@settitle Bash Reference Manual
@c %**end of header
-@ignore
-Last Change: Wed Jan 20 16:46:26 EST 1999
-@end ignore
-
-@set EDITION 2.3
-@set VERSION 2.03
-@set UPDATED 20 January 1999
-@set UPDATE-MONTH January 1999
-
-@iftex
-@finalout
-@end iftex
-
@setchapternewpage odd
-@defcodeindex bt
-@defcodeindex rw
-@set BashFeatures
-@ifinfo
-@dircategory Utilities
-@direntry
- * Bash: (bash). The GNU Bourne-Again SHell.
-@end direntry
+@include version.texi
-@format
+@copying
This text is a brief description of the features that are present in
-the Bash shell.
+the Bash shell (version @value{VERSION}, @value{UPDATED}).
This is Edition @value{EDITION}, last updated @value{UPDATED},
of @cite{The GNU Bash Reference Manual},
for @code{Bash}, Version @value{VERSION}.
-Copyright (C) 1991-1999 Free Software Foundation, Inc.
+Copyright @copyright{} 1988--2009 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.
-@ignore
-Permission is granted to process this file through TeX and print the
-results, provided the printed document carries copying permission
-notice identical to this one except for the removal of this paragraph
-(this paragraph not being relevant to the printed manual).
-
-@end ignore
-Permission is granted to copy and distribute modified versions of this
-manual under the conditions for verbatim copying, provided that the entire
-resulting derived work is distributed under the terms of a permission
-notice identical to this one.
-
-Permission is granted to copy and distribute translations of this manual
-into another language, under the above conditions for modified versions,
-except that this permission notice may be stated in a translation approved
-by the Free Software Foundation.
-@end format
-@end ifinfo
+@quotation
+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, with the Front-Cover texts being ``A GNU Manual'',
+and with the Back-Cover Texts as in (a) below. A copy of the license is
+included in the section entitled ``GNU Free Documentation License''.
+
+(a) The FSF's Back-Cover Text is: You are free to copy and modify
+this GNU manual. Buying copies from GNU Press supports the FSF in
+developing GNU and promoting software freedom.''
+
+@end quotation
+@end copying
+
+@defcodeindex bt
+@defcodeindex rw
+@set BashFeatures
+
+@dircategory Basics
+@direntry
+* Bash: (bash). The GNU Bourne-Again SHell.
+@end direntry
+
+@finalout
@titlepage
@title Bash Reference Manual
@subtitle Reference Documentation for Bash
@subtitle Edition @value{EDITION}, for @code{Bash} Version @value{VERSION}.
-@subtitle @value{UPDATE-MONTH}
+@subtitle @value{UPDATED-MONTH}
@author Chet Ramey, Case Western Reserve University
@author Brian Fox, Free Software Foundation
+
@page
@vskip 0pt plus 1filll
-Copyright @copyright{} 1991-1999 Free Software Foundation, Inc.
-
-Permission is granted to make and distribute verbatim copies of
-this manual provided the copyright notice and this permission notice
-are preserved on all copies.
+@insertcopying
-Permission is granted to copy and distribute modified versions of this
-manual under the conditions for verbatim copying, provided that the entire
-resulting derived work is distributed under the terms of a permission
-notice identical to this one.
+@sp 1
+Published by the Free Software Foundation @*
+59 Temple Place, Suite 330, @*
+Boston, MA 02111-1307 @*
+USA @*
-Permission is granted to copy and distribute translations of this manual
-into another language, under the above conditions for modified versions,
-except that this permission notice may be stated in a translation approved
-by the Free Software Foundation.
@end titlepage
-@ifinfo
+@contents
+
+@ifnottex
@node Top, Introduction, (dir), (dir)
@top Bash Features
-@end ifinfo
-@ifinfo
This text is a brief description of the features that are present in
-the Bash shell.
+the Bash shell (version @value{VERSION}, @value{UPDATED}).
This is Edition @value{EDITION}, last updated @value{UPDATED},
of @cite{The GNU Bash Reference Manual},
for @code{Bash}, Version @value{VERSION}.
-Copyright (C) 1991, 1993, 1996 Free Software Foundation, Inc.
-
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 (@file{sh}), the Korn Shell
@menu
* Introduction:: An introduction to the shell.
-
* Definitions:: Some definitions used in the rest of this
manual.
-
* Basic Shell Features:: The shell "building blocks".
-
-* Bourne Shell Features:: Features similar to those found in the
- Bourne shell.
-
+* Shell Builtin Commands:: Commands that are a part of the shell.
+* Shell Variables:: Variables used or set by Bash.
* Bash Features:: Features found only in Bash.
-
-* Job Control:: A chapter describing what job control is
- and how Bash allows you to use it.
-
-* Using History Interactively:: Chapter dealing with history expansion
- rules.
-
+* Job Control:: What job control is and how Bash allows you
+ to use it.
* Command Line Editing:: Chapter describing the command line
editing features.
-
+* Using History Interactively:: Command History Expansion
* Installing Bash:: How to build and install Bash on your system.
-
* Reporting Bugs:: How to report bugs in Bash.
-
-* Builtin Index:: Index of Bash builtin commands.
-
-* Reserved Word Index:: Index of Bash reserved words.
-
-* Variable Index:: Quick reference helps you find the
- variable you want.
-
-* Function Index:: Index of bindable Readline functions.
-
-* Concept Index:: General index for concepts described in
- this manual.
+* Major Differences From The Bourne Shell:: A terse list of the differences
+ between Bash and historical
+ versions of /bin/sh.
+* GNU Free Documentation License:: Copying and sharing this documentation.
+* Indexes:: Various indexes for this manual.
@end menu
-@end ifinfo
+@end ifnottex
@node Introduction
@chapter Introduction
@menu
* What is Bash?:: A short description of Bash.
-
* What is a shell?:: A brief introduction to shells.
@end menu
@section What is Bash?
Bash is the shell, or command language interpreter,
-that will appear in the @sc{GNU} operating system.
+for the @sc{gnu} operating system.
The name is an acronym for the @samp{Bourne-Again SHell},
-a pun on Steve Bourne, the author of the direct ancestor of the current
-Unix shell @code{/bin/sh},
+a pun on Stephen Bourne, the author of the direct ancestor of
+the current Unix shell @code{sh},
which appeared in the Seventh Edition Bell Labs Research version
of Unix.
-Bash is an @code{sh}-compatible shell that incorporates useful
+Bash is largely compatible with @code{sh} and incorporates useful
features from the Korn shell @code{ksh} and the C shell @code{csh}.
-It is intended to be a conformant implementation of the @sc{IEEE}
-@sc{POSIX} Shell and Tools specification (@sc{IEEE} Working Group 1003.2).
+It is intended to be a conformant implementation of the @sc{ieee}
+@sc{posix} Shell and Tools portion of the @sc{ieee} @sc{posix}
+specification (@sc{ieee} Standard 1003.1).
It offers functional improvements over @code{sh} for both interactive and
programming use.
-While the @sc{GNU} operating system will include a version
-of @code{csh}, Bash will be the default shell.
-Like other @sc{GNU} software, Bash is quite portable. It currently runs
+While the @sc{gnu} operating system provides other shells, including
+a version of @code{csh}, Bash is the default shell.
+Like other @sc{gnu} software, Bash is quite portable. It currently runs
on nearly every version of Unix and a few other operating systems @minus{}
-independently-supported ports exist for @sc{MS-DOS}, @sc{OS/2},
-Windows @sc{95}, and Windows @sc{NT}.
+independently-supported ports exist for @sc{ms-dos}, @sc{os/2},
+and Windows platforms.
@node What is a shell?
@section What is a shell?
At its base, a shell is simply a macro processor that executes
-commands. A Unix shell is both a command interpreter, which
-provides the user interface to the rich set of Unix utilities,
-and a programming language, allowing these utilitites to be
-combined. Files containing commands can be created, and become
+commands. The term macro processor means functionality where text
+and symbols are expanded to create larger expressions.
+
+A Unix shell is both a command interpreter and a programming
+language. As a command interpreter, the shell provides the user
+interface to the rich set of @sc{gnu} utilities. The programming
+language features allow these utilities to be combined.
+Files containing commands can be created, and become
commands themselves. These new commands have the same status as
-system commands in directories like @file{/bin}, allowing users
-or groups to establish custom environments.
+system commands in directories such as @file{/bin}, allowing users
+or groups to establish custom environments to automate their common
+tasks.
-A shell allows execution of Unix commands, both synchronously and
+Shells may be used interactively or non-interactively. In
+interactive mode, they accept input typed from the keyboard.
+When executing non-interactively, shells execute commands read
+from a file.
+
+A shell allows execution of @sc{gnu} commands, both synchronously and
asynchronously.
The shell waits for synchronous commands to complete before accepting
more input; asynchronous commands continue to execute in parallel
with the shell while it reads and executes additional commands.
The @dfn{redirection} constructs permit
-fine-grained control of the input and output of those commands,
-and the shell allows control over the contents of their
-environment. Unix shells also provide a small set of built-in
+fine-grained control of the input and output of those commands.
+Moreover, the shell allows control over the contents of commands'
+environments.
+
+Shells also provide a small set of built-in
commands (@dfn{builtins}) implementing functionality impossible
-(e.g., @code{cd}, @code{break}, @code{continue}, and
-@code{exec}), or inconvenient (@code{history}, @code{getopts},
-@code{kill}, or @code{pwd}, for example) to obtain via separate
-utilities. Shells may be used interactively or
-non-interactively: they accept input typed from the keyboard or
-from a file. All of the shell builtins are described in
+or inconvenient to obtain via separate utilities.
+For example, @code{cd}, @code{break}, @code{continue}, and
+@code{exec}) cannot be implemented outside of the shell because
+they directly manipulate the shell itself.
+The @code{history}, @code{getopts}, @code{kill}, or @code{pwd}
+builtins, among others, could be implemented in separate utilities,
+but they are more convenient to use as builtin commands.
+All of the shell builtins are described in
subsequent sections.
While executing commands is essential, most of the power (and
languages. Like any high-level language, the shell provides
variables, flow control constructs, quoting, and functions.
-Shells have begun offering features geared specifically for
+Shells offer features geared specifically for
interactive use rather than to augment the programming language.
These interactive features include job control, command line
-editing, history and aliases. Each of these features is
+editing, command history and aliases. Each of these features is
described in this manual.
@node Definitions
@item POSIX
@cindex POSIX
A family of open system standards based on Unix. Bash
-is concerned with @sc{POSIX} 1003.2, the Shell and Tools Standard.
+is primarily concerned with the Shell and Utilities portion of the
+@sc{posix} 1003.1 standard.
@item blank
A space or tab character.
@item control operator
@cindex control operator
-A @code{word} that performs a control function. It is a @code{newline}
+A @code{token} that performs a control function. It is a @code{newline}
or one of the following:
@samp{||}, @samp{&&}, @samp{&}, @samp{;}, @samp{;;},
-@samp{|}, @samp{(}, or @samp{)}.
+@samp{|}, @samp{|&}, @samp{(}, or @samp{)}.
@item exit status
@cindex exit status
-The value returned by a command to its caller.
+The value returned by a command to its caller. The value is restricted
+to eight bits, so the maximum value is 255.
@item field
@cindex field
@cindex operator, shell
A @code{control operator} or a @code{redirection operator}.
@xref{Redirections}, for a list of redirection operators.
+Operators contain at least one unquoted @code{metacharacter}.
@item process group
@cindex process group
A collection of related processes each having the same process
-group @sc{ID}.
+group @sc{id}.
@item process group ID
@cindex process group ID
-A unique identifer that represents a @code{process group}
+A unique identifier that represents a @code{process group}
during its lifetime.
@item reserved word
@item signal
@cindex signal
-A mechanism by which a process may be notified by the kernal
+A mechanism by which a process may be notified by the kernel
of an event occurring in the system.
@item special builtin
@cindex special builtin
A shell builtin command that has been classified as special by the
-@sc{POSIX.2} standard.
+@sc{posix} standard.
@item token
@cindex token
-A sequence of characters considered a single unit by the shell. It is
-either a @code{word} or an @code{operator}.
+A sequence of characters considered a single unit by the shell.
+It is either a @code{word} or an @code{operator}.
@item word
@cindex word
-A @code{token} that is not an @code{operator}.
+A sequence of characters treated as a unit by the shell.
+Words may not include unquoted @code{metacharacters}.
@end table
@node Basic Shell Features
The Bourne shell is
the traditional Unix shell originally written by Stephen Bourne.
All of the Bourne shell builtin commands are available in Bash,
-and the rules for evaluation and quoting are taken from the @sc{POSIX}
-1003.2 specification for the `standard' Unix shell.
+The rules for evaluation and quoting are taken from the @sc{posix}
+specification for the `standard' Unix shell.
This chapter briefly summarizes the shell's `building blocks':
commands, control structures, shell functions, shell @i{parameters},
* Shell Syntax:: What your input means to the shell.
* Shell Commands:: The types of commands you can use.
* Shell Functions:: Grouping commands by name.
-* Shell Parameters:: Special shell variables.
-* Shell Expansions:: How Bash expands variables and the various
+* Shell Parameters:: How the shell stores values.
+* Shell Expansions:: How Bash expands parameters and the various
expansions available.
* Redirections:: A way to control where input and output go.
* Executing Commands:: What happens when you run a command.
@section Shell Syntax
@menu
* Shell Operation:: The basic operation of the shell.
-
* Quoting:: How to remove the special meaning from characters.
-
* Comments:: How to specify comments.
@end menu
+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{#}), and the rest
+of that line.
+
+Otherwise, roughly speaking, the shell reads its input and
+divides the input into words and operators, employing the quoting rules
+to select which meanings to assign various words and characters.
+
+The shell then parses these tokens into commands and other constructs,
+removes the special meaning of certain words or characters, expands
+others, redirects input and output as needed, executes the specified
+command, waits for the command's exit status, and makes that exit status
+available for further inspection or processing.
+
@node Shell Operation
@subsection Shell Operation
@enumerate
@item
Reads its input from a file (@pxref{Shell Scripts}), from a string
-supplied as an argument to the @samp{-c} invocation option
+supplied as an argument to the @option{-c} invocation option
(@pxref{Invoking Bash}), or from the user's terminal.
@item
* Double Quotes:: How to suppress most of the interpretation of a
sequence of characters.
* ANSI-C Quoting:: How to expand ANSI-C sequences in quoted strings.
-
* Locale Translation:: How to translate strings into different languages.
@end menu
Each of the shell metacharacters (@pxref{Definitions})
has special meaning to the shell and must be quoted if it is to
-represent itself. There are three quoting mechanisms: the
+represent itself.
+When the command history expansion facilities are being used
+(@pxref{History Interaction}), the
+@var{history expansion} character, usually @samp{!}, must be quoted
+to prevent history expansion. @xref{Bash History Facilities}, for
+more details concerning history expansion.
+
+There are three quoting mechanisms: the
@var{escape character}, single quotes, and double quotes.
@node Escape Character
@node Single Quotes
@subsubsection Single Quotes
-Enclosing characters in single quotes preserves the literal value
+Enclosing characters in single quotes (@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.
@node Double Quotes
@subsubsection Double Quotes
-Enclosing characters in double quotes preserves the literal value
+Enclosing characters in double quotes (@samp{"}) preserves the literal value
of all characters within the quotes, with the exception of
-@samp{$}, @samp{`}, and @samp{\}.
+@samp{$}, @samp{`}, @samp{\},
+and, when history expansion is enabled, @samp{!}.
The characters @samp{$} and @samp{`}
retain their special meaning within double quotes (@pxref{Shell Expansions}).
The backslash retains its special meaning only when followed by one of
special meaning are left unmodified.
A double quote may be quoted within double quotes by preceding it with
a backslash.
+If enabled, history expansion will be performed unless an @samp{!}
+appearing in double quotes is escaped using a backslash.
+The backslash preceding the @samp{!} is not removed.
The special parameters @samp{*} and @samp{@@} have special meaning
when in double quotes (@pxref{Shell Parameter Expansion}).
Words of the form @code{$'@var{string}'} are treated specially. The
word expands to @var{string}, with backslash-escaped characters replaced
-as specifed by the ANSI C standard. Backslash escape sequences, if
+as specified by the ANSI C standard. Backslash escape sequences, if
present, are decoded as follows:
@table @code
vertical tab
@item \\
backslash
+@item \'
+single quote
@item \@var{nnn}
-the character whose @code{ASCII} code is the octal value @var{nnn}
-(one to three digits)
-@item \x@var{nnn}
-the character whose @code{ASCII} code is the hexadecimal value @var{nnn}
+the eight-bit character whose value is the octal value @var{nnn}
(one to three digits)
+@item \x@var{HH}
+the eight-bit character whose value is the hexadecimal value @var{HH}
+(one or two hex digits)
+@item \c@var{x}
+a control-@var{x} character
@end table
@noindent
-The result is single-quoted, as if the dollar sign had not been present.
+The expanded result is single-quoted, as if the dollar sign had not
+been present.
@node Locale Translation
@subsubsection Locale-Specific Translation
@cindex localization
+@cindex internationalization
+@cindex native languages
+@cindex translation, native languages
A double-quoted string preceded by a dollar sign (@samp{$}) will cause
the string to be translated according to the current locale.
If the string is translated and replaced, the replacement is
double-quoted.
+@vindex LC_MESSAGES
+@vindex TEXTDOMAIN
+@vindex TEXTDOMAINDIR
+Some systems use the message catalog selected by the @env{LC_MESSAGES}
+shell variable. Others create the name of the message catalog from the
+value of the @env{TEXTDOMAIN} shell variable, possibly adding a
+suffix of @samp{.mo}. If you use the @env{TEXTDOMAIN} variable, you
+may need to set the @env{TEXTDOMAINDIR} variable to the location of
+the message catalog files. Still others use both variables in this
+fashion:
+@env{TEXTDOMAINDIR}/@env{LC_MESSAGES}/LC_MESSAGES/@env{TEXTDOMAIN}.mo.
+
@node Comments
@subsection Comments
@cindex comments, shell
In a non-interactive shell, or an interactive shell in which the
@code{interactive_comments} option to the @code{shopt}
-builtin is enabled (@pxref{Bash Builtins}),
+builtin is enabled (@pxref{The Shopt Builtin}),
a word beginning with @samp{#}
causes that word and all remaining characters on that line to
be ignored. An interactive shell without the @code{interactive_comments}
option enabled does not allow comments. The @code{interactive_comments}
option is on by default in interactive shells.
-@xref{Is This Shell Interactive?}, for a description of what makes
+@xref{Interactive Shells}, for a description of what makes
a shell interactive.
@node Shell Commands
@section Shell Commands
@cindex commands, shell
+
+A simple shell command such as @code{echo a b c} consists of the command
+itself followed by arguments, separated by spaces.
+
+More complex shell commands are composed of simple commands arranged together
+in a variety of ways: in a pipeline in which the output of one command
+becomes the input of a second, in a loop or conditional construct, or in
+some other grouping.
+
@menu
* Simple Commands:: The most common type of command.
* Pipelines:: Connecting the input and output of several
commands.
* Lists:: How to execute commands sequentially.
-* Looping Constructs:: Shell commands for iterative action.
-* Conditional Constructs:: Shell commands for conditional execution.
-* Command Grouping:: Ways to group commands.
+* Compound Commands:: Shell commands for control flow.
+* Coprocesses:: Two-way communication between commands.
@end menu
@node Simple Commands
A simple command is the kind of command encountered most often.
It's just a sequence of words separated by @code{blank}s, terminated
by one of the shell's control operators (@pxref{Definitions}). The
-first word generally specifies a command to be executed.
+first word generally specifies a command to be executed, with the
+rest of the words being that command's arguments.
The return status (@pxref{Exit Status}) of a simple command is
its exit status as provided
-by the @sc{POSIX.1} @code{waitpid} function, or 128+@var{n} if the command
-was terminated by signal @var{n}.
+by the @sc{posix} 1003.1 @code{waitpid} function, or 128+@var{n} if
+the command was terminated by signal @var{n}.
@node Pipelines
@subsection Pipelines
@cindex pipeline
@cindex commands, pipelines
-A @code{pipeline} is a sequence of simple commands separated by
-@samp{|}.
+A @code{pipeline} is a sequence of simple commands separated by one of
+the control operators @samp{|} or @samp{|&}.
@rwindex time
@rwindex !
@cindex command timing
The format for a pipeline is
@example
-[@code{time} [@code{-p}]] [@code{!}] @var{command1} [@code{|} @var{command2} @dots{}]
+[@code{time} [@code{-p}]] [@code{!}] @var{command1} [ [@code{|} or @code{|&}] @var{command2} @dots{}]
@end example
@noindent
-The output of each command in the pipeline is connected to the input of
-the next command. That is, each command reads the previous command's
-output.
+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. This
+connection is performed before any redirections specified by the
+command.
+
+If @samp{|&} is used, the standard error of @var{command1} is connected to
+@var{command2}'s standard input through the pipe; it is shorthand for
+@code{2>&1 |}. This implicit redirection of the standard error is
+performed after any redirections specified by the command.
The reserved word @code{time} 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{-p} option changes the output format to that specified
-by @sc{POSIX}.
-The @code{TIMEFORMAT} variable may be set to a format string that
+The @option{-p} option changes the output format to that specified
+by @sc{posix}.
+The @env{TIMEFORMAT} variable may be set to a format string that
specifies how the timing information should be displayed.
@xref{Bash Variables}, for a description of the available formats.
The use of @code{time} as a reserved word permits the timing of
Each command in a pipeline is executed in its own subshell
(@pxref{Command Execution Environment}). The exit
status of a pipeline is the exit status of the last command in the
-pipeline. If the reserved word @samp{!} precedes the pipeline, the
-exit status is the logical negation of the exit status of the last command.
+pipeline, unless the @code{pipefail} option is enabled
+(@pxref{The Set Builtin}).
+If @code{pipefail} 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{!} 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.
@node Lists
@subsection Lists of Commands
have equal precedence, followed by @samp{;} and @samp{&},
which have equal precedence.
+A sequence of one or more newlines may appear in a @code{list}
+to delimit commands, equivalent to a semicolon.
+
If a command is terminated by the control operator @samp{&},
the shell executes the command asynchronously in a subshell.
This is known as executing the command in the @var{background}.
The shell does not wait for the command to finish, and the return
status is 0 (true).
-The standard input for asynchronous commands, in the absence of any
+When job control is not active (@pxref{Job Control}),
+the standard input for asynchronous commands, in the absence of any
explicit redirections, is redirected from @code{/dev/null}.
Commands separated by a @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.
-The control operators @samp{&&} and @samp{||}
-denote @sc{AND} lists and @sc{OR} lists, respectively.
-An @sc{AND} list has the form
+@sc{and} and @sc{or} lists are sequences of one or more pipelines
+separated by the control operators @samp{&&} and @samp{||},
+respectively. @sc{and} and @sc{or} lists are executed with left
+associativity.
+
+An @sc{and} list has the form
@example
-@var{command} && @var{command2}
+@var{command1} && @var{command2}
@end example
@noindent
-@var{command2} is executed if, and only if, @var{command}
+@var{command2} is executed if, and only if, @var{command1}
returns an exit status of zero.
-An @sc{OR} list has the form
+An @sc{or} list has the form
@example
-@var{command} || @var{command2}
+@var{command1} || @var{command2}
@end example
@noindent
-@var{command2} is executed if, and only if, @var{command}
+@var{command2} is executed if, and only if, @var{command1}
returns a non-zero exit status.
The return status of
-@sc{AND} and @sc{OR} lists is the exit status of the last command
+@sc{and} and @sc{or} lists is the exit status of the last command
executed in the list.
+@node Compound Commands
+@subsection Compound Commands
+@cindex commands, compound
+
+@menu
+* Looping Constructs:: Shell commands for iterative action.
+* Conditional Constructs:: Shell commands for conditional execution.
+* Command Grouping:: Ways to group commands.
+@end menu
+
+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 (@pxref{Redirections}) associated with a compound command
+apply to all commands within that compound command unless explicitly overridden.
+
+Bash provides looping constructs, conditional commands, and mechanisms
+to group commands and execute them as a unit.
+
@node Looping Constructs
-@subsection Looping Constructs
+@subsubsection Looping Constructs
@cindex commands, looping
Bash supports the following looping constructs.
-Note that wherever you see a @samp{;} in the description of a
+Note that wherever a @samp{;} appears in the description of a
command's syntax, it may be replaced with one or more newlines.
@table @code
@end example
Expand @var{words}, and execute @var{commands} once for each member
in the resultant list, with @var{name} bound to the current member.
-If @samp{in @var{words}} is not present, @samp{in "$@@"} is assumed.
+If @samp{in @var{words}} is not present, the @code{for} command
+executes the @var{commands} once for each positional parameter that is
+set, as if @samp{in "$@@"} had been specified
+(@pxref{Special Parameters}).
The return status is the exit status of the last command that executes.
If there are no items in the expansion of @var{words}, no commands are
executed, and the return status is zero.
+
+An alternate form of the @code{for} command is also supported:
+
+@example
+for (( @var{expr1} ; @var{expr2} ; @var{expr3} )) ; do @var{commands} ; done
+@end example
+First, the arithmetic expression @var{expr1} is evaluated according
+to the rules described below (@pxref{Shell Arithmetic}).
+The arithmetic expression @var{expr2} is then evaluated repeatedly
+until it evaluates to zero.
+Each time @var{expr2} evaluates to a non-zero value, @var{commands} are
+executed and the arithmetic expression @var{expr3} 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}
+that is executed, or false if any of the expressions is invalid.
+
@end table
The @code{break} and @code{continue} builtins (@pxref{Bourne Shell Builtins})
may be used to control loop execution.
@node Conditional Constructs
-@subsection Conditional Constructs
+@subsubsection Conditional Constructs
@cindex commands, conditional
@table @code
@code{case} will selectively execute the @var{command-list} corresponding to
the first @var{pattern} that matches @var{word}.
+If the shell option @code{nocasematch}
+(see the description of @code{shopt} in @ref{The Shopt Builtin})
+is enabled, the match is performed without regard to the case
+of alphabetic characters.
The @samp{|} is used to separate multiple patterns, and the @samp{)}
operator terminates a pattern list.
A list of patterns and an associated command-list is known
-as a @var{clause}. Each clause must be terminated with @samp{;;}.
+as a @var{clause}.
+
+Each clause must be terminated with @samp{;;}, @samp{,&}, or @samp{;;&}.
The @var{word} undergoes tilde expansion, parameter expansion, command
substitution, arithmetic expansion, and quote removal before matching is
attempted. Each @var{pattern} undergoes tilde expansion, parameter
expansion, command substitution, and arithmetic expansion.
There may be an arbitrary number of @code{case} clauses, each terminated
-by a @samp{;;}. The first pattern that matches determines the
+by a @samp{;;}, @samp{;&}, or @samp{;;&}.
+The first pattern that matches determines the
command-list that is executed.
Here is an example using @code{case} in a script that could be used to
@end example
@noindent
+
+If the @samp{;;} operator is used, no subsequent matches are attempted after
+the first pattern match.
+Using @samp{;&} in place of @samp{;;} causes execution to continue with
+the @var{command-list} associated with the next clause, if any.
+Using @samp{;;&} in place of @samp{;;} causes the shell to test the patterns
+in the next clause, if any, and execute any associated @var{command-list}
+on a successful match.
+
The return status is zero if no @var{pattern} is matched. Otherwise, the
return status is the exit status of the @var{command-list} executed.
of items. The set of expanded words is printed on the standard
error output stream, each preceded by a number. If the
@samp{in @var{words}} is omitted, the positional parameters are printed,
-as if @samp{in "$@@"} had been specifed.
-The @code{PS3} prompt is then displayed and a line is read from the
+as if @samp{in "$@@"} had been specified.
+The @env{PS3} 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} is set to that word.
If the line is empty, the words and prompt are displayed again.
If @code{EOF} is read, the @code{select} command completes.
Any other value read causes @var{name} to be set to null.
-The line read is saved in the variable @code{REPLY}.
+The line read is saved in the variable @env{REPLY}.
The @var{commands} are executed after each selection until a
-@code{break} or @code{return} command is executed, at which
+@code{break} command is executed, at which
point the @code{select} command completes.
Here is an example that allows the user to pick a filename from the
between the @samp{[[} and @samp{]]}; tilde expansion, parameter and
variable expansion, arithmetic expansion, command substitution, process
substitution, and quote removal are performed.
+Conditional operators such as @samp{-f} must be unquoted to be recognized
+as primaries.
When the @samp{==} and @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 @ref{Pattern Matching}.
-The return value is 0 if the string matches or does not match
-the pattern, respectively, and 1 otherwise.
+If the shell option @code{nocasematch}
+(see the description of @code{shopt} in @ref{The Shopt Builtin})
+is enabled, the match is performed without regard to the case
+of alphabetic characters.
+The return value is 0 if the string matches (@samp{==}) or does not
+match (@samp{!=})the pattern, and 1 otherwise.
+Any part of the pattern may be quoted to force it to be matched as a
+string.
+
+An additional binary operator, @samp{=~}, is available, with the same
+precedence as @samp{==} and @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}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}
+(see the description of @code{shopt} in @ref{The Shopt Builtin})
+is enabled, the match is performed without regard to the case
+of alphabetic characters.
Any part of the pattern may be quoted to force it to be matched as a
string.
+Substrings matched by parenthesized subexpressions within the regular
+expression are saved in the array variable @code{BASH_REMATCH}.
+The element of @code{BASH_REMATCH} with index 0 is the portion of the string
+matching the entire regular expression.
+The element of @code{BASH_REMATCH} with index @var{n} is the portion of the
+string matching the @var{n}th parenthesized subexpression.
Expressions may be combined using the following operators, listed
in decreasing order of precedence:
True if either @var{expression1} or @var{expression2} is true.
@end table
@noindent
-The && and || commands do not execute @var{expression2} if the
+The @code{&&} and @code{||} operators do not evaluate @var{expression2} if the
value of @var{expression1} is sufficient to determine the return
value of the entire conditional expression.
@end table
@node Command Grouping
-@subsection Grouping Commands
+@subsubsection Grouping Commands
@cindex commands, grouping
Bash provides two ways to group a list of commands to be executed
@end example
Placing a list of commands between parentheses causes a subshell
-to be created, and each of the commands in @var{list} to be executed
-in that subshell. Since the @var{list} is executed in a subshell,
-variable assignments do not remain in effect after the subshell completes.
+environment to be created (@pxref{Command Execution Environment}), and each
+of the commands in @var{list} to be executed in that subshell. Since the
+@var{list} is executed in a subshell, variable assignments do not remain in
+effect after the subshell completes.
@item @{@}
@rwindex @{
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}, so they must be separated from the @var{list}
-by @code{blank}s. The parentheses are @code{operators}, and are
+by @code{blank}s or other shell metacharacters.
+The parentheses are @code{operators}, and are
recognized as separate tokens by the shell even if they are not separated
from the @var{list} by whitespace.
The exit status of both of these constructs is the exit status of
@var{list}.
+@node Coprocesses
+@subsection Coprocesses
+@cindex coprocess
+
+A @code{coprocess} is a shell command preceded by the @code{coproc}
+reserved word.
+A coprocess is executed asynchronously in a subshell, as if the command
+had been terminated with the @samp{&} control operator, with a two-way pipe
+established between the executing shell and the coprocess.
+
+The format for a coprocess is:
+@example
+@code{coproc} [@var{NAME}] @var{command} [@var{redirections}]
+@end example
+
+@noindent
+This creates a coprocess named @var{NAME}.
+If @var{NAME} is not supplied, the default name is @var{COPROC}.
+
+When the coproc is executed, the shell creates an array variable
+(@pxref{Arrays})
+named @var{NAME} in the context of the executing shell.
+The standard output of @var{command}
+is connected via a pipe to a file descriptor in the executing shell,
+and that file descriptor is assigned to @var{NAME}[0].
+The standard input of @var{command}
+is connected via a pipe to a file descriptor in the executing shell,
+and that file descriptor is assigned to @var{NAME}[1].
+This pipe is established before any redirections specified by the
+command (@pxref{Redirections}).
+The file descriptors can be utilized as arguments to shell commands
+and redirections using standard word expansions.
+
+The process id of the shell spawned to execute the coprocess is
+available as the value of the variable @var{NAME}_PID.
+The @code{wait}
+builtin command may be used to wait for the coprocess to terminate.
+
+The return status of a coprocess is the exit status of @var{command}.
+
@node Shell Functions
@section Shell Functions
@cindex shell function
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. Shell functions are executed in the current
+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.
Functions are declared using this syntax:
@rwindex function
@example
-[ @code{function} ] @var{name} () @{ @var{command-list}; @}
+[ @code{function} ] @var{name} () @var{compound-command} [ @var{redirections} ]
@end example
This defines a shell function named @var{name}. The reserved
word @code{function} is optional.
If the @code{function} reserved
word is supplied, the parentheses are optional.
-The @var{body} of the function is the @var{command-list} between @{ and @}.
-This list is executed whenever @var{name} is specified as the
-name of a command. The exit status of a function is
-the exit status of the last command executed in the body.
+The @var{body} of the function is the compound command
+@var{compound-command} (@pxref{Compound Commands}).
+That command is usually a @var{list} enclosed between @{ and @}, but
+may be any compound command listed above.
+@var{compound-command} is executed whenever @var{name} is specified as the
+name of a command.
+Any redirections (@pxref{Redirections}) associated with the shell function
+are performed when the function is executed.
+
+A function definition may be deleted using the @option{-f} option to the
+@code{unset} builtin (@pxref{Bourne Shell Builtins}).
+
+The exit status of a function definition is zero unless a syntax error
+occurs or a readonly function with the same name already exists.
+When executed, the exit status of a function is the exit status of the
+last command executed in the body.
+
+Note that for historical reasons, in the most common usage the curly braces
+that surround the body of the function must be separated from the body by
+@code{blank}s or newlines.
+This is because the braces are reserved words and are only recognized
+as such when they are separated from the command list
+by whitespace or another shell metacharacter.
+Also, when using the braces, the @var{list} must be terminated by a semicolon,
+a @samp{&}, or a newline.
When a function is executed, the arguments to the
function become the positional parameters
during its execution (@pxref{Positional Parameters}).
The special parameter @samp{#} that expands to the number of
positional parameters is updated to reflect the change.
-Positional parameter @code{0} is unchanged.
+Special parameter @code{0} is unchanged.
+The first element of the @env{FUNCNAME} 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 @env{DEBUG} and @env{RETURN} traps
+are not inherited unless the function has been given the
+@code{trace} attribute using the @code{declare} builtin or
+the @code{-o functrace} option has been enabled with
+the @code{set} builtin,
+(in which case all functions inherit the @env{DEBUG} and @env{RETURN} traps).
+@xref{Bourne Shell Builtins}, for the description of the
+@code{trap} builtin.
If the builtin command @code{return}
is executed in a function, the function completes and
execution resumes with the next command after the function
-call. When a function completes, the values of the
+call.
+Any command associated with the @code{RETURN} trap is executed
+before execution resumes.
+When a function completes, the values of the
positional parameters and the special parameter @samp{#}
are restored to the values they had prior to the function's
execution. If a numeric argument is given to @code{return},
-that is the function's return status; otherwise the functions's
+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{local} builtin. These variables are visible only to
the function and the commands it invokes.
+Function names and definitions may be listed with the
+@option{-f} option to the @code{declare} or @code{typeset}
+builtin commands (@pxref{Bash Builtins}).
+The @option{-F} option to @code{declare} or @code{typeset}
+will list the function names only
+(and optionally the source file and line number, if the @code{extdebug}
+shell option is enabled).
+Functions may be exported so that subshells
+automatically have them defined with the
+@option{-f} option to the @code{export} builtin
+(@pxref{Bourne Shell Builtins}).
+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.
+
Functions may be recursive. No limit is placed on the number of
recursive calls.
@menu
* Positional Parameters:: The shell's command-line arguments.
-* Special Parameters:: Parameters with special meanings.
+* Special Parameters:: Parameters denoted by special characters.
@end menu
A @var{parameter} is an entity that stores values.
It can be a @code{name}, a number, or one of the special characters
listed below.
-For the shell's purposes, a @var{variable} is a parameter denoted by a
-@code{name}.
+A @var{variable} is a parameter denoted by a @code{name}.
+A variable has a @var{value} and zero or more @var{attributes}.
+Attributes are assigned using the @code{declare} builtin command
+(see the description of the @code{declare} builtin in @ref{Bash Builtins}).
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
@var{value}s undergo tilde expansion, parameter and variable expansion,
command substitution, arithmetic expansion, and quote
removal (detailed below). If the variable has its @code{integer}
-attribute set (see the description of the @code{declare} builtin in
-@ref{Bash Builtins}), then @var{value}
-is subject to arithmetic expansion even if the @code{$((@dots{}))}
+attribute set, then @var{value}
+is evaluated as an arithmetic expression even if the @code{$((@dots{}))}
expansion is not used (@pxref{Arithmetic Expansion}).
Word splitting is not performed, with the exception
of @code{"$@@"} as explained below.
Filename expansion is not performed.
+Assignment statements may also appear as arguments to the
+@code{alias},
+@code{declare}, @code{typeset}, @code{export}, @code{readonly},
+and @code{local} builtin commands.
+
+In the context where an assignment statement is assigning a value
+to a shell variable or array index (@pxref{Arrays}), the @samp{+=}
+operator can be used to
+append to or add to the variable's previous value.
