format.
<br><dt><code>histappend</code><dd>If set, the history list is appended to the file named by the value
of the <samp><span class="env">HISTFILE</span></samp>
variable when the shell exits, rather than overwriting the file.
<br><dt><code>histreedit</code><dd>If set, and Readline
is being used, a user is given the opportunity to re-edit a
failed history substitution.
<br><dt><code>histverify</code><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.
<br><dt><code>hostcomplete</code><dd>If set, and Readline is being used, Bash will attempt to perform
hostname completion when a word containing a `<samp><span class="samp">@</span></samp>' is being
completed (see <a href="#Commands-For-Completion">Commands For Completion</a>). This option is enabled
by default.
<br><dt><code>huponexit</code><dd>If set, Bash will send <code>SIGHUP</code> to all jobs when an interactive
login shell exits (see <a href="#Signals">Signals</a>).
<br><dt><code>interactive_comments</code><dd>Allow a word beginning with `<samp><span class="samp">#</span></samp>'
to cause that word and all remaining characters on that
line to be ignored in an interactive shell.
This option is enabled by default.
<br><dt><code>lithist</code><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.
<br><dt><code>login_shell</code><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.
<br><dt><code>mailwarn</code><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>"The mail in </code><var>mailfile</var><code> has been read"</code> is displayed.
<br><dt><code>no_empty_cmd_completion</code><dd>If set, and Readline is being used, Bash will not attempt to search
the <samp><span class="env">PATH</span></samp> for possible completions when completion is attempted
on an empty line.
<br><dt><code>nocaseglob</code><dd>If set, Bash matches filenames in a case-insensitive fashion when
performing filename expansion.
<br><dt><code>nocasematch</code><dd>If set, Bash matches patterns in a case-insensitive fashion when
performing matching while executing <code>case</code> or <code>[[</code>
conditional commands.
<br><dt><code>nullglob</code><dd>If set, Bash allows filename patterns which match no
files to expand to a null string, rather than themselves.
<br><dt><code>progcomp</code><dd>If set, the programmable completion facilities
(see <a href="#Programmable-Completion">Programmable Completion</a>) are enabled.
This option is enabled by default.
<br><dt><code>promptvars</code><dd>If set, prompt strings undergo
parameter expansion, command substitution, arithmetic
expansion, and quote removal after being expanded
as described below (see <a href="#Printing-a-Prompt">Printing a Prompt</a>).
This option is enabled by default.
<br><dt><code>restricted_shell</code><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.
<br><dt><code>shift_verbose</code><dd>If this is set, the <code>shift</code>
builtin prints an error message when the shift count exceeds the
number of positional parameters.
<br><dt><code>sourcepath</code><dd>If set, the <code>source</code> builtin uses the value of <samp><span class="env">PATH</span></samp>
to find the directory containing the file supplied as an argument.
This option is enabled by default.
<br><dt><code>xpg_echo</code><dd>If set, the <code>echo</code> builtin expands backslash-escape sequences
by default.
</dl>
<p class="noindent">The return status when listing options is zero if all <var>optnames</var>
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.
</dl>
<div class="node">
<p><hr>
<a name="Special-Builtins"></a>
Previous: <a rel="previous" accesskey="p" href="#Modifying-Shell-Behavior">Modifying Shell Behavior</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Builtin-Commands">Shell Builtin Commands</a>
</div>
<h3 class="section">4.4 Special Builtins</h3>
<p><a name="index-special-builtin-148"></a>
For historical reasons, the <span class="sc">posix</span> standard has classified
several builtin commands as <em>special</em>.
When Bash is executing in <span class="sc">posix</span> mode, the special builtins
differ from other builtin commands in three respects:
<ol type=1 start=1>
<li>Special builtins are found before shell functions during command lookup.
<li>If a special builtin returns an error status, a non-interactive shell exits.
<li>Assignment statements preceding the command stay in effect in the shell
environment after the command completes.
</ol>
<p>When Bash is not executing in <span class="sc">posix</span> mode, these builtins behave no
differently than the rest of the Bash builtin commands.
The Bash <span class="sc">posix</span> mode is described in <a href="#Bash-POSIX-Mode">Bash POSIX Mode</a>.
<p>These are the <span class="sc">posix</span> special builtins:
<pre class="example"> break : . continue eval exec exit export readonly return set<!-- /@w -->
shift trap unset<!-- /@w -->
</pre>
<div class="node">
<p><hr>
<a name="Shell-Variables"></a>
Next: <a rel="next" accesskey="n" href="#Bash-Features">Bash Features</a>,
Previous: <a rel="previous" accesskey="p" href="#Shell-Builtin-Commands">Shell Builtin Commands</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="chapter">5 Shell Variables</h2>
<ul class="menu">
<li><a accesskey="1" href="#Bourne-Shell-Variables">Bourne Shell Variables</a>: Variables which Bash uses in the same way
as the Bourne Shell.
<li><a accesskey="2" href="#Bash-Variables">Bash Variables</a>: List of variables that exist in Bash.
</ul>
<p>This chapter describes the shell variables that Bash uses.
Bash automatically assigns default values to a number of variables.
<div class="node">
<p><hr>
<a name="Bourne-Shell-Variables"></a>
Next: <a rel="next" accesskey="n" href="#Bash-Variables">Bash Variables</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Variables">Shell Variables</a>
</div>
<h3 class="section">5.1 Bourne Shell Variables</h3>
<p>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>
<dt><code>CDPATH</code><a name="index-CDPATH-149"></a><dd>A colon-separated list of directories used as a search path for
the <code>cd</code> builtin command.
<br><dt><code>HOME</code><a name="index-HOME-150"></a><dd>The current user'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>).
<br><dt><code>IFS</code><a name="index-IFS-151"></a><dd>A list of characters that separate fields; used when the shell splits
words as part of expansion.
<br><dt><code>MAIL</code><a name="index-MAIL-152"></a><dd>If this parameter is set to a filename and the <samp><span class="env">MAILPATH</span></samp> variable
is not set, Bash informs the user of the arrival of mail in
the specified file.
<br><dt><code>MAILPATH</code><a name="index-MAILPATH-153"></a><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 file name from the message with
a `<samp><span class="samp">?</span></samp>'.
When used in the text of the message, <code>$_</code> expands to the name of
the current mail file.
<br><dt><code>OPTARG</code><a name="index-OPTARG-154"></a><dd>The value of the last option argument processed by the <code>getopts</code> builtin.
<br><dt><code>OPTIND</code><a name="index-OPTIND-155"></a><dd>The index of the last option argument processed by the <code>getopts</code> builtin.
<br><dt><code>PATH</code><a name="index-PATH-156"></a><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.
<br><dt><code>PS1</code><a name="index-PS1-157"></a><dd>The primary prompt string. The default value is `<samp><span class="samp">\s-\v\$ </span></samp>'.
See <a href="#Printing-a-Prompt">Printing a Prompt</a>, for the complete list of escape
sequences that are expanded before <samp><span class="env">PS1</span></samp> is displayed.
<br><dt><code>PS2</code><a name="index-PS2-158"></a><dd>The secondary prompt string. The default value is `<samp><span class="samp">> </span></samp>'.
</dl>
<div class="node">
<p><hr>
<a name="Bash-Variables"></a>
Previous: <a rel="previous" accesskey="p" href="#Bourne-Shell-Variables">Bourne Shell Variables</a>,
Up: <a rel="up" accesskey="u" href="#Shell-Variables">Shell Variables</a>
</div>
<h3 class="section">5.2 Bash Variables</h3>
<p>These variables are set or used by Bash, but other shells
do not normally treat them specially.
<p>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>
<dt><code>BASH</code><a name="index-BASH-159"></a><dd>The full pathname used to execute the current instance of Bash.
<br><dt><code>BASHPID</code><a name="index-BASHPID-160"></a><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.
<br><dt><code>BASH_ARGC</code><a name="index-BASH_005fARGC-161"></a><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).
<br><dt><code>BASH_ARGV</code><a name="index-BASH_005fARGV-162"></a><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).
<br><dt><code>BASH_COMMAND</code><a name="index-BASH_005fCOMMAND-163"></a><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.
<br><dt><code>BASH_ENV</code><a name="index-BASH_005fENV-164"></a><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>.
<br><dt><code>BASH_EXECUTION_STRING</code><a name="index-BASH_005fEXECUTION_005fSTRING-165"></a><dd>The command argument to the <samp><span class="option">-c</span></samp> invocation option.
<br><dt><code>BASH_LINENO</code><a name="index-BASH_005fLINENO-166"></a><dd>An array variable whose members are the line numbers in source files
corresponding to each member of <var>FUNCNAME</var>.
<code>${BASH_LINENO[$i]}</code> is the line number in the source file where
<code>${FUNCNAME[$i]}</code> was called.
The corresponding source file name is <code>${BASH_SOURCE[$i]}</code>.
Use <code>LINENO</code> to obtain the current line number.
<br><dt><code>BASH_REMATCH</code><a name="index-BASH_005fREMATCH-167"></a><dd>An array variable whose members are assigned by the `<samp><span class="samp">=~</span></samp>' 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.
This variable is read-only.
<br><dt><code>BASH_SOURCE</code><a name="index-BASH_005fSOURCE-168"></a><dd>An array variable whose members are the source filenames corresponding
to the elements in the <code>FUNCNAME</code> array variable.
<br><dt><code>BASH_SUBSHELL</code><a name="index-BASH_005fSUBSHELL-169"></a><dd>Incremented by one each time a subshell or subshell environment is spawned.
The initial value is 0.
<br><dt><code>BASH_VERSINFO</code><a name="index-BASH_005fVERSINFO-170"></a><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>
<dt><code>BASH_VERSINFO[0]</code><dd>The major version number (the <var>release</var>).
<br><dt><code>BASH_VERSINFO[1]</code><dd>The minor version number (the <var>version</var>).
<br><dt><code>BASH_VERSINFO[2]</code><dd>The patch level.
<br><dt><code>BASH_VERSINFO[3]</code><dd>The build version.
<br><dt><code>BASH_VERSINFO[4]</code><dd>The release status (e.g., <var>beta1</var>).
<br><dt><code>BASH_VERSINFO[5]</code><dd>The value of <samp><span class="env">MACHTYPE</span></samp>.
</dl>
<br><dt><code>BASH_VERSION</code><a name="index-BASH_005fVERSION-171"></a><dd>The version number of the current instance of Bash.
<br><dt><code>COLUMNS</code><a name="index-COLUMNS-172"></a><dd>Used by the <code>select</code> builtin command to determine the terminal width
when printing selection lists. Automatically set upon receipt of a
<code>SIGWINCH</code>.
<br><dt><code>COMP_CWORD</code><a name="index-COMP_005fCWORD-173"></a><dd>An index into <samp><span class="env">${COMP_WORDS}</span></samp> of the word containing the current
cursor position.
This variable is available only in shell functions invoked by the
programmable completion facilities (see <a href="#Programmable-Completion">Programmable Completion</a>).
<br><dt><code>COMP_LINE</code><a name="index-COMP_005fLINE-174"></a><dd>The current command line.
This variable is available only in shell functions and external
commands invoked by the
programmable completion facilities (see <a href="#Programmable-Completion">Programmable Completion</a>).
<br><dt><code>COMP_POINT</code><a name="index-COMP_005fPOINT-175"></a><dd>The index of the current cursor position relative to the beginning of
the current command.
If the current cursor position is at the end of the current command,
the value of this variable is equal to <code>${#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>).
<br><dt><code>COMP_TYPE</code><a name="index-COMP_005fTYPE-176"></a><dd>Set to an integer value corresponding to the type of completion attempted
that caused a completion function to be called:
<var>TAB</var>, for normal completion,
`<samp><span class="samp">?</span></samp>', for listing completions after successive tabs,
`<samp><span class="samp">!</span></samp>', for listing alternatives on partial word completion,
`<samp><span class="samp">@</span></samp>', to list completions if the word is not unmodified,
or
`<samp><span class="samp">%</span></samp>', 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>).
<br><dt><code>COMP_KEY</code><a name="index-COMP_005fKEY-177"></a><dd>The key (or final key of a key sequence) used to invoke the current
completion function.
<br><dt><code>COMP_WORDBREAKS</code><a name="index-COMP_005fWORDBREAKS-178"></a><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.
<br><dt><code>COMP_WORDS</code><a name="index-COMP_005fWORDS-179"></a><dd>An array variable consisting of the individual
words in the current command line.
The words are split on shell metacharacters as the shell parser would
separate them.
This variable is available only in shell functions invoked by the
programmable completion facilities (see <a href="#Programmable-Completion">Programmable Completion</a>).
<br><dt><code>COMPREPLY</code><a name="index-COMPREPLY-180"></a><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>).
<br><dt><code>DIRSTACK</code><a name="index-DIRSTACK-181"></a><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 <samp><span class="env">DIRSTACK</span></samp> is unset, it loses its special properties, even if
it is subsequently reset.
<br><dt><code>EMACS</code><a name="index-EMACS-182"></a><dd>If Bash finds this variable in the environment when the shell
starts with value `<samp><span class="samp">t</span></samp>', it assumes that the shell is running in an
emacs shell buffer and disables line editing.
<br><dt><code>EUID</code><a name="index-EUID-183"></a><dd>The numeric effective user id of the current user. This variable
is readonly.
<br><dt><code>FCEDIT</code><a name="index-FCEDIT-184"></a><dd>The editor used as a default by the <samp><span class="option">-e</span></samp> option to the <code>fc</code>
builtin command.
<br><dt><code>FIGNORE</code><a name="index-FIGNORE-185"></a><dd>A colon-separated list of suffixes to ignore when performing
filename completion.
A file name whose suffix matches one of the entries in
<samp><span class="env">FIGNORE</span></samp>
is excluded from the list of matched file names. A sample
value is `<samp><span class="samp">.o:~</span></samp>'
<br><dt><code>FUNCNAME</code><a name="index-FUNCNAME-186"></a><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 is <code>"main"</code>.
This variable exists only when a shell function is executing.
Assignments to <samp><span class="env">FUNCNAME</span></samp> have no effect and return an error status.
If <samp><span class="env">FUNCNAME</span></samp> is unset, it loses its special properties, even if
it is subsequently reset.
<br><dt><code>GLOBIGNORE</code><a name="index-GLOBIGNORE-187"></a><dd>A colon-separated list of patterns defining the set of filenames to
be ignored by filename expansion.
If a filename matched by a filename expansion pattern also matches one
of the patterns in <samp><span class="env">GLOBIGNORE</span></samp>, it is removed from the list
of matches.
<br><dt><code>GROUPS</code><a name="index-GROUPS-188"></a><dd>An array variable containing the list of groups of which the current
user is a member.
Assignments to <samp><span class="env">GROUPS</span></samp> have no effect and return an error status.
If <samp><span class="env">GROUPS</span></samp> is unset, it loses its special properties, even if it is
subsequently reset.
<br><dt><code>histchars</code><a name="index-histchars-189"></a><dd>Up to three characters which control history expansion, quick
substitution, and tokenization (see <a href="#History-Interaction">History Interaction</a>).
The first character is the
<var>history expansion</var> character, that is, the character which signifies the
start of a history expansion, normally `<samp><span class="samp">!</span></samp>'. The second character is the
character which signifies `quick substitution' when seen as the first
character on a line, normally `<samp><span class="samp">^</span></samp>'. 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 `<samp><span class="samp">#</span></samp>'. 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.
<br><dt><code>HISTCMD</code><a name="index-HISTCMD-190"></a><dd>The history number, or index in the history list, of the current
command. If <samp><span class="env">HISTCMD</span></samp> is unset, it loses its special properties,
even if it is subsequently reset.
<br><dt><code>HISTCONTROL</code><a name="index-HISTCONTROL-191"></a><dd>A colon-separated list of values controlling how commands are saved on
the history list.
If the list of values includes `<samp><span class="samp">ignorespace</span></samp>', lines which begin
with a space character are not saved in the history list.
A value of `<samp><span class="samp">ignoredups</span></samp>' causes lines which match the previous
history entry to not be saved.
A value of `<samp><span class="samp">ignoreboth</span></samp>' is shorthand for
`<samp><span class="samp">ignorespace</span></samp>' and `<samp><span class="samp">ignoredups</span></samp>'.
A value of `<samp><span class="samp">erasedups</span></samp>' 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 <samp><span class="env">HISTCONTROL</span></samp> 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 <samp><span class="env">HISTIGNORE</span></samp>.
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
<samp><span class="env">HISTCONTROL</span></samp>.
<br><dt><code>HISTFILE</code><a name="index-HISTFILE-192"></a><dd>The name of the file to which the command history is saved. The
default value is <samp><span class="file">~/.bash_history</span></samp>.
<br><dt><code>HISTFILESIZE</code><a name="index-HISTFILESIZE-193"></a><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, by removing the oldest entries,
to contain no more than that number of lines.
The history file is also truncated to this size after
writing it when an interactive shell exits.
The default value is 500.
<br><dt><code>HISTIGNORE</code><a name="index-HISTIGNORE-194"></a><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 `<samp><span class="samp">*</span></samp>' is appended). Each pattern is tested
against the line after the checks specified by <samp><span class="env">HISTCONTROL</span></samp>
are applied. In addition to the normal shell pattern matching
characters, `<samp><span class="samp">&</span></samp>' matches the previous history line. `<samp><span class="samp">&</span></samp>'
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
<samp><span class="env">HISTIGNORE</span></samp>.
<p><samp><span class="env">HISTIGNORE</span></samp> subsumes the function of <samp><span class="env">HISTCONTROL</span></samp>. A
pattern of `<samp><span class="samp">&</span></samp>' is identical to <code>ignoredups</code>, and a
pattern of `<samp><span class="samp">[ ]*</span></samp>' is identical to <code>ignorespace</code>.
Combining these two patterns, separating them with a colon,
provides the functionality of <code>ignoreboth</code>.
<br><dt><code>HISTSIZE</code><a name="index-HISTSIZE-195"></a><dd>The maximum number of commands to remember on the history list.
The default value is 500.
<br><dt><code>HISTTIMEFORMAT</code><a name="index-HISTTIMEFORMAT-196"></a><dd>If this variable is set and not null, its value is used as a format string
for <var>strftime</var> 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.
<br><dt><code>HOSTFILE</code><a name="index-HOSTFILE-197"></a><dd>Contains the name of a file in the same format as <samp><span class="file">/etc/hosts</span></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 <samp><span class="env">HOSTFILE</span></samp> is set, but has no value, Bash attempts to read
<samp><span class="file">/etc/hosts</span></samp> to obtain the list of possible hostname completions.
When <samp><span class="env">HOSTFILE</span></samp> is unset, the hostname list is cleared.
<br><dt><code>HOSTNAME</code><a name="index-HOSTNAME-198"></a><dd>The name of the current host.
<br><dt><code>HOSTTYPE</code><a name="index-HOSTTYPE-199"></a><dd>A string describing the machine Bash is running on.
<br><dt><code>IGNOREEOF</code><a name="index-IGNOREEOF-200"></a><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.
<br><dt><code>INPUTRC</code><a name="index-INPUTRC-201"></a><dd>The name of the Readline initialization file, overriding the default
of <samp><span class="file">~/.inputrc</span></samp>.
<br><dt><code>LANG</code><a name="index-LANG-202"></a><dd>Used to determine the locale category for any category not specifically
selected with a variable starting with <code>LC_</code>.
<br><dt><code>LC_ALL</code><a name="index-LC_005fALL-203"></a><dd>This variable overrides the value of <samp><span class="env">LANG</span></samp> and any other
<code>LC_</code> variable specifying a locale category.
<br><dt><code>LC_COLLATE</code><a name="index-LC_005fCOLLATE-204"></a><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>).
<br><dt><code>LC_CTYPE</code><a name="index-LC_005fCTYPE-205"></a><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>).
<br><dt><code>LC_MESSAGES</code><a name="index-LC_005fMESSAGES-206"></a><dd>This variable determines the locale used to translate double-quoted
strings preceded by a `<samp><span class="samp">$</span></samp>' (see <a href="#Locale-Translation">Locale Translation</a>).
<br><dt><code>LC_NUMERIC</code><a name="index-LC_005fNUMERIC-207"></a><dd>This variable determines the locale category used for number formatting.
<br><dt><code>LINENO</code><a name="index-LINENO-208"></a><dd>The line number in the script or shell function currently executing.
<br><dt><code>LINES</code><a name="index-LINES-209"></a><dd>Used by the <code>select</code> builtin command to determine the column length
for printing selection lists. Automatically set upon receipt of a
<code>SIGWINCH</code>.
<br><dt><code>MACHTYPE</code><a name="index-MACHTYPE-210"></a><dd>A string that fully describes the system type on which Bash
is executing, in the standard <span class="sc">gnu</span> <var>cpu-company-system</var> format.
<br><dt><code>MAILCHECK</code><a name="index-MAILCHECK-211"></a><dd>How often (in seconds) that the shell should check for mail in the
files specified in the <samp><span class="env">MAILPATH</span></samp> or <samp><span class="env">MAIL</span></samp> 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.
<br><dt><code>OLDPWD</code><a name="index-OLDPWD-212"></a><dd>The previous working directory as set by the <code>cd</code> builtin.
<br><dt><code>OPTERR</code><a name="index-OPTERR-213"></a><dd>If set to the value 1, Bash displays error messages
generated by the <code>getopts</code> builtin command.
<br><dt><code>OSTYPE</code><a name="index-OSTYPE-214"></a><dd>A string describing the operating system Bash is running on.
<br><dt><code>PIPESTATUS</code><a name="index-PIPESTATUS-215"></a><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).
<br><dt><code>POSIXLY_CORRECT</code><a name="index-POSIXLY_005fCORRECT-216"></a><dd>If this variable is in the environment when <code>bash</code> starts, the shell
enters <span class="sc">posix</span> mode (see <a href="#Bash-POSIX-Mode">Bash POSIX Mode</a>) before reading the
startup files, as if the <samp><span class="option">--posix</span></samp> invocation option had been supplied.
If it is set while the shell is running, <code>bash</code> enables <span class="sc">posix</span> mode,
as if the command
<pre class="example"> <code>set -o posix</code>
</pre>
<p class="noindent">had been executed.
<br><dt><code>PPID</code><a name="index-PPID-217"></a><dd>The process <span class="sc">id</span> of the shell's parent process. This variable
is readonly.
<br><dt><code>PROMPT_COMMAND</code><a name="index-PROMPT_005fCOMMAND-218"></a><dd>If set, the value is interpreted as a command to execute
before the printing of each primary prompt (<samp><span class="env">$PS1</span></samp>).
<br><dt><code>PS3</code><a name="index-PS3-219"></a><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 `<samp><span class="samp">#? </span></samp>'
<br><dt><code>PS4</code><a name="index-PS4-220"></a><dd>The value is the prompt printed before the command line is echoed
when the <samp><span class="option">-x</span></samp> option is set (see <a href="#The-Set-Builtin">The Set Builtin</a>).
The first character of <samp><span class="env">PS4</span></samp> is replicated multiple times, as
necessary, to indicate multiple levels of indirection.
The default is `<samp><span class="samp">+ </span></samp>'.
<br><dt><code>PWD</code><a name="index-PWD-221"></a><dd>The current working directory as set by the <code>cd</code> builtin.
<br><dt><code>RANDOM</code><a name="index-RANDOM-222"></a><dd>Each time this parameter is referenced, a random integer
between 0 and 32767 is generated. Assigning a value to this
variable seeds the random number generator.
<br><dt><code>REPLY</code><a name="index-REPLY-223"></a><dd>The default variable for the <code>read</code> builtin.
<br><dt><code>SECONDS</code><a name="index-SECONDS-224"></a><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.
<br><dt><code>SHELL</code><a name="index-SHELL-225"></a><dd>The full pathname to the shell is kept in this environment variable.
If it is not set when the shell starts,
Bash assigns to it the full pathname of the current user's login shell.
<br><dt><code>SHELLOPTS</code><a name="index-SHELLOPTS-226"></a><dd>A colon-separated list of enabled shell options. Each word in
the list is a valid argument for the <samp><span class="option">-o</span></samp> option to the
<code>set</code> builtin command (see <a href="#The-Set-Builtin">The Set Builtin</a>).
The options appearing in <samp><span class="env">SHELLOPTS</span></samp> are those reported
as `<samp><span class="samp">on</span></samp>' by `<samp><span class="samp">set -o</span></samp>'.
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.
<br><dt><code>SHLVL</code><a name="index-SHLVL-227"></a><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.
<br><dt><code>TIMEFORMAT</code><a name="index-TIMEFORMAT-228"></a><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 `<samp><span class="samp">%</span></samp>' 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>
<dt><code>%%</code><dd>A literal `<samp><span class="samp">%</span></samp>'.
<br><dt><code>%[</code><var>p</var><code>][l]R</code><dd>The elapsed time in seconds.
<br><dt><code>%[</code><var>p</var><code>][l]U</code><dd>The number of CPU seconds spent in user mode.
<br><dt><code>%[</code><var>p</var><code>][l]S</code><dd>The number of CPU seconds spent in system mode.
<br><dt><code>%P</code><dd>The CPU percentage, computed as (%U + %S) / %R.
</dl>
<p>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.
<p>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.
<p>If this variable is not set, Bash acts as if it had the value
<pre class="example"> <code>$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'</code>
</pre>
<p>If the value is null, no timing information is displayed.
A trailing newline is added when the format string is displayed.
<br><dt><code>TMOUT</code><a name="index-TMOUT-229"></a><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 Builtins</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.
<p>In an interactive shell, the value is interpreted as
the number of seconds to wait for input after issuing the primary
prompt when the shell is interactive.
Bash terminates after that number of seconds if input does
not arrive.
<br><dt><code>TMPDIR</code><a name="index-TMPDIR-230"></a><dd>If set, Bash uses its value as the name of a directory in which
Bash creates temporary files for the shell's use.
<br><dt><code>UID</code><a name="index-UID-231"></a><dd>The numeric real user id of the current user. This variable is readonly.
</dl>
<div class="node">
<p><hr>
<a name="Bash-Features"></a>
Next: <a rel="next" accesskey="n" href="#Job-Control">Job Control</a>,
Previous: <a rel="previous" accesskey="p" href="#Shell-Variables">Shell Variables</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="chapter">6 Bash Features</h2>
<p>This section describes features unique to Bash.
<ul class="menu">
<li><a accesskey="1" href="#Invoking-Bash">Invoking Bash</a>: Command line options that you can give
to Bash.
<li><a accesskey="2" href="#Bash-Startup-Files">Bash Startup Files</a>: When and how Bash executes scripts.
<li><a accesskey="3" href="#Interactive-Shells">Interactive Shells</a>: What an interactive shell is.
<li><a accesskey="4" href="#Bash-Conditional-Expressions">Bash Conditional Expressions</a>: Primitives used in composing expressions for
the <code>test</code> builtin.
<li><a accesskey="5" href="#Shell-Arithmetic">Shell Arithmetic</a>: Arithmetic on shell variables.
<li><a accesskey="6" href="#Aliases">Aliases</a>: Substituting one command for another.
<li><a accesskey="7" href="#Arrays">Arrays</a>: Array Variables.
<li><a accesskey="8" href="#The-Directory-Stack">The Directory Stack</a>: History of visited directories.
<li><a accesskey="9" href="#Printing-a-Prompt">Printing a Prompt</a>: Controlling the PS1 string.
<li><a href="#The-Restricted-Shell">The Restricted Shell</a>: A more controlled mode of shell execution.
<li><a href="#Bash-POSIX-Mode">Bash POSIX Mode</a>: Making Bash behave more closely to what
the POSIX standard specifies.
</ul>
<div class="node">
<p><hr>
<a name="Invoking-Bash"></a>
Next: <a rel="next" accesskey="n" href="#Bash-Startup-Files">Bash Startup Files</a>,
Up: <a rel="up" accesskey="u" href="#Bash-Features">Bash Features</a>
</div>
<h3 class="section">6.1 Invoking Bash</h3>
<pre class="example"> bash [long-opt] [-ir] [-abefhkmnptuvxdBCDHP] [-o <var>option</var>] [-O <var>shopt_option</var>] [<var>argument</var> ...]
bash [long-opt] [-abefhkmnptuvxdBCDHP] [-o <var>option</var>] [-O <var>shopt_option</var>] -c <var>string</var> [<var>argument</var> ...]
bash [long-opt] -s [-abefhkmnptuvxdBCDHP] [-o <var>option</var>] [-O <var>shopt_option</var>] [<var>argument</var> ...]
</pre>
<p>In addition to the single-character shell command-line options
(see <a href="#The-Set-Builtin">The Set Builtin</a>), 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>
<dt><code>--debugger</code><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) and shell function tracing
(see <a href="#The-Set-Builtin">The Set Builtin</a> for a description of the <code>-o functrace</code>
option).
<br><dt><code>--dump-po-strings</code><dd>A list of all double-quoted strings preceded by `<samp><span class="samp">$</span></samp>'
is printed on the standard output
in the <span class="sc">gnu</span> <code>gettext</code> PO (portable object) file format.
Equivalent to <samp><span class="option">-D</span></samp> except for the output format.
<br><dt><code>--dump-strings</code><dd>Equivalent to <samp><span class="option">-D</span></samp>.
<br><dt><code>--help</code><dd>Display a usage message on standard output and exit successfully.
<br><dt><code>--init-file </code><var>filename</var><dt><code>--rcfile </code><var>filename</var><dd>Execute commands from <var>filename</var> (instead of <samp><span class="file">~/.bashrc</span></samp>)
in an interactive shell.
<br><dt><code>--login</code><dd>Equivalent to <samp><span class="option">-l</span></samp>.
<br><dt><code>--noediting</code><dd>Do not use the <span class="sc">gnu</span> Readline library (see <a href="#Command-Line-Editing">Command Line Editing</a>)
to read command lines when the shell is interactive.
<br><dt><code>--noprofile</code><dd>Don't load the system-wide startup file <samp><span class="file">/etc/profile</span></samp>
or any of the personal initialization files
<samp><span class="file">~/.bash_profile</span></samp>, <samp><span class="file">~/.bash_login</span></samp>, or <samp><span class="file">~/.profile</span></samp>
when Bash is invoked as a login shell.
<br><dt><code>--norc</code><dd>Don't read the <samp><span class="file">~/.bashrc</span></samp> initialization file in an
interactive shell. This is on by default if the shell is
invoked as <code>sh</code>.
<br><dt><code>--posix</code><dd>Change the behavior of Bash where the default operation differs
from the <span class="sc">posix</span> 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
<span class="sc">posix</span> mode.
<br><dt><code>--restricted</code><dd>Make the shell a restricted shell (see <a href="#The-Restricted-Shell">The Restricted Shell</a>).
<br><dt><code>--verbose</code><dd>Equivalent to <samp><span class="option">-v</span></samp>. Print shell input lines as they're read.
