@settitle Bash Reference Manual
@c %**end of header
-@ignore
-last change: Mon May 19 12:55:22 EDT 1997
-@end ignore
-
-@set EDITION 2.0
-@set VERSION 2.01
-@set UPDATED 19 May 1997
-@set UPDATE-MONTH May 1997
-
-@iftex
-@finalout
-@end iftex
-
@setchapternewpage odd
-@defcodeindex bt
-@defcodeindex rw
-@set BashFeatures
-@ifinfo
-@format
+@include version.texi
+
+@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, 1993, 1996 Free Software Foundation, Inc.
+Copyright @copyright{} 1988-2005 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 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 1.1 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 have freedom to copy and modify
+this GNU Manual, like GNU software. Copies published by the Free
+Software Foundation raise funds for GNU development.''
+@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{UPDATED}
+@subtitle Edition @value{EDITION}, for @code{Bash} Version @value{VERSION}.
+@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, 1993, 1996 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.
-
-* Csh Features:: Features originally found in the
- Berkeley C-Shell.
-
-* Korn Shell Features:: Features originally found in the Korn
- 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.
+* Using History Interactively:: Command History Expansion
* Command Line Editing:: Chapter describing the command line
editing features.
-
* Installing Bash:: How to build and install Bash on your system.
-
* Reporting Bugs:: How to report bugs in Bash.
-
+* Major Differences From The Bourne Shell:: A terse list of the differences
+ between Bash and historical
+ versions of /bin/sh.
+* Copying This Manual:: Copying this manual.
* 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
-@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 ultimately intended to be a
-conformant implementation of the @sc{IEEE} @sc{POSIX} Shell and Tools
-specification (@sc{IEEE} Working Group 1003.2). 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
+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 offers functional improvements over @code{sh} for both interactive and
+programming use.
+
+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{OS/2} 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. The shell reads commands either from a terminal or a
-file. 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 utilitites 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.
-
-A shell allows execution of Unix commands, both synchronously and
-asynchronously. 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
+system commands in directories such as @file{/bin}, allowing users
+or groups to establish custom environments to automate their common
+tasks.
+
+Shells may be used interactively or non-interactively. In
+interactive mode, they accept input typed from the keyboard.
+When executing non-interactively, shells execute commands read
+from a file.
+
+A shell allows execution of @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.
+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 concerned with @sc{posix} 1003.2, the Shell and Tools Standard.
@item blank
A space or tab character.
@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
@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
@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} 1003.2 standard.
@item token
@cindex token
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":
+This chapter briefly summarizes the shell's `building blocks':
commands, control structures, shell functions, shell @i{parameters},
shell expansions,
@i{redirections}, which are a way to direct input and output from
@menu
* Shell Syntax:: What your input means to the shell.
-* 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.
+* 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
Breaks the input into words and operators, obeying the quoting rules
-described in @ref{Quoting}. Tokens are separated by
+described in @ref{Quoting}. These tokens are separated by
@code{metacharacters}. Alias expansion is performed by this step
(@pxref{Aliases}).
@item
-Parses the tokens into simple and compound commands.
+Parses the tokens into simple and compound commands
+(@pxref{Shell Commands}).
@item
Performs the various shell expansions (@pxref{Shell Expansions}), breaking
@item
Optionally waits for the command to complete and collects its exit
-status.
+status (@pxref{Exit Status}).
@end enumerate
* 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
reserved words from being recognized as such, and to prevent
parameter expansion.
-Each of the shell @code{metacharacters} (@pxref{Definitions})
-has special meaning to the shell and must be quoted if they are to
-represent themselves. There are three quoting mechanisms: the
+Each of the shell metacharacters (@pxref{Definitions})
+has special meaning to the shell and must be quoted if it is to
+represent itself.
+When the command history expansion facilities are being used
+(@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
A non-quoted backslash @samp{\} is the Bash escape character.
It preserves the literal value of the next character that follows,
with the exception of @code{newline}. If a @code{\newline} pair
-appears, and the backslash is not quoted, the @code{\newline}
-is treated as a line continuation (that is, it is effectively ignored).