+When @samp{+=} is applied to a variable for which the integer attribute
+has been set, @var{value} is evaluated as an arithmetic expression and
+added to the variable's current value, which is also evaluated.
+When @samp{+=} is applied to an array variable using compound assignment
+(@pxref{Arrays}), the
+variable's value is not unset (as it is when using @samp{=}), and new
+values are appended to the array beginning at one greater than the array's
+maximum index (for indexed arrays), or added as additional key-value pairs
+in an associative array.
+When applied to a string-valued variable, @var{value} is expanded and
+appended to the variable's value.
@node Positional Parameters
@subsection Positional Parameters
digits, other than the single digit @code{0}. Positional parameters are
assigned from the shell's arguments when it is invoked,
and may be reassigned using the @code{set} builtin command.
-Positional parameter @code{N} may be referenced as @code{$@{N@}}.
-Positional parameters may not be assigned to
-with assignment statements. The positional parameters are
+Positional parameter @code{N} may be referenced as @code{$@{N@}}, or
+as @code{$N} when @code{N} consists of a single digit.
+Positional parameters may not be assigned to with assignment statements.
+The @code{set} and @code{shift} builtins are used to set and
+unset them (@pxref{Shell Builtin Commands}).
+The positional parameters are
temporarily replaced when a shell function is executed
(@pxref{Shell Functions}).
Expands to the positional parameters, starting from one. When the
expansion occurs within double quotes, it expands to a single word
with the value of each parameter separated by the first character
-of the @code{IFS}
+of the @env{IFS}
special variable. That is, @code{"$*"} is equivalent
to @code{"$1@var{c}$2@var{c}@dots{}"}, where @var{c}
is the first character of the value of the @code{IFS}
variable.
-If @code{IFS} is unset, the parameters are separated by spaces.
-If @code{IFS} is null, the parameters are joined without intervening
+If @env{IFS} is unset, the parameters are separated by spaces.
+If @env{IFS} is null, the parameters are joined without intervening
separators.
expansion occurs within double quotes, each parameter expands to a
separate word. That is, @code{"$@@"} is equivalent to
@code{"$1" "$2" @dots{}}.
+If the double-quoted expansion occurs within a word, the expansion of
+the first parameter is joined with the beginning part of the original
+word, and the expansion of the last parameter is joined with the last
+part of the original word.
When there are no positional parameters, @code{"$@@"} and
@code{$@@}
expand to nothing (i.e., they are removed).
pipeline.
@item -
-Expands to the current option flags as specified upon invocation,
-by the @code{set}
+(A hyphen.) Expands to the current option flags as specified upon
+invocation, by the @code{set}
builtin command, or those set by the shell itself
-(such as the @samp{-i} option).
+(such as the @option{-i} option).
@item $
-Expands to the process @sc{ID} of the shell. In a @code{()} subshell, it
-expands to the process @sc{ID} of the invoking shell, not the subshell.
+Expands to the process @sc{id} of the shell. In a @code{()} subshell, it
+expands to the process @sc{id} of the invoking shell, not the subshell.
@item !
-Expands to the process @sc{ID} of the most recently executed background
+Expands to the process @sc{id} of the most recently executed background
(asynchronous) command.
@item 0
Expands to the name of the shell or shell script. This is set at
shell initialization. If Bash is invoked with a file of commands
(@pxref{Shell Scripts}), @code{$0} is set to the name of that file.
-If Bash is started with the @samp{-c} option (@pxref{Invoking Bash}),
+If Bash is started with the @option{-c} option (@pxref{Invoking Bash}),
then @code{$0} 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.
@item _
-At shell startup, set to the absolute filename of the shell or shell
-script being executed as passed in the argument list.
+(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 of each command executed and placed in
-the environment exported to that command.
+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.
@end vtable
@cindex brace expansion
@cindex expansion, brace
-Brace expansion
-is a mechanism by which arbitrary strings
-may be generated. This mechanism is similar to
+Brace expansion is a mechanism by which arbitrary strings may be generated.
+This mechanism is similar to
@var{filename expansion} (@pxref{Filename Expansion}),
-but the file names generated
-need not exist. Patterns to be brace expanded take
-the form of an optional @var{preamble},
-followed by a series of comma-separated strings
-between a pair of braces, followed by an optional @var{postscript}.
-The preamble is prepended to each string contained
-within the braces, and the postscript is then appended
-to each resulting string, expanding left to right.
-
-Brace expansions may be nested. The results of each expanded
-string are not sorted; left to right order is preserved.
+but the file names generated need not exist.
+Patterns to be brace expanded take the form of an optional @var{preamble},
+followed by either a series of comma-separated strings or a seqeunce expression
+between a pair of braces,
+followed by an optional @var{postscript}.
+The preamble is prefixed to each string contained within the braces, and
+the postscript is then appended to each resulting string, expanding left
+to right.
+
+Brace expansions may be nested.
+The results of each expanded string are not sorted; left to right order
+is preserved.
For example,
@example
bash$ echo a@{d,c,b@}e
ade ace abe
@end example
+A sequence expression takes the form @code{@{@var{x}..@var{y}[@var{incr}]@}},
+where @var{x} and @var{y} are either integers or single characters,
+and @var{incr}, an optional increment, is an integer.
+When integers are supplied, the expression expands to each number between
+@var{x} and @var{y}, inclusive.
+Supplied integers may be prefixed with @samp{0} to force each term to have the
+same width. When either @var{x} or @var{y} begins with a zero, the shell
+attempts to force all generated terms to contain the same number of digits,
+zero-padding where necessary.
+When characters are supplied, the expression expands to each character
+lexicographically between @var{x} and @var{y}, inclusive. Note that
+both @var{x} and @var{y} must be of the same type.
+When the increment is supplied, it is used as the difference between
+each term. The default increment is 1 or -1 as appropriate.
+
Brace expansion is performed before any other expansions,
and any characters special to other expansions are preserved
in the result. It is strictly textual. Bash
does not apply any syntactic interpretation to the context of the
expansion or the text between the braces.
+To avoid conflicts with parameter expansion, the string @samp{$@{}
+is not considered eligible for brace expansion.
A correctly-formed brace expansion must contain unquoted opening
-and closing braces, and at least one unquoted comma.
+and closing braces, and at least one unquoted comma or a valid
+sequence expression.
Any incorrectly formed brace expansion is left unchanged.
+A @{ or @samp{,} may be quoted with a backslash to prevent its
+being considered part of a brace expression.
+To avoid conflicts with parameter expansion, the string @samp{$@{}
+is not considered eligible for brace expansion.
+
This construct is typically used as shorthand when the common
prefix of the strings to be generated is longer than in the
above example:
characters in the tilde-prefix following the tilde are treated as a
possible @var{login name}.
If this login name is the null string, the tilde is replaced with the
-value of the @code{HOME} shell variable.
-If @code{HOME} is unset, the home directory of the user executing the
+value of the @env{HOME} shell variable.
+If @env{HOME} is unset, the home directory of the user executing the
shell is substituted instead.
Otherwise, the tilde-prefix is replaced with the home directory
associated with the specified login name.
If the tilde-prefix is @samp{~+}, the value of
-the shell variable @code{PWD} replaces the tilde-prefix.
+the shell variable @env{PWD} replaces the tilde-prefix.
If the tilde-prefix is @samp{~-}, the value of the shell variable
-@code{OLDPWD}, if it is set, is substituted.
+@env{OLDPWD}, if it is set, is substituted.
If the characters following the tilde in the tilde-prefix consist of a
number @var{N}, optionally prefixed by a @samp{+} or a @samp{-},
left unchanged.
Each variable assignment is checked for unquoted tilde-prefixes immediately
-following a @samp{:} or @samp{=}.
+following a @samp{:} or the first @samp{=}.
In these cases, tilde expansion is also performed.
Consequently, one may use file names with tildes in assignments to
-@code{PATH}, @code{MAILPATH}, and @code{CDPATH},
+@env{PATH}, @env{MAILPATH}, and @env{CDPATH},
and the shell assigns the expanded value.
The following table shows how Bash treats unquoted tilde-prefixes:
expanded and that value is used in the rest of the substitution, rather
than the value of @var{parameter} itself.
This is known as @code{indirect expansion}.
+The exceptions to this are the expansions of $@{!@var{prefix*}@}
+and $@{!@var{name}[@@]@}
+described below.
+The exclamation point must immediately follow the left brace in order to
+introduce indirection.
In each of the cases below, @var{word} is subject to tilde expansion,
parameter expansion, command substitution, and arithmetic expansion.
+
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.
+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.
@table @code
If @var{parameter}
is unset or null, the expansion of @var{word}
is assigned to @var{parameter}.
-The value of @var{parameter}
-is then substituted. Positional parameters and special parameters may
-not be assigned to in this way.
+The value of @var{parameter} is then substituted.
+Positional parameters and special parameters may not be assigned to
+in this way.
@item $@{@var{parameter}:?@var{word}@}
If @var{parameter}
@item $@{@var{parameter}:@var{offset}@}
@itemx $@{@var{parameter}:@var{offset}:@var{length}@}
-Expands to up to @var{length} characters of @var{parameter},
+Expands to up to @var{length} characters of @var{parameter}
starting at the character specified by @var{offset}.
If @var{length} is omitted, expands to the substring of
-@var{parameter}, starting at the character specified by @var{offset}.
+@var{parameter} starting at the character specified by @var{offset}.
@var{length} and @var{offset} are arithmetic expressions
(@pxref{Shell Arithmetic}).
This is referred to as Substring Expansion.
is used as an offset from the end of the value of @var{parameter}.
If @var{parameter} is @samp{@@}, the result is @var{length} positional
parameters beginning at @var{offset}.
-If @var{parameter} is an array name indexed by @samp{@@} or @samp{*},
-the result is the @var{length}
+If @var{parameter} is an indexed array name subscripted
+by @samp{@@} or @samp{*}, the result is the @var{length}
members of the array beginning with @code{$@{@var{parameter}[@var{offset}]@}}.
+A negative @var{offset} is taken relative to one greater than the maximum
+index of the specified array.
+Substring expansion applied to an associative array produces undefined
+results.
+
+Note that a negative offset must be separated from the colon by at least
+one space to avoid being confused with the @samp{:-} expansion.
Substring indexing is zero-based unless the positional parameters
-are used, in which case the indexing starts at 1.
+are used, in which case the indexing starts at 1 by default.
+If @var{offset} is 0, and the positional parameters are used, @code{$@@} is
+prefixed to the list.
+
+@item $@{!@var{prefix}*@}
+@itemx $@{!@var{prefix}@@@}
+Expands to the names of variables whose names begin with @var{prefix},
+separated by the first character of the @env{IFS} special variable.
+When @samp{@@} is used and the expansion appears within double quotes, each
+variable name expands to a separate word.
+
+@item $@{!@var{name}[@@]@}
+@itemx $@{!@var{name}[*]@}
+If @var{name} is an array variable, expands to the list of array indices
+(keys) assigned in @var{name}.
+If @var{name} is not an array, expands to 0 if @var{name} is set and null
+otherwise.
+When @samp{@@} is used and the expansion appears within double quotes, each
+key expands to a separate word.
@item $@{#@var{parameter}@}
The length in characters of the expanded value of @var{parameter} is
array in turn, and the expansion is the resultant list.
@item $@{@var{parameter}/@var{pattern}/@var{string}@}
-@itemx $@{@var{parameter}//@var{pattern}/@var{string}@}
The @var{pattern} is expanded to produce a pattern just as in
filename expansion.
@var{Parameter} is expanded and the longest match of @var{pattern}
against its value is replaced with @var{string}.
-In the first form, only the first match is replaced.
-The second form causes all matches of @var{pattern} to be
-replaced with @var{string}.
+If @var{pattern} begins with @samp{/}, all matches of @var{pattern} are
+replaced with @var{string}. Normally only the first match is replaced.
If @var{pattern} begins with @samp{#}, it must match at the beginning
of the expanded value of @var{parameter}.
If @var{pattern} begins with @samp{%}, it must match at the end
the substitution operation is applied to each member of the
array in turn, and the expansion is the resultant list.
+@item $@{@var{parameter}^@var{pattern}@}
+@itemx $@{@var{parameter}^^@var{pattern}@}
+@itemx $@{@var{parameter},@var{pattern}@}
+@itemx $@{@var{parameter},,@var{pattern}@}
+This expansion modifies the case of alphabetic characters in @var{parameter}.
+The @var{pattern} is expanded to produce a pattern just as in
+pathname expansion.
+The @samp{^} operator converts lowercase letters matching @var{pattern}
+to uppercase; the @samp{,} operator converts matching uppercase letters
+to lowercase.
+The @samp{^^} and @samp{,,} expansions convert each matched character in the
+expanded value; the @samp{^} and @samp{,} expansions match and convert only
+the first character.
+If @var{pattern} is omitted, it is treated like a @samp{?}, which matches
+every character.
+If @var{parameter} is @samp{@@} or @samp{*},
+the case modification operation is applied to each positional
+parameter in turn, and the expansion is the resultant list.
+If @var{parameter}
+is an array variable subscripted with @samp{@@} or @samp{*},
+the case modification operation is applied to each member of the
+array in turn, and the expansion is the resultant list.
+
@end table
@node Command Substitution
@cindex command substitution
Command substitution allows the output of a command to replace
-the command name. There are two forms:
+the command itself.
+Command substitution occurs when a command is enclosed as follows:
@example
$(@var{command})
@end example
a double quote inside the parentheses is not treated specially.
All tokens in the expression undergo parameter expansion, command
substitution, and quote removal.
-Arithmetic substitutions may be nested.
+Arithmetic expansions may be nested.
The evaluation is performed according to the rules listed below
(@pxref{Shell Arithmetic}).
@cindex process substitution
Process substitution is supported on systems that support named
-pipes (@sc{FIFO}s) or the @file{/dev/fd} method of naming open files.
+pipes (@sc{fifo}s) or the @file{/dev/fd} method of naming open files.
It takes the form of
@example
<(@var{list})
@end example
@noindent
The process @var{list} is run with its input or output connected to a
-@sc{FIFO} or some file in @file{/dev/fd}. The name of this file is
+@sc{fifo} or some file in @file{/dev/fd}. The name of this file is
passed as an argument to the current command as the result of the
expansion. If the @code{>(@var{list})} form is used, writing to
the file will provide input for @var{list}. If the
@code{<(@var{list})} form is used, the file passed as an
argument should be read to obtain the output of @var{list}.
+Note that no space may appear between the @code{<} or @code{>}
+and the left parenthesis, otherwise the construct would be interpreted
+as a redirection.
When available, process substitution is performed simultaneously with
parameter and variable expansion, command substitution, and arithmetic
and arithmetic expansion that did not occur within double quotes for
word splitting.
-The shell treats each character of @code{$IFS}
-as a delimiter, and splits the results of the other
-expansions into words on these characters. If
-@code{IFS} is unset, or its value is exactly @code{<space><tab><newline>},
-the default, then any sequence of @code{IFS}
-characters serves to delimit words. If @code{IFS}
-has a value other than the default, then sequences of
+The shell treats each character of @env{$IFS} as a delimiter, and splits
+the results of the other expansions into words on these characters.
+If @env{IFS} is unset, or its value is exactly @code{<space><tab><newline>},
+the default, then sequences of
+@code{ <space>}, @code{<tab>}, and @code{<newline>}
+at the beginning and end of the results of the previous
+expansions are ignored, and any sequence of @env{IFS}
+characters not at the beginning or end serves to delimit words.
+If @env{IFS} has a value other than the default, then sequences of
the whitespace characters @code{space} and @code{tab}
are ignored at the beginning and end of the
word, as long as the whitespace character is in the
-value of @code{IFS} (an @code{IFS} whitespace character).
-Any character in @code{IFS} that is not @code{IFS}
-whitespace, along with any adjacent @code{IFS}
-whitespace characters, delimits a field. A sequence of @code{IFS}
+value of @env{IFS} (an @env{IFS} whitespace character).
+Any character in @env{IFS} that is not @env{IFS}
+whitespace, along with any adjacent @env{IFS}
+whitespace characters, delimits a field. A sequence of @env{IFS}
whitespace characters is also treated as a delimiter.
-If the value of @code{IFS} is null, no word splitting occurs.
+If the value of @env{IFS} is null, no word splitting occurs.
Explicit null arguments (@code{""} or @code{''}) are retained.
Unquoted implicit null arguments, resulting from the expansion of
-@var{parameter}s
-that have no values, are removed.
+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.
@cindex filename expansion
@cindex pathname expansion
-After word splitting, unless the @samp{-f} option has been set
+After word splitting, unless the @option{-f} option has been set
(@pxref{The Set Builtin}), Bash scans each word for the characters
-@samp{*}, @samp{?}, @samp{(}, and @samp{[}.
+@samp{*}, @samp{?}, and @samp{[}.
If one of these characters appears, then the word is
regarded as a @var{pattern},
and replaced with an alphabetically sorted list of
unchanged.
If the @code{nullglob} option is set, and no matches are found, the word
is removed.
+If the @code{failglob} 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} is enabled, the match is performed
without regard to the case of alphabetic characters.
matched explicitly.
In other cases, the @samp{.} character is not treated specially.
-See the description of @code{shopt} in @ref{Bash Builtins},
+See the description of @code{shopt} in @ref{The Shopt Builtin},
for a description of the @code{nocaseglob}, @code{nullglob},
-and @code{dotglob} options.
+@code{failglob}, and @code{dotglob} options.
-The @code{GLOBIGNORE}
+The @env{GLOBIGNORE}
shell variable may be used to restrict the set of filenames matching a
-pattern. If @code{GLOBIGNORE}
+pattern. If @env{GLOBIGNORE}
is set, each matching filename that also matches one of the patterns in
-@code{GLOBIGNORE} is removed from the list of matches. The filenames
+@env{GLOBIGNORE} is removed from the list of matches. The filenames
@file{.} and @file{..}
-are always ignored, even when @code{GLOBIGNORE}
-is set. However, setting @code{GLOBIGNORE} has the effect of
+are always ignored when @env{GLOBIGNORE}
+is set and not null.
+However, setting @env{GLOBIGNORE} to a non-null value has the effect of
enabling the @code{dotglob}
shell option, so all other filenames beginning with a
@samp{.} will match.
To get the old behavior of ignoring filenames beginning with a
-@samp{.}, make @samp{.*} one of the patterns in @code{GLOBIGNORE}.
-The @code{dotglob} option is disabled when @code{GLOBIGNORE}
+@samp{.}, make @samp{.*} one of the patterns in @env{GLOBIGNORE}.
+The @code{dotglob} option is disabled when @env{GLOBIGNORE}
is unset.
@node Pattern Matching
@cindex matching, pattern
Any character that appears in a pattern, other than the special pattern
-characters described below, matches itself. The NUL character may not
-occur in a pattern. The special pattern characters must be quoted if
-they are to be matched literally.
+characters described below, matches itself.
+The @sc{nul} character may not occur in a pattern.
+A backslash escapes the following character; the
+escaping backslash is discarded when matching.
+The special pattern characters must be quoted if they are to be matched
+literally.
The special pattern characters have the following meanings:
@table @code
@item *
Matches any string, including the null string.
+When the @code{globstar} shell option is enabled, and @samp{*} is used in
+a filename expansion context, two adjacent @samp{*}s used as a single
+pattern will match all files and zero or more directories and
+subdirectories.
+If followed by a @samp{/}, two adjacent @samp{*}s will match only
+directories and subdirectories.
@item ?
Matches any single character.
@item [@dots{}]
Matches any one of the enclosed characters. A pair of characters
-separated by a minus sign denotes a @var{range};
-any character lexically between those two characters, inclusive,
+separated by a hyphen denotes a @var{range expression};
+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{[} is a @samp{!} or a @samp{^}
then any character not enclosed is matched. A @samp{@minus{}}
may be matched by including it as the first or last character
in the set. A @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 @env{LC_COLLATE} shell variable,
+if set.
+
+For example, in the default C locale, @samp{[a-dx-z]} is equivalent to
+@samp{[abcdxyz]}. Many locales sort characters in dictionary order, and in
+these locales @samp{[a-dx-z]} is typically not equivalent to @samp{[abcdxyz]};
+it might be equivalent to @samp{[aBbCcDdxXyYz]}, for example. To obtain
+the traditional interpretation of ranges in bracket expressions, you can
+force the use of the C locale by setting the @env{LC_COLLATE} or
+@env{LC_ALL} environment variable to the value @samp{C}.
Within @samp{[} and @samp{]}, @var{character classes} can be specified
using the syntax
@code{[:}@var{class}@code{:]}, where @var{class} is one of the
-following classes defined in the @sc{POSIX.2} standard:
+following classes defined in the @sc{posix} standard:
@example
alnum alpha ascii blank cntrl digit graph lower
-print punct space upper xdigit
+print punct space upper word xdigit
@end example
@noindent
A character class matches any character belonging to that class.
+The @code{word} character class matches letters, digits, and the character
+@samp{_}.
Within @samp{[} and @samp{]}, an @var{equivalence class} can be
specified using the syntax @code{[=}@var{c}@code{=]}, which
Matches one or more occurrences of the given patterns.
@item @@(@var{pattern-list})
-Matches exactly one of the given patterns.
+Matches one of the given patterns.
@item !(@var{pattern-list})
Matches anything except one of the given patterns.
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, and filename expansion.
+expansion, quote removal, filename expansion, and word splitting.
If it expands to more than one word, Bash reports an error.
Note that the order of redirections is significant. For example,
ls > @var{dirlist} 2>&1
@end example
@noindent
-directs both standard output and standard error to the file
-@var{dirlist}, while the command
+directs both standard output (file descriptor 1) and standard error
+(file descriptor 2) to the file @var{dirlist}, while the command
@example
ls 2>&1 > @var{dirlist}
@end example
because the standard error was duplicated as standard output
before the standard output was redirected to @var{dirlist}.
+Bash handles several filenames specially when they are used in
+redirections, as described in the following table:
+
+@table @code
+@item /dev/fd/@var{fd}
+If @var{fd} is a valid integer, file descriptor @var{fd} is duplicated.
+
+@item /dev/stdin
+File descriptor 0 is duplicated.
+
+@item /dev/stdout
+File descriptor 1 is duplicated.
+
+@item /dev/stderr
+File descriptor 2 is duplicated.
+
+@item /dev/tcp/@var{host}/@var{port}
+If @var{host} is a valid hostname or Internet address, and @var{port}
+is an integer port number or service name, Bash attempts to open a TCP
+connection to the corresponding socket.
+
+@item /dev/udp/@var{host}/@var{port}
+If @var{host} is a valid hostname or Internet address, and @var{port}
+is an integer port number or service name, Bash attempts to open a UDP
+connection to the corresponding socket.
+
+@end table
+
A failure to open or create a file causes the redirection to fail.
+Redirections using file descriptors greater than 9 should be used with
+care, as they may conflict with file descriptors the shell uses
+internally.
+
@subsection Redirecting Input
Redirection of input causes the file whose name results from
the expansion of @var{word}
The general format for redirecting input is:
@example
-[n]<@var{word}
+[@var{n}]<@var{word}
@end example
@subsection Redirecting Output
Redirection of output causes the file whose name results from
the expansion of @var{word}
-to be opened for writing on file descriptor @code{n},
-or the standard output (file descriptor 1) if @code{n}
+to be opened for writing on file descriptor @var{n},
+or the standard output (file descriptor 1) if @var{n}
is not specified. If the file does not exist it is created;
if it does exist it is truncated to zero size.
The general format for redirecting output is:
@example
-[n]>[|]@var{word}
+[@var{n}]>[|]@var{word}
@end example
If the redirection operator is @samp{>}, and the @code{noclobber}
option to the @code{set} builtin has been enabled, the redirection
-will fail if the filename whose name results from the expansion of
+will fail if the file whose name results from the expansion of
@var{word} exists and is a regular file.
If the redirection operator is @samp{>|}, or the redirection operator is
@samp{>} and the @code{noclobber} option is not enabled, the redirection
Redirection of output in this fashion
causes the file whose name results from
the expansion of @var{word}
-to be opened for appending on file descriptor @code{n},
-or the standard output (file descriptor 1) if @code{n}
+to be opened for appending on file descriptor @var{n},
+or the standard output (file descriptor 1) if @var{n}
is not specified. If the file does not exist it is created.
The general format for appending output is:
@example
-[n]>>@var{word}
+[@var{n}]>>@var{word}
@end example
@subsection Redirecting Standard Output and Standard Error
-Bash allows both the
+This construct allows both the
standard output (file descriptor 1) and
the standard error output (file descriptor 2)
to be redirected to the file whose name is the
-expansion of @var{word} with this construct.
+expansion of @var{word}.
There are two formats for redirecting standard output and
standard error:
>@var{word} 2>&1
@end example
+@subsection Appending Standard Output and Standard Error
+This construct allows both the
+standard output (file descriptor 1) and
+the standard error output (file descriptor 2)
+to be appended to the file whose name is the
+expansion of @var{word}.
+
+The format for appending standard output and standard error is:
+@example
+&>>@var{word}
+@end example
+@noindent
+This is semantically equivalent to
+@example
+>>@var{word} 2>&1
+@end example
+
@subsection Here Documents
This type of redirection instructs the shell to read input from the
current source until a line containing only @var{word}
the lines read up to that point are then used as the standard
input for a command.
-The format of here-documents is as follows:
+The format of here-documents is:
@example
<<[@minus{}]@var{word}
@var{here-document}
@var{delimiter}
@end example
-No parameter expansion, command substitution, filename
-expansion, or arithmetic expansion is performed on
+No parameter expansion, command substitution, arithmetic expansion,
+or filename expansion is performed on
@var{word}. If any characters in @var{word} are quoted, the
@var{delimiter} is the result of quote removal on @var{word},
and the lines in the here-document are not expanded.
If @var{word} is unquoted,
all lines of the here-document are subjected to parameter expansion,
command substitution, and arithmetic expansion. In the latter
-case, the pair @code{\newline} is ignored, and @samp{\}
+case, the character sequence @code{\newline} is ignored, and @samp{\}
must be used to quote the characters
@samp{\}, @samp{$}, and @samp{`}.
This allows here-documents within shell scripts to be indented in a
natural fashion.
+@subsection Here Strings
+A variant of here documents, the format is:
+@example
+<<< @var{word}
+@end example
+
+The @var{word} is expanded and supplied to the command on its standard
+input.
+
@subsection Duplicating File Descriptors
The redirection operator
@example
-[n]<&@var{word}
+[@var{n}]<&@var{word}
@end example
@noindent
is used to duplicate input file descriptors.
If @var{word}
-expands to one or more digits, the file descriptor denoted by @code{n}
+expands to one or more digits, the file descriptor denoted by @var{n}
is made to be a copy of that file descriptor.
If the digits in @var{word} do not specify a file descriptor open for
input, a redirection error occurs.
If @var{word}
-evaluates to @samp{-}, file descriptor @code{n} is closed. If
-@code{n} is not specified, the standard input (file descriptor 0) is used.
+evaluates to @samp{-}, file descriptor @var{n} is closed. If
+@var{n} is not specified, the standard input (file descriptor 0) is used.
The operator
@example
-[n]>&@var{word}
+[@var{n}]>&@var{word}
@end example
@noindent
is used similarly to duplicate output file descriptors. If
-@code{n}
-is not specified, the standard output (file descriptor 1) is used.
+@var{n} is not specified, the standard output (file descriptor 1) is used.
If the digits in @var{word} do not specify a file descriptor open for
output, a redirection error occurs.
-As a special case, if @code{n} is omitted, and @var{word} does not
+As a special case, if @var{n} is omitted, and @var{word} does not
expand to one or more digits, the standard output and standard
error are redirected as described previously.
+@subsection Moving File Descriptors
+The redirection operator
+@example
+[@var{n}]<&@var{digit}-
+@end example
+@noindent
+moves the file descriptor @var{digit} to file descriptor @var{n},
+or the standard input (file descriptor 0) if @var{n} is not specified.
+@var{digit} is closed after being duplicated to @var{n}.
+
+Similarly, the redirection operator
+@example
+[@var{n}]>&@var{digit}-
+@end example
+@noindent
+moves the file descriptor @var{digit} to file descriptor @var{n},
+or the standard output (file descriptor 1) if @var{n} is not specified.
+
@subsection Opening File Descriptors for Reading and Writing
The redirection operator
@example
-[n]<>@var{word}
+[@var{n}]<>@var{word}
@end example
@noindent
causes the file whose name is the expansion of @var{word}
to be opened for both reading and writing on file descriptor
-@code{n}, or on file descriptor 0 if @code{n}
+@var{n}, or on file descriptor 0 if @var{n}
is not specified. If the file does not exist, it is created.
@node Executing Commands
@menu
* Simple Command Expansion:: How Bash expands simple commands before
executing them.
-
* Command Search and Execution:: How Bash finds commands and runs them.
-
* Command Execution Environment:: The environment in which Bash
executes commands that are not
shell builtins.
-
* Environment:: The environment given to a command.
-
* Exit Status:: The status returned by commands and how Bash
interprets it.
-
* Signals:: What happens when Bash or a command it runs
receives a signal.
-
@end menu
@node Simple Command Expansion
@item
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 above in @ref{Shell Functions}.
+function is invoked as described in @ref{Shell Functions}.
@item
If the name does not match a function, the shell searches for
@item
If the name is neither a shell function nor a builtin,
and contains no slashes, Bash searches each element of
-@code{$PATH} for a directory containing an executable file
+@env{$PATH} for a directory containing an executable file
by that name. Bash uses a hash table to remember the full
-pathnames of executable files to avoid multiple @code{PATH} searches
+pathnames of executable files to avoid multiple @env{PATH} searches
(see the description of @code{hash} in @ref{Bourne Shell Builtins}).
-A full search of the directories in @code{$PATH}
+A full search of the directories in @env{$PATH}
is performed only if the command is not found in the hash table.
-If the search is unsuccessful, the shell prints an error
+If the search is unsuccessful, the shell searches for a defined shell
+function named @code{command_not_found_handle}.
+If that function exists, it is invoked with the original command and
+the original command's arguments as its arguments, and the function's
+exit status becomes the exit status of the shell.
+If that function is not defined, the shell prints an error
message and returns an exit status of 127.
@item
arguments) or by @code{set}
@item
-options enabled by @code{shopt}
+options enabled by @code{shopt} (@pxref{The Shopt Builtin})
@item
shell aliases defined with @code{alias} (@pxref{Aliases})
@item
-various process IDs, including those of background jobs
+various process @sc{id}s, including those of background jobs
(@pxref{Lists}), the value of @code{$$}, and the value of
-@code{$PPID}
+@env{$PPID}
@end itemize
the file creation mode mask
@item
-shell variables marked for export, along with variables exported for
-the command, passed in the environment (@pxref{Environment})
+shell variables and functions marked for export, along with variables
+exported for the command, passed in the environment (@pxref{Environment})
@item
traps caught by the shell are reset to the values inherited from the
A command invoked in this separate environment cannot affect the
shell's execution environment.
-Command substitution and asynchronous commands are invoked in a
+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
in a subshell environment. Changes made to the subshell environment
cannot affect the shell's execution environment.
+Subshells spawned to execute command substitutions inherit the value of
+the @option{-e} option from the parent shell. When not in @sc{posix} mode,
+Bash clears the @option{-e} option in such subshells.
+
+If a command is followed by a @samp{&} and job control is not active, the
+default standard input for the command is the empty file @file{/dev/null}.
+Otherwise, the invoked command inherits the file descriptors of the calling
+shell as modified by redirections.
+
@node Environment
@subsection Environment
@cindex environment
called the @var{environment}.
This is a list of name-value pairs, of the form @code{name=value}.
-Bash allows you to manipulate the environment in several
-ways. On invocation, the shell scans its own environment and
+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}
to child processes. Executed commands inherit the environment.
These assignment statements affect only the environment seen
by that command.
-If the @samp{-k} option is set (@pxref{The Set Builtin}), then all
+If the @option{-k} option is set (@pxref{The Set Builtin}), then all
parameter assignments are placed in the environment for a command,
not just those that precede the command name.
@subsection Exit Status
@cindex exit status
+The exit status of an executed command is the value returned by the
+@var{waitpid} system call or equivalent function. Exit statuses
+fall between 0 and 255, though, as explained below, the shell may
+use values above 125 specially. Exit statuses from shell builtins and
+compound commands are also limited to this range. Under certain
+circumstances, the shell will use special values to indicate specific
+failure modes.
+
For the shell'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},
-Bash uses the value 128+@var{n} as the exit status.
+When a command terminates on a fatal signal whose number is @var{N},
+Bash uses the value 128+@var{N} as the exit status.
If a command is not found, the child process created to
execute it returns a status of 127. If a command is found
If job control is in effect (@pxref{Job Control}), Bash
ignores @code{SIGTTIN}, @code{SIGTTOU}, and @code{SIGTSTP}.
-Commands started by Bash have signal handlers set to the
+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} and @code{SIGQUIT} as well.
+ignore @code{SIGINT} and @code{SIGQUIT} in addition to these inherited
+handlers.
Commands run as a result of
command substitution ignore the keyboard-generated job control signals
@code{SIGTTIN}, @code{SIGTTOU}, and @code{SIGTSTP}.
The shell exits by default upon receipt of a @code{SIGHUP}.
-Before exiting, it resends the @code{SIGHUP} to all jobs, running
-or stopped.
+Before exiting, an interactive shell resends the @code{SIGHUP} to
+all jobs, running or stopped.
Stopped jobs are sent @code{SIGCONT} to ensure that they receive
the @code{SIGHUP}.
To prevent the shell from sending the @code{SIGHUP} signal to a
to not receive @code{SIGHUP} using @code{disown -h}.
If the @code{huponexit} shell option has been set with @code{shopt}
-(@pxref{Bash Builtins}), Bash sends a @code{SIGHUP} to all jobs when
+(@pxref{The Shopt Builtin}), Bash sends a @code{SIGHUP} to all jobs when
an interactive login shell exits.
-When Bash receives a signal for which a trap has been set while waiting
-for a command to complete, the trap will not be executed until the
-command completes.
+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} builtin, the reception of a signal for
which a trap has been set will cause the @code{wait} builtin to return
A shell script is a text file containing shell commands. When such
a file is used as the first non-option argument when invoking Bash,
-and neither the @samp{-c} nor @samp{-s} option is supplied
+and neither the @option{-c} nor @option{-s} option is supplied
(@pxref{Invoking Bash}),
Bash reads and executes commands from the file, then exits. This
-mode of operation creates a non-interactive shell. When Bash runs
+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 @env{$PATH} if not found there.
+
+When Bash runs
a shell script, it sets the special parameter @code{0} 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.
A shell script may be made executable by using the @code{chmod} command
to turn on the execute bit. When Bash finds such a file while
-searching the @code{$PATH} for a command, it spawns a subshell to
+searching the @env{$PATH} for a command, it spawns a subshell to
execute it. In other words, executing
@example
filename @var{arguments}
(see the description of @code{hash} in @ref{Bourne Shell Builtins})
are retained by the child.
-Most versions of Unix make this a part of the kernel's command
+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{#!}, the remainder of the line specifies
-an interpreter for the program. The arguments to the interpreter
+an interpreter for the program.
+Thus, you can specify Bash, @code{awk}, Perl, or some other
+interpreter and write the rest of the script file in that language.
+
+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
themselves. Note that some older versions of Unix limit the interpreter
name and argument to a maximum of 32 characters.
-@node Bourne Shell Features
-@chapter Bourne Shell Style Features
+Bash scripts often begin with @code{#! /bin/bash} (assuming that
+Bash has been installed in @file{/bin}), since this ensures that
+Bash will be used to interpret the script, even if it is executed
+under another shell.
+
+@node Shell Builtin Commands
+@chapter Shell Builtin Commands
@menu
* Bourne Shell Builtins:: Builtin commands inherited from the Bourne
Shell.
-* Bourne Shell Variables:: Variables which Bash uses in the same way
- as the Bourne Shell.
-* Other Bourne Shell Features:: Addtional aspects of Bash which behave in
- the same way as the Bourne Shell.
+* Bash Builtins:: Table of builtins specific to Bash.
+* Modifying Shell Behavior:: Builtins to modify shell attributes and
+ optional behavior.
+* Special Builtins:: Builtin commands classified specially by
+ POSIX.
@end menu
-This section briefly summarizes things which Bash inherits from
-the Bourne Shell: builtins, variables, and other features.
-It also lists the significant differences between Bash and the Bourne Shell.
-Many of the builtins have been extended by @sc{POSIX} or Bash.
+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 (@pxref{Simple Commands}), the shell executes
+the command directly, without invoking another program.
+Builtin commands are necessary to implement functionality impossible
+or inconvenient to obtain with separate utilities.
+
+This section briefly describes the builtins which Bash inherits from
+the Bourne Shell, as well as the builtin commands which are unique
+to or have been extended in Bash.
+
+Several builtin commands are described in other chapters: builtin
+commands which provide the Bash interface to the job control
+facilities (@pxref{Job Control Builtins}), the directory stack
+(@pxref{Directory Stack Builtins}), the command history
+(@pxref{Bash History Builtins}), and the programmable completion
+facilities (@pxref{Programmable Completion Builtins}).
+
+Many of the builtins have been extended by @sc{posix} or Bash.
+
+Unless otherwise noted, each builtin command documented as accepting
+options preceded by @samp{-} accepts @samp{--}
+to signify the end of the options.
+For example, the @code{:}, @code{true}, @code{false}, and @code{test}
+builtins do not accept options.