<br><dt><code>--version</code><dd>Show version information for this instance of
Bash on the standard output and exit successfully.
</dl>
<p>There are several single-character options that may be supplied at
invocation which are not available with the <code>set</code> builtin.
<dl>
<dt><code>-c </code><var>string</var><dd>Read and execute commands from <var>string</var> after processing the
options, then exit. Any remaining arguments are assigned to the
positional parameters, starting with <code>$0</code>.
<br><dt><code>-i</code><dd>Force the shell to run interactively. Interactive shells are
described in <a href="#Interactive-Shells">Interactive Shells</a>.
<br><dt><code>-l</code><dd>Make this shell act as if it had been directly invoked by login.
When the shell is interactive, this is equivalent to starting a
login shell with `<samp><span class="samp">exec -l bash</span></samp>'.
When the shell is not interactive, the login shell startup files will
be executed.
`<samp><span class="samp">exec bash -l</span></samp>' or `<samp><span class="samp">exec bash --login</span></samp>'
will replace the current shell with a Bash login shell.
See <a href="#Bash-Startup-Files">Bash Startup Files</a>, for a description of the special behavior
of a login shell.
<br><dt><code>-r</code><dd>Make the shell a restricted shell (see <a href="#The-Restricted-Shell">The Restricted Shell</a>).
<br><dt><code>-s</code><dd>If this option is present, or if no arguments remain after option
processing, then commands are read from the standard input.
This option allows the positional parameters to be set
when invoking an interactive shell.
<br><dt><code>-D</code><dd>A list of all double-quoted strings preceded by `<samp><span class="samp">$</span></samp>'
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 Translation</a>).
This implies the <samp><span class="option">-n</span></samp> option; no commands will be executed.
<br><dt><code>[-+]O [</code><var>shopt_option</var><code>]</code><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><span class="option">-O</span></samp> sets the value of that option;
<samp><span class="option">+O</span></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><span class="option">+O</span></samp>, the output is displayed in a format
that may be reused as input.
<br><dt><code>--</code><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.
</dl>
<p><a name="index-login-shell-232"></a>A <em>login</em> shell is one whose first character of argument zero is
`<samp><span class="samp">-</span></samp>', or one invoked with the <samp><span class="option">--login</span></samp> option.
<p><a name="index-interactive-shell-233"></a>An <em>interactive</em> shell is one started without non-option arguments,
unless <samp><span class="option">-s</span></samp> is specified,
without specifying the <samp><span class="option">-c</span></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><span class="option">-i</span></samp> option. See <a href="#Interactive-Shells">Interactive Shells</a>, for more
information.
<p>If arguments remain after option processing, and neither the
<samp><span class="option">-c</span></samp> nor the <samp><span class="option">-s</span></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'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.
<div class="node">
<p><hr>
<a name="Bash-Startup-Files"></a>
Next: <a rel="next" accesskey="n" href="#Interactive-Shells">Interactive Shells</a>,
Previous: <a rel="previous" accesskey="p" href="#Invoking-Bash">Invoking Bash</a>,
Up: <a rel="up" accesskey="u" href="#Bash-Features">Bash Features</a>
</div>
<h3 class="section">6.2 Bash Startup Files</h3>
<p><a name="index-startup-files-234"></a>
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 file names as described above under
Tilde Expansion (see <a href="#Tilde-Expansion">Tilde Expansion</a>).
<p>Interactive shells are described in <a href="#Interactive-Shells">Interactive Shells</a>.
<h5 class="subsubheading">Invoked as an interactive login shell, or with <samp><span class="option">--login</span></samp></h5>
<p>When Bash is invoked as an interactive login shell, or as a
non-interactive shell with the <samp><span class="option">--login</span></samp> option, it first reads and
executes commands from the file <samp><span class="file">/etc/profile</span></samp>, if that file exists.
After reading that file, it looks for <samp><span class="file">~/.bash_profile</span></samp>,
<samp><span class="file">~/.bash_login</span></samp>, and <samp><span class="file">~/.profile</span></samp>, in that order, and reads
and executes commands from the first one that exists and is readable.
The <samp><span class="option">--noprofile</span></samp> option may be used when the shell is started to
inhibit this behavior.
<p>When a login shell exits, Bash reads and executes commands from
the file <samp><span class="file">~/.bash_logout</span></samp>, if it exists.
<h5 class="subsubheading">Invoked as an interactive non-login shell</h5>
<p>When an interactive shell that is not a login shell is started, Bash
reads and executes commands from <samp><span class="file">~/.bashrc</span></samp>, if that file exists.
This may be inhibited by using the <samp><span class="option">--norc</span></samp> option.
The <samp><span class="option">--rcfile </span><var>file</var></samp> option will force Bash to read and
execute commands from <var>file</var> instead of <samp><span class="file">~/.bashrc</span></samp>.
<p>So, typically, your <samp><span class="file">~/.bash_profile</span></samp> contains the line
<pre class="example"> <code>if [ -f ~/.bashrc ]; then . ~/.bashrc; fi</code>
</pre>
<p class="noindent">after (or before) any login-specific initializations.
<h5 class="subsubheading">Invoked non-interactively</h5>
<p>When Bash is started non-interactively, to run a shell script,
for example, it looks for the variable <samp><span class="env">BASH_ENV</span></samp> 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:
<pre class="example"> <code>if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi</code>
</pre>
<p class="noindent">but the value of the <samp><span class="env">PATH</span></samp> variable is not used to search for the
file name.
<p>As noted above, if a non-interactive shell is invoked with the
<samp><span class="option">--login</span></samp> option, Bash attempts to read and execute commands from the
login shell startup files.
<h5 class="subsubheading">Invoked with name <code>sh</code></h5>
<p>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 <span class="sc">posix</span> standard as well.
<p>When invoked as an interactive login shell, or as a non-interactive
shell with the <samp><span class="option">--login</span></samp> option, it first attempts to read
and execute commands from <samp><span class="file">/etc/profile</span></samp> and <samp><span class="file">~/.profile</span></samp>, in
that order.
The <samp><span class="option">--noprofile</span></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 <samp><span class="env">ENV</span></samp>, 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><span class="option">--rcfile</span></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.
<p>When invoked as <code>sh</code>, Bash enters <span class="sc">posix</span> mode after
the startup files are read.
<h5 class="subsubheading">Invoked in <span class="sc">posix</span> mode</h5>
<p>When Bash is started in <span class="sc">posix</span> mode, as with the
<samp><span class="option">--posix</span></samp> command line option, it follows the <span class="sc">posix</span> standard
for startup files.
In this mode, interactive shells expand the <samp><span class="env">ENV</span></samp> variable
and commands are read and executed from the file whose name is the
expanded value.
No other startup files are read.
<h5 class="subsubheading">Invoked by remote shell daemon</h5>
<p>Bash attempts to determine when it is being run by the remote shell
daemon, usually <code>rshd</code>. If Bash determines it is being run by
rshd, it reads and executes commands from <samp><span class="file">~/.bashrc</span></samp>, if that
file exists and is readable.
It will not do this if invoked as <code>sh</code>.
The <samp><span class="option">--norc</span></samp> option may be used to inhibit this behavior, and the
<samp><span class="option">--rcfile</span></samp> option may be used to force another file to be read, but
<code>rshd</code> does not generally invoke the shell with those options or
allow them to be specified.
<h5 class="subsubheading">Invoked with unequal effective and real <span class="sc">uid/gid</span>s</h5>
<p>If Bash is started with the effective user (group) id not equal to the
real user (group) id, and the <code>-p</code> option is not supplied, no startup
files are read, shell functions are not inherited from the environment,
the <samp><span class="env">SHELLOPTS</span></samp> variable, if it appears in the environment, is ignored,
and the effective user id is set to the real user id.
If the <code>-p</code> option is supplied at invocation, the startup behavior is
the same, but the effective user id is not reset.
<div class="node">
<p><hr>
<a name="Interactive-Shells"></a>
Next: <a rel="next" accesskey="n" href="#Bash-Conditional-Expressions">Bash Conditional Expressions</a>,
Previous: <a rel="previous" accesskey="p" href="#Bash-Startup-Files">Bash Startup Files</a>,
Up: <a rel="up" accesskey="u" href="#Bash-Features">Bash Features</a>
</div>
<h3 class="section">6.3 Interactive Shells</h3>
<p><a name="index-interactive-shell-235"></a><a name="index-shell_002c-interactive-236"></a>
<ul class="menu">
<li><a accesskey="1" href="#What-is-an-Interactive-Shell_003f">What is an Interactive Shell?</a>: What determines whether a shell is Interactive.
<li><a accesskey="2" href="#Is-this-Shell-Interactive_003f">Is this Shell Interactive?</a>: How to tell if a shell is interactive.
<li><a accesskey="3" href="#Interactive-Shell-Behavior">Interactive Shell Behavior</a>: What changes in a interactive shell?
</ul>
<div class="node">
<p><hr>
<a name="What-is-an-Interactive-Shell%3f"></a>
<a name="What-is-an-Interactive-Shell_003f"></a>
Next: <a rel="next" accesskey="n" href="#Is-this-Shell-Interactive_003f">Is this Shell Interactive?</a>,
Up: <a rel="up" accesskey="u" href="#Interactive-Shells">Interactive Shells</a>
</div>
<h4 class="subsection">6.3.1 What is an Interactive Shell?</h4>
<p>An interactive shell
is one started without non-option arguments, unless <samp><span class="option">-s</span></samp> is
specified, without specifying the <samp><span class="option">-c</span></samp> option, and
whose input and error output are both
connected to terminals (as determined by <code>isatty(3)</code>),
or one started with the <samp><span class="option">-i</span></samp> option.
<p>An interactive shell generally reads from and writes to a user's
terminal.
<p>The <samp><span class="option">-s</span></samp> invocation option may be used to set the positional parameters
when an interactive shell is started.
<div class="node">
<p><hr>
<a name="Is-this-Shell-Interactive%3f"></a>
<a name="Is-this-Shell-Interactive_003f"></a>
Next: <a rel="next" accesskey="n" href="#Interactive-Shell-Behavior">Interactive Shell Behavior</a>,
Previous: <a rel="previous" accesskey="p" href="#What-is-an-Interactive-Shell_003f">What is an Interactive Shell?</a>,
Up: <a rel="up" accesskey="u" href="#Interactive-Shells">Interactive Shells</a>
</div>
<h4 class="subsection">6.3.2 Is this Shell Interactive?</h4>
<p>To determine within a startup script whether or not Bash is
running interactively,
test the value of the `<samp><span class="samp">-</span></samp>' special parameter.
It contains <code>i</code> when the shell is interactive. For example:
<pre class="example"> case "$-" in
*i*) echo This shell is interactive ;;
*) echo This shell is not interactive ;;
esac
</pre>
<p>Alternatively, startup scripts may examine the variable
<samp><span class="env">PS1</span></samp>; it is unset in non-interactive shells, and set in
interactive shells. Thus:
<pre class="example"> if [ -z "$PS1" ]; then
echo This shell is not interactive
else
echo This shell is interactive
fi
</pre>
<div class="node">
<p><hr>
<a name="Interactive-Shell-Behavior"></a>
Previous: <a rel="previous" accesskey="p" href="#Is-this-Shell-Interactive_003f">Is this Shell Interactive?</a>,
Up: <a rel="up" accesskey="u" href="#Interactive-Shells">Interactive Shells</a>
</div>
<h4 class="subsection">6.3.3 Interactive Shell Behavior</h4>
<p>When the shell is running interactively, it changes its behavior in
several ways.
<ol type=1 start=1>
<li>Startup files are read and executed as described in <a href="#Bash-Startup-Files">Bash Startup Files</a>.
<li>Job Control (see <a href="#Job-Control">Job Control</a>) is enabled by default. When job
control is in effect, Bash ignores the keyboard-generated job control
signals <code>SIGTTIN</code>, <code>SIGTTOU</code>, and <code>SIGTSTP</code>.
<li>Bash expands and displays <samp><span class="env">PS1</span></samp> before reading the first line
of a command, and expands and displays <samp><span class="env">PS2</span></samp> before reading the
second and subsequent lines of a multi-line command.
<li>Bash executes the value of the <samp><span class="env">PROMPT_COMMAND</span></samp> variable as a command
before printing the primary prompt, <samp><span class="env">$PS1</span></samp>
(see <a href="#Bash-Variables">Bash Variables</a>).
<li>Readline (see <a href="#Command-Line-Editing">Command Line Editing</a>) is used to read commands from
the user's terminal.
<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>Command history (see <a href="#Bash-History-Facilities">Bash History Facilities</a>)
and history expansion (see <a href="#History-Interaction">History Interaction</a>)
are enabled by default.
Bash will save the command history to the file named by <samp><span class="env">$HISTFILE</span></samp>
when an interactive shell exits.
<li>Alias expansion (see <a href="#Aliases">Aliases</a>) is performed by default.
<li>In the absence of any traps, Bash ignores <code>SIGTERM</code>
(see <a href="#Signals">Signals</a>).
<li>In the absence of any traps, <code>SIGINT</code> is caught and handled
((see <a href="#Signals">Signals</a>).
<code>SIGINT</code> will interrupt some shell builtins.
<li>An interactive login shell sends a <code>SIGHUP</code> to all jobs on exit
if the <code>huponexit</code> shell option has been enabled (see <a href="#Signals">Signals</a>).
<li>The <samp><span class="option">-n</span></samp> invocation option is ignored, and `<samp><span class="samp">set -n</span></samp>' has
no effect (see <a href="#The-Set-Builtin">The Set Builtin</a>).
<li>Bash will check for mail periodically, depending on the values of the
<samp><span class="env">MAIL</span></samp>, <samp><span class="env">MAILPATH</span></samp>, and <samp><span class="env">MAILCHECK</span></samp> shell variables
(see <a href="#Bash-Variables">Bash Variables</a>).
<li>Expansion errors due to references to unbound shell variables after
`<samp><span class="samp">set -u</span></samp>' has been enabled will not cause the shell to exit
(see <a href="#The-Set-Builtin">The Set Builtin</a>).
<li>The shell will not exit on expansion errors caused by <var>var</var> being unset
or null in <code>${</code><var>var</var><code>:?</code><var>word</var><code>}</code> expansions
(see <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>).
<li>Redirection errors encountered by shell builtins will not cause the
shell to exit.
<li>When running in <span class="sc">posix</span> 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>A failed <code>exec</code> will not cause the shell to exit
(see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>).
<li>Parser syntax errors will not cause the shell to exit.
<li>Simple spelling correction for directory arguments to the <code>cd</code>
builtin is enabled by default (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>).
<li>The shell will check the value of the <samp><span class="env">TMOUT</span></samp> variable and exit
if a command is not read within the specified number of seconds after
printing <samp><span class="env">$PS1</span></samp> (see <a href="#Bash-Variables">Bash Variables</a>).
</ol>
<div class="node">
<p><hr>
<a name="Bash-Conditional-Expressions"></a>
Next: <a rel="next" accesskey="n" href="#Shell-Arithmetic">Shell Arithmetic</a>,
Previous: <a rel="previous" accesskey="p" href="#Interactive-Shells">Interactive Shells</a>,
Up: <a rel="up" accesskey="u" href="#Bash-Features">Bash Features</a>
</div>
<h3 class="section">6.4 Bash Conditional Expressions</h3>
<p><a name="index-expressions_002c-conditional-237"></a>
Conditional expressions are used by the <code>[[</code> compound command
and the <code>test</code> and <code>[</code> builtin commands.
<p>Expressions may be unary or binary.
Unary expressions are often used to examine the status of a file.
There are string operators and numeric comparison operators as well.
If the <var>file</var> argument to one of the primaries is of the form
<samp><span class="file">/dev/fd/</span><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><span class="file">/dev/stdin</span></samp>, <samp><span class="file">/dev/stdout</span></samp>, or <samp><span class="file">/dev/stderr</span></samp>, file
descriptor 0, 1, or 2, respectively, is checked.
<p>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>
<dt><code>-a </code><var>file</var><dd>True if <var>file</var> exists.
<br><dt><code>-b </code><var>file</var><dd>True if <var>file</var> exists and is a block special file.
<br><dt><code>-c </code><var>file</var><dd>True if <var>file</var> exists and is a character special file.
<br><dt><code>-d </code><var>file</var><dd>True if <var>file</var> exists and is a directory.
<br><dt><code>-e </code><var>file</var><dd>True if <var>file</var> exists.
<br><dt><code>-f </code><var>file</var><dd>True if <var>file</var> exists and is a regular file.
<br><dt><code>-g </code><var>file</var><dd>True if <var>file</var> exists and its set-group-id bit is set.
<br><dt><code>-h </code><var>file</var><dd>True if <var>file</var> exists and is a symbolic link.
<br><dt><code>-k </code><var>file</var><dd>True if <var>file</var> exists and its "sticky" bit is set.
<br><dt><code>-p </code><var>file</var><dd>True if <var>file</var> exists and is a named pipe (FIFO).
<br><dt><code>-r </code><var>file</var><dd>True if <var>file</var> exists and is readable.
<br><dt><code>-s </code><var>file</var><dd>True if <var>file</var> exists and has a size greater than zero.
<br><dt><code>-t </code><var>fd</var><dd>True if file descriptor <var>fd</var> is open and refers to a terminal.
<br><dt><code>-u </code><var>file</var><dd>True if <var>file</var> exists and its set-user-id bit is set.
<br><dt><code>-w </code><var>file</var><dd>True if <var>file</var> exists and is writable.
<br><dt><code>-x </code><var>file</var><dd>True if <var>file</var> exists and is executable.
<br><dt><code>-O </code><var>file</var><dd>True if <var>file</var> exists and is owned by the effective user id.
<br><dt><code>-G </code><var>file</var><dd>True if <var>file</var> exists and is owned by the effective group id.
<br><dt><code>-L </code><var>file</var><dd>True if <var>file</var> exists and is a symbolic link.
<br><dt><code>-S </code><var>file</var><dd>True if <var>file</var> exists and is a socket.
<br><dt><code>-N </code><var>file</var><dd>True if <var>file</var> exists and has been modified since it was last read.
<br><dt><var>file1</var><code> -nt </code><var>file2</var><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.
<br><dt><var>file1</var><code> -ot </code><var>file2</var><dd>True if <var>file1</var> is older than <var>file2</var>,
or if <var>file2</var> exists and <var>file1</var> does not.
<br><dt><var>file1</var><code> -ef </code><var>file2</var><dd>True if <var>file1</var> and <var>file2</var> refer to the same device and
inode numbers.
<br><dt><code>-o </code><var>optname</var><dd>True if shell option <var>optname</var> is enabled.
The list of options appears in the description of the <samp><span class="option">-o</span></samp>
option to the <code>set</code> builtin (see <a href="#The-Set-Builtin">The Set Builtin</a>).
<br><dt><code>-z </code><var>string</var><dd>True if the length of <var>string</var> is zero.
<br><dt><code>-n </code><var>string</var><dt><var>string</var><dd>True if the length of <var>string</var> is non-zero.
<br><dt><var>string1</var><code> == </code><var>string2</var><dd>True if the strings are equal.
`<samp><span class="samp">=</span></samp>' may be used in place of `<samp><span class="samp">==</span></samp>' for strict <span class="sc">posix</span> compliance.
<br><dt><var>string1</var><code> != </code><var>string2</var><dd>True if the strings are not equal.
<br><dt><var>string1</var><code> < </code><var>string2</var><dd>True if <var>string1</var> sorts before <var>string2</var> lexicographically
in the current locale.
<br><dt><var>string1</var><code> > </code><var>string2</var><dd>True if <var>string1</var> sorts after <var>string2</var> lexicographically
in the current locale.
<br><dt><var>arg1</var><code> OP </code><var>arg2</var><dd><code>OP</code> is one of
`<samp><span class="samp">-eq</span></samp>', `<samp><span class="samp">-ne</span></samp>', `<samp><span class="samp">-lt</span></samp>', `<samp><span class="samp">-le</span></samp>', `<samp><span class="samp">-gt</span></samp>', or `<samp><span class="samp">-ge</span></samp>'.
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.
</dl>
<div class="node">
<p><hr>
<a name="Shell-Arithmetic"></a>
Next: <a rel="next" accesskey="n" href="#Aliases">Aliases</a>,
Previous: <a rel="previous" accesskey="p" href="#Bash-Conditional-Expressions">Bash Conditional Expressions</a>,
Up: <a rel="up" accesskey="u" href="#Bash-Features">Bash Features</a>
</div>
<h3 class="section">6.5 Shell Arithmetic</h3>
<p><a name="index-arithmetic_002c-shell-238"></a><a name="index-shell-arithmetic-239"></a><a name="index-expressions_002c-arithmetic-240"></a><a name="index-evaluation_002c-arithmetic-241"></a><a name="index-arithmetic-evaluation-242"></a>
The shell allows arithmetic expressions to be evaluated, as one of
the shell expansions or by the <code>let</code> and the <samp><span class="option">-i</span></samp> option
to the <code>declare</code> builtins.
<p>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>
<dt><var>id</var><code>++ </code><var>id</var><code>--</code><dd>variable post-increment and post-decrement
<br><dt><code>++</code><var>id</var><code> --</code><var>id</var><dd>variable pre-increment and pre-decrement
<br><dt><code>- +</code><dd>unary minus and plus
<br><dt><code>! ~</code><dd>logical and bitwise negation
<br><dt><code>**</code><dd>exponentiation
<br><dt><code>* / %</code><dd>multiplication, division, remainder
<br><dt><code>+ -</code><dd>addition, subtraction
<br><dt><code><< >></code><dd>left and right bitwise shifts
<br><dt><code><= >= < ></code><dd>comparison
<br><dt><code>== !=</code><dd>equality and inequality
<br><dt><code>&</code><dd>bitwise AND
<br><dt><code>^</code><dd>bitwise exclusive OR
<br><dt><code>|</code><dd>bitwise OR
<br><dt><code>&&</code><dd>logical AND
<br><dt><code>||</code><dd>logical OR
<br><dt><code>expr ? expr : expr</code><dd>conditional operator
<br><dt><code>= *= /= %= += -= <<= >>= &= ^= |=</code><dd>assignment
<br><dt><code>expr1 , expr2</code><dd>comma
</dl>
<p>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
<var>integer</var> attribute using `<samp><span class="samp">declare -i</span></samp>' is assigned a value.
A null value evaluates to 0.
A shell variable need not have its integer attribute turned on
to be used in an expression.
<p>Constants with a leading 0 are interpreted as octal numbers.
A leading `<samp><span class="samp">0x</span></samp>' or `<samp><span class="samp">0X</span></samp>' denotes hexadecimal. Otherwise,
numbers take the form [<var>base</var><code>#</code>]<var>n</var>, where <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.
The digits greater than 9 are represented by the lowercase letters,
the uppercase letters, `<samp><span class="samp">@</span></samp>', and `<samp><span class="samp">_</span></samp>', 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.
<p>Operators are evaluated in order of precedence. Sub-expressions in
parentheses are evaluated first and may override the precedence
rules above.
<div class="node">
<p><hr>
<a name="Aliases"></a>
Next: <a rel="next" accesskey="n" href="#Arrays">Arrays</a>,
Previous: <a rel="previous" accesskey="p" href="#Shell-Arithmetic">Shell Arithmetic</a>,
Up: <a rel="up" accesskey="u" href="#Bash-Features">Bash Features</a>
</div>
<h3 class="section">6.6 Aliases</h3>
<p><a name="index-alias-expansion-243"></a>
<var>Aliases</var> 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.
<p>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 `<samp><span class="samp">/</span></samp>', `<samp><span class="samp">$</span></samp>', `<samp><span class="samp">`</span></samp>', `<samp><span class="samp">=</span></samp>' 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>"ls -F"</code>,
for instance, and Bash does not try to recursively expand the
replacement text. If the last character of the alias value is a
space or tab character, then the next command word following the
alias is also checked for alias expansion.
<p>Aliases are created and listed with the <code>alias</code>
command, and removed with the <code>unalias</code> command.
<p>There is no mechanism for using arguments in the replacement text,
as in <code>csh</code>.
If arguments are needed, a shell function should be used
(see <a href="#Shell-Functions">Shell Functions</a>).
<p>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>).
<p>The rules concerning the definition and use of aliases are
somewhat confusing. Bash
always reads at least one complete line
of input before executing any
of the commands on that line. 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 compound 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.
<p>For almost every purpose, shell functions are preferred over aliases.
<div class="node">
<p><hr>
<a name="Arrays"></a>
Next: <a rel="next" accesskey="n" href="#The-Directory-Stack">The Directory Stack</a>,
Previous: <a rel="previous" accesskey="p" href="#Aliases">Aliases</a>,
Up: <a rel="up" accesskey="u" href="#Bash-Features">Bash Features</a>
</div>
<h3 class="section">6.7 Arrays</h3>
<p><a name="index-arrays-244"></a>
Bash provides one-dimensional array variables. Any variable may be used as
an 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. Arrays are zero-based.
<p>An array is created automatically if any variable is assigned to using
the syntax
<pre class="example"> name[<var>subscript</var>]=<var>value</var>
</pre>
<p class="noindent">The <var>subscript</var>
is treated as an arithmetic expression that must evaluate to a number
greater than or equal to zero. To explicitly declare an array, use
<pre class="example"> declare -a <var>name</var>
</pre>
<p class="noindent">The syntax
<pre class="example"> declare -a <var>name</var>[<var>subscript</var>]
</pre>
<p class="noindent">is also accepted; the <var>subscript</var> is ignored. 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.
<p>Arrays are assigned to using compound assignments of the form
<pre class="example"> name=(value<var>1</var> ... value<var>n</var>)
</pre>
<p class="noindent">where each
<var>value</var> is of the form <code>[[</code><var>subscript</var><code>]=]</code><var>string</var>. 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.
This syntax is also accepted by the <code>declare</code>
builtin. Individual array elements may be assigned to using the
<code>name[</code><var>subscript</var><code>]=</code><var>value</var> syntax introduced above.
<p>Any element of an array may be referenced using
<code>${name[</code><var>subscript</var><code>]}</code>.
The braces are required to avoid
conflicts with the shell's filename expansion operators. If the
<var>subscript</var> is `<samp><span class="samp">@</span></samp>' or `<samp><span class="samp">*</span></samp>', the word expands to all members
of the array <var>name</var>. These subscripts differ only when the word
appears within double quotes.
If the word is double-quoted,
<code>${name[*]}</code> expands to a single word with
the value of each array member separated by the first character of the
<samp><span class="env">IFS</span></samp> variable, and <code>${name[@]}</code> expands each element of
<var>name</var> to a separate word. When there are no array members,
<code>${name[@]}</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 `<samp><span class="samp">@</span></samp>' and `<samp><span class="samp">*</span></samp>'.
<code>${#name[</code><var>subscript</var><code>]}</code> expands to the length of
<code>${name[</code><var>subscript</var><code>]}</code>.
If <var>subscript</var> is `<samp><span class="samp">@</span></samp>' or
`<samp><span class="samp">*</span></samp>', the expansion is the number of elements in the array.
Referencing an array variable without a subscript is equivalent to
referencing element zero.
<p>The <code>unset</code> builtin is used to destroy arrays.
<code>unset</code> <var>name</var>[<var>subscript</var>]
destroys the array element at index <var>subscript</var>.
Care must be taken to avoid unwanted side effects caused by filename
generation.
<code>unset</code> <var>name</var>, where <var>name</var> is an array, removes the
entire array. A subscript of `<samp><span class="samp">*</span></samp>' or `<samp><span class="samp">@</span></samp>' also removes the
entire array.
<p>The <code>declare</code>, <code>local</code>, and <code>readonly</code>
builtins each accept a <samp><span class="option">-a</span></samp>
option to specify an array. The <code>read</code>
builtin accepts a <samp><span class="option">-a</span></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.
<div class="node">
<p><hr>
<a name="The-Directory-Stack"></a>
Next: <a rel="next" accesskey="n" href="#Printing-a-Prompt">Printing a Prompt</a>,
Previous: <a rel="previous" accesskey="p" href="#Arrays">Arrays</a>,
Up: <a rel="up" accesskey="u" href="#Bash-Features">Bash Features</a>
</div>
<h3 class="section">6.8 The Directory Stack</h3>
<p><a name="index-directory-stack-245"></a>
<ul class="menu">
<li><a accesskey="1" href="#Directory-Stack-Builtins">Directory Stack Builtins</a>: Bash builtin commands to manipulate
the directory stack.
</ul>
<p>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.
<p>The contents of the directory stack are also visible
as the value of the <samp><span class="env">DIRSTACK</span></samp> shell variable.
<div class="node">
<p><hr>
<a name="Directory-Stack-Builtins"></a>
Up: <a rel="up" accesskey="u" href="#The-Directory-Stack">The Directory Stack</a>
</div>
<h4 class="subsection">6.8.1 Directory Stack Builtins</h4>
<dl>
<dt><code>dirs</code><dd><a name="index-dirs-246"></a>
<pre class="example"> dirs [+<var>N</var> | -<var>N</var>] [-clpv]
</pre>
<p>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.
<dl>
<dt><code>+</code><var>N</var><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.
<br><dt><code>-</code><var>N</var><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.
<br><dt><code>-c</code><dd>Clears the directory stack by deleting all of the elements.
<br><dt><code>-l</code><dd>Produces a longer listing; the default listing format uses a
tilde to denote the home directory.
<br><dt><code>-p</code><dd>Causes <code>dirs</code> to print the directory stack with one entry per
line.
<br><dt><code>-v</code><dd>Causes <code>dirs</code> to print the directory stack with one entry per
line, prefixing each entry with its index in the stack.
</dl>
<br><dt><code>popd</code><dd><a name="index-popd-247"></a>
<pre class="example"> popd [+<var>N</var> | -<var>N</var>] [-n]
</pre>
<p>Remove the top entry from the directory stack, and <code>cd</code>
to the new top directory.
When no arguments are given, <code>popd</code>
removes the top directory from the stack and
performs a <code>cd</code> to the new top directory. The
elements are numbered from 0 starting at the first directory listed with
<code>dirs</code>; i.e., <code>popd</code> is equivalent to <code>popd +0</code>.
<dl>
<dt><code>+</code><var>N</var><dd>Removes the <var>N</var>th directory (counting from the left of the
list printed by <code>dirs</code>), starting with zero.
<br><dt><code>-</code><var>N</var><dd>Removes the <var>N</var>th directory (counting from the right of the
list printed by <code>dirs</code>), starting with zero.
<br><dt><code>-n</code><dd>Suppresses the normal change of directory when removing directories
from the stack, so that only the stack is manipulated.
</dl>
<p><a name="index-pushd-248"></a><br><dt><code>pushd</code><dd>
<pre class="example"> pushd [-n] [<var>+N</var> | <var>-N</var> | <var>dir</var> ]
</pre>
<p>Save the current directory on the top of the directory stack
and then <code>cd</code> to <var>dir</var>.