+appears, and the backslash itself is not quoted, the @code{\newline}
+is treated as a line continuation (that is, it is removed from
+the input stream and effectively ignored).
@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{$} and @samp{`}
-retain their special meaning within double quotes. The backslash
-retains its special meaning only when followed by one of the following
-characters:
+retain their special meaning within double quotes (@pxref{Shell Expansions}).
+The backslash retains its special meaning only when followed by one of
+the following characters:
@samp{$}, @samp{`}, @samp{"}, @samp{\}, or @code{newline}.
+Within double quotes, backslashes that are followed by one of these
+characters are removed. Backslashes preceding characters without a
+special meaning are left unmodified.
A double quote may be quoted within double quotes by preceding it with
a backslash.
+If enabled, history expansion will be performed unless an @samp{!}
+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{$'@var{string}'} are treated specially. The
word expands to @var{string}, with backslash-escaped characters replaced
-as specifed by the ANSI C standard. Backslash escape sequences, if
+as specified by the ANSI C standard. Backslash escape sequences, if
present, are decoded as follows:
@table @code
vertical tab
@item \\
backslash
+@item \'
+single quote
@item \@var{nnn}
-the character whose @code{ASCII} code is @var{nnn} in octal
+the eight-bit character whose value is the octal value @var{nnn}
+(one to three digits)
+@item \x@var{HH}
+the eight-bit character whose value is the hexadecimal value @var{HH}
+(one or two hex digits)
+@item \c@var{x}
+a control-@var{x} character
@end table
@noindent
-The result is single-quoted, as if the dollar sign had not been present.
+The expanded result is single-quoted, as if the dollar sign had not
+been present.
@node Locale Translation
@subsubsection Locale-Specific Translation
@cindex localization
+@cindex internationalization
+@cindex native languages
+@cindex translation, native languages
A double-quoted string preceded by a dollar sign (@samp{$}) 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
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{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.
+* Compound Commands:: Shell commands for control flow.
+@end menu
@node Simple Commands
-@section Simple Commands
+@subsection Simple Commands
@cindex commands, simple
-A simple command is the kind of command you'll encounter most often.
+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 control operators (@pxref{Definitions}). The
-first word generally specifies a command to be executed.
+by one of the shell's control operators (@pxref{Definitions}). The
+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
-@section Pipelines
+@subsection Pipelines
@cindex pipeline
@cindex commands, pipelines
@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.
The reserved word @code{time} causes timing statistics
to be printed for the pipeline once it finishes.
-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 statistics currently consist of elapsed (wall-clock) time and
+user and system time consumed by the command's execution.
+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
+shell builtins, shell functions, and pipelines. An external
+@code{time} command cannot time these easily.
-Each command in a pipeline is executed in its own subshell. The exit
+If the pipeline is not executed asynchronously (@pxref{Lists}), the
+shell waits for all commands in the pipeline to complete.
+
+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 @sc{NOT} 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
-@section Lists of Commands
+@subsection Lists of Commands
@cindex commands, lists
A @code{list} is a sequence of one or more pipelines separated by one
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 in the @var{background}
-in a subshell. The shell does not wait for the command to
-finish, and the return status is 0 (true). Commands separated by a
-@samp{;} are executed sequentially; the shell waits for each
-command to terminate in turn. The return status is the
+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).
+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
+denote @sc{and} lists and @sc{or} lists, respectively.
+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
-@section Looping Constructs
+@subsubsection Looping Constructs
@cindex commands, looping
-Note that wherever you see a @samp{;} in the description of a
-command's syntax, it may be replaced indiscriminately with
-one or more newlines.
-
Bash supports the following looping constructs.
+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
@item until
@rwindex until
@example
until @var{test-commands}; do @var{consequent-commands}; done
@end example
-Execute @var{consequent-commands} as long as the final command in
+Execute @var{consequent-commands} as long as
@var{test-commands} has an exit status which is not zero.
+The return status is the exit status of the last command executed
+in @var{consequent-commands}, or zero if none was executed.