@node Bourne Shell Builtins
@section Bourne Shell Builtins
-The following shell builtin commands are inherited from the Bourne
-Shell. These commands are implemented as specified by the @sc{POSIX}
-1003.2 standard.
+The following shell builtin commands are inherited from the Bourne Shell.
+These commands are implemented as specified by the @sc{posix} standard.
@table @code
-@item :
+@item : @r{(a colon)}
@btindex :
@example
: [@var{arguments}]
Do nothing beyond expanding @var{arguments} and performing redirections.
The return status is zero.
-@item .
+@item . @r{(a period)}
@btindex .
@example
. @var{filename} [@var{arguments}]
@end example
Read and execute commands from the @var{filename} argument in the
current shell context. If @var{filename} does not contain a slash,
-the @code{$PATH} variable is used to find
-@var{filename}. The current directory is searched if @var{filename}
-is not found in @code{$PATH}.
+the @env{PATH} variable is used to find @var{filename}.
+When Bash is not in @sc{posix} mode, the current directory is searched
+if @var{filename} is not found in @env{$PATH}.
If any @var{arguments} are supplied, they become the positional
parameters when @var{filename} 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} is not found, or
cannot be read, the return status is non-zero.
+This builtin is equivalent to @code{source}.
@item break
@btindex break
@item cd
@btindex cd
@example
-cd [-LP] [@var{directory}]
+cd [-L|-P] [@var{directory}]
@end example
-Change the current working directory to @var{directory}. If @var{directory}
-is not given, the value of the @code{HOME} shell variable is used. If the
-shell variable @code{CDPATH} exists, it is used as a search path. If
-@var{directory} begins with a slash, @code{CDPATH} is not used.
-The @samp{-P} option means
-to not follow symbolic links; symbolic links are followed by default
-or with the @samp{-L} option.
-If @var{directory} is @samp{-}, it is equivalent to @code{$OLDPWD}.
+Change the current working directory to @var{directory}.
+If @var{directory} is not given, the value of the @env{HOME} shell
+variable is used.
+If the shell variable @env{CDPATH} exists, it is used as a search path.
+If @var{directory} begins with a slash, @env{CDPATH} is not used.
+
+The @option{-P} option means to not follow symbolic links; symbolic
+links are followed by default or with the @option{-L} option.
+If @var{directory} is @samp{-}, it is equivalent to @env{$OLDPWD}.
+
+If a non-empty directory name from @env{CDPATH} is used, or if
+@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.
+
The return status is zero if the directory is successfully changed,
non-zero otherwise.
@end example
If @var{command}
is supplied, it replaces the shell without creating a new process.
-If the @samp{-l} option is supplied, the shell places a dash in the
-zeroth arg passed to @var{command}.
+If the @option{-l} option is supplied, the shell places a dash at the
+beginning of the zeroth argument passed to @var{command}.
This is what the @code{login} program does.
-The @samp{-c} option causes @var{command} to be executed with an empty
+The @option{-c} option causes @var{command} to be executed with an empty
environment.
-If @samp{-a} is supplied, the shell passes @var{name} as the zeroth
+If @option{-a} is supplied, the shell passes @var{name} as the zeroth
argument to @var{command}.
If no @var{command} is specified, redirections may be used to affect
the current shell environment. If there are no redirection errors, the
exit [@var{n}]
@end example
Exit the shell, returning a status of @var{n} to the shell's parent.
+If @var{n} is omitted, the exit status is that of the last command executed.
Any trap on @code{EXIT} is executed before the shell terminates.
@item export
export [-fn] [-p] [@var{name}[=@var{value}]]
@end example
Mark each @var{name} to be passed to child processes
-in the environment. If the @samp{-f} option is supplied, the @var{name}s
+in the environment. If the @option{-f} option is supplied, the @var{name}s
refer to shell functions; otherwise the names refer to shell variables.
-The @samp{-n} option means to no longer mark each @var{name} for export.
-If no @var{names} are supplied, or if the @samp{-p} option is given, a
+The @option{-n} option means to no longer mark each @var{name} for export.
+If no @var{names} are supplied, or if the @option{-p} option is given, a
list of exported names is displayed.
-The @samp{-p} option displays output in a form that may be reused as input.
+The @option{-p} option displays output in a form that may be reused as input.
+If a variable name is followed by =@var{value}, the value of
+the variable is set to @var{value}.
+
The return status is zero unless an invalid option is supplied, one of
-the names is not a valid shell variable name, or @samp{-f} is supplied
+the names is not a valid shell variable name, or @option{-f} is supplied
with a name that is not a shell function.
@item getopts
getopts @var{optstring} @var{name} [@var{args}]
@end example
@code{getopts} is used by shell scripts to parse positional parameters.
-@var{optstring} contains the option letters to be recognized; if a letter
-is followed by a colon, the option is expected to have an
+@var{optstring} 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{:}) and question mark (@samp{?}) may not be
+used as option characters.
Each time it is invoked, @code{getopts}
places the next option in the shell variable @var{name}, initializing
@var{name} if it does not exist,
and the index of the next argument to be processed into the
-variable @code{OPTIND}.
-@code{OPTIND} is initialized to 1 each time the shell or a shell script
+variable @env{OPTIND}.
+@env{OPTIND} is initialized to 1 each time the shell or a shell script
is invoked.
When an option requires an argument,
-@code{getopts} places that argument into the variable @code{OPTARG}.
-The shell does not reset @code{OPTIND} automatically; it must be manually
+@code{getopts} places that argument into the variable @env{OPTARG}.
+The shell does not reset @env{OPTIND} automatically; it must be manually
reset between multiple calls to @code{getopts} within the same shell
invocation if a new set of parameters is to be used.
When the end of options is encountered, @code{getopts} exits with a
return value greater than zero.
-@code{OPTIND} is set to the index of the first non-option argument,
+@env{OPTIND} is set to the index of the first non-option argument,
and @code{name} is set to @samp{?}.
@code{getopts}
error reporting is used. In normal operation diagnostic messages
are printed when invalid options or missing option arguments are
encountered.
-If the variable @code{OPTERR}
+If the variable @env{OPTERR}
is set to 0, no error messages will be displayed, even if the first
character of @code{optstring} is not a colon.
If an invalid option is seen,
@code{getopts} places @samp{?} into @var{name} and, if not silent,
-prints an error message and unsets @code{OPTARG}.
+prints an error message and unsets @env{OPTARG}.
If @code{getopts} is silent, the option character found is placed in
-@code{OPTARG} and no diagnostic message is printed.
+@env{OPTARG} and no diagnostic message is printed.
If a required argument is not found, and @code{getopts}
is not silent, a question mark (@samp{?}) is placed in @var{name},
@code{OPTARG} is unset, and a diagnostic message is printed.
If @code{getopts} is silent, then a colon (@samp{:}) is placed in
-@var{name} and @code{OPTARG} is set to the option character found.
+@var{name} and @env{OPTARG} is set to the option character found.
@item hash
@btindex hash
@example
-hash [-r] [-p @var{filename}] [@var{name}]
+hash [-r] [-p @var{filename}] [-dt] [@var{name}]
@end example
Remember the full pathnames of commands specified as @var{name} arguments,
so they need not be searched for on subsequent invocations.
The commands are found by searching through the directories listed in
-@code{$PATH}.
-The @samp{-p} option inhibits the path search, and @var{filename} is
+@env{$PATH}.
+The @option{-p} option inhibits the path search, and @var{filename} is
used as the location of @var{name}.
-The @samp{-r} option causes the shell to forget all remembered locations.
-If no arguments are given, information about remembered commands is printed.
+The @option{-r} option causes the shell to forget all remembered locations.
+The @option{-d} option causes the shell to forget the remembered location
+of each @var{name}.
+If the @option{-t} option is supplied, the full pathname to which each
+@var{name} corresponds is printed. If multiple @var{name} arguments are
+supplied with @option{-t} the @var{name} is printed before the hashed
+full pathname.
+The @option{-l} option causes output to be displayed in a format
+that may be reused as input.
+If no arguments are given, or if only @option{-l} is supplied,
+information about remembered commands is printed.
The return status is zero unless a @var{name} is not found or an invalid
option is supplied.
@example
pwd [-LP]
@end example
-Print the current working directory.
-If the @samp{-P} option is supplied, the path printed will not
+Print the absolute pathname of the current working directory.
+If the @option{-P} option is supplied, the pathname printed will not
contain symbolic links.
-If the @samp{-L} option is supplied, the path printed may contain
+If the @option{-L} 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
@item readonly
@btindex readonly
@example
-readonly [-apf] [@var{name}] @dots{}
+readonly [-aApf] [@var{name}[=@var{value}]] @dots{}
@end example
Mark each @var{name} as readonly.
The values of these names may not be changed by subsequent assignment.
-If the @samp{-f} option is supplied, each @var{name} refers to a shell
+If the @option{-f} option is supplied, each @var{name} refers to a shell
function.
-The @samp{-a} option means each @var{name} refers to an array variable.
-If no @var{name} arguments are given, or if the @samp{-p}
+The @option{-a} option means each @var{name} refers to an indexed
+array variable; the @option{-A} option means each @var{name} refers
+to an associative array variable.
+If no @var{name} arguments are given, or if the @option{-p}
option is supplied, a list of all readonly names is printed.
-The @samp{-p} option causes output to be displayed in a format that
+The @option{-p} option causes output to be displayed in a format that
may be reused as input.
+If a variable name is followed by =@var{value}, the value of
+the variable is set to @var{value}.
The return status is zero unless an invalid option is supplied, one of
the @var{name} arguments is not a valid shell variable or function name,
-or the @samp{-f} option is supplied with a name that is not a shell function.
+or the @option{-f} option is supplied with a name that is not a shell function.
@item return
@btindex return
return [@var{n}]
@end example
Cause a shell function to exit with the return value @var{n}.
+If @var{n} 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{.} builtin, returning either @var{n} or the exit status
-of the last command executed within the script as the exit status of the
-script.
-The return status is false if @code{return} is used outside a function
-and not during the execution of a script by @samp{.}.
+with the @code{.} (or @code{source}) builtin, returning either @var{n} 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} trap is executed
+before execution resumes after the function or script.
+The return status is non-zero if @code{return} is used outside a function
+and not during the execution of a script by @code{.} or @code{source}.
@item shift
@btindex shift
@end example
Shift the positional parameters to the left by @var{n}.
The positional parameters from @var{n}+1 @dots{} @code{$#} are
-renamed to @code{$1} @dots{} @code{$#}-@var{n}+1.
-Parameters represented by the numbers @code{$#} to @var{n}+1 are unset.
+renamed to @code{$1} @dots{} @code{$#}-@var{n}.
+Parameters represented by the numbers @code{$#} to @code{$#}-@var{n}+1
+are unset.
@var{n} must be a non-negative number less than or equal to @code{$#}.
If @var{n} is zero or greater than @code{$#}, the positional parameters
are not changed.
+If @var{n} is not supplied, it is assumed to be 1.
The return status is zero unless @var{n} is greater than @code{$#} or
less than zero, non-zero otherwise.
Each operator and operand must be a separate argument.
Expressions are composed of the primaries described below in
@ref{Bash Conditional Expressions}.
+@code{test} does not accept any options, nor does it accept and ignore
+an argument of @option{--} as signifying the end of options.
+
+When the @code{[} form is used, the last argument to the command must
+be a @code{]}.
Expressions may be combined using the following operators, listed in
decreasing order of precedence.
+The evaluation depends on the number of arguments; see below.
@table @code
@item ! @var{expr}
operators (@pxref{Bash Conditional Expressions}), the
result of the expression is the result of the binary test using the
first and third arguments as operands.
+The @samp{-a} and @samp{-o} operators are considered binary operators
+when there are three arguments.
If the first argument is @samp{!}, the value is the negation of
the two-argument test using the second and third arguments.
If the first argument is exactly @samp{(} and the third argument is
exactly @samp{)}, the result is the one-argument test of the second
argument.
Otherwise, the expression is false.
-The @samp{-a} and @samp{-o} operators are considered binary operators
-in this case.
@item 4 arguments
If the first argument is @samp{!}, the result is the negation of
trap [-lp] [@var{arg}] [@var{sigspec} @dots{}]
@end example
The commands in @var{arg} are to be read and executed when the
-shell receives signal @var{sigspec}. If @var{arg} is absent or
-equal to @samp{-}, all specified signals are reset to the values
-they had when the shell was started.
+shell receives signal @var{sigspec}. If @var{arg} is absent (and
+there is a single @var{sigspec}) or
+equal to @samp{-}, each specified signal's disposition is reset
+to the value it had when the shell was started.
If @var{arg} is the null string, then the signal specified by
each @var{sigspec} is ignored by the shell and commands it invokes.
-If @var{arg} is @samp{-p}, the shell displays the trap commands
-associated with each @var{sigspec}. If no arguments are supplied, or
-only @samp{-p} is given, @code{trap} prints the list of commands
+If @var{arg} is not present and @option{-p} has been supplied,
+the shell displays the trap commands associated with each @var{sigspec}.
+If no arguments are supplied, or
+only @option{-p} is given, @code{trap} prints the list of commands
associated with each signal number in a form that may be reused as
shell input.
-Each @var{sigspec} is either a signal name such as @code{SIGINT} (with
-or without the @code{SIG} prefix) or a signal number.
+The @option{-l} option causes the shell to print a list of signal names
+and their corresponding numbers.
+Each @var{sigspec} is either a signal name or a signal number.
+Signal names are case insensitive and the @code{SIG} prefix is optional.
If a @var{sigspec}
is @code{0} or @code{EXIT}, @var{arg} is executed when the shell exits.
If a @var{sigspec} is @code{DEBUG}, the command @var{arg} is executed
-after every simple command.
-The @samp{-l} option causes the shell to print a list of signal names
-and their corresponding numbers.
+before every simple command, @code{for} command, @code{case} command,
+@code{select} command, every arithmetic @code{for} command, and before
+the first command executes in a shell function.
+Refer to the description of the @code{extglob} option to the
+@code{shopt} builtin (@pxref{The Shopt Builtin}) for details of its
+effect on the @code{DEBUG} trap.
+If a @var{sigspec} is @code{ERR}, the command @var{arg}
+is executed whenever a simple command has a non-zero exit status,
+subject to the following conditions.
+The @code{ERR} trap is not executed if the failed command is part of the
+command list immediately following an @code{until} or @code{while} keyword,
+part of the test in an @code{if} statement,
+part of a command executed in a @code{&&} or @code{||} list,
+or if the command's return
+status is being inverted using @code{!}.
+These are the same conditions obeyed by the @code{errexit} option.
+If a @var{sigspec} is @code{RETURN}, the command @var{arg} is executed
+each time a shell function or a script executed with the @code{.} or
+@code{source} builtins finishes executing.
Signals ignored upon entry to the shell cannot be trapped or reset.
-Trapped signals are reset to their original values in a child
-process when it is created.
+Trapped signals that are not being ignored are reset to their original
+values in a child process when it is created.
The return status is zero unless a @var{sigspec} does not specify a
valid signal.
@var{mode} 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} command. If @var{mode} is
-omitted, the current value of the mask is printed. If the @samp{-S}
+omitted, the current value of the mask is printed. If the @option{-S}
option is supplied without a @var{mode} argument, the mask is printed
in a symbolic format.
-If the @samp{-p} option is supplied, and @var{mode}
+If the @option{-p} option is supplied, and @var{mode}
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} argument is supplied, and non-zero otherwise.
+Note that when the mode is interpreted as an octal number, each number
+of the umask is subtracted from @code{7}. Thus, a umask of @code{022}
+results in permissions of @code{755}.
+
@item unset
@btindex unset
@example
unset [-fv] [@var{name}]
@end example
Each variable or function @var{name} is removed.
-If no options are supplied, or the @samp{-v} option is given, each
+If no options are supplied, or the @option{-v} option is given, each
@var{name} refers to a shell variable.
-If the @samp{-f} option is given, the @var{name}s refer to shell
+If the @option{-f} option is given, the @var{name}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} does not exist or is
-readonly.
+The return status is zero unless a @var{name} is readonly.
@end table
-@node Bourne Shell Variables
-@section Bourne Shell Variables
-
-Bash uses certain shell variables in the same way as the Bourne shell.
-In some cases, Bash assigns a default value to the variable.
+@node Bash Builtins
+@section Bash Builtin Commands
-@vtable @code
+This section describes builtin commands which are unique to
+or have been extended in Bash.
+Some of these commands are specified in the @sc{posix} standard.
-@item CDPATH
-A colon-separated list of directories used as a search path for
-the @code{cd} builtin command.
+@table @code
-@item HOME
-The current user's home directory; the default for the @code{cd} builtin
-command.
-The value of this variable is also used by tilde expansion
-(@pxref{Tilde Expansion}).
+@item alias
+@btindex alias
+@example
+alias [@code{-p}] [@var{name}[=@var{value}] @dots{}]
+@end example
-@item IFS
-A list of characters that separate fields; used when the shell splits
-words as part of expansion.
+Without arguments or with the @option{-p} option, @code{alias} 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}
+whose @var{value} is given. If no @var{value} is given, the name
+and value of the alias is printed.
+Aliases are described in @ref{Aliases}.
-@item MAIL
-If this parameter is set to a filename and the @code{MAILPATH} variable
-is not set, Bash informs the user of the arrival of mail in
-the specified file.
+@item bind
+@btindex bind
+@example
+bind [-m @var{keymap}] [-lpsvPSV]
+bind [-m @var{keymap}] [-q @var{function}] [-u @var{function}] [-r @var{keyseq}]
+bind [-m @var{keymap}] -f @var{filename}
+bind [-m @var{keymap}] -x @var{keyseq:shell-command}
+bind [-m @var{keymap}] @var{keyseq:function-name}
+bind @var{readline-command}
+@end example
-@item MAILPATH
-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{?}.
-When used in the text of the message, @code{$_} expands to the name of
-the current mail file.
+Display current Readline (@pxref{Command Line Editing})
+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 (@pxref{Readline Init File}),
+but each binding or command must be passed as a separate argument; e.g.,
+@samp{"\C-x\C-r":re-read-init-file}.
-@item OPTARG
-The value of the last option argument processed by the @code{getopts} builtin.
+Options, if supplied, have the following meanings:
-@item OPTIND
-The index of the last option argument processed by the @code{getopts} builtin.
+@table @code
+@item -m @var{keymap}
+Use @var{keymap} as the keymap to be affected by
+the subsequent bindings. Acceptable @var{keymap}
+names are
+@code{emacs},
+@code{emacs-standard},
+@code{emacs-meta},
+@code{emacs-ctlx},
+@code{vi},
+@code{vi-move},
+@code{vi-command}, and
+@code{vi-insert}.
+@code{vi} is equivalent to @code{vi-command};
+@code{emacs} is equivalent to @code{emacs-standard}.
-@item PATH
-A colon-separated list of directories in which the shell looks for
-commands.
+@item -l
+List the names of all Readline functions.
-@item PS1
-The primary prompt string. The default value is @samp{\s-\v\$ }.
+@item -p
+Display Readline function names and bindings in such a way that they
+can be used as input or in a Readline initialization file.
-@item PS2
-The secondary prompt string. The default value is @samp{> }.
-
-@end vtable
+@item -P
+List current Readline function names and bindings.
-@node Other Bourne Shell Features
-@section Other Bourne Shell Features
+@item -v
+Display Readline variable names and values in such a way that they
+can be used as input or in a Readline initialization file.
-@menu
-* Major Differences From The Bourne Shell:: Major differences between
- Bash and the Bourne shell.
-@end menu
+@item -V
+List current Readline variable names and values.
-Bash implements essentially the same grammar, parameter and
-variable expansion, redirection, and quoting as the Bourne Shell.
-Bash uses the @sc{POSIX} 1003.2 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
-subsequent sections.
+@item -s
+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.
-@node Major Differences From The Bourne Shell
-@subsection Major Differences From The SVR4.2 Bourne Shell
+@item -S
+Display Readline key sequences bound to macros and the strings they output.
-@itemize @bullet
+@item -f @var{filename}
+Read key bindings from @var{filename}.
-@item
-Bash is @sc{POSIX}-conformant, even where the @sc{POSIX} specification
-differs from traditional @code{sh} behavior.
+@item -q @var{function}
+Query about which keys invoke the named @var{function}.
-@item
-Bash has multi-character invocation options (@pxref{Invoking Bash}).
+@item -u @var{function}
+Unbind all keys bound to the named @var{function}.
-@item
-Bash has command-line editing (@pxref{Command Line Editing}) and
-the @code{bind} builtin.
+@item -r @var{keyseq}
+Remove any current binding for @var{keyseq}.
-@item
-Bash has command history (@pxref{Bash History Facilities}) and the
-@code{history} and @code{fc} builtins to manipulate it.
+@item -x @var{keyseq:shell-command}
+Cause @var{shell-command} to be executed whenever @var{keyseq} is
+entered.
+When @var{shell-command} is executed, the shell sets the
+@code{READLINE_LINE} variable to the contents of the Readline line
+buffer and the @code{READLINE_POINT} variable to the current location
+of the insertion point.
+If the executed command changes the value of @code{READLINE_LINE} or
+@code{READLINE_POINT}, those new values will be reflected in the
+editing state.
+@end table
-@item
-Bash implements @code{csh}-like history expansion
-(@pxref{History Interaction}).
+@noindent
+The return status is zero unless an invalid option is supplied or an
+error occurs.
-@item
-Bash has one-dimensional array variables (@pxref{Arrays}), 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.
+@item builtin
+@btindex builtin
+@example
+builtin [@var{shell-builtin} [@var{args}]]
+@end example
+Run a shell builtin, passing it @var{args}, 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} is not a shell
+builtin command.
-@item
-The @code{$'@dots{}'} quoting syntax, which expands ANSI-C
-backslash-escaped characters in the text between the single quotes,
-is supported (@pxref{ANSI-C Quoting}).
+@item caller
+@btindex caller
+@example
+caller [@var{expr}]
+@end example
+Returns the context of any active subroutine call (a shell function or
+a script executed with the @code{.} or @code{source} builtins).
-@item
-Bash supports the @code{$"@dots{}"} quoting syntax to do
-locale-specific translation of the characters between the double
-quotes. The @samp{-D}, @samp{--dump-strings}, and @samp{--dump-po-strings}
-invocation options list the translatable strings found in a script
-(@pxref{Locale Translation}).
+Without @var{expr}, @code{caller} displays the line number and source
+filename of the current subroutine call.
+If a non-negative integer is supplied as @var{expr}, @code{caller}
+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.
-@item
-Bash implements the @code{!} keyword to negate the return value of
-a pipeline (@pxref{Pipelines}).
-Very useful when an @code{if} statement needs to act only if a test fails.
+The return value is 0 unless the shell is not executing a subroutine
+call or @var{expr} does not correspond to a valid position in the
+call stack.
-@item
-Bash has the @code{time} reserved word and command timing (@pxref{Pipelines}).
-The display of the timing statistics may be controlled with the
-@code{TIMEFORMAT} variable.
+@item command
+@btindex command
+@example
+command [-pVv] @var{command} [@var{arguments} @dots{}]
+@end example
+Runs @var{command} with @var{arguments} ignoring any shell function
+named @var{command}.
+Only shell builtin commands or commands found by searching the
+@env{PATH} are executed.
+If there is a shell function named @code{ls}, running @samp{command ls}
+within the function will execute the external command @code{ls}
+instead of calling the function recursively.
+The @option{-p} option means to use a default value for @env{PATH}
+that is guaranteed to find all of the standard utilities.
+The return status in this case is 127 if @var{command} cannot be
+found or an error occurred, and the exit status of @var{command}
+otherwise.
-@item
-Bash includes the @code{select} compound command, which allows the
-generation of simple menus (@pxref{Conditional Constructs}).
+If either the @option{-V} or @option{-v} option is supplied, a
+description of @var{command} is printed. The @option{-v} option
+causes a single word indicating the command or file name used to
+invoke @var{command} to be displayed; the @option{-V} option produces
+a more verbose description. In this case, the return status is
+zero if @var{command} is found, and non-zero if not.
-@item
-Bash includes the @code{[[} compound command, which makes conditional
-testing part of the shell grammar (@pxref{Conditional Constructs}).
+@item declare
+@btindex declare
+@example
+declare [-aAfFilrtux] [-p] [@var{name}[=@var{value}] @dots{}]
+@end example
-@item
-Bash includes brace expansion (@pxref{Brace Expansion}) and tilde
-expansion (@pxref{Tilde Expansion}).
+Declare variables and give them attributes. If no @var{name}s
+are given, then display the values of variables instead.
-@item
-Bash implements command aliases and the @code{alias} and @code{unalias}
-builtins (@pxref{Aliases}).
+The @option{-p} option will display the attributes and values of each
+@var{name}.
+When @option{-p} is used with @var{name} arguments, additional options
+are ignored.
+
+When @option{-p} is supplied without @var{name} arguments, @code{declare}
+will display the attributes and values of all variables having the
+attributes specified by the additional options.
+If no other options are supplied with @option{-p}, @code{declare} will
+display the attributes and values of all shell variables. The @option{-f}
+option will restrict the display to shell functions.
+
+The @option{-F} option inhibits the display of function definitions;
+only the function name and attributes are printed.
+If the @code{extdebug} shell option is enabled using @code{shopt}
+(@pxref{The Shopt Builtin}), the source file name and line number where
+the function is defined are displayed as well.
+@option{-F} implies @option{-f}.
+The following options can be used to restrict output to variables with
+the specified attributes or to give variables attributes:
-@item
-Bash provides shell arithmetic, the @code{((} compound command
-(@pxref{Conditional Constructs}),
-and arithmetic expansion (@pxref{Shell Arithmetic}).
+@table @code
+@item -a
+Each @var{name} is an indexed array variable (@pxref{Arrays}).
-@item
-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}
-command.
+@item -A
+Each @var{name} is an associative array variable (@pxref{Arrays}).
-@item
-Bash includes the @sc{POSIX} pattern removal @samp{%}, @samp{#}, @samp{%%}
-and @samp{##} expansions to remove leading or trailing substrings from
-variable values (@pxref{Shell Parameter Expansion}).
+@item -f
+Use function names only.
-@item
-The expansion @code{$@{#xx@}}, which returns the length of @code{$@{xx@}},
-is supported (@pxref{Shell Parameter Expansion}).
+@item -i
+The variable is to be treated as
+an integer; arithmetic evaluation (@pxref{Shell Arithmetic}) is
+performed when the variable is assigned a value.
-@item
-The expansion @code{$@{var:}@var{offset}@code{[:}@var{length}@code{]@}},
-which expands to the substring of @code{var}'s value of length
-@var{length}, beginning at @var{offset}, is present
-(@pxref{Shell Parameter Expansion}).
+@item -l
+When the variable is assigned a value, all upper-case characters are
+converted to lower-case.
+The upper-case attribute is disabled.
-@item
-The expansion
-@code{$@{var/[/]}@var{pattern}@code{[/}@var{replacement}@code{]@}},
-which matches @var{pattern} and replaces it with @var{replacement} in
-the value of @code{var}, is available (@pxref{Shell Parameter Expansion}).
+@item -r
+Make @var{name}s readonly. These names cannot then be assigned values
+by subsequent assignment statements or unset.
-@item
-Bash has @var{indirect} variable expansion using @code{$@{!word@}}
-(@pxref{Shell Parameter Expansion}).
+@item -t
+Give each @var{name} the @code{trace} attribute.
+Traced functions inherit the @code{DEBUG} and @code{RETURN} traps from
+the calling shell.
+The trace attribute has no special meaning for variables.
-@item
-Bash can expand positional parameters beyond @code{$9} using
-@code{$@{@var{num}@}}.
+@item -u
+When the variable is assigned a value, all lower-case characters are
+converted to upper-case.
+The lower-case attribute is disabled.
-@item
-The @sc{POSIX} @code{$()} form of command substitution
-is implemented (@pxref{Command Substitution}),
-and preferred to the Bourne shell's @code{``} (which
-is also implemented for backwards compatibility).
+@item -x
+Mark each @var{name} for export to subsequent commands via
+the environment.
+@end table
-@item
-Bash has process substitution (@pxref{Process Substitution}).
+Using @samp{+} instead of @samp{-} turns off the attribute instead,
+with the exceptions that @samp{+a}
+may not be used to destroy an array variable and @samp{+r} will not
+remove the readonly attribute.
+When used in a function, @code{declare} makes each @var{name} local,
+as with the @code{local} command. If a variable name is followed by
+=@var{value}, the value of the variable is set to @var{value}.
-@item
-Bash automatically assigns variables that provide information about the
-current user (@code{UID}, @code{EUID}, and @code{GROUPS}), the current host
-(@code{HOSTTYPE}, @code{OSTYPE}, @code{MACHTYPE}, and @code{HOSTNAME}),
-and the instance of Bash that is running (@code{BASH},
-@code{BASH_VERSION}, and @code{BASH_VERSINFO}). @xref{Bash Variables},
-for details.
+The return status is zero unless an invalid option is encountered,
+an attempt is made to define a function using @samp{-f foo=bar},
+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 (@pxref{Arrays}),
+one of the @var{names} 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 @option{-f}.
-@item
-The @code{IFS} variable is used to split only the results of expansion,
-not all words (@pxref{Word Splitting}).
-This closes a longstanding shell security hole.
+@item echo
+@btindex echo
+@example
+echo [-neE] [@var{arg} @dots{}]
+@end example
+Output the @var{arg}s, separated by spaces, terminated with a
+newline.
+The return status is always 0.
+If @option{-n} is specified, the trailing newline is suppressed.
+If the @option{-e} option is given, interpretation of the following
+backslash-escaped characters is enabled.
+The @option{-E} option disables the interpretation of these escape characters,
+even on systems where they are interpreted by default.
+The @code{xpg_echo} shell option may be used to
+dynamically determine whether or not @code{echo} expands these
+escape characters by default.
+@code{echo} does not interpret @option{--} to mean the end of options.
-@item
-Bash implements the full set of @sc{POSIX.2} filename expansion operators,
-including @var{character classes}, @var{equivalence classes}, and
-@var{collating symbols} (@pxref{Filename Expansion}).
+@code{echo} interprets the following escape sequences:
+@table @code
+@item \a
+alert (bell)
+@item \b
+backspace
+@item \c
+suppress further output
+@item \e
+escape
+@item \f
+form feed
+@item \n
+new line
+@item \r
+carriage return
+@item \t
+horizontal tab
+@item \v
+vertical tab
+@item \\
+backslash
+@item \0@var{nnn}
+the eight-bit character whose value is the octal value @var{nnn}
+(zero to three octal digits)
+@item \x@var{HH}
+the eight-bit character whose value is the hexadecimal value @var{HH}
+(one or two hex digits)
+@end table
-@item
-Bash implements extended pattern matching features when the @code{extglob}
-shell option is enabled (@pxref{Pattern Matching}).
+@item enable
+@btindex enable
+@example
+enable [-a] [-dnps] [-f @var{filename}] [@var{name} @dots{}]
+@end example
+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 @option{-n} is used, the @var{name}s become disabled. Otherwise
+@var{name}s are enabled. For example, to use the @code{test} binary
+found via @env{$PATH} instead of the shell builtin version, type
+@samp{enable -n test}.
-@item
-It is possible to have a variable and a function with the same name;
-@code{sh} does not separate the two name spaces.
+If the @option{-p} option is supplied, or no @var{name} arguments appear,
+a list of shell builtins is printed. With no other arguments, the list
+consists of all enabled shell builtins.
+The @option{-a} option means to list
+each builtin with an indication of whether or not it is enabled.
-@item
-Bash functions are permitted to have local variables using the
-@code{local} builtin, and thus useful recursive functions may be written.
+The @option{-f} option means to load the new builtin command @var{name}
+from shared object @var{filename}, on systems that support dynamic loading.
+The @option{-d} option will delete a builtin loaded with @option{-f}.
-@item
-Variable assignments preceding commands affect only that command, even
-builtins and functions (@pxref{Environment}).
-In @code{sh}, all variable assignments
-preceding commands are global unless the command is executed from the
-file system.
+If there are no options, a list of the shell builtins is displayed.
+The @option{-s} option restricts @code{enable} to the @sc{posix} special
+builtins. If @option{-s} is used with @option{-f}, the new builtin becomes
+a special builtin (@pxref{Special Builtins}).
-@item
-Bash performs filename expansion on filenames specified as operands
-to input and output redirection operators.
+The return status is zero unless a @var{name} is not a shell builtin
+or there is an error loading a new builtin from a shared object.
-@item
-Bash contains the @samp{<>} redirection operator, allowing a file to be
-opened for both reading and writing, and the @samp{&>} redirection
-operator, for directing standard output and standard error to the same
-file (@pxref{Redirections}).
+@item help
+@btindex help
+@example
+help [-dms] [@var{pattern}]
+@end example
+Display helpful information about builtin commands.
+If @var{pattern} is specified, @code{help} gives detailed help
+on all commands matching @var{pattern}, otherwise a list of
+the builtins is printed.
-@item
-The @code{noclobber} option is available to avoid overwriting existing
-files with output redirection (@pxref{The Set Builtin}).
-The @samp{>|} redirection operator may be used to override @code{noclobber}.
+Options, if supplied, have the following meanings:
-@item
-The Bash @code{cd} and @code{pwd} builtins (@pxref{Bourne Shell Builtins})
-each take @samp{-L} and @samp{-P} builtins to switch between logical and
-physical modes.
+@table @code
+@item -d
+Display a short description of each @var{pattern}
+@item -m
+Display the description of each @var{pattern} in a manpage-like format
+@item -s
+Display only a short usage synopsis for each @var{pattern}
+@end table
-@item
-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} and @code{command} builtins (@pxref{Bash Builtins}).
+The return status is zero unless no command matches @var{pattern}.
-@item
-The @code{command} builtin allows selective disabling of functions
-when command lookup is performed (@pxref{Bash Builtins}).
+@item let
+@btindex let
+@example
+let @var{expression} [@var{expression}]
+@end example
+The @code{let} builtin allows arithmetic to be performed on shell
+variables. Each @var{expression} is evaluated according to the
+rules given below in @ref{Shell Arithmetic}. If the
+last @var{expression} evaluates to 0, @code{let} returns 1;
+otherwise 0 is returned.
-@item
-Individual builtins may be enabled or disabled using the @code{enable}
-builtin (@pxref{Bash Builtins}).
+@item local
+@btindex local
+@example
+local [@var{option}] @var{name}[=@var{value}] @dots{}
+@end example
+For each argument, a local variable named @var{name} is created,
+and assigned @var{value}.
+The @var{option} can be any of the options accepted by @code{declare}.
+@code{local} can only be used within a function; it makes the variable
+@var{name} have a visible scope restricted to that function and its
+children. The return status is zero unless @code{local} is used outside
+a function, an invalid @var{name} is supplied, or @var{name} is a
+readonly variable.
-@item
-The Bash @code{exec} 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
-(@pxref{Bourne Shell Builtins}).
+@item logout
+@btindex logout
+@example
+logout [@var{n}]
+@end example
+Exit a login shell, returning a status of @var{n} to the shell's
+parent.
-@item
-Shell functions may be exported to children via the environment
-using @code{export -f} (@pxref{Shell Functions}).
+@item mapfile
+@btindex mapfile
+@example
+mapfile [-n @var{count}] [-O @var{origin}] [-s @var{count}] [-t] [-u @var{fd}] [
+-C @var{callback}] [-c @var{quantum}] [@var{array}]
+@end example
+Read lines from the standard input into array variable @var{array},
+or from file descriptor @var{fd}
+if the @option{-u} option is supplied.
+The variable @code{MAPFILE} is the default @var{array}.
+Options, if supplied, have the following meanings:
+@table @code
-@item
-The Bash @code{export}, @code{readonly}, and @code{declare} builtins can
-take a @samp{-f} option to act on shell functions, a @samp{-p} option to
-display variables with various attributes set in a format that can be
-used as shell input, a @samp{-n} option to remove various variable
-attributes, and @samp{name=value} arguments to set variable attributes
-and values simultaneously.
+@item -n
+Copy at most @var{count} lines. If @var{count} is 0, all lines are copied.
+@item -O
+Begin assigning to @var{array} at index @var{origin}.
+The default index is 0.
+@item -s
+Discard the first @var{count} lines read.
+@item -t
+Remove a trailing line from each line read.
+@item -u
+Read lines from file descriptor @var{fd} instead of the standard input.
+@item -C
+Evaluate @var{callback} each time @var{quantum}P lines are read.
+The @option{-c} option specifies @var{quantum}.
+@item -c
+Specify the number of lines read between each call to @var{callback}.
+@end table
-@item
-The Bash @code{hash} builtin allows a name to be associated with
-an arbitrary filename, even when that filename cannot be found by
-searching the @code{$PATH}, using @samp{hash -p}
-(@pxref{Bourne Shell Builtins}).
+If @option{-C} is specified without @option{-c},
+the default quantum is 5000.
-@item
-Bash includes a @code{help} builtin for quick reference to shell
-facilities (@pxref{Bash Builtins}).
+If not supplied with an explicit origin, @code{mapfile} will clear @var{array}
+before assigning to it.
-@item
-The @code{printf} builtin is available to display formatted output
-(@pxref{Bash Builtins}).
+@code{mapfile} returns successfully unless an invalid option or option
+argument is supplied, or @var{array} is invalid or unassignable.