With no arguments, <code>pushd</code> exchanges the top two directories.
<dl>
<dt><code>-n</code><dd>Suppresses the normal change of directory when adding directories
to the stack, so that only the stack is manipulated.
<br><dt><code>+</code><var>N</var><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.
<br><dt><code>-</code><var>N</var><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.
<br><dt><var>dir</var><dd>Makes the current working directory be the top of the stack, and then
executes the equivalent of `<code>cd</code> <var>dir</var>'.
<code>cd</code>s to <var>dir</var>.
</dl>
</dl>
<div class="node">
<p><hr>
<a name="Printing-a-Prompt"></a>
Next: <a rel="next" accesskey="n" href="#The-Restricted-Shell">The Restricted Shell</a>,
Previous: <a rel="previous" accesskey="p" href="#The-Directory-Stack">The Directory Stack</a>,
Up: <a rel="up" accesskey="u" href="#Bash-Features">Bash Features</a>
</div>
<h3 class="section">6.9 Controlling the Prompt</h3>
<p><a name="index-prompting-249"></a>
The value of the variable <samp><span class="env">PROMPT_COMMAND</span></samp> is examined just before
Bash prints each primary prompt. If <samp><span class="env">PROMPT_COMMAND</span></samp> is set and
has a non-null value, then the
value is executed just as if it had been typed on the command line.
<p>In addition, the following table describes the special characters which
can appear in the prompt variables:
<dl>
<dt><code>\a</code><dd>A bell character.
<br><dt><code>\d</code><dd>The date, in "Weekday Month Date" format (e.g., "Tue May 26").
<br><dt><code>\D{</code><var>format</var><code>}</code><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.
<br><dt><code>\e</code><dd>An escape character.
<br><dt><code>\h</code><dd>The hostname, up to the first `.'.
<br><dt><code>\H</code><dd>The hostname.
<br><dt><code>\j</code><dd>The number of jobs currently managed by the shell.
<br><dt><code>\l</code><dd>The basename of the shell's terminal device name.
<br><dt><code>\n</code><dd>A newline.
<br><dt><code>\r</code><dd>A carriage return.
<br><dt><code>\s</code><dd>The name of the shell, the basename of <code>$0</code> (the portion
following the final slash).
<br><dt><code>\t</code><dd>The time, in 24-hour HH:MM:SS format.
<br><dt><code>\T</code><dd>The time, in 12-hour HH:MM:SS format.
<br><dt><code>\@</code><dd>The time, in 12-hour am/pm format.
<br><dt><code>\A</code><dd>The time, in 24-hour HH:MM format.
<br><dt><code>\u</code><dd>The username of the current user.
<br><dt><code>\v</code><dd>The version of Bash (e.g., 2.00)
<br><dt><code>\V</code><dd>The release of Bash, version + patchlevel (e.g., 2.00.0)
<br><dt><code>\w</code><dd>The current working directory, with <samp><span class="env">$HOME</span></samp> abbreviated with a tilde.
<br><dt><code>\W</code><dd>The basename of <samp><span class="env">$PWD</span></samp>, with <samp><span class="env">$HOME</span></samp> abbreviated with a tilde.
<br><dt><code>\!</code><dd>The history number of this command.
<br><dt><code>\#</code><dd>The command number of this command.
<br><dt><code>\$</code><dd>If the effective uid is 0, <code>#</code>, otherwise <code>$</code>.
<br><dt><code>\</code><var>nnn</var><dd>The character whose ASCII code is the octal value <var>nnn</var>.
<br><dt><code>\\</code><dd>A backslash.
<br><dt><code>\[</code><dd>Begin a sequence of non-printing characters. This could be used to
embed a terminal control sequence into the prompt.
<br><dt><code>\]</code><dd>End a sequence of non-printing characters.
</dl>
<p>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.
<p>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="#Bash-Builtins">Bash Builtins</a>).
<div class="node">
<p><hr>
<a name="The-Restricted-Shell"></a>
Next: <a rel="next" accesskey="n" href="#Bash-POSIX-Mode">Bash POSIX Mode</a>,
Previous: <a rel="previous" accesskey="p" href="#Printing-a-Prompt">Printing a Prompt</a>,
Up: <a rel="up" accesskey="u" href="#Bash-Features">Bash Features</a>
</div>
<h3 class="section">6.10 The Restricted Shell</h3>
<p><a name="index-restricted-shell-250"></a>
If Bash is started with the name <code>rbash</code>, or the
<samp><span class="option">--restricted</span></samp>
or
<samp><span class="option">-r</span></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>Setting or unsetting the values of the <samp><span class="env">SHELL</span></samp>, <samp><span class="env">PATH</span></samp>,
<samp><span class="env">ENV</span></samp>, or <samp><span class="env">BASH_ENV</span></samp> variables.
<li>Specifying command names containing slashes.
<li>Specifying a filename containing a slash as an argument to the <code>.</code>
builtin command.
<li>Specifying a filename containing a slash as an argument to the <samp><span class="option">-p</span></samp>
option to the <code>hash</code> builtin command.
<li>Importing function definitions from the shell environment at startup.
<li>Parsing the value of <samp><span class="env">SHELLOPTS</span></samp> from the shell environment at startup.
<li>Redirecting output using the `<samp><span class="samp">></span></samp>', `<samp><span class="samp">>|</span></samp>', `<samp><span class="samp"><></span></samp>', `<samp><span class="samp">>&</span></samp>',
`<samp><span class="samp">&></span></samp>', and `<samp><span class="samp">>></span></samp>' redirection operators.
<li>Using the <code>exec</code> builtin to replace the shell with another command.
<li>Adding or deleting builtin commands with the
<samp><span class="option">-f</span></samp> and <samp><span class="option">-d</span></samp> options to the <code>enable</code> builtin.
<li>Using the <code>enable</code> builtin command to enable disabled shell builtins.
<li>Specifying the <samp><span class="option">-p</span></samp> option to the <code>command</code> builtin.
<li>Turning off restricted mode with `<samp><span class="samp">set +r</span></samp>' or `<samp><span class="samp">set +o restricted</span></samp>'.
</ul>
<p>These restrictions are enforced after any startup files are read.
<p>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.
<div class="node">
<p><hr>
<a name="Bash-POSIX-Mode"></a>
Previous: <a rel="previous" accesskey="p" href="#The-Restricted-Shell">The Restricted Shell</a>,
Up: <a rel="up" accesskey="u" href="#Bash-Features">Bash Features</a>
</div>
<h3 class="section">6.11 Bash POSIX Mode</h3>
<p><a name="index-POSIX-Mode-251"></a>
Starting Bash with the <samp><span class="option">--posix</span></samp> command-line option or executing
`<samp><span class="samp">set -o posix</span></samp>' while Bash is running will cause Bash to conform more
closely to the <span class="sc">posix</span> standard by changing the behavior to
match that specified by <span class="sc">posix</span> in areas where the Bash default differs.
<p>When invoked as <code>sh</code>, Bash enters <span class="sc">posix</span> mode after reading the
startup files.
<p>The following list is what's changed when `<span class="sc">posix</span> mode' is in effect:
<ol type=1 start=1>
<li>When a command in the hash table no longer exists, Bash will re-search
<samp><span class="env">$PATH</span></samp> to find the new location. This is also available with
`<samp><span class="samp">shopt -s checkhash</span></samp>'.
<li>The message printed by the job control code and builtins when a job
exits with a non-zero status is `Done(status)'.
<li>The message printed by the job control code and builtins when a job
is stopped is `Stopped(<var>signame</var>)', where <var>signame</var> is, for
example, <code>SIGTSTP</code>.
<li>The <code>bg</code> builtin uses the required format to describe each job placed
in the background, which does not include an indication of whether the job
is the current or previous job.
<li>Reserved words appearing in a context where reserved words are recognized
do not undergo alias expansion.
<li>The <span class="sc">posix</span> <samp><span class="env">PS1</span></samp> and <samp><span class="env">PS2</span></samp> expansions of `<samp><span class="samp">!</span></samp>' to
the history number and `<samp><span class="samp">!!</span></samp>' to `<samp><span class="samp">!</span></samp>' are enabled,
and parameter expansion is performed on the values of <samp><span class="env">PS1</span></samp> and
<samp><span class="env">PS2</span></samp> regardless of the setting of the <code>promptvars</code> option.
<li>The <span class="sc">posix</span> startup files are executed (<samp><span class="env">$ENV</span></samp>) rather than
the normal Bash files.
<li>Tilde expansion is only performed on assignments preceding a command
name, rather than on all assignment statements on the line.
<li>The default history file is <samp><span class="file">~/.sh_history</span></samp> (this is the
default value of <samp><span class="env">$HISTFILE</span></samp>).
<li>The output of `<samp><span class="samp">kill -l</span></samp>' prints all the signal names on a single line,
separated by spaces, without the `<samp><span class="samp">SIG</span></samp>' prefix.
<li>The <code>kill</code> builtin does not accept signal names with a `<samp><span class="samp">SIG</span></samp>'
prefix.
<li>Non-interactive shells exit if <var>filename</var> in <code>.</code> <var>filename</var>
is not found.
<li>Non-interactive shells exit if a syntax error in an arithmetic expansion
results in an invalid expression.
<li>Redirection operators do not perform filename expansion on the word
in the redirection unless the shell is interactive.
<li>Redirection operators do not perform word splitting on the word in the
redirection.
<li>Function names must be valid shell <code>name</code>s. That is, they may not
contain characters other than letters, digits, and underscores, and
may not start with a digit. Declaring a function with an invalid name
causes a fatal syntax error in non-interactive shells.
<li><span class="sc">posix</span> special builtins are found before shell functions
during command lookup.
<li>If a <span class="sc">posix</span> special builtin returns an error status, a
non-interactive shell exits. The fatal errors are those listed in
the POSIX standard, and include things like passing incorrect options,
redirection errors, variable assignment errors for assignments preceding
the command name, and so on.
<li>If <samp><span class="env">CDPATH</span></samp> is set, the <code>cd</code> builtin will not implicitly
append the current directory to it. This means that <code>cd</code> will
fail if no valid directory name can be constructed from
any of the entries in <samp><span class="env">$CDPATH</span></samp>, even if the a directory with
the same name as the name given as an argument to <code>cd</code> exists
in the current directory.
<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>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>Process substitution is not available.
<li>Assignment statements preceding <span class="sc">posix</span> special builtins
persist in the shell environment after the builtin completes.
<li>Assignment statements preceding shell function calls persist in the
shell environment after the function returns, as if a <span class="sc">posix</span>
special builtin command had been executed.
<li>The <code>export</code> and <code>readonly</code> builtin commands display their
output in the format required by <span class="sc">posix</span>.
<li>The <code>trap</code> builtin displays signal names without the leading
<code>SIG</code>.
<li>The <code>trap</code> builtin doesn'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 `<samp><span class="samp">-</span></samp>' as the
first argument.
<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 <samp><span class="env">PATH</span></samp>.
<li>Subshells spawned to execute command substitutions inherit the value of
the <samp><span class="option">-e</span></samp> option from the parent shell. When not in <span class="sc">posix</span> mode,
Bash clears the <samp><span class="option">-e</span></samp> option in such subshells.
<li>Alias expansion is always enabled, even in non-interactive shells.
<li>When the <code>alias</code> builtin displays alias definitions, it does not
display them with a leading `<samp><span class="samp">alias </span></samp>' unless the <samp><span class="option">-p</span></samp> option
is supplied.
<li>When the <code>set</code> builtin is invoked without options, it does not display
shell function names and definitions.
<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>When the <code>cd</code> builtin is invoked in <var>logical</var> mode, and the pathname
constructed from <code>$PWD</code> and the directory name supplied as an argument
does not refer to an existing directory, <code>cd</code> will fail instead of
falling back to <var>physical</var> mode.
<li>When the <code>pwd</code> builtin is supplied the <samp><span class="option">-P</span></samp> option, it resets
<code>$PWD</code> to a pathname containing no symlinks.
<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><span class="option">-P</span></samp> option.
<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>The default editor used by <code>fc</code> is <code>ed</code>.
<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>$PATH</code>.
<li>The <code>vi</code> editing mode will invoke the <code>vi</code> editor directly when
the `<samp><span class="samp">v</span></samp>' command is run, instead of checking <code>$FCEDIT</code> and
<code>$EDITOR</code>.
<li>When the <code>xpg_echo</code> option is enabled, Bash does not attempt to interpret
any arguments to <code>echo</code> as options. Each argument is displayed, after
escape characters are converted.
</ol>
<p>There is other <span class="sc">posix</span> behavior that Bash does not implement by
default even when in <span class="sc">posix</span> mode.
Specifically:
<ol type=1 start=1>
<li>The <code>fc</code> builtin checks <code>$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>As noted above, Bash requires the <code>xpg_echo</code> option to be enabled for
the <code>echo</code> builtin to be fully conformant.
</ol>
<p>Bash can be configured to be <span class="sc">posix</span>-conformant by default, by specifying
the <samp><span class="option">--enable-strict-posix-default</span></samp> to <code>configure</code> when building
(see <a href="#Optional-Features">Optional Features</a>).
<div class="node">
<p><hr>
<a name="Job-Control"></a>
Next: <a rel="next" accesskey="n" href="#Using-History-Interactively">Using History Interactively</a>,
Previous: <a rel="previous" accesskey="p" href="#Bash-Features">Bash Features</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="chapter">7 Job Control</h2>
<p>This chapter discusses what job control is, how it works, and how
Bash allows you to access its facilities.
<ul class="menu">
<li><a accesskey="1" href="#Job-Control-Basics">Job Control Basics</a>: How job control works.
<li><a accesskey="2" href="#Job-Control-Builtins">Job Control Builtins</a>: Bash builtin commands used to interact
with job control.
<li><a accesskey="3" href="#Job-Control-Variables">Job Control Variables</a>: Variables Bash uses to customize job
control.
</ul>
<div class="node">
<p><hr>
<a name="Job-Control-Basics"></a>
Next: <a rel="next" accesskey="n" href="#Job-Control-Builtins">Job Control Builtins</a>,
Up: <a rel="up" accesskey="u" href="#Job-Control">Job Control</a>
</div>
<h3 class="section">7.1 Job Control Basics</h3>
<p><a name="index-job-control-252"></a><a name="index-foreground-253"></a><a name="index-background-254"></a><a name="index-suspending-jobs-255"></a>
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 system's terminal driver and Bash.
<p>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:
<pre class="example"> [1] 25647
</pre>
<p class="noindent">indicating that this job is job number 1 and that the process <span class="sc">id</span>
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.
<p>To facilitate the implementation of the user interface to job
control, the operating system maintains the notion of a current terminal
process group <span class="sc">id</span>. Members of this process group (processes whose
process group <span class="sc">id</span> is equal to the current terminal process group
<span class="sc">id</span>) 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 <span class="sc">id</span> differs from the
terminal's; such processes are immune to keyboard-generated
signals. Only foreground processes are allowed to read from or
write to the terminal. Background processes which attempt to
read from (write to) the terminal are sent a <code>SIGTTIN</code>
(<code>SIGTTOU</code>) signal by the terminal driver, which, unless
caught, suspends the process.
<p>If the operating system on which Bash is running supports
job control, Bash contains facilities to use it. Typing the
<var>suspend</var> character (typically `<samp><span class="samp">^Z</span></samp>', Control-Z) while a
process is running causes that process to be stopped and returns
control to Bash. Typing the <var>delayed suspend</var> character
(typically `<samp><span class="samp">^Y</span></samp>', 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 `<samp><span class="samp">^Z</span></samp>'
takes effect immediately, and has the additional side effect of
causing pending output and typeahead to be discarded.
<p>There are a number of ways to refer to a job in the shell. The
character `<samp><span class="samp">%</span></samp>' introduces a job name.
<p>Job number <code>n</code> may be referred to as `<samp><span class="samp">%n</span></samp>'.
The symbols `<samp><span class="samp">%%</span></samp>' and `<samp><span class="samp">%+</span></samp>' refer to the shell'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 `<samp><span class="samp">%</span></samp>' (with no accompanying job specification) also refers
to the current job.
The previous job may be referenced using `<samp><span class="samp">%-</span></samp>'. In output
pertaining to jobs (e.g., the output of the <code>jobs</code> command),
the current job is always flagged with a `<samp><span class="samp">+</span></samp>', and the
previous job with a `<samp><span class="samp">-</span></samp>'.
<p>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, `<samp><span class="samp">%ce</span></samp>' refers
to a stopped <code>ce</code> job. Using `<samp><span class="samp">%?ce</span></samp>', on the
other hand, refers to any job containing the string `<samp><span class="samp">ce</span></samp>' in
its command line. If the prefix or substring matches more than one job,
Bash reports an error.
<p>Simply naming a job can be used to bring it into the foreground:
`<samp><span class="samp">%1</span></samp>' is a synonym for `<samp><span class="samp">fg %1</span></samp>', bringing job 1 from the
background into the foreground. Similarly, `<samp><span class="samp">%1 &</span></samp>' resumes
job 1 in the background, equivalent to `<samp><span class="samp">bg %1</span></samp>'
<p>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's status so as to not interrupt
any other output.
If the <samp><span class="option">-b</span></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.
<p>If an attempt to exit Bash is made while jobs are stopped, (or running, if
the <code>checkjobs</code> option is enabled – 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.
<div class="node">
<p><hr>
<a name="Job-Control-Builtins"></a>
Next: <a rel="next" accesskey="n" href="#Job-Control-Variables">Job Control Variables</a>,
Previous: <a rel="previous" accesskey="p" href="#Job-Control-Basics">Job Control Basics</a>,
Up: <a rel="up" accesskey="u" href="#Job-Control">Job Control</a>
</div>
<h3 class="section">7.2 Job Control Builtins</h3>
<dl>
<dt><code>bg</code><dd><a name="index-bg-256"></a>
<pre class="example"> bg [<var>jobspec</var> ...]
</pre>
<p>Resume each suspended job <var>jobspec</var> in the background, as if it
had been started with `<samp><span class="samp">&</span></samp>'.
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.
<br><dt><code>fg</code><dd><a name="index-fg-257"></a>
<pre class="example"> fg [<var>jobspec</var>]
</pre>
<p>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.
<br><dt><code>jobs</code><dd><a name="index-jobs-258"></a>
<pre class="example"> jobs [-lnprs] [<var>jobspec</var>]
jobs -x <var>command</var> [<var>arguments</var>]
</pre>
<p>The first form lists the active jobs. The options have the
following meanings:
<dl>
<dt><code>-l</code><dd>List process <span class="sc">id</span>s in addition to the normal information.
<br><dt><code>-n</code><dd>Display information only about jobs that have changed status since
the user was last notified of their status.
<br><dt><code>-p</code><dd>List only the process <span class="sc">id</span> of the job's process group leader.
<br><dt><code>-r</code><dd>Restrict output to running jobs.
<br><dt><code>-s</code><dd>Restrict output to stopped jobs.
</dl>
<p>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.
<p>If the <samp><span class="option">-x</span></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 <span class="sc">id</span>, and executes <var>command</var>,
passing it <var>argument</var>s, returning its exit status.
<br><dt><code>kill</code><dd><a name="index-kill-259"></a>
<pre class="example"> kill [-s <var>sigspec</var>] [-n <var>signum</var>] [-<var>sigspec</var>] <var>jobspec</var> or <var>pid</var>
kill -l [<var>exit_status</var>]
</pre>
<p>Send a signal specified by <var>sigspec</var> or <var>signum</var> to the process
named by job specification <var>jobspec</var> or process <span class="sc">id</span> <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><span class="option">-l</span></samp> option lists the signal names.
If any arguments are supplied when <samp><span class="option">-l</span></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 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.
<br><dt><code>wait</code><dd><a name="index-wait-260"></a>
<pre class="example"> wait [<var>jobspec</var> or <var>pid</var> ...]
</pre>
<p>Wait until the child process specified by each process <span class="sc">id</span> <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, all currently active child processes are
waited for, and the return status is zero.
If neither <var>jobspec</var> nor <var>pid</var> specifies an active child process
of the shell, the return status is 127.
<br><dt><code>disown</code><dd><a name="index-disown-261"></a>
<pre class="example"> disown [-ar] [-h] [<var>jobspec</var> ...]
</pre>
<p>Without options, each <var>jobspec</var> is removed from the table of
active jobs.
If the <samp><span class="option">-h</span></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><span class="option">-a</span></samp> nor <samp><span class="option">-r</span></samp>
option is supplied, the current job is used.
If no <var>jobspec</var> is supplied, the <samp><span class="option">-a</span></samp> option means to remove or
mark all jobs; the <samp><span class="option">-r</span></samp> option without a <var>jobspec</var>
argument restricts operation to running jobs.
<br><dt><code>suspend</code><dd><a name="index-suspend-262"></a>
<pre class="example"> suspend [-f]
</pre>
<p>Suspend the execution of this shell until it receives a
<code>SIGCONT</code> signal. The <samp><span class="option">-f</span></samp> option means to suspend
even if the shell is a login shell.
</dl>
<p>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 <span class="sc">id</span>s.
<div class="node">
<p><hr>
<a name="Job-Control-Variables"></a>
Previous: <a rel="previous" accesskey="p" href="#Job-Control-Builtins">Job Control Builtins</a>,
Up: <a rel="up" accesskey="u" href="#Job-Control">Job Control</a>
</div>
<h3 class="section">7.3 Job Control Variables</h3>
<dl>
<dt><code>auto_resume</code><a name="index-auto_005fresume-263"></a><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 `<samp><span class="samp">exact</span></samp>',
the string supplied must match the name of a stopped job exactly;
if set to `<samp><span class="samp">substring</span></samp>',
the string supplied needs to match a substring of the name of a
stopped job. The `<samp><span class="samp">substring</span></samp>' value provides functionality
analogous to the `<samp><span class="samp">%?</span></samp>' job <span class="sc">id</span> (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's name; this provides functionality
analogous to the `<samp><span class="samp">%</span></samp>' job <span class="sc">id</span>.
</dl>
<p><a name="index-Readline_002c-how-to-use-264"></a>
<!-- %**start of header (This is for running Texinfo on a region.) -->
<!-- %**end of header (This is for running Texinfo on a region.) -->
<!-- If you are including this manual as an appendix, then set the -->
<!-- variable readline-appendix. -->
<div class="node">
<p><hr>
<a name="Command-Line-Editing"></a>
Next: <a rel="next" accesskey="n" href="#Installing-Bash">Installing Bash</a>,
Previous: <a rel="previous" accesskey="p" href="#Using-History-Interactively">Using History Interactively</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="chapter">8 Command Line Editing</h2>
<p>This chapter describes the basic features of the <span class="sc">gnu</span>
command line editing interface.
Command line editing is provided by the Readline library, which is
used by several different programs, including Bash.
<ul class="menu">
<li><a accesskey="1" href="#Introduction-and-Notation">Introduction and Notation</a>: Notation used in this text.
<li><a accesskey="2" href="#Readline-Interaction">Readline Interaction</a>: The minimum set of commands for editing a line.
<li><a accesskey="3" href="#Readline-Init-File">Readline Init File</a>: Customizing Readline from a user's view.
<li><a accesskey="4" href="#Bindable-Readline-Commands">Bindable Readline Commands</a>: A description of most of the Readline commands
available for binding
<li><a accesskey="5" href="#Readline-vi-Mode">Readline vi Mode</a>: A short description of how to make Readline
behave like the vi editor.
<li><a accesskey="6" href="#Programmable-Completion">Programmable Completion</a>: How to specify the possible completions for
a specific command.
<li><a accesskey="7" href="#Programmable-Completion-Builtins">Programmable Completion Builtins</a>: Builtin commands to specify how to
complete arguments for a particular command.
</ul>
<div class="node">
<p><hr>
<a name="Introduction-and-Notation"></a>
Next: <a rel="next" accesskey="n" href="#Readline-Interaction">Readline Interaction</a>,
Up: <a rel="up" accesskey="u" href="#Command-Line-Editing">Command Line Editing</a>
</div>
<h3 class="section">8.1 Introduction to Line Editing</h3>
<p>The following paragraphs describe the notation used to represent
keystrokes.
<p>The text <kbd>C-k</kbd> is read as `Control-K' and describes the character
produced when the <k> key is pressed while the Control key
is depressed.
<p>The text <kbd>M-k</kbd> is read as `Meta-K' and describes the character
produced when the Meta key (if you have one) is depressed, and the <k>
key is pressed.
The Meta key is labeled <ALT> on many keyboards.
On keyboards with two keys labeled <ALT> (usually to either side of
the space bar), the <ALT> on the left side is generally set to
work as a Meta key.
The <ALT> 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.
<p>If you do not have a Meta or <ALT> key, or another key working as
a Meta key, the identical keystroke can be generated by typing <ESC>
<em>first</em>, and then typing <k>.
Either process is known as <dfn>metafying</dfn> the <k> key.
<p>The text <kbd>M-C-k</kbd> is read as `Meta-Control-k' and describes the
character produced by <dfn>metafying</dfn> <kbd>C-k</kbd>.
<p>In addition, several keys have their own names. Specifically,
<DEL>, <ESC>, <LFD>, <SPC>, <RET>, and <TAB> 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 <LFD> key, typing <C-j> will
produce the desired character.
The <RET> key may be labeled <Return> or <Enter> on
some keyboards.
<div class="node">
<p><hr>
<a name="Readline-Interaction"></a>
Next: <a rel="next" accesskey="n" href="#Readline-Init-File">Readline Init File</a>,
Previous: <a rel="previous" accesskey="p" href="#Introduction-and-Notation">Introduction and Notation</a>,
Up: <a rel="up" accesskey="u" href="#Command-Line-Editing">Command Line Editing</a>
</div>
<h3 class="section">8.2 Readline Interaction</h3>
<p><a name="index-interaction_002c-readline-265"></a>
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 <RET>. You do not have to be at the
end of the line to press <RET>; the entire line is accepted
regardless of the location of the cursor within the line.
<ul class="menu">
<li><a accesskey="1" href="#Readline-Bare-Essentials">Readline Bare Essentials</a>: The least you need to know about Readline.
<li><a accesskey="2" href="#Readline-Movement-Commands">Readline Movement Commands</a>: Moving about the input line.
<li><a accesskey="3" href="#Readline-Killing-Commands">Readline Killing Commands</a>: How to delete text, and how to get it back!
<li><a accesskey="4" href="#Readline-Arguments">Readline Arguments</a>: Giving numeric arguments to commands.
<li><a accesskey="5" href="#Searching">Searching</a>: Searching through previous lines.
</ul>
<div class="node">
<p><hr>
<a name="Readline-Bare-Essentials"></a>
Next: <a rel="next" accesskey="n" href="#Readline-Movement-Commands">Readline Movement Commands</a>,
Up: <a rel="up" accesskey="u" href="#Readline-Interaction">Readline Interaction</a>
</div>
<h4 class="subsection">8.2.1 Readline Bare Essentials</h4>
<p><a name="index-notation_002c-readline-266"></a><a name="index-command-editing-267"></a><a name="index-editing-command-lines-268"></a>
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.
<p>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>.
<p>When you add text in the middle of a line, you will notice that characters
to the right of the cursor are `pushed over' 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 `pulled back' 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>
<dt><kbd>C-b</kbd><dd>Move back one character.
<br><dt><kbd>C-f</kbd><dd>Move forward one character.
<br><dt><DEL> or <Backspace><dd>Delete the character to the left of the cursor.
<br><dt><kbd>C-d</kbd><dd>Delete the character underneath the cursor.
<br><dt>Printing characters<!-- /@w --><dd>Insert the character into the line at the cursor.
<br><dt><kbd>C-_</kbd> or <kbd>C-x C-u</kbd><dd>Undo the last editing command. You can undo all the way back to an
empty line.
</dl>
<p class="noindent">(Depending on your configuration, the <Backspace> key be set to
delete the character to the left of the cursor and the <DEL> key set
to delete the character underneath the cursor, like <kbd>C-d</kbd>, rather
than the character to the left of the cursor.)
<div class="node">
<p><hr>
<a name="Readline-Movement-Commands"></a>
Next: <a rel="next" accesskey="n" href="#Readline-Killing-Commands">Readline Killing Commands</a>,
Previous: <a rel="previous" accesskey="p" href="#Readline-Bare-Essentials">Readline Bare Essentials</a>,
Up: <a rel="up" accesskey="u" href="#Readline-Interaction">Readline Interaction</a>
</div>
<h4 class="subsection">8.2.2 Readline Movement Commands</h4>
<p>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 <DEL>. Here are some commands for moving more rapidly
about the line.
<dl>
<dt><kbd>C-a</kbd><dd>Move to the start of the line.
<br><dt><kbd>C-e</kbd><dd>Move to the end of the line.
<br><dt><kbd>M-f</kbd><dd>Move forward a word, where a word is composed of letters and digits.
<br><dt><kbd>M-b</kbd><dd>Move backward a word.
<br><dt><kbd>C-l</kbd><dd>Clear the screen, reprinting the current line at the top.
</dl>
<p>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.
<div class="node">
<p><hr>
<a name="Readline-Killing-Commands"></a>
Next: <a rel="next" accesskey="n" href="#Readline-Arguments">Readline Arguments</a>,
Previous: <a rel="previous" accesskey="p" href="#Readline-Movement-Commands">Readline Movement Commands</a>,
Up: <a rel="up" accesskey="u" href="#Readline-Interaction">Readline Interaction</a>
</div>
<h4 class="subsection">8.2.3 Readline Killing Commands</h4>
<p><a name="index-killing-text-269"></a><a name="index-yanking-text-270"></a>
<dfn>Killing</dfn> text means to delete the text from the line, but to save
it away for later use, usually by <dfn>yanking</dfn> (re-inserting)
it back into the line.
(`Cut' and `paste' are more recent jargon for `kill' and `yank'.)
<p>If the description for a command says that it `kills' text, then you can
be sure that you can get the text back in a different (or the same)
place later.
<p>When you use a kill command, the text is saved in a <dfn>kill-ring</dfn>.
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.
<a name="index-kill-ring-271"></a>
Here is the list of commands for killing text.
<dl>
<dt><kbd>C-k</kbd><dd>Kill the text from the current cursor position to the end of the line.
<br><dt><kbd>M-d</kbd><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>.
<br><dt><kbd>M-<DEL></kbd><dd>Kill from the cursor 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>.
<br><dt><kbd>C-w</kbd><dd>Kill from the cursor to the previous whitespace. This is different than
<kbd>M-<DEL></kbd> because the word boundaries differ.
</dl>
<p>Here is how to <dfn>yank</dfn> the text back into the line. Yanking
means to copy the most-recently-killed text from the kill buffer.
<dl>
<dt><kbd>C-y</kbd><dd>Yank the most recently killed text back into the buffer at the cursor.