@item while
@rwindex while
while @var{test-commands}; do @var{consequent-commands}; done
@end example
-Execute @var{consequent-commands} as long as the final command in
+Execute @var{consequent-commands} as long as
@var{test-commands} has an exit status of zero.
+The return status is the exit status of the last command executed
+in @var{consequent-commands}, or zero if none was executed.
@item for
@rwindex for
@example
for @var{name} [in @var{words} @dots{}]; do @var{commands}; done
@end example
-Execute @var{commands} for each member in @var{words}, with @var{name}
-bound to the current member. If @samp{in @var{words}} is not
-present, @samp{in "$@@"} is assumed.
+Expand @var{words}, and execute @var{commands} once for each member
+in the resultant list, with @var{name} bound to the current member.
+If @samp{in @var{words}} is not present, the @code{for} command
+executes the @var{commands} once for each positional parameter that is
+set, as if @samp{in "$@@"} 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
may be used to control loop execution.
@node Conditional Constructs
-@section Conditional Constructs
+@subsubsection Conditional Constructs
@cindex commands, conditional
@table @code
fi
@end example
-Execute @var{consequent-commands} only if the final command in
-@var{test-commands} has an exit status of zero.
-Otherwise, each @code{elif} list is executed in turn,
-and if its exit status is zero,
+The @var{test-commands} list is executed, and if its return status is zero,
+the @var{consequent-commands} list is executed.
+If @var{test-commands} returns a non-zero status, each @code{elif} list
+is executed in turn, and if its exit status is zero,
the corresponding @var{more-consequents} is executed and the
command completes.
If @samp{else @var{alternate-consequents}} is present, and
the final command in the final @code{if} or @code{elif} clause
-has a non-zero exit status, then execute @var{alternate-consequents}.
+has a non-zero exit status, then @var{alternate-consequents} is executed.
+The return status is the exit status of the last command executed, or
+zero if no condition tested true.
@item case
@rwindex case
The syntax of the @code{case} command is:
@example
-@code{case @var{word} in [ ( @var{pattern} [| @var{pattern}]@dots{}) @var{commands} ;;]@dots{} esac}
+@code{case @var{word} in [ [(] @var{pattern} [| @var{pattern}]@dots{}) @var{command-list} ;;]@dots{} esac}
@end example
-Selectively execute @var{commands} based upon @var{word} matching
-@var{pattern}. The @samp{|} is used to separate multiple patterns.
+@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{Bash Builtins})
+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{;;}.
+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
+command-list that is executed.
Here is an example using @code{case} in a script that could be used to
describe one interesting feature of an animal:
echo " legs."
@end example
+@noindent
+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.
+
+@item select
+@rwindex select
+
+The @code{select} construct allows the easy generation of menus.
+It has almost the same syntax as the @code{for} command:
+
+@example
+select @var{name} [in @var{words} @dots{}]; do @var{commands}; done
+@end example
+
+The list of words following @code{in} is expanded, generating a list
+of items. The set of expanded words is printed on the standard
+error output stream, each preceded by a number. If the
+@samp{in @var{words}} is omitted, the positional parameters are printed,
+as if @samp{in "$@@"} had been specifed.
+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 @env{REPLY}.
+
+The @var{commands} are executed after each selection until a
+@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
+current directory, and displays the name and index of the file
+selected.
+
+@example
+select fname in *;
+do
+ echo you picked $fname \($REPLY\)
+ break;
+done
+@end example
+
@item ((@dots{}))
@example
(( @var{expression} ))
@end example
-The @var{expression} is evaluated according to the rules described
-below (@pxref{Arithmetic Evaluation}).
+The arithmetic @var{expression} is evaluated according to the rules
+described below (@pxref{Shell Arithmetic}).
If the value of the expression is non-zero, the return status is 0;
otherwise the return status is 1. This is exactly equivalent to
@example
let "@var{expression}"
@end example
+@noindent
+@xref{Bash Builtins}, for a full description of the @code{let} builtin.