-@item
-The Bash @code{read} builtin (@pxref{Bash Builtins})
-will read a line ending in @samp{\} with
-the @samp{-r} option, and will use the @code{REPLY} variable as a
-default if no arguments are supplied. The Bash @code{read} builtin
-also accepts a prompt string with the @samp{-p} option and will use
-Readline to obtain the line when given the @samp{-e} option.
+@item printf
+@btindex printf
+@example
+printf [-v @var{var}] @var{format} [@var{arguments}]
+@end example
+Write the formatted @var{arguments} to the standard output under the
+control of the @var{format}.
+The @var{format} 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}.
+In addition to the standard @code{printf(1)} formats, @samp{%b} causes
+@code{printf} to expand backslash escape sequences in the corresponding
+@var{argument},
+(except that @samp{\c} terminates output, backslashes in
+@samp{\'}, @samp{\"}, and @samp{\?} are not removed, and octal escapes
+beginning with @samp{\0} may contain up to four digits),
+and @samp{%q} causes @code{printf} to output the
+corresponding @var{argument} in a format that can be reused as shell input.
-@item
-The @code{return} builtin may be used to abort execution of scripts
-executed with the @code{.} or @code{source} builtins
-(@pxref{Bourne Shell Builtins}).
+The @option{-v} option causes the output to be assigned to the variable
+@var{var} rather than being printed to the standard output.
-@item
-Bash includes the @code{shopt} builtin, for finer control of shell
-optional capabilities (@pxref{Bash Builtins}).
+The @var{format} is reused as necessary to consume all of the @var{arguments}.
+If the @var{format} requires more @var{arguments} 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.
-@item
-Bash has much more optional behavior controllable with the @code{set}
-builtin (@pxref{The Set Builtin}).
+@item read
+@btindex read
+@example
+read [-ers] [-a @var{aname}] [-d @var{delim}] [-i @var{text}] [-n @var{nchars}] [-p @var{prompt}] [-t @var{timeout}] [-u @var{fd}] [@var{name} @dots{}]
+@end example
+One line is read from the standard input, or from the file descriptor
+@var{fd} supplied as an argument to the @option{-u} option, and the first word
+is assigned to the first @var{name}, the second word to the second @var{name},
+and so on, with leftover words and their intervening separators assigned
+to the last @var{name}.
+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 @env{IFS} variable
+are used to split the line into words.
+The backslash character @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 @env{REPLY}.
+The return code is zero, unless end-of-file is encountered, @code{read}
+times out (in which case the return code is greater than 128), or an
+invalid file descriptor is supplied as the argument to @option{-u}.
-@item
-The @code{test} builtin (@pxref{Bourne Shell Builtins})
-is slightly different, as it implements the @sc{POSIX} algorithm,
-which specifies the behavior based on the number of arguments.
+Options, if supplied, have the following meanings:
-@item
-The @code{trap} builtin (@pxref{Bourne Shell Builtins})
-allows a @code{DEBUG} pseudo-signal specification,
-similar to @code{EXIT}. Commands specified with a @code{DEBUG} trap are
-executed after every simple command. The @code{DEBUG} trap is not
-inherited by shell functions.
+@table @code
+@item -a @var{aname}
+The words are assigned to sequential indices of the array variable
+@var{aname}, starting at 0.
+All elements are removed from @var{aname} before the assignment.
+Other @var{name} arguments are ignored.
-@item
-The Bash @code{type} builtin is more extensive and gives more information
-about the names it finds (@pxref{Bash Builtins}).
+@item -d @var{delim}
+The first character of @var{delim} is used to terminate the input line,
+rather than newline.
-@item
-The Bash @code{umask} builtin permits a @samp{-p} option to cause
-the output to be displayed in the form of a @code{umask} command
-that may be reused as input (@pxref{Bourne Shell Builtins}).
+@item -e
+Readline (@pxref{Command Line Editing}) is used to obtain the line.
+Readline uses the current (or default, if line editing was not previously
+active) editing settings.
-@item
-Bash implements a @code{csh}-like directory stack, and provides the
-@code{pushd}, @code{popd}, and @code{dirs} builtins to manipulate it
-(@pxref{The Directory Stack}).
-Bash also makes the directory stack visible as the value of the
-@code{DIRSTACK} shell variable.
+@item -i @var{text}
+If Readline is being used to read the line, @var{text} is placed into
+the editing buffer before editing begins.
-@item
-Bash interprets special backslash-escaped characters in the prompt
-strings when interactive (@pxref{Printing a Prompt}).
+@item -n @var{nchars}
+@code{read} returns after reading @var{nchars} characters rather than
+waiting for a complete line of input.
-@item
-The Bash restricted mode is more useful (@pxref{The Restricted Shell});
-the @sc{SVR4.2} shell restricted mode is too limited.
+@item -p @var{prompt}
+Display @var{prompt}, without a trailing newline, before attempting
+to read any input.
+The prompt is displayed only if input is coming from a terminal.
-@item
-The @code{disown} builtin can remove a job from the internal shell
-job table (@pxref{Job Control Builtins}) or suppress the sending
-of @code{SIGHUP} to a job when the shell exits as the result of a
-@code{SIGHUP}.
+@item -r
+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.
-@item
-The @sc{SVR4.2} shell has two privilege-related builtins
-(@code{mldmode} and @code{priv}) not present in Bash.
+@item -s
+Silent mode. If input is coming from a terminal, characters are
+not echoed.
+
+@item -t @var{timeout}
+Cause @code{read} to time out and return failure if a complete line of
+input is not read within @var{timeout} seconds.
+@var{timeout} may be a decimal number with a fractional portion following
+the decimal point.
+This option is only effective if @code{read} is reading input from a
+terminal, pipe, or other special file; it has no effect when reading
+from regular files.
+If @var{timeout} is 0, @code{read} returns success if input is available on
+the specified file descriptor, failure otherwise.
+The exit status is greater than 128 if the timeout is exceeded.
+
+@item -u @var{fd}
+Read input from file descriptor @var{fd}.
-@item
-Bash does not have the @code{stop} or @code{newgrp} builtins.
+@end table
-@item
-Bash does not use the @code{SHACCT} variable or perform shell accounting.
+@item source
+@btindex source
+@example
+source @var{filename}
+@end example
+A synonym for @code{.} (@pxref{Bourne Shell Builtins}).
-@item
-The @sc{SVR4.2} @code{sh} uses a @code{TIMEOUT} variable like Bash uses
-@code{TMOUT}.
+@item type
+@btindex type
+@example
+type [-afptP] [@var{name} @dots{}]
+@end example
+For each @var{name}, indicate how it would be interpreted if used as a
+command name.
-@end itemize
+If the @option{-t} option is used, @code{type} prints a single word
+which is one of @samp{alias}, @samp{function}, @samp{builtin},
+@samp{file} or @samp{keyword},
+if @var{name} is an alias, shell function, shell builtin,
+disk file, or shell reserved word, respectively.
+If the @var{name} is not found, then nothing is printed, and
+@code{type} returns a failure status.
-@noindent
-More features unique to Bash may be found in @ref{Bash Features}.
+If the @option{-p} option is used, @code{type} either returns the name
+of the disk file that would be executed, or nothing if @option{-t}
+would not return @samp{file}.
-@subsection Implementation Differences From The SVR4.2 Shell
+The @option{-P} option forces a path search for each @var{name}, even if
+@option{-t} would not return @samp{file}.
-Since Bash is a completely new implementation, it does not suffer from
-many of the limitations of the @sc{SVR4.2} shell. For instance:
+If a command is hashed, @option{-p} and @option{-P} print the hashed value,
+not necessarily the file that appears first in @code{$PATH}.
-@itemize @bullet
+If the @option{-a} option is used, @code{type} returns all of the places
+that contain an executable named @var{file}.
+This includes aliases and functions, if and only if the @option{-p} option
+is not also used.
-@item
-Bash does not fork a subshell when redirecting into or out of
-a shell control structure such as an @code{if} or @code{while}
-statement.
+If the @option{-f} option is used, @code{type} does not attempt to find
+shell functions, as with the @code{command} builtin.
-@item
-Bash does not allow unbalanced quotes. The @sc{SVR4.2} shell will silently
-insert a needed closing quote at @code{EOF} under certain circumstances.
-This can be the cause of some hard-to-find errors.
+The return status is zero if all of the @var{names} are found, non-zero
+if any are not found.
-@item
-The @sc{SVR4.2} shell uses a baroque memory management scheme based on
-trapping @code{SIGSEGV}. If the shell is started from a process with
-@code{SIGSEGV} blocked (e.g., by using the @code{system()} C library
-function call), it misbehaves badly.
+@item typeset
+@btindex typeset
+@example
+typeset [-afFrxi] [-p] [@var{name}[=@var{value}] @dots{}]
+@end example
+The @code{typeset} command is supplied for compatibility with the Korn
+shell; however, it has been deprecated in favor of the @code{declare}
+builtin command.
-@item
-In a questionable attempt at security, the @sc{SVR4.2} shell,
-when invoked without the @samp{-p} option, will alter its real
-and effective @sc{UID} and @sc{GID} if they are less than some
-magic threshold value, commonly 100.
-This can lead to unexpected results.
+@item ulimit
+@btindex ulimit
+@example
+ulimit [-abcdefilmnpqrstuvxHST] [@var{limit}]
+@end example
+@code{ulimit} 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:
+@table @code
+@item -S
+Change and report the soft limit associated with a resource.
-@item
-The @sc{SVR4.2} shell does not allow users to trap @code{SIGSEGV},
-@code{SIGALRM}, or @code{SIGCHLD}.
+@item -H
+Change and report the hard limit associated with a resource.
-@item
-The @sc{SVR4.2} shell does not allow the @code{IFS}, @code{MAILCHECK},
-@code{PATH}, @code{PS1}, or @code{PS2} variables to be unset.
+@item -a
+All current limits are reported.
-@item
-The @sc{SVR4.2} shell treats @samp{^} as the undocumented equivalent of
-@samp{|}.
+@item -b
+The maximum socket buffer size.
-@item
-Bash allows multiple option arguments when it is invoked (@code{-x -v});
-the @sc{SVR4.2} shell allows only one option argument (@code{-xv}). In
-fact, some versions of the shell dump core if the second argument begins
-with a @samp{-}.
+@item -c
+The maximum size of core files created.
-@item
-The @sc{SVR4.2} shell exits a script if any builtin fails; Bash exits
-a script only if one of the @sc{POSIX.2} special builtins fails, and
-only for certain failures, as enumerated in the @sc{POSIX.2} standard.
+@item -d
+The maximum size of a process's data segment.
-@item
-The @sc{SVR4.2} shell behaves differently when invoked as @code{jsh}
-(it turns on job control).
-@end itemize
+@item -e
+The maximum scheduling priority ("nice").
-@node Bash Features
-@chapter Bash Features
+@item -f
+The maximum size of files written by the shell and its children.
-This section describes features unique to Bash.
+@item -i
+The maximum number of pending signals.
-@menu
-* Invoking Bash:: Command line options that you can give
- to Bash.
-* Bash Startup Files:: When and how Bash executes scripts.
-* Is This Shell Interactive?:: Determining the state of a running Bash.
-* Bash Builtins:: Table of builtins specific to Bash.
-* The Set Builtin:: This builtin is so overloaded it
- deserves its own section.
-* Bash Conditional Expressions:: Primitives used in composing expressions for
- the @code{test} builtin.
-* Bash Variables:: List of variables that exist in Bash.
-* Shell Arithmetic:: Arithmetic on shell variables.
-* Aliases:: Substituting one command for another.
-* Arrays:: Array Variables.
-* The Directory Stack:: History of visited directories.
-* Printing a Prompt:: Controlling the PS1 string.
-* The Restricted Shell:: A more controlled mode of shell execution.
-* Bash POSIX Mode:: Making Bash behave more closely to what
- the POSIX standard specifies.
-@end menu
+@item -l
+The maximum size that may be locked into memory.
-@node Invoking Bash
-@section Invoking Bash
+@item -m
+The maximum resident set size.
-@example
-bash [long-opt] [-ir] [-abefhkmnptuvxdBCDHP] [-o @var{option}] [@var{argument} @dots{}]
-bash [long-opt] [-abefhkmnptuvxdBCDHP] [-o @var{option}] -c @var{string} [@var{argument} @dots{}]
-bash [long-opt] -s [-abefhkmnptuvxdBCDHP] [-o @var{option}] [@var{argument} @dots{}]
-@end example
+@item -n
+The maximum number of open file descriptors.
-In addition to the single-character shell command-line options
-(@pxref{The Set Builtin}), there are several multi-character
-options that you can use. These options must appear on the command
-line before the single-character options in order for them
-to be recognized.
+@item -p
+The pipe buffer size.
-@table @code
-@item --dump-po-strings
-Equivalent to @samp{-D}, but the output is in the GNU @code{gettext}
-PO (portable object) file format.
+@item -q
+The maximum number of bytes in POSIX message queues.
-@item --dump-strings
-Equivalent to @samp{-D}.
+@item -r
+The maximum real-time scheduling priority.
-@item --help
-Display a usage message on standard output and exit sucessfully.
+@item -s
+The maximum stack size.
-@item --login
-Make this shell act as if it were directly invoked by login.
-This is equivalent to @samp{exec -l bash} but can be issued from
-another shell, such as @code{csh}. @samp{exec bash --login}
-will replace the current shell with a Bash login shell.
+@item -t
+The maximum amount of cpu time in seconds.
-@item --noediting
-Do not use the @sc{GNU} Readline library (@pxref{Command Line Editing})
-to read interactive command lines.
+@item -u
+The maximum number of processes available to a single user.
-@item --noprofile
-Don't load the system-wide startup file @file{/etc/profile}
-or any of the personal initialization files
-@file{~/.bash_profile}, @file{~/.bash_login}, or @file{~/.profile}
-when Bash is invoked as a login shell.
+@item -v
+The maximum amount of virtual memory available to the process.
-@item --norc
-Don't read the @file{~/.bashrc} initialization file in an
-interactive shell. This is on by default if the shell is
-invoked as @code{sh}.
+@item -x
+The maximum number of file locks.
-@item --posix
-Change the behavior of Bash where the default operation differs
-from the @sc{POSIX} 1003.2 standard to match the standard. This
-is intended to make Bash behave as a strict superset of that
-standard. @xref{Bash POSIX Mode}, for a description of the Bash
-@sc{POSIX} mode.
+@item -T
+The maximum number of threads.
-@item --rcfile @var{filename}
-Execute commands from @var{filename} (instead of @file{~/.bashrc})
-in an interactive shell.
+@end table
-@item --restricted
-Make the shell a restricted shell (@pxref{The Restricted Shell}).
+If @var{limit} is given, it is the new value of the specified resource;
+the special @var{limit} values @code{hard}, @code{soft}, and
+@code{unlimited} stand for the current hard limit, the current soft limit,
+and no limit, respectively.
+A hard limit cannot be increased by a non-root user once it is set;
+a soft limit may be increased up to the value of the hard limit.
+Otherwise, the current value of the soft limit for the specified resource
+is printed, unless the @option{-H} option is supplied.
+When setting new limits, if neither @option{-H} nor @option{-S} is supplied,
+both the hard and soft limits are set.
+If no option is given, then @option{-f} is assumed. Values are in 1024-byte
+increments, except for @option{-t}, which is in seconds, @option{-p},
+which is in units of 512-byte blocks, and @option{-n} and @option{-u}, which
+are unscaled values.
-@item --verbose
-Equivalent to @samp{-v}.
+The return status is zero unless an invalid option or argument is supplied,
+or an error occurs while setting a new limit.
-@item --version
-Show version information for this instance of
-Bash on the standard output and exit successfully.
+@item unalias
+@btindex unalias
+@example
+unalias [-a] [@var{name} @dots{} ]
+@end example
+
+Remove each @var{name} from the list of aliases. If @option{-a} is
+supplied, all aliases are removed.
+Aliases are described in @ref{Aliases}.
@end table
-There are several single-character options that may be supplied at
-invocation which are not available with the @code{set} builtin.
+@node Modifying Shell Behavior
+@section Modifying Shell Behavior
+
+@menu
+* The Set Builtin:: Change the values of shell attributes and
+ positional parameters.
+* The Shopt Builtin:: Modify shell optional behavior.
+@end menu
+
+@node The Set Builtin
+@subsection The Set Builtin
+
+This builtin is so complicated that it deserves its own section. @code{set}
+allows you to change the values of shell options and set the positional
+parameters, or to display the names and values of shell variables.
@table @code
-@item -c @var{string}
-Read and execute commands from @var{string} after processing the
-options, then exit. Any remaining arguments are assigned to the
-positional parameters, starting with @code{$0}.
+@item set
+@btindex set
+@example
+set [--abefhkmnptuvxBCEHPT] [-o @var{option}] [@var{argument} @dots{}]
+set [+abefhkmnptuvxBCEHPT] [+o @var{option}] [@var{argument} @dots{}]
+@end example
-@item -i
-Force the shell to run interactively.
+If no options or arguments are supplied, @code{set} 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 @sc{posix} mode, only shell variables are listed.
-@item -r
-Make the shell a restricted shell (@pxref{The Restricted Shell}).
+When options are supplied, they set or unset shell attributes.
+Options, if specified, have the following meanings:
-@item -s
-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.
+@table @code
+@item -a
+Mark variables and function which are modified or created for export
+to the environment of subsequent commands.
-@item -D
-A list of all double-quoted strings preceded by @samp{$}
-is printed on the standard ouput.
-These are the strings that
-are subject to language translation when the current locale
-is not @code{C} or @code{POSIX} (@pxref{Locale Translation}).
-This implies the @samp{-n} option; no commands will be executed.
+@item -b
+Cause the status of terminated background jobs to be reported
+immediately, rather than before printing the next primary prompt.
-@item --
-A @code{--} signals the end of options and disables further option
-processing.
-Any arguments after the @code{--} are treated as filenames and arguments.
+@item -e
+Exit immediately if a simple command (@pxref{Simple Commands}) exits
+with a non-zero status, unless the command that fails is part of the
+command list immediately following a @code{while} or @code{until} keyword,
+part of the test in an @code{if} statement,
+part of a command executed in a @code{&&} or @code{||b} list,
+any command in a pipeline but the last,
+or if the command's return status is being inverted using @code{!}.
+Failing simple commands that are part of shell functions or command lists
+enclosed in braces or parentheses satisfying the above conditions do not
+cause the shell to exit.
+A trap on @code{ERR}, if set, is executed before the shell exits.
-@end table
+@item -f
+Disable file name generation (globbing).
-@cindex interactive shell
-An @emph{interactive} shell is one whose input and output are both
-connected to terminals (as determined by @code{isatty(3)}), or one
-started with the @samp{-i} option.
+@item -h
+Locate and remember (hash) commands as they are looked up for execution.
+This option is enabled by default.
-If arguments remain after option processing, and neither the
-@samp{-c} nor the @samp{-s}
-option has been supplied, the first argument is assumed to
-be the name of a file containing shell commands (@pxref{Shell Scripts}).
-When Bash is invoked in this fashion, @code{$0}
-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.
+@item -k
+All arguments in the form of assignment statements are placed
+in the environment for a command, not just those that precede
+the command name.
-@node Bash Startup Files
-@section Bash Startup Files
-@cindex startup files
+@item -m
+Job control is enabled (@pxref{Job Control}).
-This section describs 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 (@pxref{Tilde Expansion}).
+@item -n
+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.
-When Bash is invoked as an interactive login shell, or as a
-non-interactive shell with the @samp{--login} option, it first reads and
-executes commands from the file @file{/etc/profile}, if that file exists.
-After reading that file, it looks for @file{~/.bash_profile},
-@file{~/.bash_login}, and @file{~/.profile}, in that order, and reads
-and executes commands from the first one that exists and is readable.
-The @samp{--noprofile} option may be used when the shell is started to
-inhibit this behavior.
+@item -o @var{option-name}
-When a login shell exits, Bash reads and executes commands from
-the file @file{~/.bash_logout}, if it exists.
+Set the option corresponding to @var{option-name}:
-When an interactive shell that is not a login shell is started, Bash
-reads and executes commands from @file{~/.bashrc}, if that file exists.
-This may be inhibited by using the @samp{--norc} option.
-The @samp{--rcfile @var{file}} option will force Bash to read and
-execute commands from @var{file} instead of @file{~/.bashrc}.
+@table @code
+@item allexport
+Same as @code{-a}.
-So, typically, your @file{~/.bash_profile} contains the line
-@example
-@code{if [ -f @file{~/.bashrc} ]; then . @file{~/.bashrc}; fi}
-@end example
-@noindent
-after (or before) any login-specific initializations.
+@item braceexpand
+Same as @code{-B}.
-When Bash is started non-interactively, to run a shell script,
-for example, it looks for the variable @code{BASH_ENV} 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:
-@example
-@code{if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi}
-@end example
-@noindent
-but the value of the @code{PATH} variable is not used to search for the
-file name.
+@item emacs
+Use an @code{emacs}-style line editing interface (@pxref{Command Line Editing}).
+This also affects the editing interface used for @code{read -e}.
-If Bash is invoked with the name @code{sh}, it tries to mimic the
-startup behavior of historical versions of @code{sh} as closely as
-possible, while conforming to the @sc{POSIX} standard as well.
+@item errexit
+Same as @code{-e}.
-When invoked as an interactive login shell, or as a non-interactive
-shell with the @samp{--login} option, it first attempts to read
-and execute commands from @file{/etc/profile} and @file{~/.profile}, in
-that order.
-The @samp{--noprofile} option may be used to inhibit this behavior.
-When invoked as an interactive shell with the name @code{sh}, Bash
-looks for the variable @code{ENV}, 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} does not attempt to read and execute
-commands from any other startup files, the @samp{--rcfile} option has
-no effect.
-A non-interactive shell invoked with the name @code{sh} does not attempt
-to read any other startup files.
+@item errtrace
+Same as @code{-E}.
-When invoked as @code{sh}, Bash enters @sc{POSIX} mode after
-the startup files are read.
+@item functrace
+Same as @code{-T}.
-When Bash is started in @sc{POSIX} mode, as with the
-@samp{--posix} command line option, it follows the @sc{POSIX} standard
-for startup files.
-In this mode, interactive shells expand the @code{ENV} variable
-and commands are read and executed from the file whose name is the
-expanded value.
-No other startup files are read.
+@item hashall
+Same as @code{-h}.
-Bash attempts to determine when it is being run by the remote shell
-daemon, usually @code{rshd}. If Bash determines it is being run by
-rshd, it reads and executes commands from @file{~/.bashrc}, if that
-file exists and is readable.
-It will not do this if invoked as @code{sh}.
-The @samp{--norc} option may be used to inhibit this behavior, and the
-@samp{--rcfile} option may be used to force another file to be read, but
-@code{rshd} does not generally invoke the shell with those options or
-allow them to be specified.
+@item histexpand
+Same as @code{-H}.
-If Bash is started with the effective user (group) id not equal to the
-real user (group) id, and the @code{-p} option is not supplied, no startup
-files are read, shell functions are not inherited from the environment,
-the @code{SHELLOPTS} 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} option is supplied at invocation, the startup behavior is
-the same, but the effective user id is not reset.
+@item history
+Enable command history, as described in @ref{Bash History Facilities}.
+This option is on by default in interactive shells.
-@node Is This Shell Interactive?
-@section Is This Shell Interactive?
-@cindex interactive shell
+@item ignoreeof
+An interactive shell will not exit upon reading EOF.
-As defined in @ref{Invoking Bash}, an interactive shell
-is one whose input and output are both
-connected to terminals (as determined by @code{isatty(3)}),
-or one started with the @samp{-i} option.
+@item keyword
+Same as @code{-k}.
-To determine within a startup script whether Bash is
-running interactively or not, examine the variable
-@code{$PS1}; it is unset in non-interactive shells, and set in
-interactive shells. Thus:
+@item monitor
+Same as @code{-m}.
-@example
-if [ -z "$PS1" ]; then
- echo This shell is not interactive
-else
- echo This shell is interactive
-fi
-@end example
+@item noclobber
+Same as @code{-C}.
-Alternatively, startup scripts may test the value of the @samp{-}
-special parameter.
-It contains @code{i} when the shell is interactive. For example:
+@item noexec
+Same as @code{-n}.
-@example
-case "$-" in
-*i*) echo This shell is interactive ;;
-*) echo This shell is not interactive ;;
-esac
-@end example
+@item noglob
+Same as @code{-f}.
-@node Bash Builtins
-@section Bash Builtin Commands
+@item nolog
+Currently ignored.
-This section describes builtin commands which are unique to
-or have been extended in Bash.
+@item notify
+Same as @code{-b}.
-@table @code
+@item nounset
+Same as @code{-u}.
-@item bind
-@btindex bind
-@example
-bind [-m @var{keymap}] [-lpsvPSV]
-bind [-m @var{keymap}] [-q @var{function}] [-u @var{function}] [-r @var{keyseq}]
-bind [-m @var{keymap}] -f @var{filename}
-bind [-m @var{keymap}] @var{keyseq:function-name}
-@end example
+@item onecmd
+Same as @code{-t}.
-Display current Readline (@pxref{Command Line Editing})
-key and function bindings, or
-bind a key sequence to a Readline function or macro. The
-binding syntax accepted is identical to that of
-@file{.inputrc} (@pxref{Readline Init File}),
-but each binding must be passed as a separate argument: e.g.,
-@samp{"\C-x\C-r":re-read-init-file}.
-Options, if supplied, have the following meanings:
+@item physical
+Same as @code{-P}.
-@table @code
-@item -m @var{keymap}
-Use @var{keymap} as the keymap to be affected by
-the subsequent bindings. Acceptable @var{keymap}
-names are
-@code{emacs},
-@code{emacs-standard},
-@code{emacs-meta},
-@code{emacs-ctlx},
-@code{vi},
-@code{vi-command}, and
-@code{vi-insert}.
-@code{vi} is equivalent to @code{vi-command};
-@code{emacs} is equivalent to @code{emacs-standard}.
+@item pipefail
+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.
-@item -l
-List the names of all Readline functions.
+@item posix
+Change the behavior of Bash where the default operation differs
+from the @sc{posix} standard to match the standard
+(@pxref{Bash POSIX Mode}).
+This is intended to make Bash behave as a strict superset of that
+standard.
-@item -p
-Display Readline function names and bindings in such a way that they
-can be re-read.
+@item privileged
+Same as @code{-p}.
-@item -P
-List current Readline function names and bindings.
+@item verbose
+Same as @code{-v}.
-@item -v
-Display Readline variable names and values in such a way that they
-can be re-read.
+@item vi
+Use a @code{vi}-style line editing interface.
+This also affects the editing interface used for @code{read -e}.
-@item -V
-List current Readline variable names and values.
+@item xtrace
+Same as @code{-x}.
+@end table
-@item -s
-Display Readline key sequences bound to macros and the strings they output
-in such a way that they can be re-read.
+@item -p
+Turn on privileged mode.
+In this mode, the @env{$BASH_ENV} and @env{$ENV} files are not
+processed, shell functions are not inherited from the environment,
+and the @env{SHELLOPTS}, @env{CDPATH} and @env{GLOBIGNORE} variables,
+if they appear in the environment, are ignored.
+If the shell is started with the effective user (group) id not equal to the
+real user (group) id, and the @code{-p} option is not supplied, these actions
+are taken and the effective user id is set to the real user id.
+If the @code{-p} 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.
-@item -S
-Display Readline key sequences bound to macros and the strings they output.
+@item -t
+Exit after reading and executing one command.
-@item -f @var{filename}
-Read key bindings from @var{filename}.
+@item -u
+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.
-@item -q @var{function}
-Query about which keys invoke the named @var{function}.
+@item -v
+Print shell input lines as they are read.
-@item -u @var{function}
-Unbind all keys bound to the named @var{function}.
+@item -x
+Print a trace of simple commands, @code{for} commands, @code{case}
+commands, @code{select} commands, and arithmetic @code{for} commands
+and their arguments or associated word lists after they are
+expanded and before they are executed. The value of the @env{PS4}
+variable is expanded and the resultant value is printed before
+the command and its expanded arguments.
-@item -r @var{keyseq}
-Remove any current binding for @var{keyseq}.
+@item -B
+The shell will perform brace expansion (@pxref{Brace Expansion}).
+This option is on by default.
-@end table
+@item -C
+Prevent output redirection using @samp{>}, @samp{>&}, and @samp{<>}
+from overwriting existing files.
-@noindent
-The return status is zero unless an invalid option is supplied or an
-error occurs.
+@item -E
+If set, any trap on @code{ERR} is inherited by shell functions, command
+substitutions, and commands executed in a subshell environment.
+The @code{ERR} trap is normally not inherited in such cases.
-@item builtin
-@btindex builtin
-@example
-builtin [@var{shell-builtin} [@var{args}]]
-@end example
-Run a shell builtin, passing it @var{args}, 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} is not a shell
-builtin command.
+@item -H
+Enable @samp{!} style history substitution (@pxref{History Interaction}).
+This option is on by default for interactive shells.
-@item command
-@btindex command
+@item -P
+If set, do not follow symbolic links when performing commands such as
+@code{cd} which change the current directory. The physical directory
+is used instead. By default, Bash follows
+the logical chain of directories when performing commands
+which change the current directory.
+
+For example, if @file{/usr/sys} is a symbolic link to @file{/usr/local/sys}
+then:
@example
-command [-pVv] @var{command} [@var{arguments} @dots{}]
+$ cd /usr/sys; echo $PWD
+/usr/sys
+$ cd ..; pwd
+/usr
@end example
-Runs @var{command} with @var{arguments} ignoring any shell function
-named @var{command}.
-Only shell builtin commands or commands found by searching the
-@code{PATH} are executed.
-If there is a shell function named @code{ls}, running @samp{command ls}
-within the function will execute the external command @code{ls}
-instead of calling the function recursively.
-The @samp{-p} option means to use a default value for @code{$PATH}
-that is guaranteed to find all of the standard utilities.
-The return status in this case is 127 if @var{command} cannot be
-found or an error occurred, and the exit status of @var{command}
-otherwise.
-
-If either the @samp{-V} or @samp{-v} option is supplied, a
-description of @var{command} is printed. The @samp{-v} option
-causes a single word indicating the command or file name used to
-invoke @var{command} to be displayed; the @samp{-V} option produces
-a more verbose description. In this case, the return status is
-zero if @var{command} is found, and non-zero if not.
-@item declare
-@btindex declare
+@noindent
+If @code{set -P} is on, then:
@example
-declare [-afFrxi] [-p] [@var{name}[=@var{value}]]
+$ cd /usr/sys; echo $PWD
+/usr/local/sys
+$ cd ..; pwd
+/usr/local
@end example
-Declare variables and give them attributes. If no @var{name}s
-are given, then display the values of variables instead.
-
-The @samp{-p} option will display the attributes and values of each
-@var{name}. When @samp{-p} is used, additional options are ignored.
-The @samp{-F} option inhibits the display of function definitions;
-only the function name and attributes are printed. @samp{-F} implies
-@samp{-f}. The following options can be used to restrict output
-to variables with the specified attributes or to give variables
-attributes:
+@item -T
+If set, any trap on @code{DEBUG} and @code{RETURN} are inherited by
+shell functions, command substitutions, and commands executed
+in a subshell environment.
+The @code{DEBUG} and @code{RETURN} traps are normally not inherited
+in such cases.
-@table @code
-@item -a
-Each @var{name} is an array variable (@pxref{Arrays}).
+@item --
+If no arguments follow this option, then the positional parameters are
+unset. Otherwise, the positional parameters are set to the
+@var{arguments}, even if some of them begin with a @samp{-}.
-@item -f
-Use function names only.
+@item -
+Signal the end of options, cause all remaining @var{arguments}
+to be assigned to the positional parameters. The @option{-x}
+and @option{-v} options are turned off.
+If there are no arguments, the positional parameters remain unchanged.
+@end table
-@item -i
-The variable is to be treated as
-an integer; arithmetic evaluation (@pxref{Shell Arithmetic}) is
-performed when the variable is assigned a value.
+Using @samp{+} rather than @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{$-}.
-@item -r
-Make @var{name}s readonly. These names cannot then be assigned values
-by subsequent assignment statements or unset.
+The remaining N @var{arguments} are positional parameters and are
+assigned, in order, to @code{$1}, @code{$2}, @dots{} @code{$N}.
+The special parameter @code{#} is set to N.
-@item -x
-Mark each @var{name} for export to subsequent commands via
-the environment.
+The return status is always zero unless an invalid option is supplied.
@end table
-Using @samp{+} instead of @samp{-} turns off the attribute instead.
-When used in a function, @code{declare} makes each @var{name} local,
-as with the @code{local} command.
+@node The Shopt Builtin
+@subsection The Shopt Builtin
-The return status is zero unless an invalid option is encountered,
-an attempt is made to define a function using @code{-f foo=bar},
-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 (@pxref{Arrays}),
-one of the @var{names} is not a valid shell variable name,
-an attempt is made to turn off readonly status for a readonly variable,
-an attempt is made to turn off array status for an array variable,
-or an attempt is made to display a non-existent function with @samp{-f}.
+This builtin allows you to change additional shell optional behavior.
-@item echo
-@btindex echo
-@example
-echo [-neE] [@var{arg} @dots{}]
-@end example
-Output the @var{arg}s, separated by spaces, terminated with a
-newline.
-The return status is always 0.
-If @samp{-n} is specified, the trailing newline is suppressed.
-If the @samp{-e} option is given, interpretation of the following
-backslash-escaped characters is enabled.
-The @samp{-E} option disables the interpretation of these escape characters,
-even on systems where they are interpreted by default.
-@code{echo} interprets the following escape sequences:
@table @code
-@item \a
-alert (bell)
-@item \b
-backspace
-@item \c
-suppress trailing newline
-@item \e
-escape
-@item \f
-form feed
-@item \n
-new line
-@item \r
-carriage return
-@item \t
-horizontal tab
-@item \v
-vertical tab
-@item \\
-backslash
-@item \@var{nnn}
-the character whose @code{ASCII} code is the octal value @var{nnn}
-(one to three digits)
-@item \x@var{nnn}
-the character whose @code{ASCII} code is the hexadecimal value @var{nnn}
-(one to three digits)
-@end table
-@item enable
-@btindex enable
+@item shopt
+@btindex shopt
@example
-enable [-n] [-p] [-f @var{filename}] [-ads] [@var{name} @dots{}]
+shopt [-pqsu] [-o] [@var{optname} @dots{}]
@end example
-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 with specifying a full pathname,
-even though the shell normally searches for builtins before disk commands.
-If @samp{-n} is used, the @var{name}s become disabled. Otherwise
-@var{name}s are enabled. For example, to use the @code{test} binary
-found via @code{$PATH} instead of the shell builtin version, type
-@samp{enable -n test}.
+Toggle the values of variables controlling optional shell behavior.
+With no options, or with the @option{-p} option, a list of all settable
+options is displayed, with an indication of whether or not each is set.
+The @option{-p} option causes output to be displayed in a form that
+may be reused as input.
+Other options have the following meanings:
-If the @samp{-p} option is supplied, or no @var{name} arguments appear,
-a list of shell builtins is printed. With no other arguments, the list
-consists of all enabled shell builtins.
-The @samp{-a} option means to list
-each builtin with an indication of whether or not it is enabled.
-
-The @samp{-f} option means to load the new builtin command @var{name}
-from shared object @var{filename}, on systems that support dynamic loading.
-The @samp{-d} option will delete a builtin loaded with @samp{-f}.
-
-If there are no options, a list of the shell builtins is displayed.
-The @samp{-s} option restricts @code{enable} to the @sc{POSIX} special
-builtins. If @samp{-s} is used with @samp{-f}, the new builtin becomes
-a special builtin.
-
-The return status is zero unless a @var{name} is not a shell builtin
-or there is an error loading a new builtin from a shared object.
-
-@item help
-@btindex help
-@example
-help [@var{pattern}]
-@end example
-Display helpful information about builtin commands.
-If @var{pattern} is specified, @code{help} gives detailed help
-on all commands matching @var{pattern}, otherwise a list of
-the builtins is printed. The return status is zero unless no
-command matches @var{pattern}.
-
-@item let
-@btindex let
-@example
-let @var{expression} [@var{expression}]
-@end example
-The @code{let} builtin allows arithmetic to be performed on shell
-variables. Each @var{expression} is evaluated according to the
-rules given below in @ref{Shell Arithmetic}. If the
-last @var{expression} evaluates to 0, @code{let} returns 1;
-otherwise 0 is returned.
-
-@item local
-@btindex local
-@example
-local @var{name}[=@var{value}]
-@end example
-For each argument, a local variable named @var{name} is created,
-and assigned @var{value}.
-@code{local} can only be used within a function; it makes the variable
-@var{name} have a visible scope restricted to that function and its
-children. The return status is zero unless @code{local} is used outside
-a function or an invalid @var{name} is supplied.
-
-@item logout
-@btindex logout
-@example
-logout [@var{n}]
-@end example
-Exit a login shell, returning a status of @var{n} to the shell's
-parent.
-
-@item printf
-@btindex printf
-@example
-@code{printf} @var{format} [@var{arguments}]
-@end example
-Write the formatted @var{arguments} to the standard output under the
-control of the @var{format}.
-The @var{format} 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}.
-In addition to the standard @code{printf(1)} formats, @samp{%b} causes
-@code{printf} to expand backslash escape sequences in the corresponding
-@var{argument}, and @samp{%q} causes @code{printf} to output the
-corresponding @var{argument} in a format that can be reused as shell input.