<br><dt><kbd>M-y</kbd><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>.
</dl>
<div class="node">
<p><hr>
<a name="Readline-Arguments"></a>
Next: <a rel="next" accesskey="n" href="#Searching">Searching</a>,
Previous: <a rel="previous" accesskey="p" href="#Readline-Killing-Commands">Readline Killing Commands</a>,
Up: <a rel="up" accesskey="u" href="#Readline-Interaction">Readline Interaction</a>
</div>
<h4 class="subsection">8.2.4 Readline Arguments</h4>
<p>You can pass numeric arguments to Readline commands. Sometimes the
argument acts as a repeat count, other times it is the <i>sign</i> 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 `<samp><span class="samp">M-- C-k</span></samp>'.
<p>The general way to pass numeric arguments to a command is to type meta
digits before the command. If the first `digit' typed is a minus
sign (`<samp><span class="samp">-</span></samp>'), 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 `<samp><span class="samp">M-1 0 C-d</span></samp>',
which will delete the next ten characters on the input line.
<div class="node">
<p><hr>
<a name="Searching"></a>
Previous: <a rel="previous" accesskey="p" href="#Readline-Arguments">Readline Arguments</a>,
Up: <a rel="up" accesskey="u" href="#Readline-Interaction">Readline Interaction</a>
</div>
<h4 class="subsection">8.2.5 Searching for Commands in the History</h4>
<p>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: <dfn>incremental</dfn> and <dfn>non-incremental</dfn>.
<p>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 <ESC> 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.
<p>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 <RET> 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.
<p>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.
<p>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.
<div class="node">
<p><hr>
<a name="Readline-Init-File"></a>
Next: <a rel="next" accesskey="n" href="#Bindable-Readline-Commands">Bindable Readline Commands</a>,
Previous: <a rel="previous" accesskey="p" href="#Readline-Interaction">Readline Interaction</a>,
Up: <a rel="up" accesskey="u" href="#Command-Line-Editing">Command Line Editing</a>
</div>
<h3 class="section">8.3 Readline Init File</h3>
<p><a name="index-initialization-file_002c-readline-272"></a>
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 <dfn>inputrc</dfn> file, conventionally in his home directory.
The name of this
file is taken from the value of the shell variable <samp><span class="env">INPUTRC</span></samp>. If
that variable is unset, the default is <samp><span class="file">~/.inputrc</span></samp>. If that
file does not exist or cannot be read, the ultimate default is
<samp><span class="file">/etc/inputrc</span></samp>.
<p>When a program which uses the Readline library starts up, the
init file is read, and the key bindings are set.
<p>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="menu">
<li><a accesskey="1" href="#Readline-Init-File-Syntax">Readline Init File Syntax</a>: Syntax for the commands in the inputrc file.
<li><a accesskey="2" href="#Conditional-Init-Constructs">Conditional Init Constructs</a>: Conditional key bindings in the inputrc file.
<li><a accesskey="3" href="#Sample-Init-File">Sample Init File</a>: An example inputrc file.
</ul>
<div class="node">
<p><hr>
<a name="Readline-Init-File-Syntax"></a>
Next: <a rel="next" accesskey="n" href="#Conditional-Init-Constructs">Conditional Init Constructs</a>,
Up: <a rel="up" accesskey="u" href="#Readline-Init-File">Readline Init File</a>
</div>
<h4 class="subsection">8.3.1 Readline Init File Syntax</h4>
<p>There are only a few basic constructs allowed in the
Readline init file. Blank lines are ignored.
Lines beginning with a `<samp><span class="samp">#</span></samp>' are comments.
Lines beginning with a `<samp><span class="samp">$</span></samp>' indicate conditional
constructs (see <a href="#Conditional-Init-Constructs">Conditional Init Constructs</a>). Other lines
denote variable settings and key bindings.
<dl>
<dt>Variable Settings<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:
<pre class="example"> set <var>variable</var> <var>value</var>
</pre>
<p class="noindent">Here, for example, is how to
change from the default Emacs-like key binding to use
<code>vi</code> line editing commands:
<pre class="example"> set editing-mode vi
</pre>
<p>Variable names and values, where appropriate, are recognized without regard
to case. Unrecognized variable names are ignored.
<p>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.
<p>The <code>bind -V</code><!-- /@w --> command lists the current Readline variable names
and values. See <a href="#Bash-Builtins">Bash Builtins</a>.
<p>A great deal of run-time behavior is changeable with the following
variables.
<p><a name="index-variables_002c-readline-273"></a>
<dl>
<dt><code>bell-style</code><dd><a name="index-bell_002dstyle-274"></a>Controls what happens when Readline wants to ring the terminal bell.
If set to `<samp><span class="samp">none</span></samp>', Readline never rings the bell. If set to
`<samp><span class="samp">visible</span></samp>', Readline uses a visible bell if one is available.
If set to `<samp><span class="samp">audible</span></samp>' (the default), Readline attempts to ring
the terminal's bell.
<br><dt><code>bind-tty-special-chars</code><dd><a name="index-bind_002dtty_002dspecial_002dchars-275"></a>If set to `<samp><span class="samp">on</span></samp>', Readline attempts to bind the control characters
treated specially by the kernel's terminal driver to their Readline
equivalents.
<br><dt><code>comment-begin</code><dd><a name="index-comment_002dbegin-276"></a>The string to insert at the beginning of the line when the
<code>insert-comment</code> command is executed. The default value
is <code>"#"</code>.
<br><dt><code>completion-ignore-case</code><dd>If set to `<samp><span class="samp">on</span></samp>', Readline performs filename matching and completion
in a case-insensitive fashion.
The default value is `<samp><span class="samp">off</span></samp>'.
<br><dt><code>completion-query-items</code><dd><a name="index-completion_002dquery_002ditems-277"></a>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 this value,
Readline will ask the user whether or not he wishes to view
them; otherwise, they are simply listed.
This variable must be set to an integer value greater than or equal to 0.
A negative value means Readline should never ask.
The default limit is <code>100</code>.
<br><dt><code>convert-meta</code><dd><a name="index-convert_002dmeta-278"></a>If set to `<samp><span class="samp">on</span></samp>', Readline will convert characters with the
eighth bit set to an <span class="sc">ascii</span> key sequence by stripping the eighth
bit and prefixing an <ESC> character, converting them to a
meta-prefixed key sequence. The default value is `<samp><span class="samp">on</span></samp>'.
<br><dt><code>disable-completion</code><dd><a name="index-disable_002dcompletion-279"></a>If set to `<samp><span class="samp">On</span></samp>', 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 `<samp><span class="samp">off</span></samp>'.
<br><dt><code>editing-mode</code><dd><a name="index-editing_002dmode-280"></a>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 `<samp><span class="samp">emacs</span></samp>' or `<samp><span class="samp">vi</span></samp>'.
<br><dt><code>enable-keypad</code><dd><a name="index-enable_002dkeypad-281"></a>When set to `<samp><span class="samp">on</span></samp>', Readline will try to enable the application
keypad when it is called. Some systems need this to enable the
arrow keys. The default is `<samp><span class="samp">off</span></samp>'.
<br><dt><code>expand-tilde</code><dd><a name="index-expand_002dtilde-282"></a>If set to `<samp><span class="samp">on</span></samp>', tilde expansion is performed when Readline
attempts word completion. The default is `<samp><span class="samp">off</span></samp>'.
<br><dt><code>history-preserve-point</code><dd><a name="index-history_002dpreserve_002dpoint-283"></a>If set to `<samp><span class="samp">on</span></samp>', the history code attempts to place point at the
same location on each history line retrieved with <code>previous-history</code>
or <code>next-history</code>. The default is `<samp><span class="samp">off</span></samp>'.
<br><dt><code>horizontal-scroll-mode</code><dd><a name="index-horizontal_002dscroll_002dmode-284"></a>This variable can be set to either `<samp><span class="samp">on</span></samp>' or `<samp><span class="samp">off</span></samp>'. Setting it
to `<samp><span class="samp">on</span></samp>' 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. By default,
this variable is set to `<samp><span class="samp">off</span></samp>'.
<br><dt><code>input-meta</code><dd><a name="index-input_002dmeta-285"></a><a name="index-meta_002dflag-286"></a>If set to `<samp><span class="samp">on</span></samp>', 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 `<samp><span class="samp">off</span></samp>'. The name <code>meta-flag</code> is a
synonym for this variable.
<br><dt><code>isearch-terminators</code><dd><a name="index-isearch_002dterminators-287"></a>The string of characters that should terminate an incremental search without
subsequently executing the character as a command (see <a href="#Searching">Searching</a>).
If this variable has not been given a value, the characters <ESC> and
<kbd>C-J</kbd> will terminate an incremental search.
<br><dt><code>keymap</code><dd><a name="index-keymap-288"></a>Sets Readline's idea of the current keymap for key binding commands.
Acceptable <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>emacs</code> is
equivalent to <code>emacs-standard</code>. The default value is <code>emacs</code>.
The value of the <code>editing-mode</code> variable also affects the
default keymap.
<br><dt><code>mark-directories</code><dd>If set to `<samp><span class="samp">on</span></samp>', completed directory names have a slash
appended. The default is `<samp><span class="samp">on</span></samp>'.
<br><dt><code>mark-modified-lines</code><dd><a name="index-mark_002dmodified_002dlines-289"></a>This variable, when set to `<samp><span class="samp">on</span></samp>', causes Readline to display an
asterisk (`<samp><span class="samp">*</span></samp>') at the start of history lines which have been modified.
This variable is `<samp><span class="samp">off</span></samp>' by default.
<br><dt><code>mark-symlinked-directories</code><dd><a name="index-mark_002dsymlinked_002ddirectories-290"></a>If set to `<samp><span class="samp">on</span></samp>', completed names which are symbolic links
to directories have a slash appended (subject to the value of
<code>mark-directories</code>).
The default is `<samp><span class="samp">off</span></samp>'.
<br><dt><code>match-hidden-files</code><dd><a name="index-match_002dhidden_002dfiles-291"></a>This variable, when set to `<samp><span class="samp">on</span></samp>', causes Readline to match files whose
names begin with a `<samp><span class="samp">.</span></samp>' (hidden files) when performing filename
completion, unless the leading `<samp><span class="samp">.</span></samp>' is
supplied by the user in the filename to be completed.
This variable is `<samp><span class="samp">on</span></samp>' by default.
<br><dt><code>output-meta</code><dd><a name="index-output_002dmeta-292"></a>If set to `<samp><span class="samp">on</span></samp>', Readline will display characters with the
eighth bit set directly rather than as a meta-prefixed escape
sequence. The default is `<samp><span class="samp">off</span></samp>'.
<br><dt><code>page-completions</code><dd><a name="index-page_002dcompletions-293"></a>If set to `<samp><span class="samp">on</span></samp>', Readline uses an internal <code>more</code>-like pager
to display a screenful of possible completions at a time.
This variable is `<samp><span class="samp">on</span></samp>' by default.
<br><dt><code>print-completions-horizontally</code><dd>If set to `<samp><span class="samp">on</span></samp>', Readline will display completions with matches
sorted horizontally in alphabetical order, rather than down the screen.
The default is `<samp><span class="samp">off</span></samp>'.
<br><dt><code>show-all-if-ambiguous</code><dd><a name="index-show_002dall_002dif_002dambiguous-294"></a>This alters the default behavior of the completion functions. If
set to `<samp><span class="samp">on</span></samp>',
words which have more than one possible completion cause the
matches to be listed immediately instead of ringing the bell.
The default value is `<samp><span class="samp">off</span></samp>'.
<br><dt><code>show-all-if-unmodified</code><dd><a name="index-show_002dall_002dif_002dunmodified-295"></a>This alters the default behavior of the completion functions in
a fashion similar to <var>show-all-if-ambiguous</var>.
If set to `<samp><span class="samp">on</span></samp>',
words which have more than one possible completion without any
possible partial completion (the possible completions don't share
a common prefix) cause the matches to be listed immediately instead
of ringing the bell.
The default value is `<samp><span class="samp">off</span></samp>'.
<br><dt><code>visible-stats</code><dd><a name="index-visible_002dstats-296"></a>If set to `<samp><span class="samp">on</span></samp>', a character denoting a file's type
is appended to the filename when listing possible
completions. The default is `<samp><span class="samp">off</span></samp>'.
</dl>
<br><dt>Key Bindings<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.
<p>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 – 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.
<p>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>).
<p>The <code>bind -p</code><!-- /@w --> command displays Readline function names and
bindings in a format that can put directly into an initialization file.
See <a href="#Bash-Builtins">Bash Builtins</a>.
<dl>
<dt><var>keyname</var>: <var>function-name</var> or <var>macro</var><!-- /@w --><dd><var>keyname</var> is the name of a key spelled out in English. For example:
<pre class="example"> Control-u: universal-argument
Meta-Rubout: backward-kill-word
Control-o: "> output"
</pre>
<p>In the above example, <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
`<samp><span class="samp">> output</span></samp>' into the line).
<p>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>.
<br><dt>"<var>keyseq</var>": <var>function-name</var> or <var>macro</var><!-- /@w --><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 <span class="sc">gnu</span> Emacs style key
escapes can be used, as in the following example, but the
special character names are not recognized.
<pre class="example"> "\C-u": universal-argument
"\C-x\C-r": re-read-init-file
"\e[11~": "Function Key 1"
</pre>
<p>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),
`<samp><kbd>C-x</kbd> <kbd>C-r</kbd></samp>' is bound to the function <code>re-read-init-file</code>,
and `<samp><span class="samp"><ESC> <[> <1> <1> <~></span></samp>' is bound to insert
the text `<samp><span class="samp">Function Key 1</span></samp>'.
</dl>
<p>The following <span class="sc">gnu</span> Emacs style escape sequences are available when
specifying key sequences:
<dl>
<dt><kbd>\C-</kbd><dd>control prefix
<br><dt><kbd>\M-</kbd><dd>meta prefix
<br><dt><kbd>\e</kbd><dd>an escape character
<br><dt><kbd>\\</kbd><dd>backslash
<br><dt><kbd>\"</kbd><dd><">, a double quotation mark
<br><dt><kbd>\'</kbd><dd><'>, a single quote or apostrophe
</dl>
<p>In addition to the <span class="sc">gnu</span> Emacs style escape sequences, a second
set of backslash escapes is available:
<dl>
<dt><code>\a</code><dd>alert (bell)
<br><dt><code>\b</code><dd>backspace
<br><dt><code>\d</code><dd>delete
<br><dt><code>\f</code><dd>form feed
<br><dt><code>\n</code><dd>newline
<br><dt><code>\r</code><dd>carriage return
<br><dt><code>\t</code><dd>horizontal tab
<br><dt><code>\v</code><dd>vertical tab
<br><dt><code>\</code><var>nnn</var><dd>the eight-bit character whose value is the octal value <var>nnn</var>
(one to three digits)
<br><dt><code>\x</code><var>HH</var><dd>the eight-bit character whose value is the hexadecimal value <var>HH</var>
(one or two hex digits)
</dl>
<p>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 `<samp><span class="samp">"</span></samp>' and `<samp><span class="samp">'</span></samp>'.
For example, the following binding will make `<samp><kbd>C-x</kbd><span class="samp"> \</span></samp>'
insert a single `<samp><span class="samp">\</span></samp>' into the line:
<pre class="example"> "\C-x\\": "\\"
</pre>
</dl>
<div class="node">
<p><hr>
<a name="Conditional-Init-Constructs"></a>
Next: <a rel="next" accesskey="n" href="#Sample-Init-File">Sample Init File</a>,
Previous: <a rel="previous" accesskey="p" href="#Readline-Init-File-Syntax">Readline Init File Syntax</a>,
Up: <a rel="up" accesskey="u" href="#Readline-Init-File">Readline Init File</a>
</div>
<h4 class="subsection">8.3.2 Conditional Init Constructs</h4>
<p>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>
<dt><code>$if</code><dd>The <code>$if</code> construct allows bindings to be made based on the
editing mode, the terminal being used, or the application using
Readline. The text of the test extends to the end of the line;
no characters are required to isolate it.
<dl>
<dt><code>mode</code><dd>The <code>mode=</code> form of the <code>$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 `<samp><span class="samp">set keymap</span></samp>' 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.
<br><dt><code>term</code><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's function keys. The word on the right side of the
`<samp><span class="samp">=</span></samp>' is tested against both the full name of the terminal and
the portion of the terminal name before the first `<samp><span class="samp">-</span></samp>'. This
allows <code>sun</code> to match both <code>sun</code> and <code>sun-cmd</code>,
for instance.
<br><dt><code>application</code><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:
<pre class="example"> $if Bash
# Quote the current or previous word
"\C-xq": "\eb\"\ef\""
$endif
</pre>
</dl>
<br><dt><code>$endif</code><dd>This command, as seen in the previous example, terminates an
<code>$if</code> command.
<br><dt><code>$else</code><dd>Commands in this branch of the <code>$if</code> directive are executed if
the test fails.
<br><dt><code>$include</code><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><span class="file">/etc/inputrc</span></samp>:
<pre class="example"> $include /etc/inputrc
</pre>
</dl>
<div class="node">
<p><hr>
<a name="Sample-Init-File"></a>
Previous: <a rel="previous" accesskey="p" href="#Conditional-Init-Constructs">Conditional Init Constructs</a>,
Up: <a rel="up" accesskey="u" href="#Readline-Init-File">Readline Init File</a>
</div>
<h4 class="subsection">8.3.3 Sample Init File</h4>
<p>Here is an example of an <var>inputrc</var> file. This illustrates key
binding, variable assignment, and conditional syntax.
<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 systemwide 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
#
#"\M-OD": backward-char
#"\M-OC": forward-char
#"\M-OA": previous-history
#"\M-OB": next-history
#
# Arrow keys in ANSI mode
#
"\M-[D": backward-char
"\M-[C": forward-char
"\M-[A": previous-history
"\M-[B": next-history
#
# Arrow keys in 8 bit keypad mode
#
#"\M-\C-OD": backward-char
#"\M-\C-OC": forward-char
#"\M-\C-OA": previous-history
#"\M-\C-OB": next-history
#
# Arrow keys in 8 bit ANSI mode
#
#"\M-\C-[D": backward-char
#"\M-\C-[C": forward-char
#"\M-\C-[A": previous-history
#"\M-\C-[B": 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
$if Bash
# edit the path
"\C-xp": "PATH=${PATH}\e\C-e\C-a\ef\C-f"
# prepare to type a quoted word --
# insert open and close double quotes
# and move to just after the open quote
"\C-x\"": "\"\"\C-b"
# insert a backslash (testing backslash escapes
# in sequences and macros)
"\C-x\\": "\\"
# Quote the current or previous word
"\C-xq": "\eb\"\ef\""
# Add a binding to refresh the line, which is unbound
"\C-xr": redraw-current-line
# Edit variable on current line.
"\M-\C-v": "\C-a\C-k$\C-y\M-\C-e\C-a\C-y="
$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 more than 150 possible completions for
# a word, ask the user if he wants to see all of them
set completion-query-items 150
# For FTP
$if Ftp
"\C-xg": "get \M-?"
"\C-xt": "put \M-?"
"\M-.": yank-last-arg
$endif
</pre>
<div class="node">
<p><hr>
<a name="Bindable-Readline-Commands"></a>
Next: <a rel="next" accesskey="n" href="#Readline-vi-Mode">Readline vi Mode</a>,
Previous: <a rel="previous" accesskey="p" href="#Readline-Init-File">Readline Init File</a>,
Up: <a rel="up" accesskey="u" href="#Command-Line-Editing">Command Line Editing</a>
</div>
<h3 class="section">8.4 Bindable Readline Commands</h3>
<ul class="menu">
<li><a accesskey="1" href="#Commands-For-Moving">Commands For Moving</a>: Moving about the line.
<li><a accesskey="2" href="#Commands-For-History">Commands For History</a>: Getting at previous lines.
<li><a accesskey="3" href="#Commands-For-Text">Commands For Text</a>: Commands for changing text.
<li><a accesskey="4" href="#Commands-For-Killing">Commands For Killing</a>: Commands for killing and yanking.
<li><a accesskey="5" href="#Numeric-Arguments">Numeric Arguments</a>: Specifying numeric arguments, repeat counts.
<li><a accesskey="6" href="#Commands-For-Completion">Commands For Completion</a>: Getting Readline to do the typing for you.
<li><a accesskey="7" href="#Keyboard-Macros">Keyboard Macros</a>: Saving and re-executing typed characters
<li><a accesskey="8" href="#Miscellaneous-Commands">Miscellaneous Commands</a>: Other miscellaneous commands.
</ul>
<p>This section describes Readline commands that may be bound to key
sequences.
You can list your key bindings by executing
<code>bind -P</code><!-- /@w --> or, for a more terse format, suitable for an
<var>inputrc</var> file, <code>bind -p</code><!-- /@w -->. (See <a href="#Bash-Builtins">Bash Builtins</a>.)
Command names without an accompanying key sequence are unbound by default.
<p>In the following descriptions, <dfn>point</dfn> refers to the current cursor
position, and <dfn>mark</dfn> 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 <dfn>region</dfn>.
<div class="node">
<p><hr>
<a name="Commands-For-Moving"></a>
Next: <a rel="next" accesskey="n" href="#Commands-For-History">Commands For History</a>,
Up: <a rel="up" accesskey="u" href="#Bindable-Readline-Commands">Bindable Readline Commands</a>
</div>
<h4 class="subsection">8.4.1 Commands For Moving</h4>
<dl>
<dt><code>beginning-of-line (C-a)</code><a name="index-beginning_002dof_002dline-_0028C_002da_0029-297"></a><dd>Move to the start of the current line.
<br><dt><code>end-of-line (C-e)</code><a name="index-end_002dof_002dline-_0028C_002de_0029-298"></a><dd>Move to the end of the line.
<br><dt><code>forward-char (C-f)</code><a name="index-forward_002dchar-_0028C_002df_0029-299"></a><dd>Move forward a character.
<br><dt><code>backward-char (C-b)</code><a name="index-backward_002dchar-_0028C_002db_0029-300"></a><dd>Move back a character.
<br><dt><code>forward-word (M-f)</code><a name="index-forward_002dword-_0028M_002df_0029-301"></a><dd>Move forward to the end of the next word. Words are composed of
letters and digits.
<br><dt><code>backward-word (M-b)</code><a name="index-backward_002dword-_0028M_002db_0029-302"></a><dd>Move back to the start of the current or previous word. Words are
composed of letters and digits.
<br><dt><code>clear-screen (C-l)</code><a name="index-clear_002dscreen-_0028C_002dl_0029-303"></a><dd>Clear the screen and redraw the current line,
leaving the current line at the top of the screen.
<br><dt><code>redraw-current-line ()</code><a name="index-redraw_002dcurrent_002dline-_0028_0029-304"></a><dd>Refresh the current line. By default, this is unbound.
</dl>
<div class="node">
<p><hr>
<a name="Commands-For-History"></a>
Next: <a rel="next" accesskey="n" href="#Commands-For-Text">Commands For Text</a>,
Previous: <a rel="previous" accesskey="p" href="#Commands-For-Moving">Commands For Moving</a>,
Up: <a rel="up" accesskey="u" href="#Bindable-Readline-Commands">Bindable Readline Commands</a>
</div>
<h4 class="subsection">8.4.2 Commands For Manipulating The History</h4>
<dl>
<dt><code>accept-line (Newline or Return)</code><a name="index-accept_002dline-_0028Newline-or-Return_0029-305"></a><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 <samp><span class="env">HISTCONTROL</span></samp> and <samp><span class="env">HISTIGNORE</span></samp> variables.
If this line is a modified history line, then restore the history line
to its original state.
<br><dt><code>previous-history (C-p)</code><a name="index-previous_002dhistory-_0028C_002dp_0029-306"></a><dd>Move `back' through the history list, fetching the previous command.
<br><dt><code>next-history (C-n)</code><a name="index-next_002dhistory-_0028C_002dn_0029-307"></a><dd>Move `forward' through the history list, fetching the next command.
<br><dt><code>beginning-of-history (M-<)</code><a name="index-beginning_002dof_002dhistory-_0028M_002d_003c_0029-308"></a><dd>Move to the first line in the history.
<br><dt><code>end-of-history (M->)</code><a name="index-end_002dof_002dhistory-_0028M_002d_003e_0029-309"></a><dd>Move to the end of the input history, i.e., the line currently
being entered.
<br><dt><code>reverse-search-history (C-r)</code><a name="index-reverse_002dsearch_002dhistory-_0028C_002dr_0029-310"></a><dd>Search backward starting at the current line and moving `up' through
the history as necessary. This is an incremental search.
<br><dt><code>forward-search-history (C-s)</code><a name="index-forward_002dsearch_002dhistory-_0028C_002ds_0029-311"></a><dd>Search forward starting at the current line and moving `down' through
the the history as necessary. This is an incremental search.
<br><dt><code>non-incremental-reverse-search-history (M-p)</code><a name="index-non_002dincremental_002dreverse_002dsearch_002dhistory-_0028M_002dp_0029-312"></a><dd>Search backward starting at the current line and moving `up'
through the history as necessary using a non-incremental search
for a string supplied by the user.
<br><dt><code>non-incremental-forward-search-history (M-n)</code><a name="index-non_002dincremental_002dforward_002dsearch_002dhistory-_0028M_002dn_0029-313"></a><dd>Search forward starting at the current line and moving `down'
through the the history as necessary using a non-incremental search
for a string supplied by the user.
<br><dt><code>history-search-forward ()</code><a name="index-history_002dsearch_002dforward-_0028_0029-314"></a><dd>Search forward through the history for the string of characters
between the start of the current line and the point.
This is a non-incremental search.
By default, this command is unbound.
<br><dt><code>history-search-backward ()</code><a name="index-history_002dsearch_002dbackward-_0028_0029-315"></a><dd>Search backward through the history for the string of characters
between the start of the current line and the point. This
is a non-incremental search. By default, this command is unbound.
<br><dt><code>yank-nth-arg (M-C-y)</code><a name="index-yank_002dnth_002darg-_0028M_002dC_002dy_0029-316"></a><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 `<samp><span class="samp">!</span><var>n</var></samp>' history expansion had been specified.
<br><dt><code>yank-last-arg (M-. or M-_)</code><a name="index-yank_002dlast_002darg-_0028M_002d_002e-or-M_002d_005f_0029-317"></a><dd>Insert last argument to the previous command (the last word of the
previous history entry). With an
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 argument of each line in turn.
The history expansion facilities are used to extract the last argument,
as if the `<samp><span class="samp">!$</span></samp>' history expansion had been specified.
</dl>
<div class="node">
<p><hr>
<a name="Commands-For-Text"></a>
Next: <a rel="next" accesskey="n" href="#Commands-For-Killing">Commands For Killing</a>,
Previous: <a rel="previous" accesskey="p" href="#Commands-For-History">Commands For History</a>,
Up: <a rel="up" accesskey="u" href="#Bindable-Readline-Commands">Bindable Readline Commands</a>
</div>
<h4 class="subsection">8.4.3 Commands For Changing Text</h4>
<dl>
<dt><code>delete-char (C-d)</code><a name="index-delete_002dchar-_0028C_002dd_0029-318"></a><dd>Delete the character at point. If point is at the
beginning of the line, there are no characters in the line, and
the last character typed was not bound to <code>delete-char</code>, then
return <span class="sc">eof</span>.
<br><dt><code>backward-delete-char (Rubout)</code><a name="index-backward_002ddelete_002dchar-_0028Rubout_0029-319"></a><dd>Delete the character behind the cursor. A numeric argument means
to kill the characters instead of deleting them.
<br><dt><code>forward-backward-delete-char ()</code><a name="index-forward_002dbackward_002ddelete_002dchar-_0028_0029-320"></a><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.
<br><dt><code>quoted-insert (C-q or C-v)</code><a name="index-quoted_002dinsert-_0028C_002dq-or-C_002dv_0029-321"></a><dd>Add the next character typed to the line verbatim. This is
how to insert key sequences like <kbd>C-q</kbd>, for example.
<br><dt><code>self-insert (a, b, A, 1, !, ...)</code><a name="index-self_002dinsert-_0028a_002c-b_002c-A_002c-1_002c-_0021_002c-_0040dots_007b_007d_0029-322"></a><dd>Insert yourself.
<br><dt><code>transpose-chars (C-t)</code><a name="index-transpose_002dchars-_0028C_002dt_0029-323"></a><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.
<br><dt><code>transpose-words (M-t)</code><a name="index-transpose_002dwords-_0028M_002dt_0029-324"></a><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.
<br><dt><code>upcase-word (M-u)</code><a name="index-upcase_002dword-_0028M_002du_0029-325"></a><dd>Uppercase the current (or following) word. With a negative argument,
uppercase the previous word, but do not move the cursor.
<br><dt><code>downcase-word (M-l)</code><a name="index-downcase_002dword-_0028M_002dl_0029-326"></a><dd>Lowercase the current (or following) word. With a negative argument,
lowercase the previous word, but do not move the cursor.
<br><dt><code>capitalize-word (M-c)</code><a name="index-capitalize_002dword-_0028M_002dc_0029-327"></a><dd>Capitalize the current (or following) word. With a negative argument,
capitalize the previous word, but do not move the cursor.
<br><dt><code>overwrite-mode ()</code><a name="index-overwrite_002dmode-_0028_0029-328"></a><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.
<p>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.
<p>By default, this command is unbound.
</dl>
<div class="node">
<p><hr>
<a name="Commands-For-Killing"></a>
Next: <a rel="next" accesskey="n" href="#Numeric-Arguments">Numeric Arguments</a>,
Previous: <a rel="previous" accesskey="p" href="#Commands-For-Text">Commands For Text</a>,
Up: <a rel="up" accesskey="u" href="#Bindable-Readline-Commands">Bindable Readline Commands</a>
</div>
<h4 class="subsection">8.4.4 Killing And Yanking</h4>
<dl>
<dt><code>kill-line (C-k)</code><a name="index-kill_002dline-_0028C_002dk_0029-329"></a><dd>Kill the text from point to the end of the line.
<br><dt><code>backward-kill-line (C-x Rubout)</code><a name="index-backward_002dkill_002dline-_0028C_002dx-Rubout_0029-330"></a><dd>Kill backward to the beginning of the line.
<br><dt><code>unix-line-discard (C-u)</code><a name="index-unix_002dline_002ddiscard-_0028C_002du_0029-331"></a><dd>Kill backward from the cursor to the beginning of the current line.
<br><dt><code>kill-whole-line ()</code><a name="index-kill_002dwhole_002dline-_0028_0029-332"></a><dd>Kill all characters on the current line, no matter where point is.
By default, this is unbound.
<br><dt><code>kill-word (M-d)</code><a name="index-kill_002dword-_0028M_002dd_0029-333"></a><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>.