+
+@item [[@dots{}]]
+@rwindex [[
+@rwindex ]]
+@example
+[[ @var{expression} ]]
+@end example
+
+Return a status of 0 or 1 depending on the evaluation of
+the conditional expression @var{expression}.
+Expressions are composed of the primaries described below in
+@ref{Bash Conditional Expressions}.
+Word splitting and filename expansion are not performed on the words
+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}.
+If the shell option @code{nocasematch}
+(see the description of @code{shopt} in @ref{Bash Builtins})
+is enabled, the match is performed without regard to the case
+of alphabetic characters.
+The return value is 0 if the string matches or does not match
+the pattern, respectively, 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{Bash Builtins})
+is enabled, the match is performed without regard to the case
+of alphabetic characters.
+Substrings matched by parenthesized subexpressions within the regular
+expression are saved in the array variable @code{BASH_REMATCH}.
+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:
+
+@table @code
+@item ( @var{expression} )
+Returns the value of @var{expression}.
+This may be used to override the normal precedence of operators.
+
+@item ! @var{expression}
+True if @var{expression} is false.
+@item @var{expression1} && @var{expression2}
+True if both @var{expression1} and @var{expression2} are true.
+
+@item @var{expression1} || @var{expression2}
+True if either @var{expression1} or @var{expression2} is true.
@end table
+@noindent
+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.
-The @code{select} construct, which allows users to choose from a list
-of items presented as a menu, is also available.
-@xref{Korn Shell Constructs}, for a full description of @code{select}.
+@end table
@node Command Grouping
-@section 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 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 @{
Placing a list of commands between curly braces causes the list to
be executed in the current shell context. No subshell is created.
-The semicolon following @var{list} is required.
+The semicolon (or newline) following @var{list} is required.
@end table
In addition to the creation of a subshell, there is a subtle difference
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. 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.
+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 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.
+
+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 by whitespace.
+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 function
+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 return status.
+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}.
Variables local to the function may be declared with the
@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
is not given, the variable is assigned the null string. All
@var{value}s undergo tilde expansion, parameter and variable expansion,
command substitution, arithmetic expansion, and quote
-removal (detailed below). If the variable has its @samp{-i} 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{$((@dots{}))}
-syntax does not appear (@pxref{Arithmetic Expansion}).
+removal (detailed below). If the variable has its @code{integer}
+attribute set, then @var{value}
+is evaluated as an arithmetic expression even if the @code{$((@dots{}))}
+expansion is not used (@pxref{Arithmetic Expansion}).
Word splitting is not performed, with the exception
of @code{"$@@"} as explained below.
Filename expansion is not performed.
+Assignment statements may also appear as arguments to the
+@code{alias},
+@code{declare}, @code{typeset}, @code{export}, @code{readonly},
+and @code{local} builtin commands.
+
+In the context where an assignment statement is assigning a value
+to a shell variable or array index (@pxref{Arrays}), the @samp{+=}
+operator can be used to
+append to or add to the variable's previous value.
+When @samp{+=} is applied to a variable for which the integer attribute
+has been set, @var{value} is evaluated as an arithmetic expression and
+added to the variable's current value, which is also evaluated.
+When @samp{+=} is applied to an array variable using compound assignment
+(@pxref{Arrays}), the
+variable's value is not unset (as it is when using @samp{=}), and new
+values are appended to the array beginning at one greater than the array's
+maximum index.
+When applied to a string-valued variable, @var{value} is expanded and
+appended to the variable's value.
@node Positional Parameters
@subsection Positional Parameters
@cindex parameters, positional
-A @var{positional parameter}
-is a parameter denoted by one or more
+A @var{positional parameter} is a parameter denoted by one or more
digits, other than the single digit @code{0}. Positional parameters are
assigned from the shell's arguments when it is invoked,
-and may be reassigned using the @code{set}
-builtin command. Positional parameters may not be assigned to
-with assignment statements. The positional parameters are
+and may be reassigned using the @code{set} builtin command.
+Positional parameter @code{N} may be referenced as @code{$@{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}$2@var{c}@dots{}"}, where @var{c}
is the first character of the value of the @code{IFS}
variable.