-
-The @var{format} is reused as necessary to consume all of the @var{arguments}.
-If the @var{format} requires more @var{arguments} than are supplied, the
-extra format specifications behave as if a zero value or null string, as
-appropriate, had been supplied.
-
-@item read
-@btindex read
-@example
-read [-a @var{aname}] [-p @var{prompt}] [-er] [@var{name} @dots{}]
-@end example
-One line is read from the standard input, and the first word
-is assigned to the first @var{name}, the second word to the second @var{name},
-and so on, with leftover words and their intervening separators assigned
-to the last @var{name}.
-If there are fewer words read from the standard input than names,
-the remaining names are assigned empty values.
-The characters in the value of the @code{IFS} variable
-are used to split the line into words.
-The backslash character @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 @code{REPLY}.
-The return code is zero, unless end-of-file is encountered.
-Options, if supplied, have the following meanings:
-
-@table @code
-@item -r
-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.
-
-@item -p @var{prompt}
-Display @var{prompt}, without a
-trailing newline, before attempting to read any input. The prompt
-is displayed only if input is coming from a terminal.
-
-@item -a @var{aname}
-The words are assigned to sequential indices of the array variable
-@var{aname}, starting at 0.
-All elements are removed from @var{aname} before the assignment.
-Other @var{name} arguments are ignored.
-
-@item -e
-Readline (@pxref{Command Line Editing})
-is used to obtain the line.
-@end table
-
-@item shopt
-@btindex shopt
-@example
-shopt [-pqsu] [-o] [@var{optname} @dots{}]
-@end example
-Toggle the values of variables controlling optional shell behavior.
-With no options, or with the @samp{-p} option, a list of all settable
-options is displayed, with an indication of whether or not each is set.
-The @samp{-p} option causes output to be displayed in a form that
-may be reused as input.
-Other options have the following meanings:
-
-@table @code
-@item -s
-Enable (set) each @var{optname}.
+@table @code
+@item -s
+Enable (set) each @var{optname}.
@item -u
Disable (unset) each @var{optname}.
@item -q
Suppresses normal output; the return status
indicates whether the @var{optname} is set or unset.
-If multiple @var{optname} arguments are given with @samp{-q},
+If multiple @var{optname} arguments are given with @option{-q},
the return status is zero if all @var{optnames} are enabled;
non-zero otherwise.
@item -o
Restricts the values of
-@var{optname} to be those defined for the @samp{-o} option to the
+@var{optname} to be those defined for the @option{-o} option to the
@code{set} builtin (@pxref{The Set Builtin}).
@end table
-If either @samp{-s} or @samp{-u}
+If either @option{-s} or @option{-u}
is used with no @var{optname} arguments, the display is limited to
those options which are set or unset, respectively.
The list of @code{shopt} options is:
@table @code
+
+@item autocd
+If set, a command name that is the name of a directory is executed as if
+it were the argument to the @code{cd} command.
+This option is only used by interactive shells.
+
@item cdable_vars
-If this is set, an argument to the @code{cd}
-builtin command that
+If this is set, an argument to the @code{cd} builtin command that
is not a directory is assumed to be the name of a variable whose
value is the directory to change to.
table exists before trying to execute it. If a hashed command no
longer exists, a normal path search is performed.
+@item checkjobs
+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 (@pxref{Job Control}).
+The shell always postpones exiting if any jobs are stopped.
+
@item checkwinsize
If set, Bash checks the window size after each command
and, if necessary, updates the values of
-@code{LINES} and @code{COLUMNS}.
+@env{LINES} and @env{COLUMNS}.
@item cmdhist
If set, Bash
command in the same history entry. This allows
easy re-editing of multi-line commands.
+@item compat31
+If set, Bash
+changes its behavior to that of version 3.1 with respect to quoted
+arguments to the conditional command's =~ operator.
+
+@item dirspell
+If set, Bash
+attempts spelling correction on directory names during word completion
+if the directory name initially supplied does not exist.
+
@item dotglob
If set, Bash includes filenames beginning with a `.' in
the results of filename expansion.
fails.
@item expand_aliases
-If set, aliases are expanded as described below< under Aliases
-(@pxref{Aliases}).
+If set, aliases are expanded as described below under Aliases,
+@ref{Aliases}.
This option is enabled by default for interactive shells.
+@item extdebug
+If set, behavior intended for use by debuggers is enabled:
+
+@enumerate
+@item
+The @option{-F} option to the @code{declare} builtin (@pxref{Bash Builtins})
+displays the source file name and line number corresponding to each function
+name supplied as an argument.
+
+@item
+If the command run by the @code{DEBUG} trap returns a non-zero value, the
+next command is skipped and not executed.
+
+@item
+If the command run by the @code{DEBUG} 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{.} or @code{source} builtins), a call to
+@code{return} is simulated.
+
+@item
+@code{BASH_ARGC} and @code{BASH_ARGV} are updated as described in their
+descriptions (@pxref{Bash Variables}).
+
+@item
+Function tracing is enabled: command substitution, shell functions, and
+subshells invoked with @code{( @var{command} )} inherit the
+@code{DEBUG} and @code{RETURN} traps.
+
+@item
+Error tracing is enabled: command substitution, shell functions, and
+subshells invoked with @code{( @var{command} )} inherit the
+@code{ERROR} trap.
+@end enumerate
+
@item extglob
If set, the extended pattern matching features described above
(@pxref{Pattern Matching}) are enabled.
+@item extquote
+If set, @code{$'@var{string}'} and @code{$"@var{string}"} quoting is
+performed within @code{$@{@var{parameter}@}} expansions
+enclosed in double quotes. This option is enabled by default.
+
+@item failglob
+If set, patterns which fail to match filenames during pathname expansion
+result in an expansion error.
+
+@item force_fignore
+If set, the suffixes specified by the @env{FIGNORE} shell variable
+cause words to be ignored when performing word completion even if
+the ignored words are the only possible completions.
+@xref{Bash Variables}, for a description of @env{FIGNORE}.
+This option is enabled by default.
+
+@item globstar
+If set, the pattern @samp{**} used in a filename expansion context will
+match a files and zero or more directories and subdirectories.
+If the pattern is followed by a @samp{/}, only directories and
+subdirectories match.
+
+@item gnu_errfmt
+If set, shell error messages are written in the standard @sc{gnu} error
+message format.
+
@item histappend
If set, the history list is appended to the file named by the value
-of the @code{HISTFILE}
+of the @env{HISTFILE}
variable when the shell exits, rather than overwriting the file.
@item histreedit
option is enabled, multi-line commands are saved to the history with
embedded newlines rather than using semicolon separators where possible.
+@item login_shell
+The shell sets this option if it is started as a login shell
+(@pxref{Invoking Bash}).
+The value may not be changed.
+
@item mailwarn
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 @var{mailfile} has been read"} is displayed.
+@item no_empty_cmd_completion
+If set, and Readline is being used, Bash will not attempt to search
+the @env{PATH} for possible completions when completion is attempted
+on an empty line.
+
@item nocaseglob
If set, Bash matches filenames in a case-insensitive fashion when
performing filename expansion.
+@item nocasematch
+If set, Bash matches patterns in a case-insensitive fashion when
+performing matching while executing @code{case} or @code{[[}
+conditional commands.
+
@item nullglob
If set, Bash allows filename patterns which match no
files to expand to a null string, rather than themselves.
+@item progcomp
+If set, the programmable completion facilities
+(@pxref{Programmable Completion}) are enabled.
+This option is enabled by default.
+
@item promptvars
-If set, prompt strings undergo variable and parameter expansion after
-being expanded (@pxref{Printing a Prompt}).
+If set, prompt strings undergo
+parameter expansion, command substitution, arithmetic
+expansion, and quote removal after being expanded
+as described below (@pxref{Printing a Prompt}).
This option is enabled by default.
@item restricted_shell
number of positional parameters.
@item sourcepath
-If set, the @code{source} builtin uses the value of @code{PATH}
+If set, the @code{source} builtin uses the value of @env{PATH}
to find the directory containing the file supplied as an argument.
This option is enabled by default.
+
+@item xpg_echo
+If set, the @code{echo} builtin expands backslash-escape sequences
+by default.
+
@end table
@noindent
When setting or unsetting options, the return status is zero unless an
@var{optname} is not a valid shell option.
-@item source
-@btindex source
-@example
-source @var{filename}
-@end example
-A synonym for @code{.} (@pxref{Bourne Shell Builtins}).
+@end table
-@item type
-@btindex type
-@example
-type [-atp] [@var{name} @dots{}]
-@end example
-For each @var{name}, indicate how it would be interpreted if used as a
-command name.
+@node Special Builtins
+@section Special Builtins
+@cindex special builtin
-If the @samp{-t} option is used, @code{type} prints a single word
-which is one of @samp{alias}, @samp{function}, @samp{builtin},
-@samp{file} or @samp{keyword},
-if @var{name} is an alias, shell function, shell builtin,
-disk file, or shell reserved word, respectively.
-If the @var{name} is not found, then nothing is printed, and
-@code{type} returns a failure status.
+For historical reasons, the @sc{posix} standard has classified
+several builtin commands as @emph{special}.
+When Bash is executing in @sc{posix} mode, the special builtins
+differ from other builtin commands in three respects:
-If the @samp{-p} option is used, @code{type} either returns the name
-of the disk file that would be executed, or nothing if @samp{-t}
-would not return @samp{file}.
+@enumerate
+@item
+Special builtins are found before shell functions during command lookup.
-If the @samp{-a} option is used, @code{type} returns all of the places
-that contain an executable named @var{file}.
-This includes aliases and functions, if and only if the @samp{-p} option
-is not also used.
+@item
+If a special builtin returns an error status, a non-interactive shell exits.
-The return status is zero if any of the @var{names} are found, non-zero
-if none are found.
+@item
+Assignment statements preceding the command stay in effect in the shell
+environment after the command completes.
+@end enumerate
-@item typeset
-@btindex typeset
-@example
-typeset [-afFrxi] [-p] [@var{name}[=@var{value}]]
-@end example
-The @code{typeset} command is supplied for compatibility with the Korn
-shell; however, it has been deprecated in favor of the @code{declare}
-builtin command.
+When Bash is not executing in @sc{posix} mode, these builtins behave no
+differently than the rest of the Bash builtin commands.
+The Bash @sc{posix} mode is described in @ref{Bash POSIX Mode}.
-@item ulimit
-@btindex ulimit
+These are the @sc{posix} special builtins:
@example
-ulimit [-acdflmnpstuvSH] [@var{limit}]
+@w{break : . continue eval exec exit export readonly return set}
+@w{shift trap unset}
@end example
-@code{ulimit} 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:
-@table @code
-@item -S
-Change and report the soft limit associated with a resource.
-@item -H
-Change and report the hard limit associated with a resource.
+@node Shell Variables
+@chapter Shell Variables
-@item -a
-All current limits are reported.
+@menu
+* Bourne Shell Variables:: Variables which Bash uses in the same way
+ as the Bourne Shell.
+* Bash Variables:: List of variables that exist in Bash.
+@end menu
-@item -c
-The maximum size of core files created.
+This chapter describes the shell variables that Bash uses.
+Bash automatically assigns default values to a number of variables.
-@item -d
-The maximum size of a process's data segment.
+@node Bourne Shell Variables
+@section Bourne Shell Variables
-@item -f
-The maximum size of files created by the shell.
+Bash uses certain shell variables in the same way as the Bourne shell.
+In some cases, Bash assigns a default value to the variable.
-@item -l
-The maximum size that may be locked into memory.
+@vtable @code
-@item -m
-The maximum resident set size.
+@item CDPATH
+A colon-separated list of directories used as a search path for
+the @code{cd} builtin command.
-@item -n
-The maximum number of open file descriptors.
+@item HOME
+The current user's home directory; the default for the @code{cd} builtin
+command.
+The value of this variable is also used by tilde expansion
+(@pxref{Tilde Expansion}).
-@item -p
-The pipe buffer size.
+@item IFS
+A list of characters that separate fields; used when the shell splits
+words as part of expansion.
-@item -s
-The maximum stack size.
+@item MAIL
+If this parameter is set to a filename and the @env{MAILPATH} variable
+is not set, Bash informs the user of the arrival of mail in
+the specified file.
-@item -t
-The maximum amount of cpu time in seconds.
+@item MAILPATH
+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{?}.
+When used in the text of the message, @code{$_} expands to the name of
+the current mail file.
-@item -u
-The maximum number of processes available to a single user.
+@item OPTARG
+The value of the last option argument processed by the @code{getopts} builtin.
-@item -v
-The maximum amount of virtual memory available to the process.
+@item OPTIND
+The index of the last option argument processed by the @code{getopts} builtin.
-@end table
+@item PATH
+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} indicates the
+current directory.
+A null directory name may appear as two adjacent colons, or as an initial
+or trailing colon.
-If @var{limit} is given, it is the new value of the specified resource.
-Otherwise, the current value of the soft limit for the specified resource
-is printed, unless the @samp{-H} option is supplied.
-When setting new limits, if neither @samp{-H} nor @samp{-S} is supplied,
-both the hard and soft limits are set.
-If no option is given, then @samp{-f} is assumed. Values are in 1024-byte
-increments, except for @samp{-t}, which is in seconds, @samp{-p},
-which is in units of 512-byte blocks, and @samp{-n} and @samp{-u}, which
-are unscaled values.
-
-The return status is zero unless an invalid option is supplied, a
-non-numeric argument other than @code{unlimited} is supplied as a
-@var{limit}, or an error occurs while setting a new limit.
-@end table
+@item PS1
+The primary prompt string. The default value is @samp{\s-\v\$ }.
+@xref{Printing a Prompt}, for the complete list of escape
+sequences that are expanded before @env{PS1} is displayed.
-@node The Set Builtin
-@section The Set Builtin
+@item PS2
+The secondary prompt string. The default value is @samp{> }.
-This builtin is so complicated that it deserves its own section.
+@end vtable
-@table @code
-@item set
-@btindex set
-@example
-set [--abefhkmnptuvxBCHP] [-o @var{option}] [@var{argument} @dots{}]
-@end example
+@node Bash Variables
+@section Bash Variables
-If no options or arguments are supplied, @code{set} 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.
+These variables are set or used by Bash, but other shells
+do not normally treat them specially.
-When options are supplied, they set or unset shell attributes.
-Options, if specified, have the following meanings:
+A few variables used by Bash are described in different chapters:
+variables for controlling the job control facilities
+(@pxref{Job Control Variables}).
-@table @code
-@item -a
-Mark variables which are modified or created for export.
+@vtable @code
-@item -b
-Cause the status of terminated background jobs to be reported
-immediately, rather than before printing the next primary prompt.
+@item BASH
+The full pathname used to execute the current instance of Bash.
-@item -e
-Exit immediately if a simple command (@pxref{Simple Commands}) exits
-with a non-zero status, unless the command that fails is part of an
-@code{until} or @code{while} loop, part of an @code{if} statement,
-part of a @code{&&} or @code{||} list, or if the command's return
-status is being inverted using @code{!}.
+@item BASHPID
+Expands to the process id of the current Bash process.
+This differs from @code{$$} under certain circumstances, such as subshells
+that do not require Bash to be re-initialized.
-@item -f
-Disable file name generation (globbing).
+@item BASH_ALIASES
+An associative array variable whose members correspond to the internal
+list of aliases as maintained by the @code{alias} builtin
+(@pxref{Bourne Shell Builtins}).
+Elements added to this array appear in the alias list; unsetting array
+elements cause aliases to be removed from the alias list.
+
+@item BASH_ARGC
+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{.} or @code{source}) is at the top of the stack. When a
+subroutine is executed, the number of parameters passed is pushed onto
+@code{BASH_ARGC}.
+The shell sets @code{BASH_ARGC} only when in extended debugging mode
+(see @ref{The Shopt Builtin}
+for a description of the @code{extdebug} option to the @code{shopt}
+builtin).
+
+@item BASH_ARGV
+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}.
+The shell sets @code{BASH_ARGV} only when in extended debugging mode
+(see @ref{The Shopt Builtin}
+for a description of the @code{extdebug} option to the @code{shopt}
+builtin).
+
+@item BASH_CMDS
+An associative array variable whose members correspond to the internal
+hash table of commands as maintained by the @code{hash} builtin
+(@pxref{Bourne Shell Builtins}).
+Elements added to this array appear in the hash table; unsetting array
+elements cause commands to be removed from the hash table.
-@item -h
-Locate and remember (hash) commands as they are looked up for execution.
-This option is enabled by default.
+@item BASH_COMMAND
+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.
-@item -k
-All arguments in the form of assignment statements are placed
-in the environment for a command, not just those that precede
-the command name.
+@item BASH_ENV
+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. @xref{Bash Startup Files}.
-@item -m
-Job control is enabled (@pxref{Job Control}).
+@item BASH_EXECUTION_STRING
+The command argument to the @option{-c} invocation option.
+
+@item BASH_LINENO
+An array variable whose members are the line numbers in source files
+corresponding to each member of @var{FUNCNAME}.
+@code{$@{BASH_LINENO[$i]@}} is the line number in the source file where
+@code{$@{FUNCNAME[$i]@}} was called (or @code{$@{BASH_LINENO[$i-1]@}} if
+referenced within another shell function).
+The corresponding source file name is @code{$@{BASH_SOURCE[$i]@}}.
+Use @code{LINENO} to obtain the current line number.
+
+@item BASH_REMATCH
+An array variable whose members are assigned by the @samp{=~} binary
+operator to the @code{[[} conditional command
+(@pxref{Conditional Constructs}).
+The element with index 0 is the portion of the string
+matching the entire regular expression.
+The element with index @var{n} is the portion of the
+string matching the @var{n}th parenthesized subexpression.
+This variable is read-only.
-@item -n
-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.
+@item BASH_SOURCE
+An array variable whose members are the source filenames corresponding
+to the elements in the @code{FUNCNAME} array variable.
-@item -o @var{option-name}
+@item BASH_SUBSHELL
+Incremented by one each time a subshell or subshell environment is spawned.
+The initial value is 0.
-Set the option corresponding to @var{option-name}:
+@item BASH_VERSINFO
+A readonly array variable (@pxref{Arrays})
+whose members hold version information for this instance of Bash.
+The values assigned to the array members are as follows:
@table @code
-@item allexport
-Same as @code{-a}.
-
-@item braceexpand
-Same as @code{-B}.
-@item emacs
-Use an @code{emacs}-style line editing interface (@pxref{Command Line Editing}).
-
-@item errexit
-Same as @code{-e}.
+@item BASH_VERSINFO[0]
+The major version number (the @var{release}).
-@item hashall
-Same as @code{-h}.
+@item BASH_VERSINFO[1]
+The minor version number (the @var{version}).
-@item histexpand
-Same as @code{-H}.
+@item BASH_VERSINFO[2]
+The patch level.
-@item history
-Enable command history, as described in @ref{Bash History Facilities}.
-This option is on by default in interactive shells.
+@item BASH_VERSINFO[3]
+The build version.
-@item ignoreeof
-An interactive shell will not exit upon reading EOF.
+@item BASH_VERSINFO[4]
+The release status (e.g., @var{beta1}).
-@item keyword
-Same as @code{-k}.
+@item BASH_VERSINFO[5]
+The value of @env{MACHTYPE}.
-@item monitor
-Same as @code{-m}.
+@end table
-@item noclobber
-Same as @code{-C}.
+@item BASH_VERSION
+The version number of the current instance of Bash.
-@item noexec
-Same as @code{-n}.
+@item COLUMNS
+Used by the @code{select} builtin command to determine the terminal width
+when printing selection lists. Automatically set upon receipt of a
+@code{SIGWINCH}.
+
+@item COMP_CWORD
+An index into @env{$@{COMP_WORDS@}} of the word containing the current
+cursor position.
+This variable is available only in shell functions invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
+
+@item COMP_LINE
+The current command line.
+This variable is available only in shell functions and external
+commands invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
+
+@item COMP_POINT
+The index of the current cursor position relative to the beginning of
+the current command.
+If the current cursor position is at the end of the current command,
+the value of this variable is equal to @code{$@{#COMP_LINE@}}.
+This variable is available only in shell functions and external
+commands invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
+
+@item COMP_TYPE
+Set to an integer value corresponding to the type of completion attempted
+that caused a completion function to be called:
+@var{TAB}, for normal completion,
+@samp{?}, for listing completions after successive tabs,
+@samp{!}, for listing alternatives on partial word completion,
+@samp{@@}, to list completions if the word is not unmodified,
+or
+@samp{%}, for menu completion.
+This variable is available only in shell functions and external
+commands invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
+
+@item COMP_KEY
+The key (or final key of a key sequence) used to invoke the current
+completion function.
+
+@item COMP_WORDBREAKS
+The set of characters that the Readline library treats as word
+separators when performing word completion.
+If @code{COMP_WORDBREAKS} is unset, it loses its special properties,
+even if it is subsequently reset.
-@item noglob
-Same as @code{-f}.
+@item COMP_WORDS
+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 (@pxref{Programmable Completion}).
-@item notify
-Same as @code{-b}.
+@item COMPREPLY
+An array variable from which Bash reads the possible completions
+generated by a shell function invoked by the programmable completion
+facility (@pxref{Programmable Completion}).
-@item nounset
-Same as @code{-u}.
+@item DIRSTACK
+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} builtin.
+Assigning to members of this array variable may be used to modify
+directories already in the stack, but the @code{pushd} and @code{popd}
+builtins must be used to add and remove directories.
+Assignment to this variable will not change the current directory.
+If @env{DIRSTACK} is unset, it loses its special properties, even if
+it is subsequently reset.
-@item onecmd
-Same as @code{-t}.
+@item EMACS
+If Bash finds this variable in the environment when the shell
+starts with value @samp{t}, it assumes that the shell is running in an
+emacs shell buffer and disables line editing.
-@item physical
-Same as @code{-P}.
+@item EUID
+The numeric effective user id of the current user. This variable
+is readonly.
-@item posix
-Change the behavior of Bash where the default operation differs
-from the @sc{POSIX} 1003.2 standard to match the standard
-(@pxref{Bash POSIX Mode}).
-This is intended to make Bash behave as a strict superset of that
-standard.
+@item FCEDIT
+The editor used as a default by the @option{-e} option to the @code{fc}
+builtin command.
-@item privileged
-Same as @code{-p}.
+@item FIGNORE
+A colon-separated list of suffixes to ignore when performing
+filename completion.
+A file name whose suffix matches one of the entries in
+@env{FIGNORE}
+is excluded from the list of matched file names. A sample
+value is @samp{.o:~}
-@item verbose
-Same as @code{-v}.
+@item FUNCNAME
+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"}.
+This variable exists only when a shell function is executing.
+Assignments to @env{FUNCNAME} have no effect and return an error status.
+If @env{FUNCNAME} is unset, it loses its special properties, even if
+it is subsequently reset.
-@item vi
-Use a @code{vi}-style line editing interface.
+@item GLOBIGNORE
+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 @env{GLOBIGNORE}, it is removed from the list
+of matches.
-@item xtrace
-Same as @code{-x}.
-@end table
+@item GROUPS
+An array variable containing the list of groups of which the current
+user is a member.
+Assignments to @env{GROUPS} have no effect and return an error status.
+If @env{GROUPS} is unset, it loses its special properties, even if it is
+subsequently reset.
-@item -p
-Turn on privileged mode.
-In this mode, the @code{$BASH_ENV} and @code{$ENV} files are not
-processed, shell functions are not inherited from the environment,
-and the @code{SHELLOPTS} 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} option is not supplied, these actions
-are taken and the effective user id is set to the real user id.
-If the @code{-p} 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.
+@item histchars
+Up to three characters which control history expansion, quick
+substitution, and tokenization (@pxref{History Interaction}).
+The first character is the
+@var{history expansion} character, that is, the character which signifies the
+start of a history expansion, normally @samp{!}. The second character is the
+character which signifies `quick substitution' when seen as the first
+character on a line, normally @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{#}. 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.
-@item -t
-Exit after reading and executing one command.
+@item HISTCMD
+The history number, or index in the history list, of the current
+command. If @env{HISTCMD} is unset, it loses its special properties,
+even if it is subsequently reset.
-@item -u
-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.
+@item HISTCONTROL
+A colon-separated list of values controlling how commands are saved on
+the history list.
+If the list of values includes @samp{ignorespace}, lines which begin
+with a space character are not saved in the history list.
+A value of @samp{ignoredups} causes lines which match the previous
+history entry to not be saved.
+A value of @samp{ignoreboth} is shorthand for
+@samp{ignorespace} and @samp{ignoredups}.
+A value of @samp{erasedups} 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 @env{HISTCONTROL} 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 @env{HISTIGNORE}.
+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
+@env{HISTCONTROL}.
-@item -v
-Print shell input lines as they are read.
+@item HISTFILE
+The name of the file to which the command history is saved. The
+default value is @file{~/.bash_history}.
-@item -x
-Print a trace of simple commands and their arguments after they are
-expanded and before they are executed.
+@item HISTFILESIZE
+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.
-@item -B
-The shell will perform brace expansion (@pxref{Brace Expansion}).
-This option is on by default.
+@item HISTIGNORE
+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{*} is appended). Each pattern is tested
+against the line after the checks specified by @env{HISTCONTROL}
+are applied. In addition to the normal shell pattern matching
+characters, @samp{&} matches the previous history line. @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
+@env{HISTIGNORE}.
-@item -C
-Prevent output redirection using @samp{>}, @samp{>&}, and @samp{<>}
-from overwriting existing files.
+@env{HISTIGNORE} subsumes the function of @env{HISTCONTROL}. A
+pattern of @samp{&} is identical to @code{ignoredups}, and a
+pattern of @samp{[ ]*} is identical to @code{ignorespace}.
+Combining these two patterns, separating them with a colon,
+provides the functionality of @code{ignoreboth}.
-@item -H
-Enable @samp{!} style history substitution (@pxref{History Interaction}).
-This option is on by default for interactive shells.
+@item HISTSIZE
+The maximum number of commands to remember on the history list.
+The default value is 500.
-@item -P
-If set, do not follow symbolic links when performing commands such as
-@code{cd} 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.
+@item HISTTIMEFORMAT
+If this variable is set and not null, its value is used as a format string
+for @var{strftime} to print the time stamp associated with each history
+entry displayed by the @code{history} builtin.
+If this variable is set, time stamps are written to the history file so
+they may be preserved across shell sessions.
+This uses the history comment character to distinguish timestamps from
+other history lines.
-For example, if @file{/usr/sys} is a symbolic link to @file{/usr/local/sys}
-then:
-@example
-$ cd /usr/sys; echo $PWD
-/usr/sys
-$ cd ..; pwd
-/usr
-@end example
+@item HOSTFILE
+Contains the name of a file in the same format as @file{/etc/hosts} 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 @env{HOSTFILE} is set, but has no value, Bash attempts to read
+@file{/etc/hosts} to obtain the list of possible hostname completions.
+When @env{HOSTFILE} is unset, the hostname list is cleared.
-@noindent
-If @code{set -P} is on, then:
-@example
-$ cd /usr/sys; echo $PWD
-/usr/local/sys
-$ cd ..; pwd
-/usr/local
-@end example
+@item HOSTNAME
+The name of the current host.
-@item --
-If no arguments follow this option, then the positional parameters are
-unset. Otherwise, the positional parameters are set to the
-@var{arguments}, even if some of them begin with a @samp{-}.
+@item HOSTTYPE
+A string describing the machine Bash is running on.
-@item -
-Signal the end of options, cause all remaining @var{arguments}
-to be assigned to the positional parameters. The @samp{-x}
-and @samp{-v} options are turned off.
-If there are no arguments, the positional parameters remain unchanged.
-@end table
-
-Using @samp{+} rather than @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{$-}.
-
-The remaining N @var{arguments} are positional parameters and are
-assigned, in order, to @code{$1}, @code{$2}, @dots{} @code{$N}.
-The special parameter @code{#} is set to N.
-
-The return status is always zero unless an invalid option is supplied.
-@end table
-
-@node Bash Conditional Expressions
-@section Bash Conditional Expressions
-@cindex expressions, conditional
+@item IGNOREEOF
+Controls the action of the shell on receipt of an @code{EOF} character
+as the sole input. If set, the value denotes the number
+of consecutive @code{EOF} 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} signifies the end of
+input to the shell. This is only in effect for interactive shells.
-Conditional expressions are used by the @code{[[} compound command
-and the @code{test} and @code{[} builtin commands.
+@item INPUTRC
+The name of the Readline initialization file, overriding the default
+of @file{~/.inputrc}.
-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 any @var{file} argument to one of the primaries is of the form
-@file{/dev/fd/@var{N}}, then file descriptor @var{N} is checked.
+@item LANG
+Used to determine the locale category for any category not specifically
+selected with a variable starting with @code{LC_}.
-@table @code
-@item -a @var{file}
-True if @var{file} exists.
+@item LC_ALL
+This variable overrides the value of @env{LANG} and any other
+@code{LC_} variable specifying a locale category.
-@item -b @var{file}
-True if @var{file} exists and is a block special file.
+@item LC_COLLATE
+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
+(@pxref{Filename Expansion}).
-@item -c @var{file}
-True if @var{file} exists and is a character special file.
+@item LC_CTYPE
+This variable determines the interpretation of characters and the
+behavior of character classes within filename expansion and pattern
+matching (@pxref{Filename Expansion}).
-@item -d @var{file}
-True if @var{file} exists and is a directory.
+@item LC_MESSAGES
+This variable determines the locale used to translate double-quoted
+strings preceded by a @samp{$} (@pxref{Locale Translation}).
-@item -e @var{file}
-True if @var{file} exists.
+@item LC_NUMERIC
+This variable determines the locale category used for number formatting.
-@item -f @var{file}
-True if @var{file} exists and is a regular file.
+@item LINENO
+The line number in the script or shell function currently executing.
-@item -g @var{file}
-True if @var{file} exists and its set-group-id bit is set.
+@item LINES
+Used by the @code{select} builtin command to determine the column length
+for printing selection lists. Automatically set upon receipt of a
+@code{SIGWINCH}.
-@item -h @var{file}
-True if @var{file} exists and is a symbolic link.
+@item MACHTYPE
+A string that fully describes the system type on which Bash
+is executing, in the standard @sc{gnu} @var{cpu-company-system} format.
-@item -k @var{file}
-True if @var{file} exists and its "sticky" bit is set.
+@item MAILCHECK
+How often (in seconds) that the shell should check for mail in the
+files specified in the @env{MAILPATH} or @env{MAIL} 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.
-@item -p @var{file}
-True if @var{file} exists and is a named pipe (FIFO).
+@item OLDPWD
+The previous working directory as set by the @code{cd} builtin.
-@item -r @var{file}
-True if @var{file} exists and is readable.
+@item OPTERR
+If set to the value 1, Bash displays error messages
+generated by the @code{getopts} builtin command.
-@item -s @var{file}
-True if @var{file} exists and has a size greater than zero.
+@item OSTYPE
+A string describing the operating system Bash is running on.
-@item -t @var{fd}
-True if file descriptor @var{fd} is open and refers to a terminal.
+@item PIPESTATUS
+An array variable (@pxref{Arrays})
+containing a list of exit status values from the processes
+in the most-recently-executed foreground pipeline (which may
+contain only a single command).
-@item -u @var{file}
-True if @var{file} exists and its set-user-id bit is set.
+@item POSIXLY_CORRECT
+If this variable is in the environment when @code{bash} starts, the shell
+enters @sc{posix} mode (@pxref{Bash POSIX Mode}) before reading the
+startup files, as if the @option{--posix} invocation option had been supplied.
+If it is set while the shell is running, @code{bash} enables @sc{posix} mode,
+as if the command
+@example
+@code{set -o posix}
+@end example
+@noindent
+had been executed.
-@item -w @var{file}
-True if @var{file} exists and is writable.
+@item PPID
+The process @sc{id} of the shell's parent process. This variable
+is readonly.
-@item -x @var{file}
-True if @var{file} exists and is executable.
+@item PROMPT_COMMAND
+If set, the value is interpreted as a command to execute
+before the printing of each primary prompt (@env{$PS1}).
-@item -O @var{file}
-True if @var{file} exists and is owned by the effective user id.
+@item PROMPT_DIRTRIM
+If set to a number greater than zero, the value is used as the number of
+trailing directory components to retain when expanding the @code{\w} and
+@code{\W} prompt string escapes (@pxref{Printing a Prompt}).
+Characters removed are replaced with an ellipsis.
-@item -G @var{file}
-True if @var{file} exists and is owned by the effective group id.
+@item PS3
+The value of this variable is used as the prompt for the
+@code{select} command. If this variable is not set, the
+@code{select} command prompts with @samp{#? }
-@item -L @var{file}
-True if @var{file} exists and is a symbolic link.
+@item PS4
+The value is the prompt printed before the command line is echoed
+when the @option{-x} option is set (@pxref{The Set Builtin}).
+The first character of @env{PS4} is replicated multiple times, as
+necessary, to indicate multiple levels of indirection.
+The default is @samp{+ }.
-@item -S @var{file}
-True if @var{file} exists and is a socket.
+@item PWD
+The current working directory as set by the @code{cd} builtin.
-@item -N @var{file}
-True if @var{file} exists and has been modified since it was last read.
+@item RANDOM
+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.
-@item @var{file1} -nt @var{file2}
-True if @var{file1} is newer (according to
-modification date) than @var{file2}.
+@item REPLY
+The default variable for the @code{read} builtin.
-@item @var{file1} -ot @var{file2}
-True if @var{file1} is older than @var{file2}.
+@item SECONDS
+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.
-@item @var{file1} -ef @var{file2}
-True if @var{file1} and @var{file2} have the same device and
-inode numbers.
+@item SHELL
+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.
-@item -o @var{optname}
-True if shell option @var{optname} is enabled.
-The list of options appears in the description of the @samp{-o}
-option to the @code{set} builtin (@pxref{The Set Builtin}).
+@item SHELLOPTS
+A colon-separated list of enabled shell options. Each word in
+the list is a valid argument for the @option{-o} option to the
+@code{set} builtin command (@pxref{The Set Builtin}).
+The options appearing in @env{SHELLOPTS} are those reported
+as @samp{on} by @samp{set -o}.
+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.
-@item -z @var{string}
-True if the length of @var{string} is zero.
+@item SHLVL
+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.
-@item -n @var{string}
-@itemx @var{string}
-True if the length of @var{string} is non-zero.
+@item TIMEFORMAT
+The value of this parameter is used as a format string specifying
+how the timing information for pipelines prefixed with the @code{time}
+reserved word should be displayed.
+The @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.
-@item @var{string1} == @var{string2}
-True if the strings are equal.
-@samp{=} may be used in place of @samp{==}.
+@table @code
-@item @var{string1} != @var{string2}
-True if the strings are not equal.
+@item %%
+A literal @samp{%}.
-@item @var{string1} < @var{string2}
-True if @var{string1} sorts before @var{string2} lexicographically
-in the current locale.
+@item %[@var{p}][l]R
+The elapsed time in seconds.
-@item @var{string1} > @var{string2}
-True if @var{string1} sorts after @var{string2} lexicographically
-in the current locale.
+@item %[@var{p}][l]U
+The number of CPU seconds spent in user mode.
-@item @var{arg1} OP @var{arg2}
-@code{OP} is one of
-@samp{-eq}, @samp{-ne}, @samp{-lt}, @samp{-le}, @samp{-gt}, or @samp{-ge}.
-These arithmetic binary operators return true if @var{arg1}
-is equal to, not equal to, less than, less than or equal to,
-greater than, or greater than or equal to @var{arg2},
-respectively. @var{Arg1} and @var{arg2}
-may be positive or negative integers.
+@item %[@var{p}][l]S
+The number of CPU seconds spent in system mode.
+@item %P
+The CPU percentage, computed as (%U + %S) / %R.
@end table
-@node Bash Variables
-@section Bash Variables
-
-These variables are set or used by Bash, but other shells
-do not normally treat them specially.
-
-@vtable @code
-
-@item BASH
-The full pathname used to execute the current instance of Bash.
+The optional @var{p} 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} greater than 3 are changed to 3.
+If @var{p} is not specified, the value 3 is used.
-@item BASH_ENV
-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. @xref{Bash Startup Files}.
+The optional @code{l} specifies a longer format, including minutes, of
+the form @var{MM}m@var{SS}.@var{FF}s.
+The value of @var{p} determines whether or not the fraction is included.
-@item BASH_VERSION
-The version number of the current instance of Bash.
+If this variable is not set, Bash acts as if it had the value
+@example
+@code{$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'}
+@end example
+If the value is null, no timing information is displayed.
+A trailing newline is added when the format string is displayed.
-@item BASH_VERSINFO
-A readonly array variable whose members hold version information for
-this instance of Bash.
-The values assigned to the array members are as follows:
+@item TMOUT
+If set to a value greater than zero, @code{TMOUT} is treated as the
+default timeout for the @code{read} builtin (@pxref{Bash Builtins}).
+The @code{select} command (@pxref{Conditional Constructs}) terminates
+if input does not arrive after @code{TMOUT} seconds when input is coming
+from a terminal.
-@table @code
+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.
-@item BASH_VERSINFO[0]
-The major version number (the @var{release}).
+@item TMPDIR
+If set, Bash uses its value as the name of a directory in which
+Bash creates temporary files for the shell's use.
-@item BASH_VERSINFO[1]
-The minor version number (the @var{version}).
+@item UID
+The numeric real user id of the current user. This variable is readonly.