<br><dt><code>backward-kill-word (M-<DEL>)</code><a name="index-backward_002dkill_002dword-_0028M_002d_0040key_007bDEL_007d_0029-334"></a><dd>Kill the word behind point.
Word boundaries are the same as <code>backward-word</code>.
<br><dt><code>unix-word-rubout (C-w)</code><a name="index-unix_002dword_002drubout-_0028C_002dw_0029-335"></a><dd>Kill the word behind point, using white space as a word boundary.
The killed text is saved on the kill-ring.
<br><dt><code>unix-filename-rubout ()</code><a name="index-unix_002dfilename_002drubout-_0028_0029-336"></a><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.
<br><dt><code>delete-horizontal-space ()</code><a name="index-delete_002dhorizontal_002dspace-_0028_0029-337"></a><dd>Delete all spaces and tabs around point. By default, this is unbound.
<br><dt><code>kill-region ()</code><a name="index-kill_002dregion-_0028_0029-338"></a><dd>Kill the text in the current region.
By default, this command is unbound.
<br><dt><code>copy-region-as-kill ()</code><a name="index-copy_002dregion_002das_002dkill-_0028_0029-339"></a><dd>Copy the text in the region to the kill buffer, so it can be yanked
right away. By default, this command is unbound.
<br><dt><code>copy-backward-word ()</code><a name="index-copy_002dbackward_002dword-_0028_0029-340"></a><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.
<br><dt><code>copy-forward-word ()</code><a name="index-copy_002dforward_002dword-_0028_0029-341"></a><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.
<br><dt><code>yank (C-y)</code><a name="index-yank-_0028C_002dy_0029-342"></a><dd>Yank the top of the kill ring into the buffer at point.
<br><dt><code>yank-pop (M-y)</code><a name="index-yank_002dpop-_0028M_002dy_0029-343"></a><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>.
</dl>
<div class="node">
<p><hr>
<a name="Numeric-Arguments"></a>
Next: <a rel="next" accesskey="n" href="#Commands-For-Completion">Commands For Completion</a>,
Previous: <a rel="previous" accesskey="p" href="#Commands-For-Killing">Commands For Killing</a>,
Up: <a rel="up" accesskey="u" href="#Bindable-Readline-Commands">Bindable Readline Commands</a>
</div>
<h4 class="subsection">8.4.5 Specifying Numeric Arguments</h4>
<dl>
<dt><code>digit-argument (</code><kbd>M-0</kbd><code>, </code><kbd>M-1</kbd><code>, ... </code><kbd>M--</kbd><code>)</code><a name="index-digit_002dargument-_0028_0040kbd_007bM_002d0_007d_002c-_0040kbd_007bM_002d1_007d_002c-_0040dots_007b_007d-_0040kbd_007bM_002d_002d_007d_0029-344"></a><dd>Add this digit to the argument already accumulating, or start a new
argument. <kbd>M--</kbd> starts a negative argument.
<br><dt><code>universal-argument ()</code><a name="index-universal_002dargument-_0028_0029-345"></a><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 or 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.
</dl>
<div class="node">
<p><hr>
<a name="Commands-For-Completion"></a>
Next: <a rel="next" accesskey="n" href="#Keyboard-Macros">Keyboard Macros</a>,
Previous: <a rel="previous" accesskey="p" href="#Numeric-Arguments">Numeric Arguments</a>,
Up: <a rel="up" accesskey="u" href="#Bindable-Readline-Commands">Bindable Readline Commands</a>
</div>
<h4 class="subsection">8.4.6 Letting Readline Type For You</h4>
<dl>
<dt><code>complete (<TAB>)</code><a name="index-complete-_0028_0040key_007bTAB_007d_0029-346"></a><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 `<samp><span class="samp">$</span></samp>'), username (if the text begins with
`<samp><span class="samp">~</span></samp>'), hostname (if the text begins with `<samp><span class="samp">@</span></samp>'), or
command (including aliases and functions) in turn. If none
of these produces a match, filename completion is attempted.
<br><dt><code>possible-completions (M-?)</code><a name="index-possible_002dcompletions-_0028M_002d_003f_0029-347"></a><dd>List the possible completions of the text before point.
<br><dt><code>insert-completions (M-*)</code><a name="index-insert_002dcompletions-_0028M_002d_002a_0029-348"></a><dd>Insert all completions of the text before point that would have
been generated by <code>possible-completions</code>.
<br><dt><code>menu-complete ()</code><a name="index-menu_002dcomplete-_0028_0029-349"></a><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 <TAB>, but is unbound
by default.
<br><dt><code>delete-char-or-list ()</code><a name="index-delete_002dchar_002dor_002dlist-_0028_0029-350"></a><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.
<br><dt><code>complete-filename (M-/)</code><dd>Attempt filename completion on the text before point.
<br><dt><code>possible-filename-completions (C-x /)</code><dd>List the possible completions of the text before point,
treating it as a filename.
<br><dt><code>complete-username (M-~)</code><dd>Attempt completion on the text before point, treating
it as a username.
<br><dt><code>possible-username-completions (C-x ~)</code><dd>List the possible completions of the text before point,
treating it as a username.
<br><dt><code>complete-variable (M-$)</code><dd>Attempt completion on the text before point, treating
it as a shell variable.
<br><dt><code>possible-variable-completions (C-x $)</code><dd>List the possible completions of the text before point,
treating it as a shell variable.
<br><dt><code>complete-hostname (M-@)</code><dd>Attempt completion on the text before point, treating
it as a hostname.
<br><dt><code>possible-hostname-completions (C-x @)</code><dd>List the possible completions of the text before point,
treating it as a hostname.
<br><dt><code>complete-command (M-!)</code><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.
<br><dt><code>possible-command-completions (C-x !)</code><dd>List the possible completions of the text before point,
treating it as a command name.
<br><dt><code>dynamic-complete-history (M-<TAB>)</code><dd>Attempt completion on the text before point, comparing
the text against lines from the history list for possible
completion matches.
<br><dt><code>complete-into-braces (M-{)</code><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>).
</dl>
<div class="node">
<p><hr>
<a name="Keyboard-Macros"></a>
Next: <a rel="next" accesskey="n" href="#Miscellaneous-Commands">Miscellaneous Commands</a>,
Previous: <a rel="previous" accesskey="p" href="#Commands-For-Completion">Commands For Completion</a>,
Up: <a rel="up" accesskey="u" href="#Bindable-Readline-Commands">Bindable Readline Commands</a>
</div>
<h4 class="subsection">8.4.7 Keyboard Macros</h4>
<dl>
<dt><code>start-kbd-macro (C-x ()</code><a name="index-start_002dkbd_002dmacro-_0028C_002dx-_0028_0029-351"></a><dd>Begin saving the characters typed into the current keyboard macro.
<br><dt><code>end-kbd-macro (C-x ))</code><a name="index-end_002dkbd_002dmacro-_0028C_002dx-_0029_0029-352"></a><dd>Stop saving the characters typed into the current keyboard macro
and save the definition.
<br><dt><code>call-last-kbd-macro (C-x e)</code><a name="index-call_002dlast_002dkbd_002dmacro-_0028C_002dx-e_0029-353"></a><dd>Re-execute the last keyboard macro defined, by making the characters
in the macro appear as if typed at the keyboard.
</dl>
<div class="node">
<p><hr>
<a name="Miscellaneous-Commands"></a>
Previous: <a rel="previous" accesskey="p" href="#Keyboard-Macros">Keyboard Macros</a>,
Up: <a rel="up" accesskey="u" href="#Bindable-Readline-Commands">Bindable Readline Commands</a>
</div>
<h4 class="subsection">8.4.8 Some Miscellaneous Commands</h4>
<dl>
<dt><code>re-read-init-file (C-x C-r)</code><a name="index-re_002dread_002dinit_002dfile-_0028C_002dx-C_002dr_0029-354"></a><dd>Read in the contents of the <var>inputrc</var> file, and incorporate
any bindings or variable assignments found there.
<br><dt><code>abort (C-g)</code><a name="index-abort-_0028C_002dg_0029-355"></a><dd>Abort the current editing command and
ring the terminal's bell (subject to the setting of
<code>bell-style</code>).
<br><dt><code>do-uppercase-version (M-a, M-b, M-</code><var>x</var><code>, ...)</code><a name="index-do_002duppercase_002dversion-_0028M_002da_002c-M_002db_002c-M_002d_0040var_007bx_007d_002c-_0040dots_007b_007d_0029-356"></a><dd>If the metafied character <var>x</var> is lowercase, run the command
that is bound to the corresponding uppercase character.
<br><dt><code>prefix-meta (<ESC>)</code><a name="index-prefix_002dmeta-_0028_0040key_007bESC_007d_0029-357"></a><dd>Metafy the next character typed. This is for keyboards
without a meta key. Typing `<samp><span class="samp"><ESC> f</span></samp>' is equivalent to typing
<kbd>M-f</kbd>.
<br><dt><code>undo (C-_ or C-x C-u)</code><a name="index-undo-_0028C_002d_005f-or-C_002dx-C_002du_0029-358"></a><dd>Incremental undo, separately remembered for each line.
<br><dt><code>revert-line (M-r)</code><a name="index-revert_002dline-_0028M_002dr_0029-359"></a><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.
<br><dt><code>tilde-expand (M-&)</code><dd>Perform tilde expansion on the current word.
<br><dt><code>set-mark (C-@)</code><a name="index-set_002dmark-_0028C_002d_0040_0040_0029-360"></a><dd>Set the mark to the point. If a
numeric argument is supplied, the mark is set to that position.
<br><dt><code>exchange-point-and-mark (C-x C-x)</code><a name="index-exchange_002dpoint_002dand_002dmark-_0028C_002dx-C_002dx_0029-361"></a><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.
<br><dt><code>character-search (C-])</code><a name="index-character_002dsearch-_0028C_002d_005d_0029-362"></a><dd>A character is read and point is moved to the next occurrence of that
character. A negative count searches for previous occurrences.
<br><dt><code>character-search-backward (M-C-])</code><a name="index-character_002dsearch_002dbackward-_0028M_002dC_002d_005d_0029-363"></a><dd>A character is read and point is moved to the previous occurrence
of that character. A negative count searches for subsequent
occurrences.
<br><dt><code>insert-comment (M-#)</code><a name="index-insert_002dcomment-_0028M_002d_0023_0029-364"></a><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.
<br><dt><code>dump-functions ()</code><a name="index-dump_002dfunctions-_0028_0029-365"></a><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.
<br><dt><code>dump-variables ()</code><a name="index-dump_002dvariables-_0028_0029-366"></a><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.
<br><dt><code>dump-macros ()</code><a name="index-dump_002dmacros-_0028_0029-367"></a><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.
<br><dt><code>glob-complete-word (M-g)</code><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.
<br><dt><code>glob-expand-word (C-x *)</code><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 `<samp><span class="samp">*</span></samp>' is appended before
pathname expansion.
<br><dt><code>glob-list-expansions (C-x g)</code><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 `<samp><span class="samp">*</span></samp>' is appended before
pathname expansion.
<br><dt><code>display-shell-version (C-x C-v)</code><dd>Display version information about the current instance of Bash.
<br><dt><code>shell-expand-line (M-C-e)</code><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>).
<br><dt><code>history-expand-line (M-^)</code><dd>Perform history expansion on the current line.
<br><dt><code>magic-space ()</code><dd>Perform history expansion on the current line and insert a space
(see <a href="#History-Interaction">History Interaction</a>).
<br><dt><code>alias-expand-line ()</code><dd>Perform alias expansion on the current line (see <a href="#Aliases">Aliases</a>).
<br><dt><code>history-and-alias-expand-line ()</code><dd>Perform history and alias expansion on the current line.
<br><dt><code>insert-last-argument (M-. or M-_)</code><dd>A synonym for <code>yank-last-arg</code>.
<br><dt><code>operate-and-get-next (C-o)</code><dd>Accept the current line for execution and fetch the next line
relative to the current line from the history for editing. Any
argument is ignored.
<br><dt><code>edit-and-execute-command (C-xC-e)</code><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.
</dl>
<div class="node">
<p><hr>
<a name="Readline-vi-Mode"></a>
Next: <a rel="next" accesskey="n" href="#Programmable-Completion">Programmable Completion</a>,
Previous: <a rel="previous" accesskey="p" href="#Bindable-Readline-Commands">Bindable Readline Commands</a>,
Up: <a rel="up" accesskey="u" href="#Command-Line-Editing">Command Line Editing</a>
</div>
<h3 class="section">8.5 Readline vi Mode</h3>
<p>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 <span class="sc">posix</span> 1003.2 standard.
<p>In order to switch interactively between <code>emacs</code> and <code>vi</code>
editing modes, use the `<samp><span class="samp">set -o emacs</span></samp>' and `<samp><span class="samp">set -o vi</span></samp>'
commands (see <a href="#The-Set-Builtin">The Set Builtin</a>).
The Readline default is <code>emacs</code> mode.
<p>When you enter a line in <code>vi</code> mode, you are already placed in
`insertion' mode, as if you had typed an `<samp><span class="samp">i</span></samp>'. Pressing <ESC>
switches you into `command' mode, where you can edit the text of the
line with the standard <code>vi</code> movement keys, move to previous
history lines with `<samp><span class="samp">k</span></samp>' and subsequent lines with `<samp><span class="samp">j</span></samp>', and
so forth.
<div class="node">
<p><hr>
<a name="Programmable-Completion"></a>
Next: <a rel="next" accesskey="n" href="#Programmable-Completion-Builtins">Programmable Completion Builtins</a>,
Previous: <a rel="previous" accesskey="p" href="#Readline-vi-Mode">Readline vi Mode</a>,
Up: <a rel="up" accesskey="u" href="#Command-Line-Editing">Command Line Editing</a>
</div>
<h3 class="section">8.6 Programmable Completion</h3>
<p><a name="index-programmable-completion-368"></a>
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.
<p>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 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.
<p>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">Commands For Completion</a>) is performed.
<p>First, the actions specified by the compspec are used.
Only matches which are prefixed by the word being completed are
returned.
When the <samp><span class="option">-f</span></samp> or <samp><span class="option">-d</span></samp> option is used for filename or
directory name completion, the shell variable <samp><span class="env">FIGNORE</span></samp> is
used to filter the matches.
See <a href="#Bash-Variables">Bash Variables</a>, for a description of <samp><span class="env">FIGNORE</span></samp>.
<p>Any completions specified by a filename expansion pattern to the
<samp><span class="option">-G</span></samp> option are generated next.
The words generated by the pattern need not match the word being completed.
The <samp><span class="env">GLOBIGNORE</span></samp> shell variable is not used to filter the matches,
but the <samp><span class="env">FIGNORE</span></samp> shell variable is used.
<p>Next, the string specified as the argument to the <samp><span class="option">-W</span></samp> option
is considered.
The string is first split using the characters in the <samp><span class="env">IFS</span></samp>
special variable as delimiters.
Shell quoting is honored.
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.
<p>After these matches have been generated, any shell function or command
specified with the <samp><span class="option">-F</span></samp> and <samp><span class="option">-C</span></samp> options is invoked.
When the command or function is invoked, the <samp><span class="env">COMP_LINE</span></samp>,
<samp><span class="env">COMP_POINT</span></samp>, <samp><span class="env">COMP_KEY</span></samp>, and <samp><span class="env">COMP_TYPE</span></samp> variables are
assigned values as described above (see <a href="#Bash-Variables">Bash Variables</a>).
If a shell function is being invoked, the <samp><span class="env">COMP_WORDS</span></samp> and
<samp><span class="env">COMP_CWORD</span></samp> variables are also set.
When the function or command is invoked, the first argument is the
name of the command whose arguments are being completed, the
second argument is the word being completed, and the third argument
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.
<p>Any function specified with <samp><span class="option">-F</span></samp> is invoked first.
The function may use any of the shell facilities, including the
<code>compgen</code> builtin described below
(see <a href="#Programmable-Completion-Builtins">Programmable Completion Builtins</a>), to generate the matches.
It must put the possible completions in the <samp><span class="env">COMPREPLY</span></samp> array
variable.
<p>Next, any command specified with the <samp><span class="option">-C</span></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.
<p>After all of the possible completions are generated, any filter
specified with the <samp><span class="option">-X</span></samp> option is applied to the list.
The filter is a pattern as used for pathname expansion; a `<samp><span class="samp">&</span></samp>'
in the pattern is replaced with the text of the word being completed.
A literal `<samp><span class="samp">&</span></samp>' 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 `<samp><span class="samp">!</span></samp>' negates the pattern; in this case any completion
not matching the pattern will be removed.
<p>Finally, any prefix and suffix specified with the <samp><span class="option">-P</span></samp> and <samp><span class="option">-S</span></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.
<p>If the previously-applied actions do not generate any matches, and the
<samp><span class="option">-o dirnames</span></samp> option was supplied to <code>complete</code> when the
compspec was defined, directory name completion is attempted.
<p>If the <samp><span class="option">-o plusdirs</span></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.
<p>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><span class="option">-o bashdefault</span></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><span class="option">-o default</span></samp> option was supplied to <code>complete</code> when the
compspec was defined, Readline's default completion will be performed
if the compspec (and, if attempted, the default Bash completions)
generate no matches.
<p>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.
<div class="node">
<p><hr>
<a name="Programmable-Completion-Builtins"></a>
Previous: <a rel="previous" accesskey="p" href="#Programmable-Completion">Programmable Completion</a>,
Up: <a rel="up" accesskey="u" href="#Command-Line-Editing">Command Line Editing</a>
</div>
<h3 class="section">8.7 Programmable Completion Builtins</h3>
<p><a name="index-completion-builtins-369"></a>
Two builtin commands are available to manipulate the programmable completion
facilities.
<dl>
<dt><code>compgen</code><dd><a name="index-compgen-370"></a>
<pre class="example"> <code>compgen [</code><var>option</var><code>] [</code><var>word</var><code>]</code>
</pre>
<p>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><span class="option">-p</span></samp> and <samp><span class="option">-r</span></samp>, and write
the matches to the standard output.
When using the <samp><span class="option">-F</span></samp> or <samp><span class="option">-C</span></samp> options, the various shell variables
set by the programmable completion facilities, while available, will not
have useful values.
<p>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.
<p>The return value is true unless an invalid option is supplied, or no
matches were generated.
<br><dt><code>complete</code><dd><a name="index-complete-371"></a>
<pre class="example"> <code>complete [-abcdefgjksuv] [-o </code><var>comp-option</var><code>] [-A </code><var>action</var><code>] [-G </code><var>globpat</var><code>] [-W </code><var>wordlist</var><code>]
[-F </code><var>function</var><code>] [-C </code><var>command</var><code>] [-X </code><var>filterpat</var><code>]
[-P </code><var>prefix</var><code>] [-S </code><var>suffix</var><code>] </code><var>name</var><code> [</code><var>name</var><code> ...]</code>
<code>complete -pr [</code><var>name</var><code> ...]</code>
</pre>
<p>Specify how arguments to each <var>name</var> should be completed.
If the <samp><span class="option">-p</span></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><span class="option">-r</span></samp> option removes a completion specification for
each <var>name</var>, or, if no <var>name</var>s are supplied, all
completion specifications.
<p>The process of applying these completion specifications when word completion
is attempted is described above (see <a href="#Programmable-Completion">Programmable Completion</a>).
<p>Other options, if specified, have the following meanings.
The arguments to the <samp><span class="option">-G</span></samp>, <samp><span class="option">-W</span></samp>, and <samp><span class="option">-X</span></samp> options
(and, if necessary, the <samp><span class="option">-P</span></samp> and <samp><span class="option">-S</span></samp> options)
should be quoted to protect them from expansion before the
<code>complete</code> builtin is invoked.
<dl>
<dt><code>-o </code><var>comp-option</var><dd>The <var>comp-option</var> controls several aspects of the compspec's behavior
beyond the simple generation of completions.
<var>comp-option</var> may be one of:
<dl>
<dt><code>bashdefault</code><dd>Perform the rest of the default Bash completions if the compspec
generates no matches.
<br><dt><code>default</code><dd>Use Readline's default filename completion if the compspec generates
no matches.
<br><dt><code>dirnames</code><dd>Perform directory name completion if the compspec generates no matches.
<br><dt><code>filenames</code><dd>Tell Readline that the compspec generates filenames, so it can perform any
filename-specific processing (like adding a slash to directory names or
suppressing trailing spaces). This option is intended to be used with
shell functions specified with <samp><span class="option">-F</span></samp>.
<br><dt><code>nospace</code><dd>Tell Readline not to append a space (the default) to words completed at
the end of the line.
<br><dt><code>plusdirs</code><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.
</dl>
<br><dt><code>-A </code><var>action</var><dd>The <var>action</var> may be one of the following to generate a list of possible
completions:
<dl>
<dt><code>alias</code><dd>Alias names. May also be specified as <samp><span class="option">-a</span></samp>.
<br><dt><code>arrayvar</code><dd>Array variable names.
<br><dt><code>binding</code><dd>Readline key binding names (see <a href="#Bindable-Readline-Commands">Bindable Readline Commands</a>).
<br><dt><code>builtin</code><dd>Names of shell builtin commands. May also be specified as <samp><span class="option">-b</span></samp>.
<br><dt><code>command</code><dd>Command names. May also be specified as <samp><span class="option">-c</span></samp>.
<br><dt><code>directory</code><dd>Directory names. May also be specified as <samp><span class="option">-d</span></samp>.
<br><dt><code>disabled</code><dd>Names of disabled shell builtins.
<br><dt><code>enabled</code><dd>Names of enabled shell builtins.
<br><dt><code>export</code><dd>Names of exported shell variables. May also be specified as <samp><span class="option">-e</span></samp>.
<br><dt><code>file</code><dd>File names. May also be specified as <samp><span class="option">-f</span></samp>.
<br><dt><code>function</code><dd>Names of shell functions.
<br><dt><code>group</code><dd>Group names. May also be specified as <samp><span class="option">-g</span></samp>.
<br><dt><code>helptopic</code><dd>Help topics as accepted by the <code>help</code> builtin (see <a href="#Bash-Builtins">Bash Builtins</a>).
<br><dt><code>hostname</code><dd>Hostnames, as taken from the file specified by the
<samp><span class="env">HOSTFILE</span></samp> shell variable (see <a href="#Bash-Variables">Bash Variables</a>).
<br><dt><code>job</code><dd>Job names, if job control is active. May also be specified as <samp><span class="option">-j</span></samp>.
<br><dt><code>keyword</code><dd>Shell reserved words. May also be specified as <samp><span class="option">-k</span></samp>.
<br><dt><code>running</code><dd>Names of running jobs, if job control is active.
<br><dt><code>service</code><dd>Service names. May also be specified as <samp><span class="option">-s</span></samp>.
<br><dt><code>setopt</code><dd>Valid arguments for the <samp><span class="option">-o</span></samp> option to the <code>set</code> builtin
(see <a href="#The-Set-Builtin">The Set Builtin</a>).
<br><dt><code>shopt</code><dd>Shell option names as accepted by the <code>shopt</code> builtin
(see <a href="#Bash-Builtins">Bash Builtins</a>).
<br><dt><code>signal</code><dd>Signal names.
<br><dt><code>stopped</code><dd>Names of stopped jobs, if job control is active.
<br><dt><code>user</code><dd>User names. May also be specified as <samp><span class="option">-u</span></samp>.
<br><dt><code>variable</code><dd>Names of all shell variables. May also be specified as <samp><span class="option">-v</span></samp>.
</dl>
<br><dt><code>-G </code><var>globpat</var><dd>The filename expansion pattern <var>globpat</var> is expanded to generate
the possible completions.
<br><dt><code>-W </code><var>wordlist</var><dd>The <var>wordlist</var> is split using the characters in the
<samp><span class="env">IFS</span></samp> 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.
<br><dt><code>-C </code><var>command</var><dd><var>command</var> is executed in a subshell environment, and its output is
used as the possible completions.
<br><dt><code>-F </code><var>function</var><dd>The shell function <var>function</var> is executed in the current shell
environment.
When it finishes, the possible completions are retrieved from the value
of the <samp><span class="env">COMPREPLY</span></samp> array variable.
<br><dt><code>-X </code><var>filterpat</var><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 `<samp><span class="samp">!</span></samp>' in <var>filterpat</var> negates the pattern; in this
case, any completion not matching <var>filterpat</var> is removed.
<br><dt><code>-P </code><var>prefix</var><dd><var>prefix</var> is added at the beginning of each possible completion
after all other options have been applied.
<br><dt><code>-S </code><var>suffix</var><dd><var>suffix</var> is appended to each possible completion
after all other options have been applied.
</dl>
<p>The return value is true unless an invalid option is supplied, an option
other than <samp><span class="option">-p</span></samp> or <samp><span class="option">-r</span></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.
</dl>
<a name="index-History_002c-how-to-use-372"></a>
<div class="node">
<p><hr>
<a name="Using-History-Interactively"></a>
Next: <a rel="next" accesskey="n" href="#Command-Line-Editing">Command Line Editing</a>,
Previous: <a rel="previous" accesskey="p" href="#Job-Control">Job Control</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="chapter">9 Using History Interactively</h2>
<p>This chapter describes how to use the <span class="sc">gnu</span> History Library
interactively, from a user's standpoint.
It should be considered a user's guide.
For information on using the <span class="sc">gnu</span> History Library in other programs,
see the <span class="sc">gnu</span> Readline Library Manual.
<ul class="menu">
<li><a accesskey="1" href="#Bash-History-Facilities">Bash History Facilities</a>: How Bash lets you manipulate your command
history.
<li><a accesskey="2" href="#Bash-History-Builtins">Bash History Builtins</a>: The Bash builtin commands that manipulate
the command history.
<li><a accesskey="3" href="#History-Interaction">History Interaction</a>: What it feels like using History as a user.
</ul>
<div class="node">
<p><hr>
<a name="Bash-History-Facilities"></a>
Next: <a rel="next" accesskey="n" href="#Bash-History-Builtins">Bash History Builtins</a>,
Up: <a rel="up" accesskey="u" href="#Using-History-Interactively">Using History Interactively</a>
</div>
<h3 class="section">9.1 Bash History Facilities</h3>
<p><a name="index-command-history-373"></a><a name="index-history-list-374"></a>
When the <samp><span class="option">-o history</span></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 <dfn>command history</dfn>,
the list of commands previously typed.
The value of the <samp><span class="env">HISTSIZE</span></samp> shell variable is used as the
number of commands to save in a history list.
The text of the last <samp><span class="env">$HISTSIZE</span></samp>
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
<samp><span class="env">HISTIGNORE</span></samp> and <samp><span class="env">HISTCONTROL</span></samp>.
<p>When the shell starts up, the history is initialized from the
file named by the <samp><span class="env">HISTFILE</span></samp> variable (default <samp><span class="file">~/.bash_history</span></samp>).
The file named by the value of <samp><span class="env">HISTFILE</span></samp> is truncated, if
necessary, to contain no more than the number of lines specified by
the value of the <samp><span class="env">HISTFILESIZE</span></samp> variable.
When an interactive shell exits, the last
<samp><span class="env">$HISTSIZE</span></samp> lines are copied from the history list to the file
named by <samp><span class="env">$HISTFILE</span></samp>.
If the <code>histappend</code> shell option is set (see <a href="#Bash-Builtins">Bash Builtins</a>),
the lines are appended to the history file,
otherwise the history file is overwritten.
If <samp><span class="env">HISTFILE</span></samp>
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 <samp><span class="env">$HISTFILESIZE</span></samp>
lines. If <samp><span class="env">HISTFILESIZE</span></samp> is not set, no truncation is performed.
<p>If the <samp><span class="env">HISTTIMEFORMAT</span></samp> is set, the time stamp information
associated with each history entry is written to the history file.
<p>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 History</a>).
<p>The shell allows control over which commands are saved on the history
list. The <samp><span class="env">HISTCONTROL</span></samp> and <samp><span class="env">HISTIGNORE</span></samp>
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="#Bash-Builtins">Bash Builtins</a>, for a description of <code>shopt</code>.
<div class="node">
<p><hr>
<a name="Bash-History-Builtins"></a>
Next: <a rel="next" accesskey="n" href="#History-Interaction">History Interaction</a>,
Previous: <a rel="previous" accesskey="p" href="#Bash-History-Facilities">Bash History Facilities</a>,
Up: <a rel="up" accesskey="u" href="#Using-History-Interactively">Using History Interactively</a>
</div>
<h3 class="section">9.2 Bash History Builtins</h3>
<p><a name="index-history-builtins-375"></a>
Bash provides two builtin commands which manipulate the
history list and history file.
<dl>
<dt><code>fc</code><dd><a name="index-fc-376"></a>
<pre class="example"> <code>fc [-e </code><var>ename</var><code>] [-lnr] [</code><var>first</var><code>] [</code><var>last</var><code>]</code>
<code>fc -s [</code><var>pat</var><code>=</code><var>rep</var><code>] [</code><var>command</var><code>]</code>
</pre>
<p>Fix Command. In the first form, a range of commands from <var>first</var> to
<var>last</var> is selected from the history list. 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). 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><span class="option">-l</span></samp> flag is
given, the commands are listed on standard output. The <samp><span class="option">-n</span></samp> flag
suppresses the command numbers when listing. The <samp><span class="option">-r</span></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 <samp><span class="env">FCEDIT</span></samp> variable if set, or the value of the
<samp><span class="env">EDITOR</span></samp> variable if that is set, or <code>vi</code> if neither is set.
When editing is complete, the edited commands are echoed and executed.
<p>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>.
<p>A useful alias to use with the <code>fc</code> command is <code>r='fc -s'</code>, so
that typing `<samp><span class="samp">r cc</span></samp>' runs the last command beginning with <code>cc</code>
and typing `<samp><span class="samp">r</span></samp>' re-executes the last command (see <a href="#Aliases">Aliases</a>).
<br><dt><code>history</code><dd><a name="index-history-377"></a>
<pre class="example"> history [<var>n</var>]
history -c
history -d <var>offset</var>
history [-anrw] [<var>filename</var>]
history -ps <var>arg</var>
</pre>
<p>With no options, display the history list with line numbers.
Lines prefixed with a `<samp><span class="samp">*</span></samp>' have been modified.
An argument of <var>n</var> lists only the last <var>n</var> lines.
If the shell variable <samp><span class="env">HISTTIMEFORMAT</span></samp> 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.
<p>Options, if supplied, have the following meanings:
<dl>
<dt><code>-c</code><dd>Clear the history list. This may be combined
with the other options to replace the history list completely.
<br><dt><code>-d </code><var>offset</var><dd>Delete the history entry at position <var>offset</var>.
<var>offset</var> should be specified as it appears when the history is
displayed.
<br><dt><code>-a</code><dd>Append the new
history lines (history lines entered since the beginning of the
current Bash session) to the history file.
<br><dt><code>-n</code><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.
<br><dt><code>-r</code><dd>Read the current history file and append its contents to
the history list.