-@item BASH_VERSINFO[2]
-The patch level.
+@end vtable
-@item BASH_VERSINFO[3]
-The build version.
+@node Bash Features
+@chapter Bash Features
-@item BASH_VERSINFO[4]
-The release status (e.g., @var{beta1}).
+This section describes features unique to Bash.
-@item BASH_VERSINFO[5]
-The value of @code{MACHTYPE}.
+@menu
+* Invoking Bash:: Command line options that you can give
+ to Bash.
+* Bash Startup Files:: When and how Bash executes scripts.
+* Interactive Shells:: What an interactive shell is.
+* Bash Conditional Expressions:: Primitives used in composing expressions for
+ the @code{test} builtin.
+* Shell Arithmetic:: Arithmetic on shell variables.
+* Aliases:: Substituting one command for another.
+* Arrays:: Array Variables.
+* The Directory Stack:: History of visited directories.
+* Printing a Prompt:: Controlling the PS1 string.
+* The Restricted Shell:: A more controlled mode of shell execution.
+* Bash POSIX Mode:: Making Bash behave more closely to what
+ the POSIX standard specifies.
+@end menu
-@end table
+@node Invoking Bash
+@section Invoking Bash
-@item DIRSTACK
-An array variable (@pxref{Arrays})
-containing the current contents of the directory stack.
-Directories appear in the stack in the order they are displayed by the
-@code{dirs} builtin.
-Assigning to members of this array variable may be used to modify
-directories already in the stack, but the @code{pushd} and @code{popd}
-builtins must be used to add and remove directories.
-Assignment to this variable will not change the current directory.
-If @code{DIRSTACK} is unset, it loses its special properties, even if
-it is subsequently reset.
+@example
+bash [long-opt] [-ir] [-abefhkmnptuvxdBCDHP] [-o @var{option}] [-O @var{shopt_option}] [@var{argument} @dots{}]
+bash [long-opt] [-abefhkmnptuvxdBCDHP] [-o @var{option}] [-O @var{shopt_option}] -c @var{string} [@var{argument} @dots{}]
+bash [long-opt] -s [-abefhkmnptuvxdBCDHP] [-o @var{option}] [-O @var{shopt_option}] [@var{argument} @dots{}]
+@end example
-@item EUID
-The numeric effective user id of the current user. This variable
-is readonly.
+In addition to the single-character shell command-line options
+(@pxref{The Set Builtin}), 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.
-@item FCEDIT
-The editor used as a default by the @samp{-e} option to the @code{fc}
-builtin command.
+@table @code
+@item --debugger
+Arrange for the debugger profile to be executed before the shell
+starts. Turns on extended debugging mode (see @ref{The Shopt Builtin}
+for a description of the @code{extdebug} option to the @code{shopt}
+builtin) and shell function tracing
+(see @ref{The Set Builtin} for a description of the @code{-o functrace}
+option).
-@item FIGNORE
-A colon-separated list of suffixes to ignore when performing
-filename completion.
-A file name whose suffix matches one of the entries in
-@code{FIGNORE}
-is excluded from the list of matched file names. A sample
-value is @samp{.o:~}
+@item --dump-po-strings
+A list of all double-quoted strings preceded by @samp{$}
+is printed on the standard output
+in the @sc{gnu} @code{gettext} PO (portable object) file format.
+Equivalent to @option{-D} except for the output format.
-@item GLOBIGNORE
-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 @code{GLOBIGNORE}, it is removed from the list
-of matches.
+@item --dump-strings
+Equivalent to @option{-D}.
-@item GROUPS
-An array variable containing the list of groups of which the current
-user is a member. This variable is readonly.
+@item --help
+Display a usage message on standard output and exit successfully.
-@item histchars
-Up to three characters which control history expansion, quick
-substitution, and tokenization (@pxref{History Interaction}).
-The first character is the
-@dfn{history-expansion-char}, that is, the character which signifies the
-start of a history expansion, normally @samp{!}. The second character is the
-character which signifies `quick substitution' when seen as the first
-character on a line, normally @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{#}. 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.
+@item --init-file @var{filename}
+@itemx --rcfile @var{filename}
+Execute commands from @var{filename} (instead of @file{~/.bashrc})
+in an interactive shell.
-@item HISTCMD
-The history number, or index in the history list, of the current
-command. If @code{HISTCMD} is unset, it loses its special properties,
-even if it is subsequently reset.
+@item --login
+Equivalent to @option{-l}.
-@item HISTCONTROL
-Set to a value of @samp{ignorespace}, it means don't enter lines which
-begin with a space or tab into the history list. Set to a value
-of @samp{ignoredups}, it means don't enter lines which match the last
-entered line. A value of @samp{ignoreboth} combines the two options.
-Unset, or set to any other value than those above, means to save
-all lines on the history list.
-The second and subsequent lines of a multi-line compound command are
-not tested, and are added to the history regardless of the value of
-@code{HISTCONTROL}.
+@item --noediting
+Do not use the @sc{gnu} Readline library (@pxref{Command Line Editing})
+to read command lines when the shell is interactive.
-@item HISTIGNORE
-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 fully specify the
-line (no implicit @samp{*} is appended). Each pattern is tested
-against the line after the checks specified by @code{HISTCONTROL}
-are applied. In addition to the normal shell pattern matching
-characters, @samp{&} matches the previous history line. @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
-@code{HISTIGNORE}.
+@item --noprofile
+Don't load the system-wide startup file @file{/etc/profile}
+or any of the personal initialization files
+@file{~/.bash_profile}, @file{~/.bash_login}, or @file{~/.profile}
+when Bash is invoked as a login shell.
-@code{HISTIGNORE} subsumes the function of @code{HISTCONTROL}. A
-pattern of @samp{&} is identical to @code{ignoredups}, and a
-pattern of @samp{[ ]*} is identical to @code{ignorespace}.
-Combining these two patterns, separating them with a colon,
-provides the functionality of @code{ignoreboth}.
+@item --norc
+Don't read the @file{~/.bashrc} initialization file in an
+interactive shell. This is on by default if the shell is
+invoked as @code{sh}.
-@item HISTFILE
-The name of the file to which the command history is saved. The
-default is @file{~/.bash_history}.
+@item --posix
+Change the behavior of Bash where the default operation differs
+from the @sc{posix} standard to match the standard. This
+is intended to make Bash behave as a strict superset of that
+standard. @xref{Bash POSIX Mode}, for a description of the Bash
+@sc{posix} mode.
-@item HISTSIZE
-The maximum number of commands to remember on the history list.
-The default value is 500.
+@item --restricted
+Make the shell a restricted shell (@pxref{The Restricted Shell}).
-@item HISTFILESIZE
-The maximum number of lines contained in the history file. When this
-variable is assigned a value, the history file is truncated, if
-necessary, to contain no more than that number of lines. The default
-value is 500. The history file is also truncated to this size after
-writing it when an interactive shell exits.
+@item --verbose
+Equivalent to @option{-v}. Print shell input lines as they're read.
-@item HOSTFILE
-Contains the name of a file in the same format as @file{/etc/hosts} that
-should be read when the shell needs to complete a hostname. You can
-change the file interactively; the next time you attempt to complete a
-hostname, Bash will add the contents of the new file to the already
-existing database.
+@item --version
+Show version information for this instance of
+Bash on the standard output and exit successfully.
-@item HOSTNAME
-The name of the current host.
+@end table
-@item HOSTTYPE
-A string describing the machine Bash is running on.
+There are several single-character options that may be supplied at
+invocation which are not available with the @code{set} builtin.
-@item IGNOREEOF
-Controls the action of the shell on receipt of an @code{EOF} character
-as the sole input. If set, the value denotes the number
-of consecutive @code{EOF} 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} signifies the end of
-input to the shell. This is only in effect for interactive shells.
+@table @code
+@item -c @var{string}
+Read and execute commands from @var{string} after processing the
+options, then exit. Any remaining arguments are assigned to the
+positional parameters, starting with @code{$0}.
-@item INPUTRC
-The name of the Readline startup file, overriding the default
-of @file{~/.inputrc}.
+@item -i
+Force the shell to run interactively. Interactive shells are
+described in @ref{Interactive Shells}.
-@item LANG
-Used to determine the locale category for any category not specifically
-selected with a variable starting with @code{LC_}.
+@item -l
+Make this shell act as if it had been directly invoked by login.
+When the shell is interactive, this is equivalent to starting a
+login shell with @samp{exec -l bash}.
+When the shell is not interactive, the login shell startup files will
+be executed.
+@samp{exec bash -l} or @samp{exec bash --login}
+will replace the current shell with a Bash login shell.
+@xref{Bash Startup Files}, for a description of the special behavior
+of a login shell.
-@item LC_ALL
-This variable overrides the value of @code{LANG} and any other
-@code{LC_} variable specifying a locale category.
+@item -r
+Make the shell a restricted shell (@pxref{The Restricted Shell}).
-@item LC_COLLATE
-This variable determines the collation order used when sorting the
-results of filename expansion, and
-determines the behavior of range expressions, equivalence classes,
-and collating sequences within filename expansion and pattern matching
-(@pxref{Filename Expansion}).
+@item -s
+If this option is present, or if no arguments remain after option
+processing, then commands are read from the standard input.
+This option allows the positional parameters to be set
+when invoking an interactive shell.
-@item LC_CTYPE
-This variable determines the interpretation of characters and the
-behavior of character classes within filename expansion and pattern
-matching (@pxref{Filename Expansion}).
+@item -D
+A list of all double-quoted strings preceded by @samp{$}
+is printed on the standard output.
+These are the strings that
+are subject to language translation when the current locale
+is not @code{C} or @code{POSIX} (@pxref{Locale Translation}).
+This implies the @option{-n} option; no commands will be executed.
+
+@item [-+]O [@var{shopt_option}]
+@var{shopt_option} is one of the shell options accepted by the
+@code{shopt} builtin (@pxref{The Shopt Builtin}).
+If @var{shopt_option} is present, @option{-O} sets the value of that option;
+@option{+O} unsets it.
+If @var{shopt_option} is not supplied, the names and values of the shell
+options accepted by @code{shopt} are printed on the standard output.
+If the invocation option is @option{+O}, the output is displayed in a format
+that may be reused as input.
-@item LC_MESSAGES
-This variable determines the locale used to translate double-quoted
-strings preceded by a @samp{$} (@pxref{Locale Translation}).
+@item --
+A @code{--} signals the end of options and disables further option
+processing.
+Any arguments after the @code{--} are treated as filenames and arguments.
-@item LINENO
-The line number in the script or shell function currently executing.
+@end table
-@item MACHTYPE
-A string that fully describes the system type on which Bash
-is executing, in the standard GNU @var{cpu-company-system} format.
+@cindex login shell
+A @emph{login} shell is one whose first character of argument zero is
+@samp{-}, or one invoked with the @option{--login} option.
-@item MAILCHECK
-How often (in seconds) that the shell should check for mail in the
-files specified in the @code{MAILPATH} or @code{MAIL} variables.
+@cindex interactive shell
+An @emph{interactive} shell is one started without non-option arguments,
+unless @option{-s} is specified,
+without specifying the @option{-c} option, and whose input and output are both
+connected to terminals (as determined by @code{isatty(3)}), or one
+started with the @option{-i} option. @xref{Interactive Shells}, for more
+information.
-@item OLDPWD
-The previous working directory as set by the @code{cd} builtin.
+If arguments remain after option processing, and neither the
+@option{-c} nor the @option{-s}
+option has been supplied, the first argument is assumed to
+be the name of a file containing shell commands (@pxref{Shell Scripts}).
+When Bash is invoked in this fashion, @code{$0}
+is set to the name of the file, and the positional parameters
+are set to the remaining arguments.
+Bash reads and executes commands from this file, then exits.
+Bash's exit status is the exit status of the last command executed
+in the script. If no commands are executed, the exit status is 0.
-@item OPTERR
-If set to the value 1, Bash displays error messages
-generated by the @code{getopts} builtin command.
+@node Bash Startup Files
+@section Bash Startup Files
+@cindex startup files
-@item OSTYPE
-A string describing the operating system Bash is running on.
+This section describes how Bash executes its startup files.
+If any of the files exist but cannot be read, Bash reports an error.
+Tildes are expanded in file names as described above under
+Tilde Expansion (@pxref{Tilde Expansion}).
-@item PIPESTATUS
-An array variable (@pxref{Arrays})
-containing a list of exit status values from the processes
-in the most-recently-executed foreground pipeline (which may
-contain only a single command).
+Interactive shells are described in @ref{Interactive Shells}.
-@item PPID
-The process id of the shell's parent process. This variable
-is readonly.
+@subsubheading Invoked as an interactive login shell, or with @option{--login}
-@item PROMPT_COMMAND
-If present, this contains a string which is a command to execute
-before the printing of each primary prompt (@code{$PS1}).
+When Bash is invoked as an interactive login shell, or as a
+non-interactive shell with the @option{--login} option, it first reads and
+executes commands from the file @file{/etc/profile}, if that file exists.
+After reading that file, it looks for @file{~/.bash_profile},
+@file{~/.bash_login}, and @file{~/.profile}, in that order, and reads
+and executes commands from the first one that exists and is readable.
+The @option{--noprofile} option may be used when the shell is started to
+inhibit this behavior.
-@item PS3
-The value of this variable is used as the prompt for the
-@code{select} command. If this variable is not set, the
-@code{select} command prompts with @samp{#? }
+When a login shell exits, Bash reads and executes commands from
+the file @file{~/.bash_logout}, if it exists.
-@item PS4
-This is the prompt printed before the command line is echoed
-when the @samp{-x} option is set (@pxref{The Set Builtin}).
-The first character of @code{PS4} is replicated multiple times, as
-necessary, to indicate multiple levels of indirection.
-The default is @samp{+ }.
+@subsubheading Invoked as an interactive non-login shell
-@item PWD
-The current working directory as set by the @code{cd} builtin.
+When an interactive shell that is not a login shell is started, Bash
+reads and executes commands from @file{~/.bashrc}, if that file exists.
+This may be inhibited by using the @option{--norc} option.
+The @option{--rcfile @var{file}} option will force Bash to read and
+execute commands from @var{file} instead of @file{~/.bashrc}.
-@item RANDOM
-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.
+So, typically, your @file{~/.bash_profile} contains the line
+@example
+@code{if [ -f ~/.bashrc ]; then . ~/.bashrc; fi}
+@end example
+@noindent
+after (or before) any login-specific initializations.
-@item REPLY
-The default variable for the @code{read} builtin.
+@subsubheading Invoked non-interactively
-@item SECONDS
-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.
+When Bash is started non-interactively, to run a shell script,
+for example, it looks for the variable @env{BASH_ENV} 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:
+@example
+@code{if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi}
+@end example
+@noindent
+but the value of the @env{PATH} variable is not used to search for the
+file name.
-@item SHELLOPTS
-A colon-separated list of enabled shell options. Each word in
-the list is a valid argument for the @samp{-o} option to the
-@code{set} builtin command (@pxref{The Set Builtin}).
-The options appearing in @code{SHELLOPTS} are those reported
-as @samp{on} by @samp{set -o}.
-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.
+As noted above, if a non-interactive shell is invoked with the
+@option{--login} option, Bash attempts to read and execute commands from the
+login shell startup files.
-@item SHLVL
-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.
+@subsubheading Invoked with name @code{sh}
-@item TIMEFORMAT
-The value of this parameter is used as a format string specifying
-how the timing information for pipelines prefixed with the @code{time}
-reserved word should be displayed.
-The @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.
+If Bash is invoked with the name @code{sh}, it tries to mimic the
+startup behavior of historical versions of @code{sh} as closely as
+possible, while conforming to the @sc{posix} standard as well.
-@table @code
+When invoked as an interactive login shell, or as a non-interactive
+shell with the @option{--login} option, it first attempts to read
+and execute commands from @file{/etc/profile} and @file{~/.profile}, in
+that order.
+The @option{--noprofile} option may be used to inhibit this behavior.
+When invoked as an interactive shell with the name @code{sh}, Bash
+looks for the variable @env{ENV}, 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} does not attempt to read and execute
+commands from any other startup files, the @option{--rcfile} option has
+no effect.
+A non-interactive shell invoked with the name @code{sh} does not attempt
+to read any other startup files.
-@item %%
-A literal @samp{%}.
+When invoked as @code{sh}, Bash enters @sc{posix} mode after
+the startup files are read.
-@item %[@var{p}][l]R
-The elapsed time in seconds.
+@subsubheading Invoked in @sc{posix} mode
-@item %[@var{p}][l]U
-The number of CPU seconds spent in user mode.
+When Bash is started in @sc{posix} mode, as with the
+@option{--posix} command line option, it follows the @sc{posix} standard
+for startup files.
+In this mode, interactive shells expand the @env{ENV} variable
+and commands are read and executed from the file whose name is the
+expanded value.
+No other startup files are read.
-@item %[@var{p}][l]S
-The number of CPU seconds spent in system mode.
+@subsubheading Invoked by remote shell daemon
-@item %P
-The CPU percentage, computed as (%U + %S) / %R.
-@end table
+Bash attempts to determine when it is being run with its standard input
+connected to a a network connection, as if by the remote shell
+daemon, usually @code{rshd}, or the secure shell daemon @code{sshd}.
+If Bash determines it is being run in
+this fashion, it reads and executes commands from @file{~/.bashrc}, if that
+file exists and is readable.
+It will not do this if invoked as @code{sh}.
+The @option{--norc} option may be used to inhibit this behavior, and the
+@option{--rcfile} option may be used to force another file to be read, but
+@code{rshd} does not generally invoke the shell with those options or
+allow them to be specified.
-The optional @var{p} 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} greater than 3 are changed to 3.
-If @var{p} is not specified, the value 3 is used.
+@subsubheading Invoked with unequal effective and real @sc{uid/gid}s
-The optional @code{l} specifies a longer format, including minutes, of
-the form @var{MM}m@var{SS}.@var{FF}s.
-The value of @var{p} determines whether or not the fraction is included.
+If Bash is started with the effective user (group) id not equal to the
+real user (group) id, and the @code{-p} option is not supplied, no startup
+files are read, shell functions are not inherited from the environment,
+the @env{SHELLOPTS} 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} option is supplied at invocation, the startup behavior is
+the same, but the effective user id is not reset.
-If this variable is not set, Bash acts as if it had the value
-@example
-@code{$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'}
-@end example
-If the value is null, no timing information is displayed.
-A trailing newline is added when the format string is displayed.
+@node Interactive Shells
+@section Interactive Shells
+@cindex interactive shell
+@cindex shell, interactive
-@item TMOUT
-If set to a value greater than zero, the value is interpreted as
-the number of seconds to wait for input after issuing the primary
-prompt.
-Bash terminates after that number of seconds if input does
-not arrive.
+@menu
+* What is an Interactive Shell?:: What determines whether a shell is Interactive.
+* Is this Shell Interactive?:: How to tell if a shell is interactive.
+* Interactive Shell Behavior:: What changes in a interactive shell?
+@end menu
-@item UID
-The numeric real user id of the current user. This variable is readonly.
+@node What is an Interactive Shell?
+@subsection What is an Interactive Shell?
-@end vtable
+An interactive shell
+is one started without non-option arguments, unless @option{-s} is
+specified, without specifying the @option{-c} option, and
+whose input and error output are both
+connected to terminals (as determined by @code{isatty(3)}),
+or one started with the @option{-i} option.
-@node Shell Arithmetic
-@section Shell Arithmetic
-@cindex arithmetic, shell
-@cindex shell arithmetic
-@cindex expressions, arithmetic
-@cindex evaluation, arithmetic
-@cindex arithmetic evaluation
+An interactive shell generally reads from and writes to a user's
+terminal.
-The shell allows arithmetic expressions to be evaluated, as one of
-the shell expansions or by the @code{let} builtin.
+The @option{-s} invocation option may be used to set the positional parameters
+when an interactive shell is started.
-Evaluation is done in long integers with no check for overflow,
-though division by 0 is trapped and flagged as an error. The
-following list of operators is grouped into levels of
-equal-precedence operators. The levels are listed in order of
-decreasing precedence.
+@node Is this Shell Interactive?
+@subsection Is this Shell Interactive?
-@table @code
-@item - +
-unary minus and plus
+To determine within a startup script whether or not Bash is
+running interactively,
+test the value of the @samp{-} special parameter.
+It contains @code{i} when the shell is interactive. For example:
-@item ! ~
-logical and bitwise negation
+@example
+case "$-" in
+*i*) echo This shell is interactive ;;
+*) echo This shell is not interactive ;;
+esac
+@end example
-@item **
-exponentiation
+Alternatively, startup scripts may examine the variable
+@env{PS1}; it is unset in non-interactive shells, and set in
+interactive shells. Thus:
-@item * / %
-multiplication, division, remainder
+@example
+if [ -z "$PS1" ]; then
+ echo This shell is not interactive
+else
+ echo This shell is interactive
+fi
+@end example
-@item + -
-addition, subtraction
+@node Interactive Shell Behavior
+@subsection Interactive Shell Behavior
-@item << >>
-left and right bitwise shifts
+When the shell is running interactively, it changes its behavior in
+several ways.
-@item <= >= < >
-comparison
+@enumerate
+@item
+Startup files are read and executed as described in @ref{Bash Startup Files}.
-@item == !=
-equality and inequality
+@item
+Job Control (@pxref{Job Control}) is enabled by default. When job
+control is in effect, Bash ignores the keyboard-generated job control
+signals @code{SIGTTIN}, @code{SIGTTOU}, and @code{SIGTSTP}.
-@item &
-bitwise AND
+@item
+Bash expands and displays @env{PS1} before reading the first line
+of a command, and expands and displays @env{PS2} before reading the
+second and subsequent lines of a multi-line command.
-@item ^
-bitwise exclusive OR
+@item
+Bash executes the value of the @env{PROMPT_COMMAND} variable as a command
+before printing the primary prompt, @env{$PS1}
+(@pxref{Bash Variables}).
-@item |
-bitwise OR
+@item
+Readline (@pxref{Command Line Editing}) is used to read commands from
+the user's terminal.
-@item &&
-logical AND
+@item
+Bash inspects the value of the @code{ignoreeof} option to @code{set -o}
+instead of exiting immediately when it receives an @code{EOF} on its
+standard input when reading a command (@pxref{The Set Builtin}).
-@item ||
-logical OR
+@item
+Command history (@pxref{Bash History Facilities})
+and history expansion (@pxref{History Interaction})
+are enabled by default.
+Bash will save the command history to the file named by @env{$HISTFILE}
+when an interactive shell exits.
-@item expr ? expr : expr
-conditional evaluation
+@item
+Alias expansion (@pxref{Aliases}) is performed by default.
-@item = *= /= %= += -= <<= >>= &= ^= |=
-assignment
-@end table
+@item
+In the absence of any traps, Bash ignores @code{SIGTERM}
+(@pxref{Signals}).
-Shell variables are allowed as operands; parameter expansion is
-performed before the expression is evaluated.
-The value of a parameter is coerced to a long integer within
-an expression. A shell variable need not have its integer attribute
-turned on to be used in an expression.
+@item
+In the absence of any traps, @code{SIGINT} is caught and handled
+((@pxref{Signals}).
+@code{SIGINT} will interrupt some shell builtins.
-Constants with a leading 0 are interpreted as octal numbers.
-A leading @samp{0x} or @samp{0X} denotes hexadecimal. Otherwise,
-numbers take the form [@var{base}@code{#}]@var{n}, where @var{base}
-is a decimal number between 2 and 64 representing the arithmetic
-base, and @var{n} is a number in that base. If @var{base} is
-omitted, then base 10 is used.
-The digits greater than 9 are represented by the lowercase letters,
-the uppercase letters, @samp{_}, and @samp{@@}, in that order.
-If @var{base} is less than or equal to 36, lowercase and uppercase
-letters may be used interchangably to represent numbers between 10
-and 35.
+@item
+An interactive login shell sends a @code{SIGHUP} to all jobs on exit
+if the @code{huponexit} shell option has been enabled (@pxref{Signals}).
-Operators are evaluated in order of precedence. Sub-expressions in
-parentheses are evaluated first and may override the precedence
-rules above.
+@item
+The @option{-n} invocation option is ignored, and @samp{set -n} has
+no effect (@pxref{The Set Builtin}).
-@node Aliases
-@section Aliases
-@cindex alias expansion
+@item
+Bash will check for mail periodically, depending on the values of the
+@env{MAIL}, @env{MAILPATH}, and @env{MAILCHECK} shell variables
+(@pxref{Bash Variables}).
-@menu
-* Alias Builtins:: Builtins commands to maniuplate aliases.
-@end menu
+@item
+Expansion errors due to references to unbound shell variables after
+@samp{set -u} has been enabled will not cause the shell to exit
+(@pxref{The Set Builtin}).
-Aliases allow a string to be substituted for a word when it is used
-as the first word of a simple command.
-The shell maintains a list of @var{aliases}
-that may be set and unset with the @code{alias} and
-@code{unalias} builtin commands.
+@item
+The shell will not exit on expansion errors caused by @var{var} being unset
+or null in @code{$@{@var{var}:?@var{word}@}} expansions
+(@pxref{Shell Parameter Expansion}).
-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 alias name and the replacement text may contain any valid
-shell input, including shell metacharacters, with the exception
-that the alias name may not contain @samp{=}.
-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} to @code{"ls -F"},
-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.
+@item
+Redirection errors encountered by shell builtins will not cause the
+shell to exit.
-Aliases are created and listed with the @code{alias}
-command, and removed with the @code{unalias} command.
+@item
+When running in @sc{posix} mode, a special builtin returning an error
+status will not cause the shell to exit (@pxref{Bash POSIX Mode}).
-There is no mechanism for using arguments in the replacement text,
-as in @code{csh}.
-If arguments are needed, a shell function should be used
-(@pxref{Shell Functions}).
+@item
+A failed @code{exec} will not cause the shell to exit
+(@pxref{Bourne Shell Builtins}).
-Aliases are not expanded when the shell is not interactive,
-unless the @code{expand_aliases} shell option is set using
-@code{shopt} (@pxref{Bash Builtins}).
+@item
+Parser syntax errors will not cause the shell to exit.
-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}
-in compound commands.
+@item
+Simple spelling correction for directory arguments to the @code{cd}
+builtin is enabled by default (see the description of the @code{cdspell}
+option to the @code{shopt} builtin in @ref{The Shopt Builtin}).
-For almost every purpose, aliases are superseded by
-shell functions.
+@item
+The shell will check the value of the @env{TMOUT} variable and exit
+if a command is not read within the specified number of seconds after
+printing @env{$PS1} (@pxref{Bash Variables}).
-@node Alias Builtins
-@subsection Alias Builtins
+@end enumerate
-@table @code
+@node Bash Conditional Expressions
+@section Bash Conditional Expressions
+@cindex expressions, conditional
-@item alias
-@btindex alias
-@example
-alias [@code{-p}] [@var{name}[=@var{value}] @dots{}]
-@end example
+Conditional expressions are used by the @code{[[} compound command
+and the @code{test} and @code{[} builtin commands.
-Without arguments or with the @samp{-p} option, @code{alias} 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}
-whose @var{value} is given. If no @var{value} is given, the name
-and value of the alias is printed.
+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} argument to one of the primaries is of the form
+@file{/dev/fd/@var{N}}, then file descriptor @var{N} is checked.
+If the @var{file} argument to one of the primaries is one of
+@file{/dev/stdin}, @file{/dev/stdout}, or @file{/dev/stderr}, file
+descriptor 0, 1, or 2, respectively, is checked.
-@item unalias
-@btindex unalias
-@example
-unalias [-a] [@var{name} @dots{} ]
-@end example
+Unless otherwise specified, primaries that operate on files follow symbolic
+links and operate on the target of the link, rather than the link itself.
-Remove each @var{name} from the list of aliases. If @samp{-a} is
-supplied, all aliases are removed.
-@end table
+@table @code
+@item -a @var{file}
+True if @var{file} exists.
+
+@item -b @var{file}
+True if @var{file} exists and is a block special file.
+
+@item -c @var{file}
+True if @var{file} exists and is a character special file.
+
+@item -d @var{file}
+True if @var{file} exists and is a directory.
+
+@item -e @var{file}
+True if @var{file} exists.
+
+@item -f @var{file}
+True if @var{file} exists and is a regular file.
+
+@item -g @var{file}
+True if @var{file} exists and its set-group-id bit is set.
+
+@item -h @var{file}
+True if @var{file} exists and is a symbolic link.
+
+@item -k @var{file}
+True if @var{file} exists and its "sticky" bit is set.
+
+@item -p @var{file}
+True if @var{file} exists and is a named pipe (FIFO).
+
+@item -r @var{file}
+True if @var{file} exists and is readable.
+
+@item -s @var{file}
+True if @var{file} exists and has a size greater than zero.
+
+@item -t @var{fd}
+True if file descriptor @var{fd} is open and refers to a terminal.
+
+@item -u @var{file}
+True if @var{file} exists and its set-user-id bit is set.
+
+@item -w @var{file}
+True if @var{file} exists and is writable.
+
+@item -x @var{file}
+True if @var{file} exists and is executable.
+
+@item -O @var{file}
+True if @var{file} exists and is owned by the effective user id.
+
+@item -G @var{file}
+True if @var{file} exists and is owned by the effective group id.
+
+@item -L @var{file}
+True if @var{file} exists and is a symbolic link.
+
+@item -S @var{file}
+True if @var{file} exists and is a socket.
+
+@item -N @var{file}
+True if @var{file} exists and has been modified since it was last read.
+
+@item @var{file1} -nt @var{file2}
+True if @var{file1} is newer (according to modification date)
+than @var{file2}, or if @var{file1} exists and @var{file2} does not.
+
+@item @var{file1} -ot @var{file2}
+True if @var{file1} is older than @var{file2},
+or if @var{file2} exists and @var{file1} does not.
+
+@item @var{file1} -ef @var{file2}
+True if @var{file1} and @var{file2} refer to the same device and
+inode numbers.
+
+@item -o @var{optname}
+True if shell option @var{optname} is enabled.
+The list of options appears in the description of the @option{-o}
+option to the @code{set} builtin (@pxref{The Set Builtin}).
+
+@item -z @var{string}
+True if the length of @var{string} is zero.
+
+@item -n @var{string}
+@itemx @var{string}
+True if the length of @var{string} is non-zero.
+
+@item @var{string1} == @var{string2}
+True if the strings are equal.
+@samp{=} may be used in place of @samp{==} for strict @sc{posix} compliance.
+
+@item @var{string1} != @var{string2}
+True if the strings are not equal.
+
+@item @var{string1} < @var{string2}
+True if @var{string1} sorts before @var{string2} lexicographically
+in the current locale.
+
+@item @var{string1} > @var{string2}
+True if @var{string1} sorts after @var{string2} lexicographically
+in the current locale.
+
+@item @var{arg1} OP @var{arg2}
+@code{OP} is one of
+@samp{-eq}, @samp{-ne}, @samp{-lt}, @samp{-le}, @samp{-gt}, or @samp{-ge}.
+These arithmetic binary operators return true if @var{arg1}
+is equal to, not equal to, less than, less than or equal to,
+greater than, or greater than or equal to @var{arg2},
+respectively. @var{Arg1} and @var{arg2}
+may be positive or negative integers.
+
+@end table
+
+@node Shell Arithmetic
+@section Shell Arithmetic
+@cindex arithmetic, shell
+@cindex shell arithmetic
+@cindex expressions, arithmetic
+@cindex evaluation, arithmetic
+@cindex arithmetic evaluation
+
+The shell allows arithmetic expressions to be evaluated, as one of
+the shell expansions or by the @code{let} and the @option{-i} option
+to the @code{declare} builtins.
+
+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.
+
+@table @code
+
+@item @var{id}++ @var{id}--
+variable post-increment and post-decrement
+
+@item ++@var{id} --@var{id}
+variable pre-increment and pre-decrement
+
+@item - +
+unary minus and plus
+
+@item ! ~
+logical and bitwise negation
+
+@item **
+exponentiation
+
+@item * / %
+multiplication, division, remainder
+
+@item + -
+addition, subtraction
+
+@item << >>
+left and right bitwise shifts
+
+@item <= >= < >
+comparison
+
+@item == !=
+equality and inequality
+
+@item &
+bitwise AND
+
+@item ^
+bitwise exclusive OR
+
+@item |
+bitwise OR
+
+@item &&
+logical AND
+
+@item ||
+logical OR
+
+@item expr ? expr : expr
+conditional operator
+
+@item = *= /= %= += -= <<= >>= &= ^= |=
+assignment
+
+@item expr1 , expr2
+comma
+@end table
+
+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} attribute using @samp{declare -i} 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.
+
+Constants with a leading 0 are interpreted as octal numbers.
+A leading @samp{0x} or @samp{0X} denotes hexadecimal. Otherwise,
+numbers take the form [@var{base}@code{#}]@var{n}, where @var{base}
+is a decimal number between 2 and 64 representing the arithmetic
+base, and @var{n} is a number in that base. If @var{base}@code{#} is
+omitted, then base 10 is used.
+The digits greater than 9 are represented by the lowercase letters,
+the uppercase letters, @samp{@@}, and @samp{_}, in that order.
+If @var{base} is less than or equal to 36, lowercase and uppercase
+letters may be used interchangeably to represent numbers between 10
+and 35.
+
+Operators are evaluated in order of precedence. Sub-expressions in
+parentheses are evaluated first and may override the precedence
+rules above.
+
+@node Aliases
+@section Aliases
+@cindex alias expansion
+
+@var{Aliases} allow a string to be substituted for a word when it is used
+as the first word of a simple command.
+The shell maintains a list of aliases that may be set and unset with
+the @code{alias} and @code{unalias} builtin commands.
+
+The first word of each simple command, if unquoted, is checked to see
+if it has an alias.
+If so, that word is replaced by the text of the alias.
+The characters @samp{/}, @samp{$}, @samp{`}, @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} to @code{"ls -F"},
+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.
+
+Aliases are created and listed with the @code{alias}
+command, and removed with the @code{unalias} command.
+
+There is no mechanism for using arguments in the replacement text,
+as in @code{csh}.
+If arguments are needed, a shell function should be used
+(@pxref{Shell Functions}).
+
+Aliases are not expanded when the shell is not interactive,
+unless the @code{expand_aliases} shell option is set using
+@code{shopt} (@pxref{The Shopt Builtin}).
+
+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}
+in compound commands.
+
+For almost every purpose, shell functions are preferred over aliases.
@node Arrays
@section Arrays
@cindex arrays
-Bash provides one-dimensional array variables. Any variable may be used as
-an array; the @code{declare} builtin will explicitly declare an array.
+Bash provides one-dimensional indexed and associative array variables.
+Any variable may be used as an indexed array;
+the @code{declare} 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.
+be indexed or assigned contiguously.
+Indexed arrays are referenced using integers (including arithmetic
+expressions (@pxref{Shell Arithmetic}) and are zero-based;
+associative arrays use arbitrary strings.
-An array is created automatically if any variable is assigned to using
-the syntax
+An indexed array is created automatically if any variable is assigned to
+using the syntax
@example
name[@var{subscript}]=@var{value}
@end example
declare -a @var{name}[@var{subscript}]
@end example
@noindent
-is also accepted; the @var{subscript} is ignored. Attributes may be
+is also accepted; the @var{subscript} is ignored.
+
+Associative arrays are created using
+@example
+declare -A @var{name}.
+@end example
+
+Attributes may be
specified for an array variable using the @code{declare} and
@code{readonly} builtins. Each attribute applies to all members of
an array.
@end example
@noindent
where each
-@var{value} is of the form @code{[[@var{subscript}]=]}@var{string}. If
+@var{value} is of the form @code{[@var{subscript}]=}@var{string}.
+Indexed array assignments do not require the bracket and subscript.
+When assigning to indexed arrays, if
the optional subscript is supplied, that index is assigned to;
otherwise the index of the element assigned is the last index assigned
to by the statement plus one. Indexing starts at zero.
+
+When assigning to an associative array, the subscript is required.
+
This syntax is also accepted by the @code{declare}
builtin. Individual array elements may be assigned to using the
@code{name[}@var{subscript}@code{]=}@var{value} syntax introduced above.
conflicts with the shell's filename expansion operators. If the
@var{subscript} is @samp{@@} or @samp{*}, the word expands to all members
of the array @var{name}. These subscripts differ only when the word
-appears within double quotes. If the word is double-quoted,
+appears within double quotes.
+If the word is double-quoted,
@code{$@{name[*]@}} expands to a single word with
the value of each array member separated by the first character of the
-@code{IFS} variable, and @code{$@{name[@@]@}} expands each element of
+@env{IFS} variable, and @code{$@{name[@@]@}} expands each element of
@var{name} to a separate word. When there are no array members,
-@code{$@{name[@@]@}} expands to nothing. This is analogous to the
+@code{$@{name[@@]@}} expands to nothing.
+If the double-quoted expansion occurs within a word, the expansion of
+the first parameter is joined with the beginning part of the original
+word, and the expansion of the last parameter is joined with the last
+part of the original word.
+This is analogous to the
expansion of the special parameters @samp{@@} and @samp{*}.
@code{$@{#name[}@var{subscript}@code{]@}} expands to the length of
@code{$@{name[}@var{subscript}@code{]@}}.
If @var{subscript} is @samp{@@} or
@samp{*}, the expansion is the number of elements in the array.
Referencing an array variable without a subscript is equivalent to
-referencing element zero.