<br><dt><code>-w</code><dd>Write out the current history to the history file.
<br><dt><code>-p</code><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.
<br><dt><code>-s</code><dd>The <var>arg</var>s are added to the end of
the history list as a single entry.
</dl>
<p>When any of the <samp><span class="option">-w</span></samp>, <samp><span class="option">-r</span></samp>, <samp><span class="option">-a</span></samp>, or <samp><span class="option">-n</span></samp> options is
used, if <var>filename</var>
is given, then it is used as the history file. If not, then
the value of the <samp><span class="env">HISTFILE</span></samp> variable is used.
</dl>
<div class="node">
<p><hr>
<a name="History-Interaction"></a>
Previous: <a rel="previous" accesskey="p" href="#Bash-History-Builtins">Bash History Builtins</a>,
Up: <a rel="up" accesskey="u" href="#Using-History-Interactively">Using History Interactively</a>
</div>
<h3 class="section">9.3 History Expansion</h3>
<p><a name="index-history-expansion-378"></a>
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.
<p>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.
<p>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
<dfn>event</dfn>, and the portions of that line that are acted upon are
called <dfn>words</dfn>. Various <dfn>modifiers</dfn> 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 `<samp><span class="samp">!</span></samp>' by default.
Only `<samp><span class="samp">\</span></samp>' and `<samp><span class="samp">'</span></samp>' may be used to escape the history expansion
character.
<p>Several shell options settable with the <code>shopt</code>
builtin (see <a href="#Bash-Builtins">Bash Builtins</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><span class="option">-p</span></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><span class="option">-s</span></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.
<p>The shell allows control of the various characters used by the
history expansion mechanism with the <code>histchars</code> variable.
<ul class="menu">
<li><a accesskey="1" href="#Event-Designators">Event Designators</a>: How to specify which history line to use.
<li><a accesskey="2" href="#Word-Designators">Word Designators</a>: Specifying which words are of interest.
<li><a accesskey="3" href="#Modifiers">Modifiers</a>: Modifying the results of substitution.
</ul>
<div class="node">
<p><hr>
<a name="Event-Designators"></a>
Next: <a rel="next" accesskey="n" href="#Word-Designators">Word Designators</a>,
Up: <a rel="up" accesskey="u" href="#History-Interaction">History Interaction</a>
</div>
<h4 class="subsection">9.3.1 Event Designators</h4>
<p><a name="index-event-designators-379"></a>
An event designator is a reference to a command line entry in the
history list.
<a name="index-history-events-380"></a>
<dl>
<dt><code>!</code><dd>Start a history substitution, except when followed by a space, tab,
the end of the line, `<samp><span class="samp">=</span></samp>' or `<samp><span class="samp">(</span></samp>' (when the
<code>extglob</code> shell option is enabled using the <code>shopt</code> builtin).
<br><dt><code>!</code><var>n</var><dd>Refer to command line <var>n</var>.
<br><dt><code>!-</code><var>n</var><dd>Refer to the command <var>n</var> lines back.
<br><dt><code>!!</code><dd>Refer to the previous command. This is a synonym for `<samp><span class="samp">!-1</span></samp>'.
<br><dt><code>!</code><var>string</var><dd>Refer to the most recent command starting with <var>string</var>.
<br><dt><code>!?</code><var>string</var><code>[?]</code><dd>Refer to the most recent command containing <var>string</var>. The trailing
`<samp><span class="samp">?</span></samp>' may be omitted if the <var>string</var> is followed immediately by
a newline.
<br><dt><code>^</code><var>string1</var><code>^</code><var>string2</var><code>^</code><dd>Quick Substitution. Repeat the last command, replacing <var>string1</var>
with <var>string2</var>. Equivalent to
<code>!!:s/</code><var>string1</var><code>/</code><var>string2</var><code>/</code>.
<br><dt><code>!#</code><dd>The entire command line typed so far.
</dl>
<div class="node">
<p><hr>
<a name="Word-Designators"></a>
Next: <a rel="next" accesskey="n" href="#Modifiers">Modifiers</a>,
Previous: <a rel="previous" accesskey="p" href="#Event-Designators">Event Designators</a>,
Up: <a rel="up" accesskey="u" href="#History-Interaction">History Interaction</a>
</div>
<h4 class="subsection">9.3.2 Word Designators</h4>
<p>Word designators are used to select desired words from the event.
A `<samp><span class="samp">:</span></samp>' separates the event specification from the word designator. It
may be omitted if the word designator begins with a `<samp><span class="samp">^</span></samp>', `<samp><span class="samp">$</span></samp>',
`<samp><span class="samp">*</span></samp>', `<samp><span class="samp">-</span></samp>', or `<samp><span class="samp">%</span></samp>'. 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.
<p>For example,
<dl>
<dt><code>!!</code><dd>designates the preceding command. When you type this, the preceding
command is repeated in toto.
<br><dt><code>!!:$</code><dd>designates the last argument of the preceding command. This may be
shortened to <code>!$</code>.
<br><dt><code>!fi:2</code><dd>designates the second argument of the most recent command starting with
the letters <code>fi</code>.
</dl>
<p>Here are the word designators:
<dl>
<dt><code>0 (zero)</code><dd>The <code>0</code>th word. For many applications, this is the command word.
<br><dt><var>n</var><dd>The <var>n</var>th word.
<br><dt><code>^</code><dd>The first argument; that is, word 1.
<br><dt><code>$</code><dd>The last argument.
<br><dt><code>%</code><dd>The word matched by the most recent `<samp><span class="samp">?</span><var>string</var><span class="samp">?</span></samp>' search.
<br><dt><var>x</var><code>-</code><var>y</var><dd>A range of words; `<samp><span class="samp">-</span><var>y</var></samp>' abbreviates `<samp><span class="samp">0-</span><var>y</var></samp>'.
<br><dt><code>*</code><dd>All of the words, except the <code>0</code>th. This is a synonym for `<samp><span class="samp">1-$</span></samp>'.
It is not an error to use `<samp><span class="samp">*</span></samp>' if there is just one word in the event;
the empty string is returned in that case.
<br><dt><var>x</var><code>*</code><dd>Abbreviates `<samp><var>x</var><span class="samp">-$</span></samp>'
<br><dt><var>x</var><code>-</code><dd>Abbreviates `<samp><var>x</var><span class="samp">-$</span></samp>' like `<samp><var>x</var><span class="samp">*</span></samp>', but omits the last word.
</dl>
<p>If a word designator is supplied without an event specification, the
previous command is used as the event.
<div class="node">
<p><hr>
<a name="Modifiers"></a>
Previous: <a rel="previous" accesskey="p" href="#Word-Designators">Word Designators</a>,
Up: <a rel="up" accesskey="u" href="#History-Interaction">History Interaction</a>
</div>
<h4 class="subsection">9.3.3 Modifiers</h4>
<p>After the optional word designator, you can add a sequence of one or more
of the following modifiers, each preceded by a `<samp><span class="samp">:</span></samp>'.
<dl>
<dt><code>h</code><dd>Remove a trailing pathname component, leaving only the head.
<br><dt><code>t</code><dd>Remove all leading pathname components, leaving the tail.
<br><dt><code>r</code><dd>Remove a trailing suffix of the form `<samp><span class="samp">.</span><var>suffix</var></samp>', leaving
the basename.
<br><dt><code>e</code><dd>Remove all but the trailing suffix.
<br><dt><code>p</code><dd>Print the new command but do not execute it.
<br><dt><code>q</code><dd>Quote the substituted words, escaping further substitutions.
<br><dt><code>x</code><dd>Quote the substituted words as with `<samp><span class="samp">q</span></samp>',
but break into words at spaces, tabs, and newlines.
<br><dt><code>s/</code><var>old</var><code>/</code><var>new</var><code>/</code><dd>Substitute <var>new</var> for the first occurrence of <var>old</var> in the
event line. Any delimiter may be used in place of `<samp><span class="samp">/</span></samp>'.
The delimiter may be quoted in <var>old</var> and <var>new</var>
with a single backslash. If `<samp><span class="samp">&</span></samp>' appears in <var>new</var>,
it is replaced by <var>old</var>. A single backslash will quote
the `<samp><span class="samp">&</span></samp>'. The final delimiter is optional if it is the last
character on the input line.
<br><dt><code>&</code><dd>Repeat the previous substitution.
<br><dt><code>g</code><dt><code>a</code><dd>Cause changes to be applied over the entire event line. Used in
conjunction with `<samp><span class="samp">s</span></samp>', as in <code>gs/</code><var>old</var><code>/</code><var>new</var><code>/</code>,
or with `<samp><span class="samp">&</span></samp>'.
<br><dt><code>G</code><dd>Apply the following `<samp><span class="samp">s</span></samp>' modifier once to each word in the event.
</dl>
<div class="node">
<p><hr>
<a name="Installing-Bash"></a>
Next: <a rel="next" accesskey="n" href="#Reporting-Bugs">Reporting Bugs</a>,
Previous: <a rel="previous" accesskey="p" href="#Command-Line-Editing">Command Line Editing</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="chapter">10 Installing Bash</h2>
<p>This chapter provides basic instructions for installing Bash on
the various supported platforms. The distribution supports the
<span class="sc">gnu</span> operating systems, nearly every version of Unix, and several
non-Unix systems such as BeOS and Interix.
Other independent ports exist for
<span class="sc">ms-dos</span>, <span class="sc">os/2</span>, and Windows platforms.
<ul class="menu">
<li><a accesskey="1" href="#Basic-Installation">Basic Installation</a>: Installation instructions.
<li><a accesskey="2" href="#Compilers-and-Options">Compilers and Options</a>: How to set special options for various
systems.
<li><a accesskey="3" href="#Compiling-For-Multiple-Architectures">Compiling For Multiple Architectures</a>: How to compile Bash for more
than one kind of system from
the same source tree.
<li><a accesskey="4" href="#Installation-Names">Installation Names</a>: How to set the various paths used by the installation.
<li><a accesskey="5" href="#Specifying-the-System-Type">Specifying the System Type</a>: How to configure Bash for a particular system.
<li><a accesskey="6" href="#Sharing-Defaults">Sharing Defaults</a>: How to share default configuration values among GNU
programs.
<li><a accesskey="7" href="#Operation-Controls">Operation Controls</a>: Options recognized by the configuration program.
<li><a accesskey="8" href="#Optional-Features">Optional Features</a>: How to enable and disable optional features when
building Bash.
</ul>
<div class="node">
<p><hr>
<a name="Basic-Installation"></a>
Next: <a rel="next" accesskey="n" href="#Compilers-and-Options">Compilers and Options</a>,
Up: <a rel="up" accesskey="u" href="#Installing-Bash">Installing Bash</a>
</div>
<h3 class="section">10.1 Basic Installation</h3>
<p><a name="index-installation-381"></a><a name="index-configuration-382"></a><a name="index-Bash-installation-383"></a><a name="index-Bash-configuration-384"></a>
These are installation instructions for Bash.
<p>The simplest way to compile Bash is:
<ol type=1 start=1>
<li><code>cd</code> to the directory containing the source code and type
`<samp><span class="samp">./configure</span></samp>' to configure Bash for your system. If you're
using <code>csh</code> on an old version of System V, you might need to
type `<samp><span class="samp">sh ./configure</span></samp>' instead to prevent <code>csh</code> from trying
to execute <code>configure</code> itself.
<p>Running <code>configure</code> takes some time.
While running, it prints messages telling which features it is
checking for.
<li>Type `<samp><span class="samp">make</span></samp>' to compile Bash and build the <code>bashbug</code> bug
reporting script.
<li>Optionally, type `<samp><span class="samp">make tests</span></samp>' to run the Bash test suite.
<li>Type `<samp><span class="samp">make install</span></samp>' to install <code>bash</code> and <code>bashbug</code>.
This will also install the manual pages and Info file.
</ol>
<p>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><span class="file">Makefile</span></samp> in
each directory of the package (the top directory, the
<samp><span class="file">builtins</span></samp>, <samp><span class="file">doc</span></samp>, and <samp><span class="file">support</span></samp> directories,
each directory under <samp><span class="file">lib</span></samp>, and several others). It also creates a
<samp><span class="file">config.h</span></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><span class="file">config.cache</span></samp> that saves the results of its tests to
speed up reconfiguring, and a file <samp><span class="file">config.log</span></samp> containing
compiler output (useful mainly for debugging <code>configure</code>).
If at some point
<samp><span class="file">config.cache</span></samp> contains results you don't want to keep, you
may remove or edit it.
<p>To find out more about the options and arguments that the
<code>configure</code> script understands, type
<pre class="example"> bash-2.04$ ./configure --help
</pre>
<p class="noindent">at the Bash prompt in your Bash source directory.
<p>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.
<p>The file <samp><span class="file">configure.in</span></samp> is used to create <code>configure</code>
by a program called Autoconf. You only need
<samp><span class="file">configure.in</span></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 2.50 or
newer.
<p>You can remove the program binaries and object files from the
source code directory by typing `<samp><span class="samp">make clean</span></samp>'. To also remove the
files that <code>configure</code> created (so you can compile Bash for
a different kind of computer), type `<samp><span class="samp">make distclean</span></samp>'.
<div class="node">
<p><hr>
<a name="Compilers-and-Options"></a>
Next: <a rel="next" accesskey="n" href="#Compiling-For-Multiple-Architectures">Compiling For Multiple Architectures</a>,
Previous: <a rel="previous" accesskey="p" href="#Basic-Installation">Basic Installation</a>,
Up: <a rel="up" accesskey="u" href="#Installing-Bash">Installing Bash</a>
</div>
<h3 class="section">10.2 Compilers and Options</h3>
<p>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:
<pre class="example"> CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure
</pre>
<p>On systems that have the <code>env</code> program, you can do it like this:
<pre class="example"> env CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure
</pre>
<p>The configuration process uses GCC to build Bash if it
is available.
<div class="node">
<p><hr>
<a name="Compiling-For-Multiple-Architectures"></a>
Next: <a rel="next" accesskey="n" href="#Installation-Names">Installation Names</a>,
Previous: <a rel="previous" accesskey="p" href="#Compilers-and-Options">Compilers and Options</a>,
Up: <a rel="up" accesskey="u" href="#Installing-Bash">Installing Bash</a>
</div>
<h3 class="section">10.3 Compiling For Multiple Architectures</h3>
<p>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. You may need to
supply the <samp><span class="option">--srcdir=PATH</span></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 `..'.
<p>If you have to use a <code>make</code> that does not supports 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 `<samp><span class="samp">make distclean</span></samp>' before
reconfiguring for another architecture.
<p>Alternatively, if your system supports symbolic links, you can use the
<samp><span class="file">support/mkclone</span></samp> script to create a build tree which has
symbolic links back to each file in the source directory. Here's an
example that creates a build directory in the current directory from a
source directory <samp><span class="file">/usr/gnu/src/bash-2.0</span></samp>:
<pre class="example"> bash /usr/gnu/src/bash-2.0/support/mkclone -s /usr/gnu/src/bash-2.0 .
</pre>
<p class="noindent">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.
<div class="node">
<p><hr>
<a name="Installation-Names"></a>
Next: <a rel="next" accesskey="n" href="#Specifying-the-System-Type">Specifying the System Type</a>,
Previous: <a rel="previous" accesskey="p" href="#Compiling-For-Multiple-Architectures">Compiling For Multiple Architectures</a>,
Up: <a rel="up" accesskey="u" href="#Installing-Bash">Installing Bash</a>
</div>
<h3 class="section">10.4 Installation Names</h3>
<p>By default, `<samp><span class="samp">make install</span></samp>' will install into
<samp><span class="file">/usr/local/bin</span></samp>, <samp><span class="file">/usr/local/man</span></samp>, etc. You can
specify an installation prefix other than <samp><span class="file">/usr/local</span></samp> by
giving <code>configure</code> the option <samp><span class="option">--prefix=</span><var>PATH</var></samp>,
or by specifying a value for the <code>DESTDIR</code> `<samp><span class="samp">make</span></samp>'
variable when running `<samp><span class="samp">make install</span></samp>'.
<p>You can specify separate installation prefixes for
architecture-specific files and architecture-independent files.
If you give <code>configure</code> the option
<samp><span class="option">--exec-prefix=</span><var>PATH</var></samp>, `<samp><span class="samp">make install</span></samp>' will use
<var>PATH</var> as the prefix for installing programs and libraries.
Documentation and other data files will still use the regular prefix.
<div class="node">
<p><hr>
<a name="Specifying-the-System-Type"></a>
Next: <a rel="next" accesskey="n" href="#Sharing-Defaults">Sharing Defaults</a>,
Previous: <a rel="previous" accesskey="p" href="#Installation-Names">Installation Names</a>,
Up: <a rel="up" accesskey="u" href="#Installing-Bash">Installing Bash</a>
</div>
<h3 class="section">10.5 Specifying the System Type</h3>
<p>There may be some features <code>configure</code> can not figure out
automatically, but need 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><span class="option">--host=TYPE</span></samp> option. `<samp><span class="samp">TYPE</span></samp>' can
either be a short name for the system type, such as `<samp><span class="samp">sun4</span></samp>',
or a canonical name with three fields: `<samp><span class="samp">CPU-COMPANY-SYSTEM</span></samp>'
(e.g., `<samp><span class="samp">i386-unknown-freebsd4.2</span></samp>').
<p>See the file <samp><span class="file">support/config.sub</span></samp> for the possible
values of each field.
<div class="node">
<p><hr>
<a name="Sharing-Defaults"></a>
Next: <a rel="next" accesskey="n" href="#Operation-Controls">Operation Controls</a>,
Previous: <a rel="previous" accesskey="p" href="#Specifying-the-System-Type">Specifying the System Type</a>,
Up: <a rel="up" accesskey="u" href="#Installing-Bash">Installing Bash</a>
</div>
<h3 class="section">10.6 Sharing Defaults</h3>
<p>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><span class="file">PREFIX/share/config.site</span></samp> if it exists, then
<samp><span class="file">PREFIX/etc/config.site</span></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.
<div class="node">
<p><hr>
<a name="Operation-Controls"></a>
Next: <a rel="next" accesskey="n" href="#Optional-Features">Optional Features</a>,
Previous: <a rel="previous" accesskey="p" href="#Sharing-Defaults">Sharing Defaults</a>,
Up: <a rel="up" accesskey="u" href="#Installing-Bash">Installing Bash</a>
</div>
<h3 class="section">10.7 Operation Controls</h3>
<p><code>configure</code> recognizes the following options to control how it
operates.
<dl>
<dt><code>--cache-file=</code><var>file</var><dd>Use and save the results of the tests in
<var>file</var> instead of <samp><span class="file">./config.cache</span></samp>. Set <var>file</var> to
<samp><span class="file">/dev/null</span></samp> to disable caching, for debugging
<code>configure</code>.
<br><dt><code>--help</code><dd>Print a summary of the options to <code>configure</code>, and exit.
<br><dt><code>--quiet</code><dt><code>--silent</code><dt><code>-q</code><dd>Do not print messages saying which checks are being made.
<br><dt><code>--srcdir=</code><var>dir</var><dd>Look for the Bash source code in directory <var>dir</var>. Usually
<code>configure</code> can determine that directory automatically.
<br><dt><code>--version</code><dd>Print the version of Autoconf used to generate the <code>configure</code>
script, and exit.
</dl>
<p><code>configure</code> also accepts some other, not widely used, boilerplate
options. `<samp><span class="samp">configure --help</span></samp>' prints the complete list.
<div class="node">
<p><hr>
<a name="Optional-Features"></a>
Previous: <a rel="previous" accesskey="p" href="#Operation-Controls">Operation Controls</a>,
Up: <a rel="up" accesskey="u" href="#Installing-Bash">Installing Bash</a>
</div>
<h3 class="section">10.8 Optional Features</h3>
<p>The Bash <code>configure</code> has a number of <samp><span class="option">--enable-</span><var>feature</var></samp>
options, where <var>feature</var> indicates an optional part of Bash.
There are also several <samp><span class="option">--with-</span><var>package</var></samp> options,
where <var>package</var> is something like `<samp><span class="samp">bash-malloc</span></samp>' or `<samp><span class="samp">purify</span></samp>'.
To turn off the default use of a package, use
<samp><span class="option">--without-</span><var>package</var></samp>. To configure Bash without a feature
that is enabled by default, use <samp><span class="option">--disable-</span><var>feature</var></samp>.
<p>Here is a complete list of the <samp><span class="option">--enable-</span></samp> and
<samp><span class="option">--with-</span></samp> options that the Bash <code>configure</code> recognizes.
<dl>
<dt><code>--with-afs</code><dd>Define if you are using the Andrew File System from Transarc.
<br><dt><code>--with-bash-malloc</code><dd>Use the Bash version of
<code>malloc</code> in the directory <samp><span class="file">lib/malloc</span></samp>. This is not the same
<code>malloc</code> that appears in <span class="sc">gnu</span> libc, but an older version
originally derived from the 4.2 <span class="sc">bsd</span> <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><span class="file">NOTES</span></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.
<br><dt><code>--with-curses</code><dd>Use the curses library instead of the termcap library. This should
be supplied if your system has an inadequate or incomplete termcap
database.
<br><dt><code>--with-gnu-malloc</code><dd>A synonym for <code>--with-bash-malloc</code>.
<br><dt><code>--with-installed-readline[=</code><var>PREFIX</var><code>]</code><dd>Define this to make Bash link with a locally-installed version of Readline
rather than the version in <samp><span class="file">lib/readline</span></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><span class="file">lib/readline</span></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>).
<br><dt><code>--with-purify</code><dd>Define this to use the Purify memory allocation checker from Rational
Software.
<br><dt><code>--enable-minimal-config</code><dd>This produces a shell with minimal features, close to the historical
Bourne shell.
</dl>
<p>There are several <samp><span class="option">--enable-</span></samp> options that alter how Bash is
compiled and linked, rather than changing run-time features.
<dl>
<dt><code>--enable-largefile</code><dd>Enable support for <a href="http://www.sas.com/standards/large_file/x_open.20Mar96.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.
<br><dt><code>--enable-profiling</code><dd>This builds a Bash binary that produces profiling information to be
processed by <code>gprof</code> each time it is executed.
<br><dt><code>--enable-static-link</code><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's shell.
</dl>
<p>The `<samp><span class="samp">minimal-config</span></samp>' option can be used to disable all of
the following options, but it is processed first, so individual
options may be enabled using `<samp><span class="samp">enable-</span><var>feature</var></samp>'.
<p>All of the following options except for `<samp><span class="samp">disabled-builtins</span></samp>' and
`<samp><span class="samp">xpg-echo-default</span></samp>' are
enabled by default, unless the operating system does not provide the
necessary support.
<dl>
<dt><code>--enable-alias</code><dd>Allow alias expansion and include the <code>alias</code> and <code>unalias</code>
builtins (see <a href="#Aliases">Aliases</a>).
<br><dt><code>--enable-arith-for-command</code><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>).
<br><dt><code>--enable-array-variables</code><dd>Include support for one-dimensional array shell variables
(see <a href="#Arrays">Arrays</a>).
<br><dt><code>--enable-bang-history</code><dd>Include support for <code>csh</code>-like history substitution
(see <a href="#History-Interaction">History Interaction</a>).
<br><dt><code>--enable-brace-expansion</code><dd>Include <code>csh</code>-like brace expansion
( <code>b{a,b}c</code> ==> <code>bac bbc</code> ).
See <a href="#Brace-Expansion">Brace Expansion</a>, for a complete description.
<br><dt><code>--enable-command-timing</code><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.
<br><dt><code>--enable-cond-command</code><dd>Include support for the <code>[[</code> conditional command.
(see <a href="#Conditional-Constructs">Conditional Constructs</a>).
<br><dt><code>--enable-cond-regexp</code><dd>Include support for matching POSIX regular expressions using the
`<samp><span class="samp">=~</span></samp>' binary operator in the <code>[[</code> conditional command.
(see <a href="#Conditional-Constructs">Conditional Constructs</a>).
<br><dt><code>--enable-debugger</code><dd>Include support for the bash debugger (distributed separately).
<br><dt><code>--enable-directory-stack</code><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>).
<br><dt><code>--enable-disabled-builtins</code><dd>Allow builtin commands to be invoked via `<samp><span class="samp">builtin xxx</span></samp>'
even after <code>xxx</code> has been disabled using `<samp><span class="samp">enable -n xxx</span></samp>'.
See <a href="#Bash-Builtins">Bash Builtins</a>, for details of the <code>builtin</code> and
<code>enable</code> builtin commands.
<br><dt><code>--enable-dparen-arithmetic</code><dd>Include support for the <code>((...))</code> command
(see <a href="#Conditional-Constructs">Conditional Constructs</a>).
<br><dt><code>--enable-extended-glob</code><dd>Include support for the extended pattern matching features described
above under <a href="#Pattern-Matching">Pattern Matching</a>.
<br><dt><code>--enable-help-builtin</code><dd>Include the <code>help</code> builtin, which displays help on shell builtins and
variables (see <a href="#Bash-Builtins">Bash Builtins</a>).
<br><dt><code>--enable-history</code><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>).
<br><dt><code>--enable-job-control</code><dd>This enables the job control features (see <a href="#Job-Control">Job Control</a>),
if the operating system supports them.
<br><dt><code>--enable-multibyte</code><dd>This enables support for multibyte characters if the operating
system provides the necessary support.
<br><dt><code>--enable-net-redirections</code><dd>This enables the special handling of filenames of the form
<code>/dev/tcp/</code><var>host</var><code>/</code><var>port</var> and
<code>/dev/udp/</code><var>host</var><code>/</code><var>port</var>
when used in redirections (see <a href="#Redirections">Redirections</a>).
<br><dt><code>--enable-process-substitution</code><dd>This enables process substitution (see <a href="#Process-Substitution">Process Substitution</a>) if
the operating system provides the necessary support.
<br><dt><code>--enable-progcomp</code><dd>Enable the programmable completion facilities
(see <a href="#Programmable-Completion">Programmable Completion</a>).
If Readline is not enabled, this option has no effect.
<br><dt><code>--enable-prompt-string-decoding</code><dd>Turn on the interpretation of a number of backslash-escaped characters
in the <samp><span class="env">$PS1</span></samp>, <samp><span class="env">$PS2</span></samp>, <samp><span class="env">$PS3</span></samp>, and <samp><span class="env">$PS4</span></samp> prompt
strings. See <a href="#Printing-a-Prompt">Printing a Prompt</a>, for a complete list of prompt
string escape sequences.
<br><dt><code>--enable-readline</code><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>).
<br><dt><code>--enable-restricted</code><dd>Include support for a <dfn>restricted shell</dfn>. 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.
<br><dt><code>--enable-select</code><dd>Include the <code>select</code> builtin, which allows the generation of simple
menus (see <a href="#Conditional-Constructs">Conditional Constructs</a>).
<br><dt><code>--enable-separate-helpfiles</code><dd>Use external files for the documentation displayed by the <code>help</code> builtin
instead of storing the text internally.
<br><dt><code>--enable-single-help-strings</code><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.
<br><dt><code>--enable-strict-posix-default</code><dd>Make Bash <span class="sc">posix</span>-conformant by default (see <a href="#Bash-POSIX-Mode">Bash POSIX Mode</a>).
<br><dt><code>--enable-usg-echo-default</code><dd>A synonym for <code>--enable-xpg-echo-default</code>.
<br><dt><code>--enable-xpg-echo-default</code><dd>Make the <code>echo</code> builtin expand backslash-escaped characters by default,
without requiring the <samp><span class="option">-e</span></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 Builtins</a>, for a description of the escape sequences that
<code>echo</code> recognizes.
</dl>
<p>The file <samp><span class="file">config-top.h</span></samp> contains C Preprocessor
`<samp><span class="samp">#define</span></samp>' 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.
<div class="node">
<p><hr>
<a name="Reporting-Bugs"></a>
Next: <a rel="next" accesskey="n" href="#Major-Differences-From-The-Bourne-Shell">Major Differences From The Bourne Shell</a>,
Previous: <a rel="previous" accesskey="p" href="#Installing-Bash">Installing Bash</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="appendix">Appendix A Reporting Bugs</h2>
<p>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/bash/">ftp://ftp.gnu.org/pub/bash/</a>.
<p>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 `philosophical' 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>.
<p>All bug reports should include:
<ul>
<li>The version number of Bash.
<li>The hardware and operating system.
<li>The compiler used to compile Bash.
<li>A description of the bug behaviour.
<li>A short script or `recipe' which exercises the bug and may be used
to reproduce it.
</ul>
<p class="noindent"><code>bashbug</code> inserts the first three items automatically into
the template it provides for filing a bug report.
<p>Please send all reports concerning this manual to
<a href="mailto:chet@po.CWRU.Edu">chet@po.CWRU.Edu</a>.
<div class="node">
<p><hr>
<a name="Major-Differences-From-The-Bourne-Shell"></a>
Next: <a rel="next" accesskey="n" href="#Copying-This-Manual">Copying This Manual</a>,
Previous: <a rel="previous" accesskey="p" href="#Reporting-Bugs">Reporting Bugs</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="appendix">Appendix B Major Differences From The Bourne Shell</h2>
<p>Bash implements essentially the same grammar, parameter and
variable expansion, redirection, and quoting as the Bourne Shell.
Bash uses the <span class="sc">posix</span> 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 <span class="sc">posix</span>-conformant, even where the <span class="sc">posix</span> specification
differs from traditional <code>sh</code> behavior (see <a href="#Bash-POSIX-Mode">Bash POSIX Mode</a>).
<li>Bash has multi-character invocation options (see <a href="#Invoking-Bash">Invoking Bash</a>).
<li>Bash has command-line editing (see <a href="#Command-Line-Editing">Command Line Editing</a>) and
the <code>bind</code> builtin.
<li>Bash provides a programmable word completion mechanism
(see <a href="#Programmable-Completion">Programmable Completion</a>), and two builtin commands,
<code>complete</code> and <code>compgen</code>, to manipulate it.
<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>Bash implements <code>csh</code>-like history expansion
(see <a href="#History-Interaction">History Interaction</a>).
<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>The <code>$'...'</code> quoting syntax, which expands ANSI-C
backslash-escaped characters in the text between the single quotes,
is supported (see <a href="#ANSI_002dC-Quoting">ANSI-C Quoting</a>).
<li>Bash supports the <code>$"..."</code> quoting syntax to do
locale-specific translation of the characters between the double
quotes. The <samp><span class="option">-D</span></samp>, <samp><span class="option">--dump-strings</span></samp>, and <samp><span class="option">--dump-po-strings</span></samp>
invocation options list the translatable strings found in a script
(see <a href="#Locale-Translation">Locale Translation</a>).
<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 `<samp><span class="samp">-o pipefail</span></samp>' option to <code>set</code> will cause a pipeline to
return a failure status if any command fails.
<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
<samp><span class="env">TIMEFORMAT</span></samp> variable.
<li>Bash implements the <code>for (( </code><var>expr1</var><code> ; </code><var>expr2</var><code> ; </code><var>expr3</var><code> ))</code>
arithmetic for command, similar to the C language (see <a href="#Looping-Constructs">Looping Constructs</a>).
<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>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>Bash provides optional case-insensitive matching for the <code>case</code> and
<code>[[</code> constructs.
<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>Bash implements command aliases and the <code>alias</code> and <code>unalias</code>
builtins (see <a href="#Aliases">Aliases</a>).
<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>Variables present in the shell'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>Bash supports the `<samp><span class="samp">+=</span></samp>' assignment operator, which appends to the value
of the variable named on the left hand side.
<li>Bash includes the <span class="sc">posix</span> pattern removal `<samp><span class="samp">%</span></samp>', `<samp><span class="samp">#</span></samp>', `<samp><span class="samp">%%</span></samp>'
and `<samp><span class="samp">##</span></samp>' expansions to remove leading or trailing substrings from
variable values (see <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>).
<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>The expansion <code>${var:</code><var>offset</var><code>[:</code><var>length</var><code>]}</code>,
which expands to the substring of <code>var</code>'s value of length
<var>length</var>, beginning at <var>offset</var>, is present
(see <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>).
<li>The expansion
<code>${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 <code>var</code>, is available (see <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>).
<li>The expansion <code>${!</code><var>prefix}*</var> expansion, which expands to
the names of all shell variables whose names begin with <var>prefix</var>,
is available (see <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>).
<li>Bash has <var>indirect</var> variable expansion using <code>${!word}</code>
(see <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a>).
<li>Bash can expand positional parameters beyond <code>$9</code> using
<code>${</code><var>num</var><code>}</code>.
<li>The <span class="sc">posix</span> <code>$()</code> form of command substitution
is implemented (see <a href="#Command-Substitution">Command Substitution</a>),
and preferred to the Bourne shell's <code>``</code> (which
is also implemented for backwards compatibility).
<li>Bash has process substitution (see <a href="#Process-Substitution">Process Substitution</a>).
<li>Bash automatically assigns variables that provide information about the
current user (<samp><span class="env">UID</span></samp>, <samp><span class="env">EUID</span></samp>, and <samp><span class="env">GROUPS</span></samp>), the current host
(<samp><span class="env">HOSTTYPE</span></samp>, <samp><span class="env">OSTYPE</span></samp>, <samp><span class="env">MACHTYPE</span></samp>, and <samp><span class="env">HOSTNAME</span></samp>),
and the instance of Bash that is running (<samp><span class="env">BASH</span></samp>,
<samp><span class="env">BASH_VERSION</span></samp>, and <samp><span class="env">BASH_VERSINFO</span></samp>). See <a href="#Bash-Variables">Bash Variables</a>,
for details.
<li>The <samp><span class="env">IFS</span></samp> 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>Bash implements the full set of <span class="sc">posix</span> filename expansion operators,
including <var>character classes</var>, <var>equivalence classes</var>, and
<var>collating symbols</var> (see <a href="#Filename-Expansion">Filename Expansion</a>).
<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>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>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 Builtins</a>).
<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>Bash performs filename expansion on filenames specified as operands
to input and output redirection operators (see <a href="#Redirections">Redirections</a>).
<li>Bash contains the `<samp><span class="samp"><></span></samp>' redirection operator, allowing a file to be
opened for both reading and writing, and the `<samp><span class="samp">&></span></samp>' redirection
operator, for directing standard output and standard error to the same
file (see <a href="#Redirections">Redirections</a>).
<li>Bash includes the `<samp><span class="samp"><<<</span></samp>' redirection operator, allowing a string to
be used as the standard input to a command.
<li>Bash implements the `<samp><span class="samp">[n]<&</span><var>word</var></samp>' and `<samp><span class="samp">[n]>&</span><var>word</var></samp>'
redirection operators, which move one file descriptor to another.
<li>Bash treats a number of filenames specially when they are
used in redirection operators (see <a href="#Redirections">Redirections</a>).
<li>Bash can open network connections to arbitrary machines and services
with the redirection operators (see <a href="#Redirections">Redirections</a>).
<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 `<samp><span class="samp">>|</span></samp>' redirection operator may be used to override <code>noclobber</code>.
<li>The Bash <code>cd</code> and <code>pwd</code> builtins (see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>)
each take <samp><span class="option">-L</span></samp> and <samp><span class="option">-P</span></samp> options to switch between logical and
physical modes.
<li>Bash allows a function to override a builtin with the same name, and provides
access to that builtin's functionality within the function via the
<code>builtin</code> and <code>command</code> builtins (see <a href="#Bash-Builtins">Bash Builtins</a>).
<li>The <code>command</code> builtin allows selective disabling of functions
when command lookup is performed (see <a href="#Bash-Builtins">Bash Builtins</a>).
<li>Individual builtins may be enabled or disabled using the <code>enable</code>
builtin (see <a href="#Bash-Builtins">Bash Builtins</a>).
<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>Shell functions may be exported to children via the environment
using <code>export -f</code> (see <a href="#Shell-Functions">Shell Functions</a>).
<li>The Bash <code>export</code>, <code>readonly</code>, and <code>declare</code> builtins can
take a <samp><span class="option">-f</span></samp> option to act on shell functions, a <samp><span class="option">-p</span></samp> option to
display variables with various attributes set in a format that can be
used as shell input, a <samp><span class="option">-n</span></samp> option to remove various variable
attributes, and `<samp><span class="samp">name=value</span></samp>' arguments to set variable attributes
and values simultaneously.
<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 <samp><span class="env">$PATH</span></samp>, using `<samp><span class="samp">hash -p</span></samp>'
(see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>).
<li>Bash includes a <code>help</code> builtin for quick reference to shell
facilities (see <a href="#Bash-Builtins">Bash Builtins</a>).
<li>The <code>printf</code> builtin is available to display formatted output
(see <a href="#Bash-Builtins">Bash Builtins</a>).
<li>The Bash <code>read</code> builtin (see <a href="#Bash-Builtins">Bash Builtins</a>)
will read a line ending in `<samp><span class="samp">\</span></samp>' with
the <samp><span class="option">-r</span></samp> option, and will use the <samp><span class="env">REPLY</span></samp> 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><span class="option">-p</span></samp> option and will use
Readline to obtain the line when given the <samp><span class="option">-e</span></samp> option.
The <code>read</code> builtin also has additional options to control input:
the <samp><span class="option">-s</span></samp> option will turn off echoing of input characters as
they are read, the <samp><span class="option">-t</span></samp> option will allow <code>read</code> to time out
if input does not arrive within a specified number of seconds, the
<samp><span class="option">-n</span></samp> option will allow reading only a specified number of
characters rather than a full line, and the <samp><span class="option">-d</span></samp> option will read
until a particular character rather than newline.
<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>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>Bash has much more optional behavior controllable with the <code>set</code>
builtin (see <a href="#The-Set-Builtin">The Set Builtin</a>).
<li>The `<samp><span class="samp">-x</span></samp>' (<code>xtrace</code>) option displays commands other than
simple commands when performing an execution trace
(see <a href="#The-Set-Builtin">The Set Builtin</a>).
<li>The <code>test</code> builtin (see <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a>)
is slightly different, as it implements the <span class="sc">posix</span> algorithm,
which specifies the behavior based on the number of arguments.
<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>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.
<p>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.
<p>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 an <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>The Bash <code>type</code> builtin is more extensive and gives more information
about the names it finds (see <a href="#Bash-Builtins">Bash Builtins</a>).
<li>The Bash <code>umask</code> builtin permits a <samp><span class="option">-p</span></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>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
<samp><span class="env">DIRSTACK</span></samp> shell variable.
<li>Bash interprets special backslash-escaped characters in the prompt
strings when interactive (see <a href="#Printing-a-Prompt">Printing a Prompt</a>).
<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>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>Bash includes a number of features to support a separate debugger for
shell scripts.
<li>The SVR4.2 shell has two privilege-related builtins
(<code>mldmode</code> and <code>priv</code>) not present in Bash.
<li>Bash does not have the <code>stop</code> or <code>newgrp</code> builtins.
<li>Bash does not use the <samp><span class="env">SHACCT</span></samp> variable or perform shell accounting.
<li>The SVR4.2 <code>sh</code> uses a <samp><span class="env">TIMEOUT</span></samp> variable like Bash uses
<samp><span class="env">TMOUT</span></samp>.
</ul>
<p class="noindent">More features unique to Bash may be found in <a href="#Bash-Features">Bash Features</a>.
<h3 class="appendixsec">B.1 Implementation Differences From The SVR4.2 Shell</h3>
<p>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>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>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>In a questionable attempt at security, the SVR4.2 shell,
when invoked without the <samp><span class="option">-p</span></samp> option, will alter its real
and effective <span class="sc">uid</span> and <span class="sc">gid</span> if they are less than some
magic threshold value, commonly 100.
This can lead to unexpected results.
<li>The SVR4.2 shell does not allow users to trap <code>SIGSEGV</code>,
<code>SIGALRM</code>, or <code>SIGCHLD</code>.
<li>The SVR4.2 shell does not allow the <samp><span class="env">IFS</span></samp>, <samp><span class="env">MAILCHECK</span></samp>,
<samp><span class="env">PATH</span></samp>, <samp><span class="env">PS1</span></samp>, or <samp><span class="env">PS2</span></samp> variables to be unset.
<li>The SVR4.2 shell treats `<samp><span class="samp">^</span></samp>' as the undocumented equivalent of
`<samp><span class="samp">|</span></samp>'.
<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 `<samp><span class="samp">-</span></samp>'.
<li>The SVR4.2 shell exits a script if any builtin fails; Bash exits
a script only if one of the <span class="sc">posix</span> special builtins fails, and
only for certain failures, as enumerated in the <span class="sc">posix</span> standard.
<li>The SVR4.2 shell behaves differently when invoked as <code>jsh</code>
(it turns on job control).
</ul>
<div class="node">
<p><hr>
<a name="Copying-This-Manual"></a>
Next: <a rel="next" accesskey="n" href="#Builtin-Index">Builtin Index</a>,
Previous: <a rel="previous" accesskey="p" href="#Major-Differences-From-The-Bourne-Shell">Major Differences From The Bourne Shell</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="appendix">Appendix C Copying This Manual</h2>
<ul class="menu">
<li><a accesskey="1" href="#GNU-Free-Documentation-License">GNU Free Documentation License</a>: License for copying this manual.
</ul>
<div class="node">
<p><hr>
<a name="GNU-Free-Documentation-License"></a>
Up: <a rel="up" accesskey="u" href="#Copying-This-Manual">Copying This Manual</a>
</div>
<h3 class="appendixsec">C.1 GNU Free Documentation License</h3>
<p><a name="index-FDL_002c-GNU-Free-Documentation-License-385"></a><div align="center">Version 1.2, November 2002</div>
<pre class="display"> Copyright © 2000,2001,2002 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA 02111-1307, USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
</pre>
<ol type=1 start=0>
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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.
<p>The “Title Page” 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, “Title Page” means
the text near the most prominent appearance of the work's title,
preceding the beginning of the body of the text.
<p>A section “Entitled XYZ” 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 “Acknowledgements”,
“Dedications”, “Endorsements”, or “History”.) To “Preserve the Title”
of such a section when you modify the Document means that it remains a
section “Entitled XYZ” according to this definition.
<p>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>VERBATIM COPYING
<p>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.
<p>You may also lend copies, under the same conditions stated above, and
you may publicly display copies.
<li>COPYING IN QUANTITY
<p>If you publish printed copies (or copies in media that commonly have
printed covers) of the Document, numbering more than 100, and the
Document'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.
<p>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.
<p>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.
<p>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>MODIFICATIONS
<p>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>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>State on the Title page the name of the publisher of the
Modified Version, as the publisher.
<li>Preserve all the copyright notices of the Document.
<li>Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.
<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>Preserve in that license notice the full lists of Invariant Sections
and required Cover Texts given in the Document's license notice.
<li>Include an unaltered copy of this License.
<li>Preserve the section Entitled “History”, 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 “History” 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>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 “History” 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>For any section Entitled “Acknowledgements” or “Dedications”, 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>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>Delete any section Entitled “Endorsements”. Such a section
may not be included in the Modified Version.
<li>Do not retitle any existing section to be Entitled “Endorsements” or
to conflict in title with any Invariant Section.
<li>Preserve any Warranty Disclaimers.
</ol>
<p>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's license notice.
These titles must be distinct from any other section titles.
<p>You may add a section Entitled “Endorsements”, provided it contains
nothing but endorsements of your Modified Version by various
parties—for example, statements of peer review or that the text has
been approved by an organization as the authoritative definition of a
standard.
<p>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
through arrangements made by) any one entity. If the Document already
includes a cover text for the same cover, previously added by you or
by arrangement made by the same entity you are acting on behalf of,
you may not add another; but you may replace the old one, on explicit
permission from the previous publisher that added the old one.
<p>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>COMBINING DOCUMENTS
<p>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.
<p>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
author or publisher of that section if known, or else a unique number.
Make the same adjustment to the section titles in the list of
Invariant Sections in the license notice of the combined work.
<p>In the combination, you must combine any sections Entitled “History”
in the various original documents, forming one section Entitled
“History”; likewise combine any sections Entitled “Acknowledgements”,
and any sections Entitled “Dedications”. You must delete all
sections Entitled “Endorsements.”
<li>COLLECTIONS OF DOCUMENTS
<p>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.
<p>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>AGGREGATION WITH INDEPENDENT WORKS
<p>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 “aggregate” if the copyright
resulting from the compilation is not used to limit the legal rights
of the compilation's users beyond what the individual works permit.
When the Document is included an aggregate, this License does not
apply to the other works in the aggregate which are not themselves
derivative works of the Document.
<p>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'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>TRANSLATION
<p>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.
<p>If a section in the Document is Entitled “Acknowledgements”,
“Dedications”, or “History”, the requirement (section 4) to Preserve
its Title (section 1) will typically require changing the actual
title.
<li>TERMINATION
<p>You may not copy, modify, sublicense, or distribute the Document except
as expressly provided for under this License. Any other attempt to
copy, modify, sublicense or distribute the Document is void, and will
automatically terminate your rights under this License. However,
parties who have received copies, or rights, from you under this
License will not have their licenses terminated so long as such
parties remain in full compliance.
<li>FUTURE REVISIONS OF THIS LICENSE
<p>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>.
<p>Each version of the License is given a distinguishing version number.
If the Document specifies that a particular numbered version of this
License “or any later version” 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
Free Software Foundation. If the Document does not specify a version
number of this License, you may choose any version ever published (not
as a draft) by the Free Software Foundation.
</ol>
<h4 class="appendixsubsec">C.1.1 ADDENDUM: How to use this License for your documents</h4>
<p>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:
<pre class="smallexample"> 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 1.2
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>
<p>If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the “with...Texts.” line with this:
<pre class="smallexample"> 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>
<p>If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.
<p>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.
<!-- Local Variables: -->
<!-- ispell-local-pdict: "ispell-dict" -->
<!-- End: -->
<div class="node">
<p><hr>
<a name="Builtin-Index"></a>
Next: <a rel="next" accesskey="n" href="#Reserved-Word-Index">Reserved Word Index</a>,
Previous: <a rel="previous" accesskey="p" href="#Copying-This-Manual">Copying This Manual</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="unnumbered">Index of Shell Builtin Commands</h2>
<ul class="index-bt" compact>
<li><a href="#index-g_t_002e-107"><code>.</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-g_t_003a-106"><code>:</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-g_t_005b-122"><code>[</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-alias-127"><code>alias</code></a>: <a href="#Bash-Builtins">Bash Builtins</a></li>
<li><a href="#index-bg-256"><code>bg</code></a>: <a href="#Job-Control-Builtins">Job Control Builtins</a></li>
<li><a href="#index-bind-128"><code>bind</code></a>: <a href="#Bash-Builtins">Bash Builtins</a></li>
<li><a href="#index-break-108"><code>break</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-builtin-129"><code>builtin</code></a>: <a href="#Bash-Builtins">Bash Builtins</a></li>
<li><a href="#index-caller-130"><code>caller</code></a>: <a href="#Bash-Builtins">Bash Builtins</a></li>
<li><a href="#index-cd-109"><code>cd</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-command-131"><code>command</code></a>: <a href="#Bash-Builtins">Bash Builtins</a></li>
<li><a href="#index-compgen-370"><code>compgen</code></a>: <a href="#Programmable-Completion-Builtins">Programmable Completion Builtins</a></li>
<li><a href="#index-complete-371"><code>complete</code></a>: <a href="#Programmable-Completion-Builtins">Programmable Completion Builtins</a></li>
<li><a href="#index-continue-110"><code>continue</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-declare-132"><code>declare</code></a>: <a href="#Bash-Builtins">Bash Builtins</a></li>
<li><a href="#index-dirs-246"><code>dirs</code></a>: <a href="#Directory-Stack-Builtins">Directory Stack Builtins</a></li>
<li><a href="#index-disown-261"><code>disown</code></a>: <a href="#Job-Control-Builtins">Job Control Builtins</a></li>
<li><a href="#index-echo-133"><code>echo</code></a>: <a href="#Bash-Builtins">Bash Builtins</a></li>
<li><a href="#index-enable-134"><code>enable</code></a>: <a href="#Bash-Builtins">Bash Builtins</a></li>
<li><a href="#index-eval-111"><code>eval</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-exec-112"><code>exec</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-exit-113"><code>exit</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-export-114"><code>export</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-fc-376"><code>fc</code></a>: <a href="#Bash-History-Builtins">Bash History Builtins</a></li>
<li><a href="#index-fg-257"><code>fg</code></a>: <a href="#Job-Control-Builtins">Job Control Builtins</a></li>
<li><a href="#index-getopts-115"><code>getopts</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-hash-116"><code>hash</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-help-135"><code>help</code></a>: <a href="#Bash-Builtins">Bash Builtins</a></li>
<li><a href="#index-history-377"><code>history</code></a>: <a href="#Bash-History-Builtins">Bash History Builtins</a></li>
<li><a href="#index-jobs-258"><code>jobs</code></a>: <a href="#Job-Control-Builtins">Job Control Builtins</a></li>
<li><a href="#index-kill-259"><code>kill</code></a>: <a href="#Job-Control-Builtins">Job Control Builtins</a></li>
<li><a href="#index-let-136"><code>let</code></a>: <a href="#Bash-Builtins">Bash Builtins</a></li>
<li><a href="#index-local-137"><code>local</code></a>: <a href="#Bash-Builtins">Bash Builtins</a></li>
<li><a href="#index-logout-138"><code>logout</code></a>: <a href="#Bash-Builtins">Bash Builtins</a></li>
<li><a href="#index-popd-247"><code>popd</code></a>: <a href="#Directory-Stack-Builtins">Directory Stack Builtins</a></li>
<li><a href="#index-printf-139"><code>printf</code></a>: <a href="#Bash-Builtins">Bash Builtins</a></li>
<li><a href="#index-pushd-248"><code>pushd</code></a>: <a href="#Directory-Stack-Builtins">Directory Stack Builtins</a></li>
<li><a href="#index-pwd-117"><code>pwd</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-read-140"><code>read</code></a>: <a href="#Bash-Builtins">Bash Builtins</a></li>
<li><a href="#index-readonly-118"><code>readonly</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-return-119"><code>return</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-set-146"><code>set</code></a>: <a href="#The-Set-Builtin">The Set Builtin</a></li>
<li><a href="#index-shift-120"><code>shift</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-shopt-147"><code>shopt</code></a>: <a href="#The-Shopt-Builtin">The Shopt Builtin</a></li>
<li><a href="#index-source-141"><code>source</code></a>: <a href="#Bash-Builtins">Bash Builtins</a></li>
<li><a href="#index-suspend-262"><code>suspend</code></a>: <a href="#Job-Control-Builtins">Job Control Builtins</a></li>
<li><a href="#index-test-121"><code>test</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-times-123"><code>times</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-trap-124"><code>trap</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-type-142"><code>type</code></a>: <a href="#Bash-Builtins">Bash Builtins</a></li>
<li><a href="#index-typeset-143"><code>typeset</code></a>: <a href="#Bash-Builtins">Bash Builtins</a></li>
<li><a href="#index-ulimit-144"><code>ulimit</code></a>: <a href="#Bash-Builtins">Bash Builtins</a></li>
<li><a href="#index-umask-125"><code>umask</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-unalias-145"><code>unalias</code></a>: <a href="#Bash-Builtins">Bash Builtins</a></li>
<li><a href="#index-unset-126"><code>unset</code></a>: <a href="#Bourne-Shell-Builtins">Bourne Shell Builtins</a></li>
<li><a href="#index-wait-260"><code>wait</code></a>: <a href="#Job-Control-Builtins">Job Control Builtins</a></li>
</ul><div class="node">
<p><hr>
<a name="Reserved-Word-Index"></a>
Next: <a rel="next" accesskey="n" href="#Variable-Index">Variable Index</a>,
Previous: <a rel="previous" accesskey="p" href="#Builtin-Index">Builtin Index</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="unnumbered">Index of Shell Reserved Words</h2>
<ul class="index-rw" compact>
<li><a href="#index-g_t_0021-37"><code>!</code></a>: <a href="#Pipelines">Pipelines</a></li>
<li><a href="#index-g_t_005b_005b-57"><code>[[</code></a>: <a href="#Conditional-Constructs">Conditional Constructs</a></li>
<li><a href="#index-g_t_005d_005d-58"><code>]]</code></a>: <a href="#Conditional-Constructs">Conditional Constructs</a></li>
<li><a href="#index-case-53"><code>case</code></a>: <a href="#Conditional-Constructs">Conditional Constructs</a></li>
<li><a href="#index-do-43"><code>do</code></a>: <a href="#Looping-Constructs">Looping Constructs</a></li>
<li><a href="#index-done-44"><code>done</code></a>: <a href="#Looping-Constructs">Looping Constructs</a></li>
<li><a href="#index-elif-51"><code>elif</code></a>: <a href="#Conditional-Constructs">Conditional Constructs</a></li>
<li><a href="#index-else-50"><code>else</code></a>: <a href="#Conditional-Constructs">Conditional Constructs</a></li>
<li><a href="#index-esac-55"><code>esac</code></a>: <a href="#Conditional-Constructs">Conditional Constructs</a></li>
<li><a href="#index-fi-52"><code>fi</code></a>: <a href="#Conditional-Constructs">Conditional Constructs</a></li>
<li><a href="#index-for-46"><code>for</code></a>: <a href="#Looping-Constructs">Looping Constructs</a></li>
<li><a href="#index-function-64"><code>function</code></a>: <a href="#Shell-Functions">Shell Functions</a></li>
<li><a href="#index-if-48"><code>if</code></a>: <a href="#Conditional-Constructs">Conditional Constructs</a></li>
<li><a href="#index-in-54"><code>in</code></a>: <a href="#Conditional-Constructs">Conditional Constructs</a></li>
<li><a href="#index-select-56"><code>select</code></a>: <a href="#Conditional-Constructs">Conditional Constructs</a></li>
<li><a href="#index-then-49"><code>then</code></a>: <a href="#Conditional-Constructs">Conditional Constructs</a></li>
<li><a href="#index-time-36"><code>time</code></a>: <a href="#Pipelines">Pipelines</a></li>
<li><a href="#index-until-42"><code>until</code></a>: <a href="#Looping-Constructs">Looping Constructs</a></li>
<li><a href="#index-while-45"><code>while</code></a>: <a href="#Looping-Constructs">Looping Constructs</a></li>
<li><a href="#index-g_t_0040_007b-60"><code>{</code></a>: <a href="#Command-Grouping">Command Grouping</a></li>
<li><a href="#index-g_t_0040_007d-61"><code>}</code></a>: <a href="#Command-Grouping">Command Grouping</a></li>
</ul><div class="node">
<p><hr>
<a name="Variable-Index"></a>
Next: <a rel="next" accesskey="n" href="#Function-Index">Function Index</a>,
Previous: <a rel="previous" accesskey="p" href="#Reserved-Word-Index">Reserved Word Index</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="unnumbered">Parameter and Variable Index</h2>
<ul class="index-vr" compact>
<li><a href="#index-g_t_0021-76"><code>!</code></a>: <a href="#Special-Parameters">Special Parameters</a></li>
<li><a href="#index-g_t_0023-72"><code>#</code></a>: <a href="#Special-Parameters">Special Parameters</a></li>
<li><a href="#index-g_t_0024-75"><code>$</code></a>: <a href="#Special-Parameters">Special Parameters</a></li>
<li><a href="#index-g_t_002a-70"><code>*</code></a>: <a href="#Special-Parameters">Special Parameters</a></li>
<li><a href="#index-g_t_002d-74"><code>-</code></a>: <a href="#Special-Parameters">Special Parameters</a></li>
<li><a href="#index-g_t0-77"><code>0</code></a>: <a href="#Special-Parameters">Special Parameters</a></li>
<li><a href="#index-g_t_003f-73"><code>?</code></a>: <a href="#Special-Parameters">Special Parameters</a></li>
<li><a href="#index-g_t_0040_0040-71"><code>@</code></a>: <a href="#Special-Parameters">Special Parameters</a></li>
<li><a href="#index-g_t_005f-78"><code>_</code></a>: <a href="#Special-Parameters">Special Parameters</a></li>
<li><a href="#index-auto_005fresume-263"><code>auto_resume</code></a>: <a href="#Job-Control-Variables">Job Control Variables</a></li>
<li><a href="#index-BASH-159"><code>BASH</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-BASH_005fARGC-161"><code>BASH_ARGC</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-BASH_005fARGV-162"><code>BASH_ARGV</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-BASH_005fCOMMAND-163"><code>BASH_COMMAND</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-BASH_005fENV-164"><code>BASH_ENV</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-BASH_005fEXECUTION_005fSTRING-165"><code>BASH_EXECUTION_STRING</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-BASH_005fLINENO-166"><code>BASH_LINENO</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-BASH_005fREMATCH-167"><code>BASH_REMATCH</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-BASH_005fSOURCE-168"><code>BASH_SOURCE</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-BASH_005fSUBSHELL-169"><code>BASH_SUBSHELL</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-BASH_005fVERSINFO-170"><code>BASH_VERSINFO</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-BASH_005fVERSION-171"><code>BASH_VERSION</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-BASHPID-160"><code>BASHPID</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-bell_002dstyle-274"><code>bell-style</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-bind_002dtty_002dspecial_002dchars-275"><code>bind-tty-special-chars</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-CDPATH-149"><code>CDPATH</code></a>: <a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></li>
<li><a href="#index-COLUMNS-172"><code>COLUMNS</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-comment_002dbegin-276"><code>comment-begin</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-COMP_005fCWORD-173"><code>COMP_CWORD</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-COMP_005fKEY-177"><code>COMP_KEY</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-COMP_005fLINE-174"><code>COMP_LINE</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-COMP_005fPOINT-175"><code>COMP_POINT</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-COMP_005fTYPE-176"><code>COMP_TYPE</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-COMP_005fWORDBREAKS-178"><code>COMP_WORDBREAKS</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-COMP_005fWORDS-179"><code>COMP_WORDS</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-completion_002dquery_002ditems-277"><code>completion-query-items</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-COMPREPLY-180"><code>COMPREPLY</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-convert_002dmeta-278"><code>convert-meta</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-DIRSTACK-181"><code>DIRSTACK</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-disable_002dcompletion-279"><code>disable-completion</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-editing_002dmode-280"><code>editing-mode</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-EMACS-182"><code>EMACS</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-enable_002dkeypad-281"><code>enable-keypad</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-EUID-183"><code>EUID</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-expand_002dtilde-282"><code>expand-tilde</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-FCEDIT-184"><code>FCEDIT</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-FIGNORE-185"><code>FIGNORE</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-FUNCNAME-186"><code>FUNCNAME</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-GLOBIGNORE-187"><code>GLOBIGNORE</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-GROUPS-188"><code>GROUPS</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-histchars-189"><code>histchars</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-HISTCMD-190"><code>HISTCMD</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-HISTCONTROL-191"><code>HISTCONTROL</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-HISTFILE-192"><code>HISTFILE</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-HISTFILESIZE-193"><code>HISTFILESIZE</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-HISTIGNORE-194"><code>HISTIGNORE</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-history_002dpreserve_002dpoint-283"><code>history-preserve-point</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-HISTSIZE-195"><code>HISTSIZE</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-HISTTIMEFORMAT-196"><code>HISTTIMEFORMAT</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-HOME-150"><code>HOME</code></a>: <a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></li>