+referencing with a subscript of 0.
The @code{unset} builtin is used to destroy arrays.
-@code{unset} @code{name[@var{subscript}]}
+@code{unset} @var{name}[@var{subscript}]
destroys the array element at index @var{subscript}.
+Care must be taken to avoid unwanted side effects caused by filename
+generation.
@code{unset} @var{name}, where @var{name} is an array, removes the
entire array. A subscript of @samp{*} or @samp{@@} also removes the
entire array.
The @code{declare}, @code{local}, and @code{readonly}
-builtins each accept a @samp{-a}
-option to specify an array. The @code{read}
-builtin accepts a @samp{-a}
+builtins each accept a @option{-a} option to specify an indexed
+array and a @option{-A} option to specify an associative array.
+The @code{read} builtin accepts a @option{-a}
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} and @code{declare}
@section The Directory Stack
@cindex directory stack
+@menu
+* Directory Stack Builtins:: Bash builtin commands to manipulate
+ the directory stack.
+@end menu
+
The directory stack is a list of recently-visited directories. The
@code{pushd} builtin adds directories to the stack as it changes
the current directory, and the @code{popd} builtin removes specified
of the directory stack.
The contents of the directory stack are also visible
-as the value of the @code{DIRSTACK} shell variable.
+as the value of the @env{DIRSTACK} shell variable.
+
+@node Directory Stack Builtins
+@subsection Directory Stack Builtins
@table @code
@item dirs
@btindex dirs
@example
-dirs [+@var{N} | -@var{N}] [-clvp]
+dirs [+@var{N} | -@var{N}] [-clpv]
@end example
Display the list of currently remembered directories. Directories
are added to the list with the @code{pushd} command; the
@btindex pushd
@item pushd
@example
-pushd [@var{dir} | @var{+N} | @var{-N}] [-n]
+pushd [-n] [@var{+N} | @var{-N} | @var{dir} ]
@end example
Save the current directory on the top of the directory stack
With no arguments, @code{pushd} exchanges the top two directories.
@table @code
+@item -n
+Suppresses the normal change of directory when adding directories
+to the stack, so that only the stack is manipulated.
@item +@var{N}
Brings the @var{N}th directory (counting from the left of the
list printed by @code{dirs}, starting with zero) to the top of
Brings the @var{N}th directory (counting from the right of the
list printed by @code{dirs}, starting with zero) to the top of
the list by rotating the stack.
-@item -n
-Suppresses the normal change of directory when adding directories
-to the stack, so that only the stack is manipulated.
@item @var{dir}
Makes the current working directory be the top of the stack, and then
executes the equivalent of `@code{cd} @var{dir}'.
@section Controlling the Prompt
@cindex prompting
-The value of the variable @code{PROMPT_COMMAND} is examined just before
-Bash prints each primary prompt. If it is set and non-null, then the
+The value of the variable @env{PROMPT_COMMAND} is examined just before
+Bash prints each primary prompt. If @env{PROMPT_COMMAND} is set and
+has a non-null value, then the
value is executed just as if it had been typed on the command line.
In addition, the following table describes the special characters which
A bell character.
@item \d
The date, in "Weekday Month Date" format (e.g., "Tue May 26").
+@item \D@{@var{format}@}
+The @var{format} is passed to @code{strftime}(3) and the result is inserted
+into the prompt string; an empty @var{format} results in a locale-specific
+time representation. The braces are required.
@item \e
An escape character.
@item \h
The hostname, up to the first `.'.
@item \H
The hostname.
+@item \j
+The number of jobs currently managed by the shell.
+@item \l
+The basename of the shell's terminal device name.
@item \n
A newline.
@item \r
The time, in 12-hour HH:MM:SS format.
@item \@@
The time, in 12-hour am/pm format.
+@item \A
+The time, in 24-hour HH:MM format.
@item \u
The username of the current user.
@item \v
@item \V
The release of Bash, version + patchlevel (e.g., 2.00.0)
@item \w
-The current working directory.
+The current working directory, with @env{$HOME} abbreviated with a tilde
+(uses the @env{$PROMPT_DIRTRIM} variable).
@item \W
-The basename of @code{$PWD}.
+The basename of @env{$PWD}, with @env{$HOME} abbreviated with a tilde.
@item \!
The history number of this command.
@item \#
End a sequence of non-printing characters.
@end table
+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
+(@pxref{Bash History Facilities}), while the command number is
+the position in the sequence of commands executed during the current
+shell session.
+
+After the string is decoded, it is expanded via
+parameter expansion, command substitution, arithmetic
+expansion, and quote removal, subject to the value of the
+@code{promptvars} shell option (@pxref{Bash Builtins}).
+
@node The Restricted Shell
@section The Restricted Shell
@cindex restricted shell
If Bash is started with the name @code{rbash}, or the
-@samp{--restricted}
+@option{--restricted}
+or
+@option{-r}
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}
-with the exception that the following are disallowed:
+with the exception that the following are disallowed or not performed:
+
@itemize @bullet
@item
Changing directories with the @code{cd} builtin.
@item
-Setting or unsetting the values of the @code{SHELL}, @code{PATH},
-@code{ENV}, or @code{BASH_ENV} variables.
+Setting or unsetting the values of the @env{SHELL}, @env{PATH},
+@env{ENV}, or @env{BASH_ENV} variables.
@item
Specifying command names containing slashes.
@item
Specifying a filename containing a slash as an argument to the @code{.}
builtin command.
@item
+Specifying a filename containing a slash as an argument to the @option{-p}
+option to the @code{hash} builtin command.
+@item
Importing function definitions from the shell environment at startup.
@item
-Parsing the value of @code{SHELLOPTS} from the shell environment at startup.
+Parsing the value of @env{SHELLOPTS} from the shell environment at startup.
@item
Redirecting output using the @samp{>}, @samp{>|}, @samp{<>}, @samp{>&},
@samp{&>}, and @samp{>>} redirection operators.
Using the @code{exec} builtin to replace the shell with another command.
@item
Adding or deleting builtin commands with the
-@samp{-f} and @samp{-d} options to the @code{enable} builtin.
+@option{-f} and @option{-d} options to the @code{enable} builtin.
+@item
+Using the @code{enable} builtin command to enable disabled shell builtins.
@item
-Specifying the @samp{-p} option to the @code{command} builtin.
+Specifying the @option{-p} option to the @code{command} builtin.
@item
Turning off restricted mode with @samp{set +r} or @samp{set +o restricted}.
@end itemize
+These restrictions are enforced after any startup files are read.
+
+When a command that is found to be a shell script is executed
+(@pxref{Shell Scripts}), @code{rbash} turns off any restrictions in
+the shell spawned to execute the script.
+
@node Bash POSIX Mode
@section Bash POSIX Mode
@cindex POSIX Mode
-Starting Bash with the @samp{--posix} command-line option or executing
+Starting Bash with the @option{--posix} command-line option or executing
@samp{set -o posix} while Bash is running will cause Bash to conform more
-closely to the @sc{POSIX.2} standard by changing the behavior to match that
-specified by @sc{POSIX.2} in areas where the Bash default differs.
+closely to the @sc{posix} standard by changing the behavior to
+match that specified by @sc{posix} in areas where the Bash default differs.
-The following list is what's changed when `@sc{POSIX} mode' is in effect:
+When invoked as @code{sh}, Bash enters @sc{posix} mode after reading the
+startup files.
+
+The following list is what's changed when `@sc{posix} mode' is in effect:
@enumerate
@item
When a command in the hash table no longer exists, Bash will re-search
-@code{$PATH} to find the new location. This is also available with
+@env{$PATH} to find the new location. This is also available with
@samp{shopt -s checkhash}.
@item
-The @samp{>&} redirection does not redirect stdout and stderr.
+The message printed by the job control code and builtins when a job
+exits with a non-zero status is `Done(status)'.
@item
The message printed by the job control code and builtins when a job
-exits with a non-zero status is `Done(status)'.
+is stopped is `Stopped(@var{signame})', where @var{signame} is, for
+example, @code{SIGTSTP}.
@item
-Reserved words may not be aliased.
+The @code{bg} 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.
@item
-The @sc{POSIX.2} @code{PS1} and @code{PS2} expansions of @samp{!} to
-the history number and @samp{!!} to @samp{!} are enabled,
-and parameter expansion is performed on the values of @code{PS1} and
-@code{PS2} regardless of the setting of the @code{promptvars} option.
+Reserved words appearing in a context where reserved words are recognized
+do not undergo alias expansion.
@item
-Interactive comments are enabled by default. (Bash has them on by
-default anyway.)
+The @sc{posix} @env{PS1} and @env{PS2} expansions of @samp{!} to
+the history number and @samp{!!} to @samp{!} are enabled,
+and parameter expansion is performed on the values of @env{PS1} and
+@env{PS2} regardless of the setting of the @code{promptvars} option.
@item
-The @sc{POSIX.2} startup files are executed (@code{$ENV}) rather than
+The @sc{posix} startup files are executed (@env{$ENV}) rather than
the normal Bash files.
@item
@item
The default history file is @file{~/.sh_history} (this is the
-default value of @code{$HISTFILE}).
+default value of @env{$HISTFILE}).
@item
The output of @samp{kill -l} prints all the signal names on a single line,
-separated by spaces.
+separated by spaces, without the @samp{SIG} prefix.
+
+@item
+The @code{kill} builtin does not accept signal names with a @samp{SIG}
+prefix.
@item
Non-interactive shells exit if @var{filename} in @code{.} @var{filename}
in the redirection unless the shell is interactive.
@item
+Redirection operators do not perform word splitting on the word in the
+redirection.
+
+@item
Function names must be valid shell @code{name}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.
@item
-@sc{POSIX.2} `special' builtins are found before shell functions
+@sc{posix} special builtins are found before shell functions
during command lookup.
@item
-If a @sc{POSIX.2} special builtin returns an error status, a
+If a @sc{posix} special builtin returns an error status, a
non-interactive shell exits. The fatal errors are those listed in
-the POSIX.2 standard, and include things like passing incorrect options,
+the POSIX standard, and include things like passing incorrect options,
redirection errors, variable assignment errors for assignments preceding
the command name, and so on.
@item
-If the @code{cd} builtin finds a directory to change to
-using @code{$CDPATH}, the
-value it assigns to the @code{PWD} variable does not contain any
-symbolic links, as if @samp{cd -P} had been executed.
-
-@item
-If @code{$CDPATH} is set, the @code{cd} builtin will not implicitly
+If @env{CDPATH} is set, the @code{cd} builtin will not implicitly
append the current directory to it. This means that @code{cd} will
fail if no valid directory name can be constructed from
-any of the entries in @code{$CDPATH}, even if the a directory with
+any of the entries in @env{$CDPATH}, even if the a directory with
the same name as the name given as an argument to @code{cd} exists
in the current directory.
Process substitution is not available.
@item
-Assignment statements preceding @sc{POSIX.2} special builtins
+Assignment statements preceding @sc{posix} special builtins
persist in the shell environment after the builtin completes.
@item
+Assignment statements preceding shell function calls persist in the
+shell environment after the function returns, as if a @sc{posix}
+special builtin command had been executed.
+
+@item
The @code{export} and @code{readonly} builtin commands display their
-output in the format required by @sc{POSIX.2}.
+output in the format required by @sc{posix}.
+
+@item
+The @code{trap} builtin displays signal names without the leading
+@code{SIG}.
+
+@item
+The @code{trap} 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{-} as the
+first argument.
+
+@item
+The @code{.} and @code{source} builtins do not search the current directory
+for the filename argument if it is not found by searching @env{PATH}.
+
+@item
+Subshells spawned to execute command substitutions inherit the value of
+the @option{-e} option from the parent shell. When not in @sc{posix} mode,
+Bash clears the @option{-e} option in such subshells.
+
+@item
+Alias expansion is always enabled, even in non-interactive shells.
+
+@item
+When the @code{alias} builtin displays alias definitions, it does not
+display them with a leading @samp{alias } unless the @option{-p} option
+is supplied.
+
+@item
+When the @code{set} builtin is invoked without options, it does not display
+shell function names and definitions.
+
+@item
+When the @code{set} builtin is invoked without options, it displays
+variable values without quotes, unless they contain shell metacharacters,
+even if the result contains nonprinting characters.
+
+@item
+When the @code{cd} builtin is invoked in @var{logical} mode, and the pathname
+constructed from @code{$PWD} and the directory name supplied as an argument
+does not refer to an existing directory, @code{cd} will fail instead of
+falling back to @var{physical} mode.
+
+@item
+When the @code{pwd} builtin is supplied the @option{-P} option, it resets
+@code{$PWD} to a pathname containing no symlinks.
+
+@item
+The @code{pwd} 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
+@option{-P} option.
+
+@item
+When listing the history, the @code{fc} builtin does not include an
+indication of whether or not a history entry has been modified.
+
+@item
+The default editor used by @code{fc} is @code{ed}.
+
+@item
+The @code{type} and @code{command} 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{$PATH}.
+
+@item
+The @code{vi} editing mode will invoke the @code{vi} editor directly when
+the @samp{v} command is run, instead of checking @code{$VISUAL} and
+@code{$EDITOR}.
+
+@item
+When the @code{xpg_echo} option is enabled, Bash does not attempt to interpret
+any arguments to @code{echo} as options. Each argument is displayed, after
+escape characters are converted.
+
+@item
+The @code{ulimit} builtin uses a block size of 512 bytes for the @option{-c}
+and @option{-f} options.
@end enumerate
-There is other @sc{POSIX.2} behavior that Bash does not implement.
+There is other @sc{posix} behavior that Bash does not implement by
+default even when in @sc{posix} mode.
Specifically:
@enumerate
+
+@item
+The @code{fc} builtin checks @code{$EDITOR} as a program to edit history
+entries if @code{FCEDIT} is unset, rather than defaulting directly to
+@code{ed}. @code{fc} uses @code{ed} if @code{EDITOR} is unset.
+
@item
-Assignment statements affect the execution environment of all
-builtins, not just special ones.
+As noted above, Bash requires the @code{xpg_echo} option to be enabled for
+the @code{echo} builtin to be fully conformant.
+
@end enumerate
+Bash can be configured to be @sc{posix}-conformant by default, by specifying
+the @option{--enable-strict-posix-default} to @code{configure} when building
+(@pxref{Optional Features}).
+
@node Job Control
@chapter Job Control
[1] 25647
@end example
@noindent
-indicating that this job is job number 1 and that the process @sc{ID}
+indicating that this job is job number 1 and that the process @sc{id}
of the last process in the pipeline associated with this job is
25647. All of the processes in a single pipeline are members of
the same job. Bash uses the @var{job} abstraction as the
basis for job control.
To facilitate the implementation of the user interface to job
-control, the system maintains the notion of a current terminal
-process group @sc{ID}. Members of this process group (processes whose
-process group @sc{ID} is equal to the current terminal process group
-@sc{ID}) receive keyboard-generated signals such as @code{SIGINT}.
+control, the operating system maintains the notion of a current terminal
+process group @sc{id}. Members of this process group (processes whose
+process group @sc{id} is equal to the current terminal process group
+@sc{id}) receive keyboard-generated signals such as @code{SIGINT}.
These processes are said to be in the foreground. Background
-processes are those whose process group @sc{ID} differs from the
+processes are those whose process group @sc{id} 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
takes effect immediately, and has the additional side effect of
causing pending output and typeahead to be discarded.
-There are a number of ways to refer to a job in the shell. The
-character @samp{%} introduces a job name. Job number @code{n}
-may be referred to as @samp{%n}. 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{%ce} refers
-to a stopped @code{ce} job. Using @samp{%?ce}, on the
-other hand, refers to any job containing the string @samp{ce} in
-its command line. If the prefix or substring matches more than one job,
-Bash reports an error. The symbols @samp{%%} and
-@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. The
-previous job may be referenced using @samp{%-}. In output
-pertaining to jobs (e.g., the output of the @code{jobs} command),
-the current job is always flagged with a @samp{+}, and the
-previous job with a @samp{-}.
+There are a number of ways to refer to a job in the shell. The
+character @samp{%} introduces a job specification (@var{jobspec}).
+
+Job number @code{n} may be referred to as @samp{%n}.
+The symbols @samp{%%} and @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{%} (with no accompanying job specification) also refers
+to the current job.
+The previous job may be referenced using @samp{%-}.
+If there is only a single job, @samp{%+} and @samp{%-} can both be used
+to refer to that job.
+In output pertaining to jobs (e.g., the output of the @code{jobs}
+command), the current job is always flagged with a @samp{+}, and the
+previous job with a @samp{-}.
+
+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{%ce} refers
+to a stopped @code{ce} job. Using @samp{%?ce}, on the
+other hand, refers to any job containing the string @samp{ce} in
+its command line. If the prefix or substring matches more than one job,
+Bash reports an error.
+
+Simply naming a job can be used to bring it into the foreground:
+@samp{%1} is a synonym for @samp{fg %1}, bringing job 1 from the
+background into the foreground. Similarly, @samp{%1 &} resumes
+job 1 in the background, equivalent to @samp{bg %1}
+
+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 @option{-b} option to the @code{set} builtin is enabled,
+Bash reports such changes immediately (@pxref{The Set Builtin}).
+Any trap on @code{SIGCHLD} is executed for each child process
+that exits.
+
+If an attempt to exit Bash is made while jobs are stopped, (or running, if
+the @code{checkjobs} option is enabled -- see @ref{The Shopt Builtin}), the
+shell prints a warning message, and if the @code{checkjobs} option is
+enabled, lists the jobs and their statuses.
+The @code{jobs} 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.
+
+@node Job Control Builtins
+@section Job Control Builtins
+
+@table @code
+
+@item bg
+@btindex bg
+@example
+bg [@var{jobspec} @dots{}]
+@end example
+Resume each suspended job @var{jobspec} in the background, as if it
+had been started with @samp{&}.
+If @var{jobspec} 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} was not found or specifies a job
+that was started without job control.
+
+@item fg
+@btindex fg
+@example
+fg [@var{jobspec}]
+@end example
+Resume the job @var{jobspec} in the foreground and make it the current job.
+If @var{jobspec} 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} does not specify a valid job or
+@var{jobspec} specifies a job that was started without job control.
+
+@item jobs
+@btindex jobs
+@example
+jobs [-lnprs] [@var{jobspec}]
+jobs -x @var{command} [@var{arguments}]
+@end example
+
+The first form lists the active jobs. The options have the
+following meanings:
+
+@table @code
+@item -l
+List process @sc{id}s in addition to the normal information.
+
+@item -n
+Display information only about jobs that have changed status since
+the user was last notified of their status.
+
+@item -p
+List only the process @sc{id} of the job's process group leader.
+
+@item -r
+Restrict output to running jobs.
+
+@item -s
+Restrict output to stopped jobs.
+@end table
+
+If @var{jobspec} is given,
+output is restricted to information about that job.
+If @var{jobspec} is not supplied, the status of all jobs is
+listed.
+
+If the @option{-x} option is supplied, @code{jobs} replaces any
+@var{jobspec} found in @var{command} or @var{arguments} with the
+corresponding process group @sc{id}, and executes @var{command},
+passing it @var{argument}s, returning its exit status.
+
+@item kill
+@btindex kill
+@example
+kill [-s @var{sigspec}] [-n @var{signum}] [-@var{sigspec}] @var{jobspec} or @var{pid}
+kill -l [@var{exit_status}]
+@end example
+Send a signal specified by @var{sigspec} or @var{signum} to the process
+named by job specification @var{jobspec} or process @sc{id} @var{pid}.
+@var{sigspec} is either a case-insensitive signal name such as
+@code{SIGINT} (with or without the @code{SIG} prefix)
+or a signal number; @var{signum} is a signal number.
+If @var{sigspec} and @var{signum} are not present, @code{SIGTERM} is used.
+The @option{-l} option lists the signal names.
+If any arguments are supplied when @option{-l} is given, the names of the
+signals corresponding to the arguments are listed, and the return status
+is zero.
+@var{exit_status} 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.
+
+@item wait
+@btindex wait
+@example
+wait [@var{jobspec} or @var{pid} ...]
+@end example
+Wait until the child process specified by each process @sc{id} @var{pid}
+or job specification @var{jobspec} 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} nor @var{pid} specifies an active child process
+of the shell, the return status is 127.
+
+@item disown
+@btindex disown
+@example
+disown [-ar] [-h] [@var{jobspec} @dots{}]
+@end example
+Without options, each @var{jobspec} is removed from the table of
+active jobs.
+If the @option{-h} option is given, the job is not removed from the table,
+but is marked so that @code{SIGHUP} is not sent to the job if the shell
+receives a @code{SIGHUP}.
+If @var{jobspec} is not present, and neither the @option{-a} nor @option{-r}
+option is supplied, the current job is used.
+If no @var{jobspec} is supplied, the @option{-a} option means to remove or
+mark all jobs; the @option{-r} option without a @var{jobspec}
+argument restricts operation to running jobs.
+
+@item suspend
+@btindex suspend
+@example
+suspend [-f]
+@end example
+Suspend the execution of this shell until it receives a
+@code{SIGCONT} signal.
+A login shell cannot be suspended; the @option{-f}
+option can be used to override this and force the suspension.
+
+@end table
+
+When job control is not active, the @code{kill} and @code{wait}
+builtins do not accept @var{jobspec} arguments. They must be
+supplied process @sc{id}s.
+
+@node Job Control Variables
+@section Job Control Variables
+
+@vtable @code
+
+@item auto_resume
+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{exact},
+the string supplied must match the name of a stopped job exactly;
+if set to @samp{substring},
+the string supplied needs to match a substring of the name of a
+stopped job. The @samp{substring} value provides functionality
+analogous to the @samp{%?} job @sc{id} (@pxref{Job Control Basics}).
+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{%} job @sc{id}.
+
+@end vtable
+
+@set readline-appendix
+@set history-appendix
+@cindex Readline, how to use
+@include rluser.texi
+@cindex History, how to use
+@include hsuser.texi
+@clear readline-appendix
+@clear history-appendix
+
+@node Installing Bash
+@chapter Installing Bash
+
+This chapter provides basic instructions for installing Bash on
+the various supported platforms. The distribution supports the
+@sc{gnu} operating systems, nearly every version of Unix, and several
+non-Unix systems such as BeOS and Interix.
+Other independent ports exist for
+@sc{ms-dos}, @sc{os/2}, and Windows platforms.
+
+@menu
+* Basic Installation:: Installation instructions.
+* Compilers and Options:: How to set special options for various
+ systems.
+* Compiling For Multiple Architectures:: How to compile Bash for more
+ than one kind of system from
+ the same source tree.
+* Installation Names:: How to set the various paths used by the installation.
+* Specifying the System Type:: How to configure Bash for a particular system.
+* Sharing Defaults:: How to share default configuration values among GNU
+ programs.
+* Operation Controls:: Options recognized by the configuration program.
+* Optional Features:: How to enable and disable optional features when
+ building Bash.
+@end menu
+
+@node Basic Installation
+@section Basic Installation
+@cindex installation
+@cindex configuration
+@cindex Bash installation
+@cindex Bash configuration
+
+These are installation instructions for Bash.
+
+The simplest way to compile Bash is:
+
+@enumerate
+@item
+@code{cd} to the directory containing the source code and type
+@samp{./configure} to configure Bash for your system. If you're
+using @code{csh} on an old version of System V, you might need to
+type @samp{sh ./configure} instead to prevent @code{csh} from trying
+to execute @code{configure} itself.
+
+Running @code{configure} takes some time.
+While running, it prints messages telling which features it is
+checking for.
+
+@item
+Type @samp{make} to compile Bash and build the @code{bashbug} bug
+reporting script.
+
+@item
+Optionally, type @samp{make tests} to run the Bash test suite.
+
+@item
+Type @samp{make install} to install @code{bash} and @code{bashbug}.
+This will also install the manual pages and Info file.
+
+@end enumerate
+
+The @code{configure} shell script attempts to guess correct
+values for various system-dependent variables used during
+compilation. It uses those values to create a @file{Makefile} in
+each directory of the package (the top directory, the
+@file{builtins}, @file{doc}, and @file{support} directories,
+each directory under @file{lib}, and several others). It also creates a
+@file{config.h} file containing system-dependent definitions.
+Finally, it creates a shell script named @code{config.status} that you
+can run in the future to recreate the current configuration, a
+file @file{config.cache} that saves the results of its tests to
+speed up reconfiguring, and a file @file{config.log} containing
+compiler output (useful mainly for debugging @code{configure}).
+If at some point
+@file{config.cache} contains results you don't want to keep, you
+may remove or edit it.
+
+To find out more about the options and arguments that the
+@code{configure} script understands, type
+
+@example
+bash-2.04$ ./configure --help
+@end example
+
+@noindent
+at the Bash prompt in your Bash source directory.
+
+If you need to do unusual things to compile Bash, please
+try to figure out how @code{configure} could check whether or not
+to do them, and mail diffs or instructions to
+@email{bash-maintainers@@gnu.org} so they can be
+considered for the next release.
+
+The file @file{configure.in} is used to create @code{configure}
+by a program called Autoconf. You only need
+@file{configure.in} if you want to change it or regenerate
+@code{configure} using a newer version of Autoconf. If
+you do this, make sure you are using Autoconf version 2.50 or
+newer.
+
+You can remove the program binaries and object files from the
+source code directory by typing @samp{make clean}. To also remove the
+files that @code{configure} created (so you can compile Bash for
+a different kind of computer), type @samp{make distclean}.
+
+@node Compilers and Options
+@section Compilers and Options
+
+Some systems require unusual options for compilation or linking
+that the @code{configure} script does not know about. You can
+give @code{configure} 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:
+
+@example
+CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure
+@end example
+
+On systems that have the @code{env} program, you can do it like this:
+
+@example
+env CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure
+@end example
+
+The configuration process uses GCC to build Bash if it
+is available.
+
+@node Compiling For Multiple Architectures
+@section Compiling For Multiple Architectures
+
+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} that
+supports the @code{VPATH} variable, such as GNU @code{make}.
+@code{cd} to the
+directory where you want the object files and executables to go and run
+the @code{configure} script from the source directory. You may need to
+supply the @option{--srcdir=PATH} argument to tell @code{configure} where the
+source files are. @code{configure} automatically checks for the
+source code in the directory that @code{configure} is in and in `..'.
+
+If you have to use a @code{make} that does not supports the @code{VPATH}
+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{make distclean} before
+reconfiguring for another architecture.
+
+Alternatively, if your system supports symbolic links, you can use the
+@file{support/mkclone} 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 @file{/usr/gnu/src/bash-2.0}:
+
+@example
+bash /usr/gnu/src/bash-2.0/support/mkclone -s /usr/gnu/src/bash-2.0 .
+@end example
+
+@noindent
+The @code{mkclone} script requires Bash, so you must have already built
+Bash for at least one architecture before you can create build
+directories for other architectures.
+
+@node Installation Names
+@section Installation Names
+
+By default, @samp{make install} will install into
+@file{/usr/local/bin}, @file{/usr/local/man}, etc. You can
+specify an installation prefix other than @file{/usr/local} by
+giving @code{configure} the option @option{--prefix=@var{PATH}},
+or by specifying a value for the @code{DESTDIR} @samp{make}
+variable when running @samp{make install}.
+
+You can specify separate installation prefixes for
+architecture-specific files and architecture-independent files.
+If you give @code{configure} the option
+@option{--exec-prefix=@var{PATH}}, @samp{make install} will use
+@var{PATH} as the prefix for installing programs and libraries.
+Documentation and other data files will still use the regular prefix.
+
+@node Specifying the System Type
+@section Specifying the System Type
+
+There may be some features @code{configure} can not figure out
+automatically, but need to determine by the type of host Bash
+will run on. Usually @code{configure} can figure that
+out, but if it prints a message saying it can not guess the host
+type, give it the @option{--host=TYPE} option. @samp{TYPE} can
+either be a short name for the system type, such as @samp{sun4},
+or a canonical name with three fields: @samp{CPU-COMPANY-SYSTEM}
+(e.g., @samp{i386-unknown-freebsd4.2}).
+
+See the file @file{support/config.sub} for the possible
+values of each field.
+
+@node Sharing Defaults
+@section Sharing Defaults
+
+If you want to set default values for @code{configure} scripts to
+share, you can create a site shell script called
+@code{config.site} that gives default values for variables like
+@code{CC}, @code{cache_file}, and @code{prefix}. @code{configure}
+looks for @file{PREFIX/share/config.site} if it exists, then
+@file{PREFIX/etc/config.site} if it exists. Or, you can set the
+@code{CONFIG_SITE} environment variable to the location of the site
+script. A warning: the Bash @code{configure} looks for a site script,
+but not all @code{configure} scripts do.
+
+@node Operation Controls
+@section Operation Controls
+
+@code{configure} recognizes the following options to control how it
+operates.
+
+@table @code
+
+@item --cache-file=@var{file}
+Use and save the results of the tests in
+@var{file} instead of @file{./config.cache}. Set @var{file} to
+@file{/dev/null} to disable caching, for debugging
+@code{configure}.
+
+@item --help
+Print a summary of the options to @code{configure}, and exit.
+
+@item --quiet
+@itemx --silent
+@itemx -q
+Do not print messages saying which checks are being made.
+
+@item --srcdir=@var{dir}
+Look for the Bash source code in directory @var{dir}. Usually
+@code{configure} can determine that directory automatically.
+
+@item --version
+Print the version of Autoconf used to generate the @code{configure}
+script, and exit.
+@end table
+
+@code{configure} also accepts some other, not widely used, boilerplate
+options. @samp{configure --help} prints the complete list.
+
+@node Optional Features
+@section Optional Features
+
+The Bash @code{configure} has a number of @option{--enable-@var{feature}}
+options, where @var{feature} indicates an optional part of Bash.
+There are also several @option{--with-@var{package}} options,
+where @var{package} is something like @samp{bash-malloc} or @samp{purify}.
+To turn off the default use of a package, use
+@option{--without-@var{package}}. To configure Bash without a feature
+that is enabled by default, use @option{--disable-@var{feature}}.
+
+Here is a complete list of the @option{--enable-} and
+@option{--with-} options that the Bash @code{configure} recognizes.
+
+@table @code
+@item --with-afs
+Define if you are using the Andrew File System from Transarc.
+
+@item --with-bash-malloc
+Use the Bash version of
+@code{malloc} in the directory @file{lib/malloc}. This is not the same
+@code{malloc} that appears in @sc{gnu} libc, but an older version
+originally derived from the 4.2 @sc{bsd} @code{malloc}. This @code{malloc}
+is very fast, but wastes some space on each allocation.
+This option is enabled by default.
+The @file{NOTES} file contains a list of systems for
+which this should be turned off, and @code{configure} disables this
+option automatically for a number of systems.
+
+@item --with-curses
+Use the curses library instead of the termcap library. This should
+be supplied if your system has an inadequate or incomplete termcap
+database.
+
+@item --with-gnu-malloc
+A synonym for @code{--with-bash-malloc}.
+
+@item --with-installed-readline[=@var{PREFIX}]
+Define this to make Bash link with a locally-installed version of Readline
+rather than the version in @file{lib/readline}. This works only with
+Readline 5.0 and later versions. If @var{PREFIX} is @code{yes} or not
+supplied, @code{configure} uses the values of the make variables
+@code{includedir} and @code{libdir}, which are subdirectories of @code{prefix}
+by default, to find the installed version of Readline if it is not in
+the standard system include and library directories.
+If @var{PREFIX} is @code{no}, Bash links with the version in
+@file{lib/readline}.
+If @var{PREFIX} is set to any other value, @code{configure} treats it as
+a directory pathname and looks for
+the installed version of Readline in subdirectories of that directory
+(include files in @var{PREFIX}/@code{include} and the library in
+@var{PREFIX}/@code{lib}).
+
+@item --with-purify
+Define this to use the Purify memory allocation checker from Rational
+Software.
+
+@item --enable-minimal-config
+This produces a shell with minimal features, close to the historical
+Bourne shell.
+@end table
+
+There are several @option{--enable-} options that alter how Bash is
+compiled and linked, rather than changing run-time features.
+
+@table @code
+@item --enable-largefile
+Enable support for @uref{http://www.sas.com/standards/large_file/x_open.20Mar96.html,
+large files} 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.
+
+@item --enable-profiling
+This builds a Bash binary that produces profiling information to be
+processed by @code{gprof} each time it is executed.
+
+@item --enable-static-link
+This causes Bash to be linked statically, if @code{gcc} is being used.
+This could be used to build a version to use as root's shell.
+@end table
+
+The @samp{minimal-config} option can be used to disable all of
+the following options, but it is processed first, so individual
+options may be enabled using @samp{enable-@var{feature}}.
+
+All of the following options except for @samp{disabled-builtins} and
+@samp{xpg-echo-default} are
+enabled by default, unless the operating system does not provide the
+necessary support.
-Simply naming a job can be used to bring it into the foreground:
-@samp{%1} is a synonym for @samp{fg %1}, bringing job 1 from the
-background into the foreground. Similarly, @samp{%1 &} resumes
-job 1 in the background, equivalent to @samp{bg %1}
+@table @code
+@item --enable-alias
+Allow alias expansion and include the @code{alias} and @code{unalias}
+builtins (@pxref{Aliases}).
-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
-the @samp{-b} option to the @code{set} builtin is enabled,
-Bash reports such changes immediately (@pxref{The Set Builtin}).
+@item --enable-arith-for-command
+Include support for the alternate form of the @code{for} command
+that behaves like the C language @code{for} statement
+(@pxref{Looping Constructs}).
-If an attempt to exit Bash is while jobs are stopped, the
-shell prints a message warning that there are stopped jobs.
-The @code{jobs} 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 the stopped jobs are terminated.
+@item --enable-array-variables
+Include support for one-dimensional array shell variables
+(@pxref{Arrays}).
-@node Job Control Builtins
-@section Job Control Builtins
+@item --enable-bang-history
+Include support for @code{csh}-like history substitution
+(@pxref{History Interaction}).
-@table @code
+@item --enable-brace-expansion
+Include @code{csh}-like brace expansion
+( @code{b@{a,b@}c} @expansion{} @code{bac bbc} ).
+See @ref{Brace Expansion}, for a complete description.
-@item bg
-@btindex bg
-@example
-bg [@var{jobspec}]
-@end example
-Resume the suspended job @var{jobspec} in the background, as if it
-had been started with @samp{&}.
-If @var{jobspec} 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, if @var{jobspec} was
-not found or @var{jobspec} specifies a job that was started without
-job control.
+@item --enable-casemod-attributes
+Include support for case-modifying attributes in the @code{declare} builtin
+and assignment statements. Variables with the @var{uppercase} attribute,
+for example, will have their values converted to uppercase upon assignment.
-@item fg
-@btindex fg
-@example
-fg [@var{jobspec}]
-@end example
-Resume the job @var{jobspec} in the foreground and make it the current job.
-If @var{jobspec} 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} does not specify a valid job or
-@var{jobspec} specifies a job that was started without job control.
+@item --enable-casemod-expansion
+Include support for case-modifying word expansions.
-@item jobs
-@btindex jobs
-@example
-jobs [-lpnrs] [@var{jobspec}]
-jobs -x @var{command} [@var{arguments}]
-@end example
+@item --enable-command-timing
+Include support for recognizing @code{time} as a reserved word and for
+displaying timing statistics for the pipeline following @code{time}
+(@pxref{Pipelines}).
+This allows pipelines as well as shell builtins and functions to be timed.
-The first form lists the active jobs. The options have the
-following meanings:
+@item --enable-cond-command
+Include support for the @code{[[} conditional command.
+(@pxref{Conditional Constructs}).
-@table @code
-@item -l
-List process @sc{ID}s in addition to the normal information.
+@item --enable-cond-regexp
+Include support for matching POSIX regular expressions using the
+@samp{=~} binary operator in the @code{[[} conditional command.
+(@pxref{Conditional Constructs}).
-@item -n
-Display information only about jobs that have changed status since
-the user was last notified of their status.
+@item --enable-coprocesses
+Include support for coprocesses and the @code{coproc} reserved word
+(@pxref{Pipelines}).
-@item -p
-List only the process @sc{ID} of the job's process group leader.
+@item --enable-debugger
+Include support for the bash debugger (distributed separately).
-@item -r
-Restrict output to running jobs.
+@item --enable-directory-stack
+Include support for a @code{csh}-like directory stack and the
+@code{pushd}, @code{popd}, and @code{dirs} builtins
+(@pxref{The Directory Stack}).
-@item -s
-Restrict output to stopped jobs.
-@end table
+@item --enable-disabled-builtins
+Allow builtin commands to be invoked via @samp{builtin xxx}
+even after @code{xxx} has been disabled using @samp{enable -n xxx}.
+See @ref{Bash Builtins}, for details of the @code{builtin} and
+@code{enable} builtin commands.
-If @var{jobspec} is given,
-output is restricted to information about that job.
-If @var{jobspec} is not supplied, the status of all jobs is
-listed.
+@item --enable-dparen-arithmetic
+Include support for the @code{((@dots{}))} command
+(@pxref{Conditional Constructs}).
-If the @samp{-x} option is supplied, @code{jobs} replaces any
-@var{jobspec} found in @var{command} or @var{arguments} with the
-corresponding process group @sc{ID}, and executes @var{command},
-passing it @var{argument}s, returning its exit status.
+@item --enable-extended-glob
+Include support for the extended pattern matching features described
+above under @ref{Pattern Matching}.