<li><a href="#index-horizontal_002dscroll_002dmode-284"><code>horizontal-scroll-mode</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-HOSTFILE-197"><code>HOSTFILE</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-HOSTNAME-198"><code>HOSTNAME</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-HOSTTYPE-199"><code>HOSTTYPE</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-IFS-151"><code>IFS</code></a>: <a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></li>
<li><a href="#index-IGNOREEOF-200"><code>IGNOREEOF</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-input_002dmeta-285"><code>input-meta</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-INPUTRC-201"><code>INPUTRC</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-isearch_002dterminators-287"><code>isearch-terminators</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-keymap-288"><code>keymap</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-LANG-202"><code>LANG</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-LC_005fALL-203"><code>LC_ALL</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-LC_005fCOLLATE-204"><code>LC_COLLATE</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-LC_005fCTYPE-205"><code>LC_CTYPE</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-LC_005fMESSAGES-28"><code>LC_MESSAGES</code></a>: <a href="#Locale-Translation">Locale Translation</a></li>
<li><a href="#index-LC_005fMESSAGES-206"><code>LC_MESSAGES</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-LC_005fNUMERIC-207"><code>LC_NUMERIC</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-LINENO-208"><code>LINENO</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-LINES-209"><code>LINES</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-MACHTYPE-210"><code>MACHTYPE</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-MAIL-152"><code>MAIL</code></a>: <a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></li>
<li><a href="#index-MAILCHECK-211"><code>MAILCHECK</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-MAILPATH-153"><code>MAILPATH</code></a>: <a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></li>
<li><a href="#index-mark_002dmodified_002dlines-289"><code>mark-modified-lines</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-mark_002dsymlinked_002ddirectories-290"><code>mark-symlinked-directories</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-match_002dhidden_002dfiles-291"><code>match-hidden-files</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-meta_002dflag-286"><code>meta-flag</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-OLDPWD-212"><code>OLDPWD</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-OPTARG-154"><code>OPTARG</code></a>: <a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></li>
<li><a href="#index-OPTERR-213"><code>OPTERR</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-OPTIND-155"><code>OPTIND</code></a>: <a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></li>
<li><a href="#index-OSTYPE-214"><code>OSTYPE</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-output_002dmeta-292"><code>output-meta</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-page_002dcompletions-293"><code>page-completions</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-PATH-156"><code>PATH</code></a>: <a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></li>
<li><a href="#index-PIPESTATUS-215"><code>PIPESTATUS</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-POSIXLY_005fCORRECT-216"><code>POSIXLY_CORRECT</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-PPID-217"><code>PPID</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-PROMPT_005fCOMMAND-218"><code>PROMPT_COMMAND</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-PS1-157"><code>PS1</code></a>: <a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></li>
<li><a href="#index-PS2-158"><code>PS2</code></a>: <a href="#Bourne-Shell-Variables">Bourne Shell Variables</a></li>
<li><a href="#index-PS3-219"><code>PS3</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-PS4-220"><code>PS4</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-PWD-221"><code>PWD</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-RANDOM-222"><code>RANDOM</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-REPLY-223"><code>REPLY</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-SECONDS-224"><code>SECONDS</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-SHELL-225"><code>SHELL</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-SHELLOPTS-226"><code>SHELLOPTS</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-SHLVL-227"><code>SHLVL</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-show_002dall_002dif_002dambiguous-294"><code>show-all-if-ambiguous</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-show_002dall_002dif_002dunmodified-295"><code>show-all-if-unmodified</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-TEXTDOMAIN-29"><code>TEXTDOMAIN</code></a>: <a href="#Locale-Translation">Locale Translation</a></li>
<li><a href="#index-TEXTDOMAINDIR-30"><code>TEXTDOMAINDIR</code></a>: <a href="#Locale-Translation">Locale Translation</a></li>
<li><a href="#index-TIMEFORMAT-228"><code>TIMEFORMAT</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-TMOUT-229"><code>TMOUT</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-TMPDIR-230"><code>TMPDIR</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-UID-231"><code>UID</code></a>: <a href="#Bash-Variables">Bash Variables</a></li>
<li><a href="#index-visible_002dstats-296"><code>visible-stats</code></a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
</ul><div class="node">
<p><hr>
<a name="Function-Index"></a>
Next: <a rel="next" accesskey="n" href="#Concept-Index">Concept Index</a>,
Previous: <a rel="previous" accesskey="p" href="#Variable-Index">Variable Index</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="unnumbered">Function Index</h2>
<ul class="index-fn" compact>
<li><a href="#index-abort-_0028C_002dg_0029-355"><code>abort (C-g)</code></a>: <a href="#Miscellaneous-Commands">Miscellaneous Commands</a></li>
<li><a href="#index-accept_002dline-_0028Newline-or-Return_0029-305"><code>accept-line (Newline or Return)</code></a>: <a href="#Commands-For-History">Commands For History</a></li>
<li><a href="#index-backward_002dchar-_0028C_002db_0029-300"><code>backward-char (C-b)</code></a>: <a href="#Commands-For-Moving">Commands For Moving</a></li>
<li><a href="#index-backward_002ddelete_002dchar-_0028Rubout_0029-319"><code>backward-delete-char (Rubout)</code></a>: <a href="#Commands-For-Text">Commands For Text</a></li>
<li><a href="#index-backward_002dkill_002dline-_0028C_002dx-Rubout_0029-330"><code>backward-kill-line (C-x Rubout)</code></a>: <a href="#Commands-For-Killing">Commands For Killing</a></li>
<li><a href="#index-backward_002dkill_002dword-_0028M_002d_0040key_007bDEL_007d_0029-334"><code>backward-kill-word (M-<DEL>)</code></a>: <a href="#Commands-For-Killing">Commands For Killing</a></li>
<li><a href="#index-backward_002dword-_0028M_002db_0029-302"><code>backward-word (M-b)</code></a>: <a href="#Commands-For-Moving">Commands For Moving</a></li>
<li><a href="#index-beginning_002dof_002dhistory-_0028M_002d_003c_0029-308"><code>beginning-of-history (M-<)</code></a>: <a href="#Commands-For-History">Commands For History</a></li>
<li><a href="#index-beginning_002dof_002dline-_0028C_002da_0029-297"><code>beginning-of-line (C-a)</code></a>: <a href="#Commands-For-Moving">Commands For Moving</a></li>
<li><a href="#index-call_002dlast_002dkbd_002dmacro-_0028C_002dx-e_0029-353"><code>call-last-kbd-macro (C-x e)</code></a>: <a href="#Keyboard-Macros">Keyboard Macros</a></li>
<li><a href="#index-capitalize_002dword-_0028M_002dc_0029-327"><code>capitalize-word (M-c)</code></a>: <a href="#Commands-For-Text">Commands For Text</a></li>
<li><a href="#index-character_002dsearch-_0028C_002d_005d_0029-362"><code>character-search (C-])</code></a>: <a href="#Miscellaneous-Commands">Miscellaneous Commands</a></li>
<li><a href="#index-character_002dsearch_002dbackward-_0028M_002dC_002d_005d_0029-363"><code>character-search-backward (M-C-])</code></a>: <a href="#Miscellaneous-Commands">Miscellaneous Commands</a></li>
<li><a href="#index-clear_002dscreen-_0028C_002dl_0029-303"><code>clear-screen (C-l)</code></a>: <a href="#Commands-For-Moving">Commands For Moving</a></li>
<li><a href="#index-complete-_0028_0040key_007bTAB_007d_0029-346"><code>complete (<TAB>)</code></a>: <a href="#Commands-For-Completion">Commands For Completion</a></li>
<li><a href="#index-copy_002dbackward_002dword-_0028_0029-340"><code>copy-backward-word ()</code></a>: <a href="#Commands-For-Killing">Commands For Killing</a></li>
<li><a href="#index-copy_002dforward_002dword-_0028_0029-341"><code>copy-forward-word ()</code></a>: <a href="#Commands-For-Killing">Commands For Killing</a></li>
<li><a href="#index-copy_002dregion_002das_002dkill-_0028_0029-339"><code>copy-region-as-kill ()</code></a>: <a href="#Commands-For-Killing">Commands For Killing</a></li>
<li><a href="#index-delete_002dchar-_0028C_002dd_0029-318"><code>delete-char (C-d)</code></a>: <a href="#Commands-For-Text">Commands For Text</a></li>
<li><a href="#index-delete_002dchar_002dor_002dlist-_0028_0029-350"><code>delete-char-or-list ()</code></a>: <a href="#Commands-For-Completion">Commands For Completion</a></li>
<li><a href="#index-delete_002dhorizontal_002dspace-_0028_0029-337"><code>delete-horizontal-space ()</code></a>: <a href="#Commands-For-Killing">Commands For Killing</a></li>
<li><a href="#index-digit_002dargument-_0028_0040kbd_007bM_002d0_007d_002c-_0040kbd_007bM_002d1_007d_002c-_0040dots_007b_007d-_0040kbd_007bM_002d_002d_007d_0029-344"><code>digit-argument (</code><kbd>M-0</kbd><code>, </code><kbd>M-1</kbd><code>, ... </code><kbd>M--</kbd><code>)</code></a>: <a href="#Numeric-Arguments">Numeric Arguments</a></li>
<li><a href="#index-do_002duppercase_002dversion-_0028M_002da_002c-M_002db_002c-M_002d_0040var_007bx_007d_002c-_0040dots_007b_007d_0029-356"><code>do-uppercase-version (M-a, M-b, M-</code><var>x</var><code>, ...)</code></a>: <a href="#Miscellaneous-Commands">Miscellaneous Commands</a></li>
<li><a href="#index-downcase_002dword-_0028M_002dl_0029-326"><code>downcase-word (M-l)</code></a>: <a href="#Commands-For-Text">Commands For Text</a></li>
<li><a href="#index-dump_002dfunctions-_0028_0029-365"><code>dump-functions ()</code></a>: <a href="#Miscellaneous-Commands">Miscellaneous Commands</a></li>
<li><a href="#index-dump_002dmacros-_0028_0029-367"><code>dump-macros ()</code></a>: <a href="#Miscellaneous-Commands">Miscellaneous Commands</a></li>
<li><a href="#index-dump_002dvariables-_0028_0029-366"><code>dump-variables ()</code></a>: <a href="#Miscellaneous-Commands">Miscellaneous Commands</a></li>
<li><a href="#index-end_002dkbd_002dmacro-_0028C_002dx-_0029_0029-352"><code>end-kbd-macro (C-x ))</code></a>: <a href="#Keyboard-Macros">Keyboard Macros</a></li>
<li><a href="#index-end_002dof_002dhistory-_0028M_002d_003e_0029-309"><code>end-of-history (M->)</code></a>: <a href="#Commands-For-History">Commands For History</a></li>
<li><a href="#index-end_002dof_002dline-_0028C_002de_0029-298"><code>end-of-line (C-e)</code></a>: <a href="#Commands-For-Moving">Commands For Moving</a></li>
<li><a href="#index-exchange_002dpoint_002dand_002dmark-_0028C_002dx-C_002dx_0029-361"><code>exchange-point-and-mark (C-x C-x)</code></a>: <a href="#Miscellaneous-Commands">Miscellaneous Commands</a></li>
<li><a href="#index-forward_002dbackward_002ddelete_002dchar-_0028_0029-320"><code>forward-backward-delete-char ()</code></a>: <a href="#Commands-For-Text">Commands For Text</a></li>
<li><a href="#index-forward_002dchar-_0028C_002df_0029-299"><code>forward-char (C-f)</code></a>: <a href="#Commands-For-Moving">Commands For Moving</a></li>
<li><a href="#index-forward_002dsearch_002dhistory-_0028C_002ds_0029-311"><code>forward-search-history (C-s)</code></a>: <a href="#Commands-For-History">Commands For History</a></li>
<li><a href="#index-forward_002dword-_0028M_002df_0029-301"><code>forward-word (M-f)</code></a>: <a href="#Commands-For-Moving">Commands For Moving</a></li>
<li><a href="#index-history_002dsearch_002dbackward-_0028_0029-315"><code>history-search-backward ()</code></a>: <a href="#Commands-For-History">Commands For History</a></li>
<li><a href="#index-history_002dsearch_002dforward-_0028_0029-314"><code>history-search-forward ()</code></a>: <a href="#Commands-For-History">Commands For History</a></li>
<li><a href="#index-insert_002dcomment-_0028M_002d_0023_0029-364"><code>insert-comment (M-#)</code></a>: <a href="#Miscellaneous-Commands">Miscellaneous Commands</a></li>
<li><a href="#index-insert_002dcompletions-_0028M_002d_002a_0029-348"><code>insert-completions (M-*)</code></a>: <a href="#Commands-For-Completion">Commands For Completion</a></li>
<li><a href="#index-kill_002dline-_0028C_002dk_0029-329"><code>kill-line (C-k)</code></a>: <a href="#Commands-For-Killing">Commands For Killing</a></li>
<li><a href="#index-kill_002dregion-_0028_0029-338"><code>kill-region ()</code></a>: <a href="#Commands-For-Killing">Commands For Killing</a></li>
<li><a href="#index-kill_002dwhole_002dline-_0028_0029-332"><code>kill-whole-line ()</code></a>: <a href="#Commands-For-Killing">Commands For Killing</a></li>
<li><a href="#index-kill_002dword-_0028M_002dd_0029-333"><code>kill-word (M-d)</code></a>: <a href="#Commands-For-Killing">Commands For Killing</a></li>
<li><a href="#index-menu_002dcomplete-_0028_0029-349"><code>menu-complete ()</code></a>: <a href="#Commands-For-Completion">Commands For Completion</a></li>
<li><a href="#index-next_002dhistory-_0028C_002dn_0029-307"><code>next-history (C-n)</code></a>: <a href="#Commands-For-History">Commands For History</a></li>
<li><a href="#index-non_002dincremental_002dforward_002dsearch_002dhistory-_0028M_002dn_0029-313"><code>non-incremental-forward-search-history (M-n)</code></a>: <a href="#Commands-For-History">Commands For History</a></li>
<li><a href="#index-non_002dincremental_002dreverse_002dsearch_002dhistory-_0028M_002dp_0029-312"><code>non-incremental-reverse-search-history (M-p)</code></a>: <a href="#Commands-For-History">Commands For History</a></li>
<li><a href="#index-overwrite_002dmode-_0028_0029-328"><code>overwrite-mode ()</code></a>: <a href="#Commands-For-Text">Commands For Text</a></li>
<li><a href="#index-possible_002dcompletions-_0028M_002d_003f_0029-347"><code>possible-completions (M-?)</code></a>: <a href="#Commands-For-Completion">Commands For Completion</a></li>
<li><a href="#index-prefix_002dmeta-_0028_0040key_007bESC_007d_0029-357"><code>prefix-meta (<ESC>)</code></a>: <a href="#Miscellaneous-Commands">Miscellaneous Commands</a></li>
<li><a href="#index-previous_002dhistory-_0028C_002dp_0029-306"><code>previous-history (C-p)</code></a>: <a href="#Commands-For-History">Commands For History</a></li>
<li><a href="#index-quoted_002dinsert-_0028C_002dq-or-C_002dv_0029-321"><code>quoted-insert (C-q or C-v)</code></a>: <a href="#Commands-For-Text">Commands For Text</a></li>
<li><a href="#index-re_002dread_002dinit_002dfile-_0028C_002dx-C_002dr_0029-354"><code>re-read-init-file (C-x C-r)</code></a>: <a href="#Miscellaneous-Commands">Miscellaneous Commands</a></li>
<li><a href="#index-redraw_002dcurrent_002dline-_0028_0029-304"><code>redraw-current-line ()</code></a>: <a href="#Commands-For-Moving">Commands For Moving</a></li>
<li><a href="#index-reverse_002dsearch_002dhistory-_0028C_002dr_0029-310"><code>reverse-search-history (C-r)</code></a>: <a href="#Commands-For-History">Commands For History</a></li>
<li><a href="#index-revert_002dline-_0028M_002dr_0029-359"><code>revert-line (M-r)</code></a>: <a href="#Miscellaneous-Commands">Miscellaneous Commands</a></li>
<li><a href="#index-self_002dinsert-_0028a_002c-b_002c-A_002c-1_002c-_0021_002c-_0040dots_007b_007d_0029-322"><code>self-insert (a, b, A, 1, !, ...)</code></a>: <a href="#Commands-For-Text">Commands For Text</a></li>
<li><a href="#index-set_002dmark-_0028C_002d_0040_0040_0029-360"><code>set-mark (C-@)</code></a>: <a href="#Miscellaneous-Commands">Miscellaneous Commands</a></li>
<li><a href="#index-start_002dkbd_002dmacro-_0028C_002dx-_0028_0029-351"><code>start-kbd-macro (C-x ()</code></a>: <a href="#Keyboard-Macros">Keyboard Macros</a></li>
<li><a href="#index-transpose_002dchars-_0028C_002dt_0029-323"><code>transpose-chars (C-t)</code></a>: <a href="#Commands-For-Text">Commands For Text</a></li>
<li><a href="#index-transpose_002dwords-_0028M_002dt_0029-324"><code>transpose-words (M-t)</code></a>: <a href="#Commands-For-Text">Commands For Text</a></li>
<li><a href="#index-undo-_0028C_002d_005f-or-C_002dx-C_002du_0029-358"><code>undo (C-_ or C-x C-u)</code></a>: <a href="#Miscellaneous-Commands">Miscellaneous Commands</a></li>
<li><a href="#index-universal_002dargument-_0028_0029-345"><code>universal-argument ()</code></a>: <a href="#Numeric-Arguments">Numeric Arguments</a></li>
<li><a href="#index-unix_002dfilename_002drubout-_0028_0029-336"><code>unix-filename-rubout ()</code></a>: <a href="#Commands-For-Killing">Commands For Killing</a></li>
<li><a href="#index-unix_002dline_002ddiscard-_0028C_002du_0029-331"><code>unix-line-discard (C-u)</code></a>: <a href="#Commands-For-Killing">Commands For Killing</a></li>
<li><a href="#index-unix_002dword_002drubout-_0028C_002dw_0029-335"><code>unix-word-rubout (C-w)</code></a>: <a href="#Commands-For-Killing">Commands For Killing</a></li>
<li><a href="#index-upcase_002dword-_0028M_002du_0029-325"><code>upcase-word (M-u)</code></a>: <a href="#Commands-For-Text">Commands For Text</a></li>
<li><a href="#index-yank-_0028C_002dy_0029-342"><code>yank (C-y)</code></a>: <a href="#Commands-For-Killing">Commands For Killing</a></li>
<li><a href="#index-yank_002dlast_002darg-_0028M_002d_002e-or-M_002d_005f_0029-317"><code>yank-last-arg (M-. or M-_)</code></a>: <a href="#Commands-For-History">Commands For History</a></li>
<li><a href="#index-yank_002dnth_002darg-_0028M_002dC_002dy_0029-316"><code>yank-nth-arg (M-C-y)</code></a>: <a href="#Commands-For-History">Commands For History</a></li>
<li><a href="#index-yank_002dpop-_0028M_002dy_0029-343"><code>yank-pop (M-y)</code></a>: <a href="#Commands-For-Killing">Commands For Killing</a></li>
</ul><div class="node">
<p><hr>
<a name="Concept-Index"></a>
Previous: <a rel="previous" accesskey="p" href="#Function-Index">Function Index</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="unnumbered">Concept Index</h2>
<ul class="index-cp" compact>
<li><a href="#index-alias-expansion-243">alias expansion</a>: <a href="#Aliases">Aliases</a></li>
<li><a href="#index-arithmetic-evaluation-242">arithmetic evaluation</a>: <a href="#Shell-Arithmetic">Shell Arithmetic</a></li>
<li><a href="#index-arithmetic-expansion-88">arithmetic expansion</a>: <a href="#Arithmetic-Expansion">Arithmetic Expansion</a></li>
<li><a href="#index-arithmetic_002c-shell-238">arithmetic, shell</a>: <a href="#Shell-Arithmetic">Shell Arithmetic</a></li>
<li><a href="#index-arrays-244">arrays</a>: <a href="#Arrays">Arrays</a></li>
<li><a href="#index-background-254">background</a>: <a href="#Job-Control-Basics">Job Control Basics</a></li>
<li><a href="#index-Bash-configuration-384">Bash configuration</a>: <a href="#Basic-Installation">Basic Installation</a></li>
<li><a href="#index-Bash-installation-383">Bash installation</a>: <a href="#Basic-Installation">Basic Installation</a></li>
<li><a href="#index-Bourne-shell-21">Bourne shell</a>: <a href="#Basic-Shell-Features">Basic Shell Features</a></li>
<li><a href="#index-brace-expansion-80">brace expansion</a>: <a href="#Brace-Expansion">Brace Expansion</a></li>
<li><a href="#index-builtin-2">builtin</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-command-editing-267">command editing</a>: <a href="#Readline-Bare-Essentials">Readline Bare Essentials</a></li>
<li><a href="#index-command-execution-99">command execution</a>: <a href="#Command-Search-and-Execution">Command Search and Execution</a></li>
<li><a href="#index-command-expansion-98">command expansion</a>: <a href="#Simple-Command-Expansion">Simple Command Expansion</a></li>
<li><a href="#index-command-history-373">command history</a>: <a href="#Bash-History-Facilities">Bash History Facilities</a></li>
<li><a href="#index-command-search-100">command search</a>: <a href="#Command-Search-and-Execution">Command Search and Execution</a></li>
<li><a href="#index-command-substitution-86">command substitution</a>: <a href="#Command-Substitution">Command Substitution</a></li>
<li><a href="#index-command-timing-38">command timing</a>: <a href="#Pipelines">Pipelines</a></li>
<li><a href="#index-commands_002c-compound-40">commands, compound</a>: <a href="#Compound-Commands">Compound Commands</a></li>
<li><a href="#index-commands_002c-conditional-47">commands, conditional</a>: <a href="#Conditional-Constructs">Conditional Constructs</a></li>
<li><a href="#index-commands_002c-grouping-59">commands, grouping</a>: <a href="#Command-Grouping">Command Grouping</a></li>
<li><a href="#index-commands_002c-lists-39">commands, lists</a>: <a href="#Lists">Lists</a></li>
<li><a href="#index-commands_002c-looping-41">commands, looping</a>: <a href="#Looping-Constructs">Looping Constructs</a></li>
<li><a href="#index-commands_002c-pipelines-35">commands, pipelines</a>: <a href="#Pipelines">Pipelines</a></li>
<li><a href="#index-commands_002c-shell-32">commands, shell</a>: <a href="#Shell-Commands">Shell Commands</a></li>
<li><a href="#index-commands_002c-simple-33">commands, simple</a>: <a href="#Simple-Commands">Simple Commands</a></li>
<li><a href="#index-comments_002c-shell-31">comments, shell</a>: <a href="#Comments">Comments</a></li>
<li><a href="#index-completion-builtins-369">completion builtins</a>: <a href="#Programmable-Completion-Builtins">Programmable Completion Builtins</a></li>
<li><a href="#index-configuration-382">configuration</a>: <a href="#Basic-Installation">Basic Installation</a></li>
<li><a href="#index-control-operator-3">control operator</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-directory-stack-245">directory stack</a>: <a href="#The-Directory-Stack">The Directory Stack</a></li>
<li><a href="#index-editing-command-lines-268">editing command lines</a>: <a href="#Readline-Bare-Essentials">Readline Bare Essentials</a></li>
<li><a href="#index-environment-102">environment</a>: <a href="#Environment">Environment</a></li>
<li><a href="#index-evaluation_002c-arithmetic-241">evaluation, arithmetic</a>: <a href="#Shell-Arithmetic">Shell Arithmetic</a></li>
<li><a href="#index-event-designators-379">event designators</a>: <a href="#Event-Designators">Event Designators</a></li>
<li><a href="#index-execution-environment-101">execution environment</a>: <a href="#Command-Execution-Environment">Command Execution Environment</a></li>
<li><a href="#index-exit-status-103">exit status</a>: <a href="#Exit-Status">Exit Status</a></li>
<li><a href="#index-exit-status-4">exit status</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-expansion-79">expansion</a>: <a href="#Shell-Expansions">Shell Expansions</a></li>
<li><a href="#index-expansion_002c-arithmetic-87">expansion, arithmetic</a>: <a href="#Arithmetic-Expansion">Arithmetic Expansion</a></li>
<li><a href="#index-expansion_002c-brace-81">expansion, brace</a>: <a href="#Brace-Expansion">Brace Expansion</a></li>
<li><a href="#index-expansion_002c-filename-91">expansion, filename</a>: <a href="#Filename-Expansion">Filename Expansion</a></li>
<li><a href="#index-expansion_002c-parameter-85">expansion, parameter</a>: <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a></li>
<li><a href="#index-expansion_002c-pathname-92">expansion, pathname</a>: <a href="#Filename-Expansion">Filename Expansion</a></li>
<li><a href="#index-expansion_002c-tilde-83">expansion, tilde</a>: <a href="#Tilde-Expansion">Tilde Expansion</a></li>
<li><a href="#index-expressions_002c-arithmetic-240">expressions, arithmetic</a>: <a href="#Shell-Arithmetic">Shell Arithmetic</a></li>
<li><a href="#index-expressions_002c-conditional-237">expressions, conditional</a>: <a href="#Bash-Conditional-Expressions">Bash Conditional Expressions</a></li>
<li><a href="#index-FDL_002c-GNU-Free-Documentation-License-385">FDL, GNU Free Documentation License</a>: <a href="#GNU-Free-Documentation-License">GNU Free Documentation License</a></li>
<li><a href="#index-field-5">field</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-filename-6">filename</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-filename-expansion-93">filename expansion</a>: <a href="#Filename-Expansion">Filename Expansion</a></li>
<li><a href="#index-foreground-253">foreground</a>: <a href="#Job-Control-Basics">Job Control Basics</a></li>
<li><a href="#index-functions_002c-shell-63">functions, shell</a>: <a href="#Shell-Functions">Shell Functions</a></li>
<li><a href="#index-history-builtins-375">history builtins</a>: <a href="#Bash-History-Builtins">Bash History Builtins</a></li>
<li><a href="#index-history-events-380">history events</a>: <a href="#Event-Designators">Event Designators</a></li>
<li><a href="#index-history-expansion-378">history expansion</a>: <a href="#History-Interaction">History Interaction</a></li>
<li><a href="#index-history-list-374">history list</a>: <a href="#Bash-History-Facilities">Bash History Facilities</a></li>
<li><a href="#index-History_002c-how-to-use-372">History, how to use</a>: <a href="#Programmable-Completion-Builtins">Programmable Completion Builtins</a></li>
<li><a href="#index-identifier-11">identifier</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-initialization-file_002c-readline-272">initialization file, readline</a>: <a href="#Readline-Init-File">Readline Init File</a></li>
<li><a href="#index-installation-381">installation</a>: <a href="#Basic-Installation">Basic Installation</a></li>
<li><a href="#index-interaction_002c-readline-265">interaction, readline</a>: <a href="#Readline-Interaction">Readline Interaction</a></li>
<li><a href="#index-interactive-shell-235">interactive shell</a>: <a href="#Interactive-Shells">Interactive Shells</a></li>
<li><a href="#index-interactive-shell-233">interactive shell</a>: <a href="#Invoking-Bash">Invoking Bash</a></li>
<li><a href="#index-internationalization-25">internationalization</a>: <a href="#Locale-Translation">Locale Translation</a></li>
<li><a href="#index-job-7">job</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-job-control-8">job control</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-job-control-252">job control</a>: <a href="#Job-Control-Basics">Job Control Basics</a></li>
<li><a href="#index-kill-ring-271">kill ring</a>: <a href="#Readline-Killing-Commands">Readline Killing Commands</a></li>
<li><a href="#index-killing-text-269">killing text</a>: <a href="#Readline-Killing-Commands">Readline Killing Commands</a></li>
<li><a href="#index-localization-24">localization</a>: <a href="#Locale-Translation">Locale Translation</a></li>
<li><a href="#index-login-shell-232">login shell</a>: <a href="#Invoking-Bash">Invoking Bash</a></li>
<li><a href="#index-matching_002c-pattern-96">matching, pattern</a>: <a href="#Pattern-Matching">Pattern Matching</a></li>
<li><a href="#index-metacharacter-9">metacharacter</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-name-10">name</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-native-languages-26">native languages</a>: <a href="#Locale-Translation">Locale Translation</a></li>
<li><a href="#index-notation_002c-readline-266">notation, readline</a>: <a href="#Readline-Bare-Essentials">Readline Bare Essentials</a></li>
<li><a href="#index-operator_002c-shell-12">operator, shell</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-parameter-expansion-84">parameter expansion</a>: <a href="#Shell-Parameter-Expansion">Shell Parameter Expansion</a></li>
<li><a href="#index-parameters-65">parameters</a>: <a href="#Shell-Parameters">Shell Parameters</a></li>
<li><a href="#index-parameters_002c-positional-68">parameters, positional</a>: <a href="#Positional-Parameters">Positional Parameters</a></li>
<li><a href="#index-parameters_002c-special-69">parameters, special</a>: <a href="#Special-Parameters">Special Parameters</a></li>
<li><a href="#index-pathname-expansion-94">pathname expansion</a>: <a href="#Filename-Expansion">Filename Expansion</a></li>
<li><a href="#index-pattern-matching-95">pattern matching</a>: <a href="#Pattern-Matching">Pattern Matching</a></li>
<li><a href="#index-pipeline-34">pipeline</a>: <a href="#Pipelines">Pipelines</a></li>
<li><a href="#index-POSIX-1">POSIX</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-POSIX-Mode-251">POSIX Mode</a>: <a href="#Bash-POSIX-Mode">Bash POSIX Mode</a></li>
<li><a href="#index-process-group-13">process group</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-process-group-ID-14">process group ID</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-process-substitution-89">process substitution</a>: <a href="#Process-Substitution">Process Substitution</a></li>
<li><a href="#index-programmable-completion-368">programmable completion</a>: <a href="#Programmable-Completion">Programmable Completion</a></li>
<li><a href="#index-prompting-249">prompting</a>: <a href="#Printing-a-Prompt">Printing a Prompt</a></li>
<li><a href="#index-quoting-22">quoting</a>: <a href="#Quoting">Quoting</a></li>
<li><a href="#index-quoting_002c-ANSI-23">quoting, ANSI</a>: <a href="#ANSI_002dC-Quoting">ANSI-C Quoting</a></li>
<li><a href="#index-Readline_002c-how-to-use-264">Readline, how to use</a>: <a href="#Job-Control-Variables">Job Control Variables</a></li>
<li><a href="#index-redirection-97">redirection</a>: <a href="#Redirections">Redirections</a></li>
<li><a href="#index-reserved-word-15">reserved word</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-restricted-shell-250">restricted shell</a>: <a href="#The-Restricted-Shell">The Restricted Shell</a></li>
<li><a href="#index-return-status-16">return status</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-shell-arithmetic-239">shell arithmetic</a>: <a href="#Shell-Arithmetic">Shell Arithmetic</a></li>
<li><a href="#index-shell-function-62">shell function</a>: <a href="#Shell-Functions">Shell Functions</a></li>
<li><a href="#index-shell-script-105">shell script</a>: <a href="#Shell-Scripts">Shell Scripts</a></li>
<li><a href="#index-shell-variable-67">shell variable</a>: <a href="#Shell-Parameters">Shell Parameters</a></li>
<li><a href="#index-shell_002c-interactive-236">shell, interactive</a>: <a href="#Interactive-Shells">Interactive Shells</a></li>
<li><a href="#index-signal-17">signal</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-signal-handling-104">signal handling</a>: <a href="#Signals">Signals</a></li>
<li><a href="#index-special-builtin-18">special builtin</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-special-builtin-148">special builtin</a>: <a href="#Special-Builtins">Special Builtins</a></li>
<li><a href="#index-startup-files-234">startup files</a>: <a href="#Bash-Startup-Files">Bash Startup Files</a></li>
<li><a href="#index-suspending-jobs-255">suspending jobs</a>: <a href="#Job-Control-Basics">Job Control Basics</a></li>
<li><a href="#index-tilde-expansion-82">tilde expansion</a>: <a href="#Tilde-Expansion">Tilde Expansion</a></li>
<li><a href="#index-token-19">token</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-translation_002c-native-languages-27">translation, native languages</a>: <a href="#Locale-Translation">Locale Translation</a></li>
<li><a href="#index-variable_002c-shell-66">variable, shell</a>: <a href="#Shell-Parameters">Shell Parameters</a></li>
<li><a href="#index-variables_002c-readline-273">variables, readline</a>: <a href="#Readline-Init-File-Syntax">Readline Init File Syntax</a></li>
<li><a href="#index-word-20">word</a>: <a href="#Definitions">Definitions</a></li>
<li><a href="#index-word-splitting-90">word splitting</a>: <a href="#Word-Splitting">Word Splitting</a></li>
<li><a href="#index-yanking-text-270">yanking text</a>: <a href="#Readline-Killing-Commands">Readline Killing Commands</a></li>
</ul></body></html>
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