-@item kill
-@btindex kill
-@example
-kill [-s @var{sigspec}] [-n @var{signum}] [-@var{sigspec}] @var{jobspec} or @var{pid}
-kill -l [@var{exit_status}]
-@end example
-Send a signal specified by @var{sigspec} or @var{signum} to the process
-named by job specification @var{jobspec} or process ID @var{pid}.
-@var{sigspec} is either a signal name such as @code{SIGINT} (with or without
-the @code{SIG} prefix) or a signal number; @var{signum} is a signal number.
-If @var{sigspec} and @var{signum} are not present, @code{SIGTERM} is used.
-The @samp{-l} option lists the signal names.
-If any arguments are supplied when @samp{-l} is given, the names of the
-signals corresponding to the arguments are listed, and the return status
-is zero.
-@var{exit_status} 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.
+@item --enable-help-builtin
+Include the @code{help} builtin, which displays help on shell builtins and
+variables (@pxref{Bash Builtins}).
-@item wait
-@btindex wait
-@example
-wait [@var{jobspec}|@var{pid}]
-@end example
-Wait until the child process specified by process @sc{ID} @var{pid} or job
-specification @var{jobspec} 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} nor @var{pid} specifies an active child process
-of the shell, the return status is 127.
+@item --enable-history
+Include command history and the @code{fc} and @code{history}
+builtin commands (@pxref{Bash History Facilities}).
-@item disown
-@btindex disown
-@example
-disown [-ar] [-h] [@var{jobspec} @dots{}]
-@end example
-Without options, each @var{jobspec} is removed from the table of
-active jobs.
-If the @samp{-h} option is given, the job is not removed from the table,
-but is marked so that @code{SIGHUP} is not sent to the job if the shell
-receives a @code{SIGHUP}.
-If @var{jobspec} is not present, and neither the @samp{-a} nor @samp{-r}
-option is supplied, the current job is used.
-If no @var{jobspec} is supplied, the @samp{-a} option means to remove or
-mark all jobs; the @samp{-r} option without a @var{jobspec}
-argument restricts operation to running jobs.
+@item --enable-job-control
+This enables the job control features (@pxref{Job Control}),
+if the operating system supports them.
-@item suspend
-@btindex suspend
-@example
-suspend [-f]
-@end example
-Suspend the execution of this shell until it receives a
-@code{SIGCONT} signal. The @samp{-f} option means to suspend
-even if the shell is a login shell.
+@item --enable-multibyte
+This enables support for multibyte characters if the operating
+system provides the necessary support.
-@end table
+@item --enable-net-redirections
+This enables the special handling of filenames of the form
+@code{/dev/tcp/@var{host}/@var{port}} and
+@code{/dev/udp/@var{host}/@var{port}}
+when used in redirections (@pxref{Redirections}).
-When job control is not active, the @code{kill} and @code{wait}
-builtins do not accept @var{jobspec} arguments. They must be
-supplied process @sc{ID}s.
+@item --enable-process-substitution
+This enables process substitution (@pxref{Process Substitution}) if
+the operating system provides the necessary support.
-@node Job Control Variables
-@section Job Control Variables
+@item --enable-progcomp
+Enable the programmable completion facilities
+(@pxref{Programmable Completion}).
+If Readline is not enabled, this option has no effect.
-@vtable @code
+@item --enable-prompt-string-decoding
+Turn on the interpretation of a number of backslash-escaped characters
+in the @env{$PS1}, @env{$PS2}, @env{$PS3}, and @env{$PS4} prompt
+strings. See @ref{Printing a Prompt}, for a complete list of prompt
+string escape sequences.
-@item auto_resume
-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{exact},
-the string supplied must match the name of a stopped job exactly;
-if set to @samp{substring},
-the string supplied needs to match a substring of the name of a
-stopped job. The @samp{substring} value provides functionality
-analogous to the @samp{%?} job @sc{ID} (@pxref{Job Control Basics}).
-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{%} job @sc{ID}.
+@item --enable-readline
+Include support for command-line editing and history with the Bash
+version of the Readline library (@pxref{Command Line Editing}).
-@end vtable
+@item --enable-restricted
+Include support for a @dfn{restricted shell}. If this is enabled, Bash,
+when called as @code{rbash}, enters a restricted mode. See
+@ref{The Restricted Shell}, for a description of restricted mode.
-@set readline-appendix
-@set history-appendix
-@cindex History, how to use
-@include hsuser.texinfo
-@cindex Readline, how to use
-@include rluser.texinfo
-@clear readline-appendix
-@clear history-appendix
+@item --enable-select
+Include the @code{select} builtin, which allows the generation of simple
+menus (@pxref{Conditional Constructs}).
-@node Installing Bash
-@chapter Installing Bash
+@item --enable-separate-helpfiles
+Use external files for the documentation displayed by the @code{help} builtin
+instead of storing the text internally.
-This chapter provides basic instructions for installing Bash on
-the various supported platforms. The distribution supports nearly every
-version of Unix (and, someday, @sc{GNU}). Other independent ports exist for
-@sc{MS-DOS}, @sc{OS/2}, Windows @sc{95}, and Windows @sc{NT}.
+@item --enable-single-help-strings
+Store the text displayed by the @code{help} 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.
-@menu
-* Basic Installation:: Installation instructions.
+@item --enable-strict-posix-default
+Make Bash @sc{posix}-conformant by default (@pxref{Bash POSIX Mode}).
-* Compilers and Options:: How to set special options for various
- systems.
+@item --enable-usg-echo-default
+A synonym for @code{--enable-xpg-echo-default}.
-* Compiling For Multiple Architectures:: How to compile Bash for more
- than one kind of system from
- the same source tree.
+@item --enable-xpg-echo-default
+Make the @code{echo} builtin expand backslash-escaped characters by default,
+without requiring the @option{-e} option.
+This sets the default value of the @code{xpg_echo} shell option to @code{on},
+which makes the Bash @code{echo} behave more like the version specified in
+the Single Unix Specification, version 3.
+@xref{Bash Builtins}, for a description of the escape sequences that
+@code{echo} recognizes.
-* Installation Names:: How to set the various paths used by the installation.
+@end table
-* Specifying the System Type:: How to configure Bash for a particular system.
+The file @file{config-top.h} contains C Preprocessor
+@samp{#define} statements for options which are not settable from
+@code{configure}.
+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.
-* Sharing Defaults:: How to share default configuration values among GNU
- programs.
+@node Reporting Bugs
+@appendix Reporting Bugs
-* Operation Controls:: Options recognized by the configuration program.
+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
+@uref{ftp://ftp.gnu.org/pub/bash/}.
-* Optional Features:: How to enable and disable optional features when
- building Bash.
-@end menu
+Once you have determined that a bug actually exists, use the
+@code{bashbug} 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 @email{bug-bash@@gnu.org} or posted to the Usenet
+newsgroup @code{gnu.bash.bug}.
-@node Basic Installation
-@section Basic Installation
-@cindex installation
-@cindex configuration
-@cindex Bash installation
-@cindex Bash configuration
+All bug reports should include:
+@itemize @bullet
+@item
+The version number of Bash.
+@item
+The hardware and operating system.
+@item
+The compiler used to compile Bash.
+@item
+A description of the bug behaviour.
+@item
+A short script or `recipe' which exercises the bug and may be used
+to reproduce it.
+@end itemize
+
+@noindent
+@code{bashbug} inserts the first three items automatically into
+the template it provides for filing a bug report.
+
+Please send all reports concerning this manual to
+@email{chet@@po.CWRU.Edu}.
-These are installation instructions for Bash.
+@node Major Differences From The Bourne Shell
+@appendix Major Differences From The Bourne Shell
-The @code{configure} shell script attempts to guess correct
-values for various system-dependent variables used during
-compilation. It uses those values to create a @file{Makefile} in
-each directory of the package (the top directory, the
-@file{builtins} and @file{doc} directories, and the
-each directory under @file{lib}). It also creates a
-@file{config.h} file containing system-dependent definitions.
-Finally, it creates a shell script named @code{config.status} that you
-can run in the future to recreate the current configuration, a
-file @file{config.cache} that saves the results of its tests to
-speed up reconfiguring, and a file @file{config.log} containing
-compiler output (useful mainly for debugging @code{configure}).
-If at some point
-@file{config.cache} contains results you don't want to keep, you
-may remove or edit it.
+Bash implements essentially the same grammar, parameter and
+variable expansion, redirection, and quoting as the Bourne Shell.
+Bash uses the @sc{posix} standard as the specification of
+how these features are to be implemented. There are some
+differences between the traditional Bourne shell and Bash; this
+section quickly details the differences of significance. A
+number of these differences are explained in greater depth in
+previous sections.
+This section uses the version of @code{sh} included in SVR4.2 (the
+last version of the historical Bourne shell) as the baseline reference.
-If you need to do unusual things to compile Bash, please
-try to figure out how @code{configure} could check whether or not
-to do them, and mail diffs or instructions to
-@email{bash-maintainers@@gnu.org} so they can be
-considered for the next release.
+@itemize @bullet
-The file @file{configure.in} is used to create @code{configure}
-by a program called Autoconf. You only need
-@file{configure.in} if you want to change it or regenerate
-@code{configure} using a newer version of Autoconf. If
-you do this, make sure you are using Autoconf version 2.10 or
-newer.
+@item
+Bash is @sc{posix}-conformant, even where the @sc{posix} specification
+differs from traditional @code{sh} behavior (@pxref{Bash POSIX Mode}).
-If you need to change @file{configure.in} or regenerate
-@code{configure}, you will need to create two files:
-@file{_distribution} and @file{_patchlevel}. @file{_distribution}
-should contain the major and minor version numbers of the Bash
-distribution, for example @samp{2.01}. @file{_patchlevel} should
-contain the patch level of the Bash distribution, @samp{0} for
-example. The script @file{support/mkconffiles} has been provided
-to automate the creation of these files.
+@item
+Bash has multi-character invocation options (@pxref{Invoking Bash}).
-The simplest way to compile Bash is:
+@item
+Bash has command-line editing (@pxref{Command Line Editing}) and
+the @code{bind} builtin.
-@enumerate
@item
-@code{cd} to the directory containing the source code and type
-@samp{./configure} to configure Bash for your system. If you're
-using @code{csh} on an old version of System V, you might need to
-type @samp{sh ./configure} instead to prevent @code{csh} from trying
-to execute @code{configure} itself.
+Bash provides a programmable word completion mechanism
+(@pxref{Programmable Completion}), and builtin commands
+@code{complete}, @code{compgen}, and @code{compopt}, to
+manipulate it.
-Running @code{configure} takes awhile. While running, it prints some
-messages telling which features it is checking for.
+@item
+Bash has command history (@pxref{Bash History Facilities}) and the
+@code{history} and @code{fc} builtins to manipulate it.
+The Bash history list maintains timestamp information and uses the
+value of the @code{HISTTIMEFORMAT} variable to display it.
@item
-Type @samp{make} to compile Bash and build the @code{bashbug} bug
-reporting script.
+Bash implements @code{csh}-like history expansion
+(@pxref{History Interaction}).
@item
-Optionally, type @samp{make tests} to run the Bash test suite.
+Bash has one-dimensional array variables (@pxref{Arrays}), 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.
@item
-Type @samp{make install} to install @code{bash} and @code{bashbug}.
-This will also install the manual pages and Info file.
+The @code{$'@dots{}'} quoting syntax, which expands ANSI-C
+backslash-escaped characters in the text between the single quotes,
+is supported (@pxref{ANSI-C Quoting}).
-@end enumerate
+@item
+Bash supports the @code{$"@dots{}"} quoting syntax to do
+locale-specific translation of the characters between the double
+quotes. The @option{-D}, @option{--dump-strings}, and @option{--dump-po-strings}
+invocation options list the translatable strings found in a script
+(@pxref{Locale Translation}).
-You can remove the program binaries and object files from the
-source code directory by typing @samp{make clean}. To also remove the
-files that @code{configure} created (so you can compile Bash for
-a different kind of computer), type @samp{make distclean}.
+@item
+Bash implements the @code{!} keyword to negate the return value of
+a pipeline (@pxref{Pipelines}).
+Very useful when an @code{if} statement needs to act only if a test fails.
+The Bash @samp{-o pipefail} option to @code{set} will cause a pipeline to
+return a failure status if any command fails.
-@node Compilers and Options
-@section Compilers and Options
+@item
+Bash has the @code{time} reserved word and command timing (@pxref{Pipelines}).
+The display of the timing statistics may be controlled with the
+@env{TIMEFORMAT} variable.
-Some systems require unusual options for compilation or linking
-that the @code{configure} script does not know about. You can
-give @code{configure} 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:
+@item
+Bash implements the @code{for (( @var{expr1} ; @var{expr2} ; @var{expr3} ))}
+arithmetic for command, similar to the C language (@pxref{Looping Constructs}).
-@example
-CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure
-@end example
+@item
+Bash includes the @code{select} compound command, which allows the
+generation of simple menus (@pxref{Conditional Constructs}).
-On systems that have the @code{env} program, you can do it like this:
+@item
+Bash includes the @code{[[} compound command, which makes conditional
+testing part of the shell grammar (@pxref{Conditional Constructs}), including
+optional regular expression matching.
-@example
-env CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure
-@end example
+@item
+Bash provides optional case-insensitive matching for the @code{case} and
+@code{[[} constructs.
-The configuration process uses GCC to build Bash if it
-is available.
+@item
+Bash includes brace expansion (@pxref{Brace Expansion}) and tilde
+expansion (@pxref{Tilde Expansion}).
-@node Compiling For Multiple Architectures
-@section Compiling For Multiple Architectures
+@item
+Bash implements command aliases and the @code{alias} and @code{unalias}
+builtins (@pxref{Aliases}).
-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} that
-supports the @code{VPATH} variable, such as GNU @code{make}.
-@code{cd} to the
-directory where you want the object files and executables to go and run
-the @code{configure} script from the source directory. You may need to
-supply the @samp{--srcdir=PATH} argument to tell @code{configure} where the
-source files are. @code{configure} automatically checks for the
-source code in the directory that @code{configure} is in and in `..'.
+@item
+Bash provides shell arithmetic, the @code{((} compound command
+(@pxref{Conditional Constructs}),
+and arithmetic expansion (@pxref{Shell Arithmetic}).
-If you have to use a @code{make} that does not supports the @code{VPATH}
-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{make distclean} before
-reconfiguring for another architecture.
+@item
+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}
+command.
-Alternatively, if your system supports symbolic links, you can use the
-@file{support/mkclone} 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 @file{/usr/gnu/src/bash-2.0}:
+@item
+Bash supports the @samp{+=} assignment operator, which appends to the value
+of the variable named on the left hand side.
-@example
-bash /usr/gnu/src/bash-2.0/support/mkclone -s /usr/gnu/src/bash-2.0 .
-@end example
+@item
+Bash includes the @sc{posix} pattern removal @samp{%}, @samp{#}, @samp{%%}
+and @samp{##} expansions to remove leading or trailing substrings from
+variable values (@pxref{Shell Parameter Expansion}).
-@noindent
-The @code{mkclone} script requires Bash, so you must have already built
-Bash for at least one architecture before you can create build
-directories for other architectures.
+@item
+The expansion @code{$@{#xx@}}, which returns the length of @code{$@{xx@}},
+is supported (@pxref{Shell Parameter Expansion}).
-@node Installation Names
-@section Installation Names
+@item
+The expansion @code{$@{var:}@var{offset}@code{[:}@var{length}@code{]@}},
+which expands to the substring of @code{var}'s value of length
+@var{length}, beginning at @var{offset}, is present
+(@pxref{Shell Parameter Expansion}).
-By default, @samp{make install} will install into
-@file{/usr/local/bin}, @file{/usr/local/man}, etc. You can
-specify an installation prefix other than @file{/usr/local} by
-giving @code{configure} the option @samp{--prefix=PATH}.
+@item
+The expansion
+@code{$@{var/[/]}@var{pattern}@code{[/}@var{replacement}@code{]@}},
+which matches @var{pattern} and replaces it with @var{replacement} in
+the value of @code{var}, is available (@pxref{Shell Parameter Expansion}).
-You can specify separate installation prefixes for
-architecture-specific files and architecture-independent files.
-If you give @code{configure} the option
-@samp{--exec-prefix=PATH}, @samp{make install} will use @samp{PATH} as the
-prefix for installing programs and libraries. Documentation and
-other data files will still use the regular prefix.
+@item
+The expansion @code{$@{!@var{prefix@}*}} expansion, which expands to
+the names of all shell variables whose names begin with @var{prefix},
+is available (@pxref{Shell Parameter Expansion}).
-@node Specifying the System Type
-@section Specifying the System Type
+@item
+Bash has @var{indirect} variable expansion using @code{$@{!word@}}
+(@pxref{Shell Parameter Expansion}).
-There may be some features @code{configure} can not figure out
-automatically, but needs to determine by the type of host Bash
-will run on. Usually @code{configure} can figure that
-out, but if it prints a message saying it can not guess the host
-type, give it the @samp{--host=TYPE} option. @samp{TYPE} can
-either be a short name for the system type, such as @samp{sun4},
-or a canonical name with three fields: @samp{CPU-COMPANY-SYSTEM}
-(e.g., @samp{sparc-sun-sunos4.1.2}).
+@item
+Bash can expand positional parameters beyond @code{$9} using
+@code{$@{@var{num}@}}.
-@noindent See the file @file{support/config.sub} for the possible
-values of each field.
+@item
+The @sc{posix} @code{$()} form of command substitution
+is implemented (@pxref{Command Substitution}),
+and preferred to the Bourne shell's @code{``} (which
+is also implemented for backwards compatibility).
-@node Sharing Defaults
-@section Sharing Defaults
+@item
+Bash has process substitution (@pxref{Process Substitution}).
-If you want to set default values for @code{configure} scripts to
-share, you can create a site shell script called
-@code{config.site} that gives default values for variables like
-@code{CC}, @code{cache_file}, and @code{prefix}. @code{configure}
-looks for @file{PREFIX/share/config.site} if it exists, then
-@file{PREFIX/etc/config.site} if it exists. Or, you can set the
-@code{CONFIG_SITE} environment variable to the location of the site
-script. A warning: the Bash @code{configure} looks for a site script,
-but not all @code{configure} scripts do.
+@item
+Bash automatically assigns variables that provide information about the
+current user (@env{UID}, @env{EUID}, and @env{GROUPS}), the current host
+(@env{HOSTTYPE}, @env{OSTYPE}, @env{MACHTYPE}, and @env{HOSTNAME}),
+and the instance of Bash that is running (@env{BASH},
+@env{BASH_VERSION}, and @env{BASH_VERSINFO}). @xref{Bash Variables},
+for details.
-@node Operation Controls
-@section Operation Controls
+@item
+The @env{IFS} variable is used to split only the results of expansion,
+not all words (@pxref{Word Splitting}).
+This closes a longstanding shell security hole.
-@code{configure} recognizes the following options to control how it
-operates.
+@item
+Bash implements the full set of @sc{posix} filename expansion operators,
+including @var{character classes}, @var{equivalence classes}, and
+@var{collating symbols} (@pxref{Filename Expansion}).
-@table @code
+@item
+Bash implements extended pattern matching features when the @code{extglob}
+shell option is enabled (@pxref{Pattern Matching}).
-@item --cache-file=@var{FILE}
-Use and save the results of the tests in
-@var{FILE} instead of @file{./config.cache}. Set @var{FILE} to
-@file{/dev/null} to disable caching, for debugging
-@code{configure}.
+@item
+It is possible to have a variable and a function with the same name;
+@code{sh} does not separate the two name spaces.
-@item --help
-Print a summary of the options to @code{configure}, and exit.
+@item
+Bash functions are permitted to have local variables using the
+@code{local} builtin, and thus useful recursive functions may be written
+(@pxref{Bash Builtins}).
-@item --quiet
-@itemx --silent
-@itemx -q
-Do not print messages saying which checks are being made.
+@item
+Variable assignments preceding commands affect only that command, even
+builtins and functions (@pxref{Environment}).
+In @code{sh}, all variable assignments
+preceding commands are global unless the command is executed from the
+file system.
-@item --srcdir=@var{DIR}
-Look for the Bash source code in directory @var{DIR}. Usually
-@code{configure} can determine that directory automatically.
+@item
+Bash performs filename expansion on filenames specified as operands
+to input and output redirection operators (@pxref{Redirections}).
-@item --version
-Print the version of Autoconf used to generate the @code{configure}
-script, and exit.
-@end table
+@item
+Bash contains the @samp{<>} redirection operator, allowing a file to be
+opened for both reading and writing, and the @samp{&>} redirection
+operator, for directing standard output and standard error to the same
+file (@pxref{Redirections}).
+
+@item
+Bash includes the @samp{<<<} redirection operator, allowing a string to
+be used as the standard input to a command.
+
+@item
+Bash implements the @samp{[n]<&@var{word}} and @samp{[n]>&@var{word}}
+redirection operators, which move one file descriptor to another.
-@code{configure} also accepts some other, not widely used, boilerplate
-options.
+@item
+Bash treats a number of filenames specially when they are
+used in redirection operators (@pxref{Redirections}).
-@node Optional Features
-@section Optional Features
+@item
+Bash can open network connections to arbitrary machines and services
+with the redirection operators (@pxref{Redirections}).
-The Bash @code{configure} has a number of @samp{--enable-@var{FEATURE}}
-options, where @var{FEATURE} indicates an optional part of Bash.
-There are also several @samp{--with-@var{PACKAGE}} options,
-where @var{PACKAGE} is something like @samp{gnu-malloc} or @samp{purify}.
-To turn off the default use of a package, use
-@samp{--without-@var{PACKAGE}}. To configure Bash without a feature
-that is enabled by default, use @samp{--disable-@var{FEATURE}}.
+@item
+The @code{noclobber} option is available to avoid overwriting existing
+files with output redirection (@pxref{The Set Builtin}).
+The @samp{>|} redirection operator may be used to override @code{noclobber}.
-Here is a complete list of the @samp{--enable-} and
-@samp{--with-} options that the Bash @code{configure} recognizes.
+@item
+The Bash @code{cd} and @code{pwd} builtins (@pxref{Bourne Shell Builtins})
+each take @option{-L} and @option{-P} options to switch between logical and
+physical modes.
-@table @code
-@item --with-afs
-Define if you are using the Andrew File System from Transarc.
+@item
+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} and @code{command} builtins (@pxref{Bash Builtins}).
-@item --with-curses
-Use the curses library instead of the termcap library. This should
-be supplied if your system has an inadequate or incomplete termcap
-database.
+@item
+The @code{command} builtin allows selective disabling of functions
+when command lookup is performed (@pxref{Bash Builtins}).
-@item --with-glibc-malloc
-Use the @sc{GNU} libc version of @code{malloc} in
-@file{lib/malloc/gmalloc.c}. This is not the version of @code{malloc}
-that appears in glibc version 2, but a modified version of the
-@code{malloc} from glibc version 1. This is somewhat slower than the
-default @code{malloc}, but wastes less space on a per-allocation
-basis, and will return memory to the operating system under
-some circumstances.
+@item
+Individual builtins may be enabled or disabled using the @code{enable}
+builtin (@pxref{Bash Builtins}).
-@item --with-gnu-malloc
-Use the @sc{GNU} version of
-@code{malloc} in @file{lib/malloc/malloc.c}. This is not the same
-@code{malloc} that appears in @sc{GNU} libc, but an older version
-derived from the 4.2 @sc{BSD} @code{malloc}. This @code{malloc} is
-very fast, but wastes some space on each allocation.
-This option is enabled by default.
-The @file{NOTES} file contains a list of systems for
-which this should be turned off, and @code{configure} disables this
-option automatically for a number of systems.
+@item
+The Bash @code{exec} 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
+(@pxref{Bourne Shell Builtins}).
-@item --with-installed-readline
-Define this to make bash link with a locally-installed version of Readline
-rather than the version in lib/readline. This works only with readline 4.0
-and later versions.
+@item
+Shell functions may be exported to children via the environment
+using @code{export -f} (@pxref{Shell Functions}).
-@item --with-purify
-Define this to use the Purify memory allocation checker from Pure
-Software.
+@item
+The Bash @code{export}, @code{readonly}, and @code{declare} builtins can
+take a @option{-f} option to act on shell functions, a @option{-p} option to
+display variables with various attributes set in a format that can be
+used as shell input, a @option{-n} option to remove various variable
+attributes, and @samp{name=value} arguments to set variable attributes
+and values simultaneously.
-@item --enable-minimal-config
-This produces a shell with minimal features, close to the historical
-Bourne shell.
-@end table
+@item
+The Bash @code{hash} builtin allows a name to be associated with
+an arbitrary filename, even when that filename cannot be found by
+searching the @env{$PATH}, using @samp{hash -p}
+(@pxref{Bourne Shell Builtins}).
-There are several @samp{--enable-} options that alter how Bash is
-compiled and linked, rather than changing run-time features.
+@item
+Bash includes a @code{help} builtin for quick reference to shell
+facilities (@pxref{Bash Builtins}).
-@table @code
-@item --enable-profiling
-This builds a Bash binary that produces profiling information to be
-processed by @code{gprof} each time it is executed.
+@item
+The @code{printf} builtin is available to display formatted output
+(@pxref{Bash Builtins}).
-@item --enable-static-link
-This causes Bash to be linked statically, if @code{gcc} is being used.
-This could be used to build a version to use as root's shell.
-@end table
+@item
+The Bash @code{read} builtin (@pxref{Bash Builtins})
+will read a line ending in @samp{\} with
+the @option{-r} option, and will use the @env{REPLY} variable as a
+default if no non-option arguments are supplied.
+The Bash @code{read} builtin
+also accepts a prompt string with the @option{-p} option and will use
+Readline to obtain the line when given the @option{-e} option.
+The @code{read} builtin also has additional options to control input:
+the @option{-s} option will turn off echoing of input characters as
+they are read, the @option{-t} option will allow @code{read} to time out
+if input does not arrive within a specified number of seconds, the
+@option{-n} option will allow reading only a specified number of
+characters rather than a full line, and the @option{-d} option will read
+until a particular character rather than newline.
-The @samp{minimal-config} option can be used to disable all of
-the following options, but it is processed first, so individual
-options may be enabled using @samp{enable-@var{FEATURE}}.
+@item
+The @code{return} builtin may be used to abort execution of scripts
+executed with the @code{.} or @code{source} builtins
+(@pxref{Bourne Shell Builtins}).
-All of the following options except for @samp{disabled-builtins} and
-@samp{usg-echo-default} are
-enabled by default, unless the operating system does not provide the
-necessary support.
+@item
+Bash includes the @code{shopt} builtin, for finer control of shell
+optional capabilities (@pxref{The Shopt Builtin}), and allows these options
+to be set and unset at shell invocation (@pxref{Invoking Bash}).
-@table @code
-@item --enable-alias
-Allow alias expansion and include the @code{alias} and @code{unalias}
-builtins (@pxref{Aliases}).
+@item
+Bash has much more optional behavior controllable with the @code{set}
+builtin (@pxref{The Set Builtin}).
-@item --enable-array-variables
-Include support for one-dimensional array shell variables
-(@pxref{Arrays}).
+@item
+The @samp{-x} (@code{xtrace}) option displays commands other than
+simple commands when performing an execution trace
+(@pxref{The Set Builtin}).
-@item --enable-bang-history
-Include support for @code{csh}-like history substitution
-(@pxref{History Interaction}).
+@item
+The @code{test} builtin (@pxref{Bourne Shell Builtins})
+is slightly different, as it implements the @sc{posix} algorithm,
+which specifies the behavior based on the number of arguments.
-@item --enable-brace-expansion
-Include @code{csh}-like brace expansion
-( @code{b@{a,b@}c} @expansion{} @code{bac bbc} ).
-See @ref{Brace Expansion}, for a complete description.
+@item
+Bash includes the @code{caller} builtin, which displays the context of
+any active subroutine call (a shell function or a script executed with
+the @code{.} or @code{source} builtins). This supports the bash
+debugger.
+
+@item
+The @code{trap} builtin (@pxref{Bourne Shell Builtins}) allows a
+@code{DEBUG} pseudo-signal specification, similar to @code{EXIT}.
+Commands specified with a @code{DEBUG} trap are executed before every
+simple command, @code{for} command, @code{case} command,
+@code{select} command, every arithmetic @code{for} command, and before
+the first command executes in a shell function.
+The @code{DEBUG} trap is not inherited by shell functions unless the
+function has been given the @code{trace} attribute or the
+@code{functrace} option has been enabled using the @code{shopt} builtin.
+The @code{extdebug} shell option has additional effects on the
+@code{DEBUG} trap.
+
+The @code{trap} builtin (@pxref{Bourne Shell Builtins}) allows an
+@code{ERR} pseudo-signal specification, similar to @code{EXIT} and @code{DEBUG}.
+Commands specified with an @code{ERR} trap are executed after a simple
+command fails, with a few exceptions.
+The @code{ERR} trap is not inherited by shell functions unless the
+@code{-o errtrace} option to the @code{set} builtin is enabled.
+
+The @code{trap} builtin (@pxref{Bourne Shell Builtins}) allows a
+@code{RETURN} pseudo-signal specification, similar to
+@code{EXIT} and @code{DEBUG}.
+Commands specified with an @code{RETURN} trap are executed before
+execution resumes after a shell function or a shell script executed with
+@code{.} or @code{source} returns.
+The @code{RETURN} trap is not inherited by shell functions unless the
+function has been given the @code{trace} attribute or the
+@code{functrace} option has been enabled using the @code{shopt} builtin.
-@item --enable-command-timing
-Include support for recognizing @code{time} as a reserved word and for
-displaying timing statistics for the pipeline following @code{time}. This
-allows pipelines as well as shell builtins and functions to be timed.
+@item
+The Bash @code{type} builtin is more extensive and gives more information
+about the names it finds (@pxref{Bash Builtins}).
-@item --enable-cond-command
-Include support for the @code{[[} conditional command
-(@pxref{Conditional Constructs}).
+@item
+The Bash @code{umask} builtin permits a @option{-p} option to cause
+the output to be displayed in the form of a @code{umask} command
+that may be reused as input (@pxref{Bourne Shell Builtins}).
-@item --enable-directory-stack
-Include support for a @code{csh}-like directory stack and the
-@code{pushd}, @code{popd}, and @code{dirs} builtins
+@item
+Bash implements a @code{csh}-like directory stack, and provides the
+@code{pushd}, @code{popd}, and @code{dirs} builtins to manipulate it
(@pxref{The Directory Stack}).
+Bash also makes the directory stack visible as the value of the
+@env{DIRSTACK} shell variable.
-@item --enable-disabled-builtins
-Allow builtin commands to be invoked via @samp{builtin xxx}
-even after @code{xxx} has been disabled using @samp{enable -n xxx}.
-See @ref{Bash Builtins}, for details of the @code{builtin} and
-@code{enable} builtin commands.
+@item
+Bash interprets special backslash-escaped characters in the prompt
+strings when interactive (@pxref{Printing a Prompt}).
-@item --enable-dparen-arithmetic
-Include support for the @code{((@dots{}))} command
-(@pxref{Conditional Constructs}).
+@item
+The Bash restricted mode is more useful (@pxref{The Restricted Shell});
+the SVR4.2 shell restricted mode is too limited.
-@item --enable-extended-glob
-Include support for the extended pattern matching features described
-above under @ref{Pattern Matching}.
+@item
+The @code{disown} builtin can remove a job from the internal shell
+job table (@pxref{Job Control Builtins}) or suppress the sending
+of @code{SIGHUP} to a job when the shell exits as the result of a
+@code{SIGHUP}.
-@item --enable-help-builtin
-Include the @code{help} builtin, which displays help on shell builtins and
-variables.
+@item
+Bash includes a number of features to support a separate debugger for
+shell scripts.
-@item --enable-history
-Include command history and the @code{fc} and @code{history}
-builtin commands.
+@item
+The SVR4.2 shell has two privilege-related builtins
+(@code{mldmode} and @code{priv}) not present in Bash.
-@item --enable-job-control
-This enables the job control features (@pxref{Job Control}),
-if the operating system supports them.
+@item
+Bash does not have the @code{stop} or @code{newgrp} builtins.
-@item --enable-process-substitution
-This enables process substitution (@pxref{Process Substitution}) if
-the operating system provides the necessary support.
+@item
+Bash does not use the @env{SHACCT} variable or perform shell accounting.
-@item --enable-prompt-string-decoding
-Turn on the interpretation of a number of backslash-escaped characters
-in the @code{$PS1}, @code{$PS2}, @code{$PS3}, and @code{$PS4} prompt
-strings. See @ref{Printing a Prompt}, for a complete list of prompt
-string escape sequences.
+@item
+The SVR4.2 @code{sh} uses a @env{TIMEOUT} variable like Bash uses
+@env{TMOUT}.
-@item --enable-readline
-Include support for command-line editing and history with the Bash
-version of the Readline library (@pxref{Command Line Editing}).
+@end itemize
-@item --enable-restricted
-Include support for a @dfn{restricted shell}. If this is enabled, Bash,
-when called as @code{rbash}, enters a restricted mode. See
-@ref{The Restricted Shell}, for a description of restricted mode.
+@noindent
+More features unique to Bash may be found in @ref{Bash Features}.
-@item --enable-select
-Include the @code{select} builtin, which allows the generation of simple
-menus (@pxref{Conditional Constructs}).
-@item --enable-usg-echo-default
-Make the @code{echo} builtin expand backslash-escaped characters by default,
-without requiring the @samp{-e} option. This makes the Bash @code{echo}
-behave more like the System V version.
+@appendixsec Implementation Differences From The SVR4.2 Shell
-@end table
+Since Bash is a completely new implementation, it does not suffer from
+many of the limitations of the SVR4.2 shell. For instance:
-The file @file{config.h.top} contains C Preprocessor
-@samp{#define} statements for options which are not settable from
-@code{configure}.
-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.
+@itemize @bullet
-@node Reporting Bugs
-@appendix Reporting Bugs
+@item
+Bash does not fork a subshell when redirecting into or out of
+a shell control structure such as an @code{if} or @code{while}
+statement.
-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 that you have.
+@item
+Bash does not allow unbalanced quotes. The SVR4.2 shell will silently
+insert a needed closing quote at @code{EOF} under certain circumstances.
+This can be the cause of some hard-to-find errors.
-Once you have determined that a bug actually exists, use the
-@code{bashbug} 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 @email{bug-bash@@gnu.org} or posted to the Usenet
-newsgroup @code{gnu.bash.bug}.
+@item
+The SVR4.2 shell uses a baroque memory management scheme based on
+trapping @code{SIGSEGV}. If the shell is started from a process with
+@code{SIGSEGV} blocked (e.g., by using the @code{system()} C library
+function call), it misbehaves badly.
-All bug reports should include:
-@itemize @bullet
@item
-The version number of Bash.
+In a questionable attempt at security, the SVR4.2 shell,
+when invoked without the @option{-p} option, will alter its real
+and effective @sc{uid} and @sc{gid} if they are less than some
+magic threshold value, commonly 100.
+This can lead to unexpected results.
+
@item
-The hardware and operating system.
+The SVR4.2 shell does not allow users to trap @code{SIGSEGV},
+@code{SIGALRM}, or @code{SIGCHLD}.
+
@item
-The compiler used to compile Bash.
+The SVR4.2 shell does not allow the @env{IFS}, @env{MAILCHECK},
+@env{PATH}, @env{PS1}, or @env{PS2} variables to be unset.
+
@item
-A description of the bug behaviour.
+The SVR4.2 shell treats @samp{^} as the undocumented equivalent of
+@samp{|}.
+
@item
-A short script or `recipe' which exercises the bug and may be used
-to reproduce it.
+Bash allows multiple option arguments when it is invoked (@code{-x -v});
+the SVR4.2 shell allows only one option argument (@code{-xv}). In
+fact, some versions of the shell dump core if the second argument begins
+with a @samp{-}.
+
+@item
+The SVR4.2 shell exits a script if any builtin fails; Bash exits
+a script only if one of the @sc{posix} special builtins fails, and
+only for certain failures, as enumerated in the @sc{posix} standard.
+
+@item
+The SVR4.2 shell behaves differently when invoked as @code{jsh}
+(it turns on job control).
@end itemize
-@noindent
-@code{bashbug} inserts the first three items automatically into
-the template it provides for filing a bug report.
+@node GNU Free Documentation License
+@appendix GNU Free Documentation License
-Please send all reports concerning this manual to
-@email{chet@@po.CWRU.Edu}.
+@include fdl.texi
+
+@node Indexes
+@appendix Indexes
+
+@menu
+* Builtin Index:: Index of Bash builtin commands.
+* Reserved Word Index:: Index of Bash reserved words.
+* Variable Index:: Quick reference helps you find the
+ variable you want.
+* Function Index:: Index of bindable Readline functions.
+* Concept Index:: General index for concepts described in
+ this manual.
+@end menu
@node Builtin Index
-@appendix Index of Shell Builtin Commands
+@appendixsec Index of Shell Builtin Commands
@printindex bt
@node Reserved Word Index
-@appendix Shell Reserved Words
+@appendixsec Index of Shell Reserved Words
@printindex rw
@node Variable Index
-@appendix Parameter and Variable Index
+@appendixsec Parameter and Variable Index
@printindex vr
@node Function Index
-@appendix Function Index
+@appendixsec Function Index
@printindex fn
@node Concept Index
-@appendix Concept Index
+@appendixsec Concept Index
@printindex cp
-@contents
@bye
projects / platform / upstream / bash.git / blobdiff