-If @code{IFS} is unset, the parameters are separated by spaces.
-If @code{IFS} is null, the parameters are joined without intervening
+If @env{IFS} is unset, the parameters are separated by spaces.
+If @env{IFS} is null, the parameters are joined without intervening
separators.
@item @@
Expands to the positional parameters, starting from one. When the
-expansion occurs within double quotes, each parameter expands as a
+expansion occurs within double quotes, each parameter expands to a
separate word. That is, @code{"$@@"} 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 current 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,
-@code{$0} is set to the name of that file. If Bash
-is started with the @samp{-c} option, then @code{$0}
-is set to the first argument after the string to be
+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 @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 filename 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
@end itemize
@menu
+* Brace Expansion:: Expansion of expressions within braces.
+* Tilde Expansion:: Expansion of the ~ character.
* Shell Parameter Expansion:: How Bash expands variables to their values.
* Command Substitution:: Using the output of a command as an argument.
+* Arithmetic Expansion:: How to use arithmetic in shell expansions.
* Process Substitution:: A way to write and read to and from a
command.
* Word Splitting:: How the results of expansion are split into separate
words.
@end menu
-Brace expansion, tilde expansion, and arithmetic expansion are described
-in other sections. For brace expansion, see @ref{Brace Expansion}; for
-tilde expansion, see @ref{Tilde Expansion}; and for arithmetic expansion,
-see @ref{Arithmetic Expansion}.
-
The order of expansions is: brace expansion, tilde expansion,
parameter, variable, and arithmetic expansion and
command substitution
On systems that can support it, there is an additional expansion
available: @var{process substitution}. This is performed at the
-same time as parameter, variable, and arithemtic expansion and
+same time as parameter, variable, and arithmetic expansion and
command substitution.
Only brace expansion, word splitting, and filename expansion
After all expansions, @code{quote removal} (@pxref{Quote Removal})
is performed.
+@node Brace Expansion
+@subsection Brace Expansion
+@cindex brace expansion
+@cindex expansion, brace
+
+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 either a series of comma-separated strings or a sequnce 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}@}},
+where @var{x} and @var{y} are either integers or single characters.
+When integers are supplied, the expression expands to each number between
+@var{x} and @var{y}, inclusive.
+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.
+
+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{$@{}
+is not considered eligible for brace expansion.
+
+A correctly-formed brace expansion must contain unquoted opening
+and closing braces, and at least one unquoted comma or a valid
+sequence expression.
+Any incorrectly formed brace expansion is left unchanged.
+
+A @{ or @samp{,} may be quoted with a backslash to prevent its
+being considered part of a brace expression.
+To avoid conflicts with parameter expansion, the string @samp{$@{}
+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:
+@example
+mkdir /usr/local/src/bash/@{old,new,dist,bugs@}
+@end example
+or
+@example
+chown root /usr/@{ucb/@{ex,edit@},lib/@{ex?.?*,how_ex@}@}
+@end example
+
+@node Tilde Expansion
+@subsection Tilde Expansion
+@cindex tilde expansion
+@cindex expansion, tilde
+
+If a word begins with an unquoted tilde character (@samp{~}), all of the
+characters up to the first unquoted slash (or all characters,
+if there is no unquoted slash) are considered a @var{tilde-prefix}.
+If none of the characters in the tilde-prefix are quoted, the
+characters in the tilde-prefix following the tilde are treated as a
+possible @var{login name}.
+If this login name is the null string, the tilde is replaced with 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 @env{PWD} replaces the tilde-prefix.
+If the tilde-prefix is @samp{~-}, the value of the shell variable
+@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{-},
+the tilde-prefix is replaced with the
+corresponding element from the directory stack, as it would be displayed
+by the @code{dirs} builtin invoked with the characters following tilde
+in the tilde-prefix as an argument (@pxref{The Directory Stack}).
+If the tilde-prefix, sans the tilde, consists of a number without a
+leading @samp{+} or @samp{-}, @samp{+} is assumed.
+
+If the login name is invalid, or the tilde expansion fails, the word is
+left unchanged.
+
+Each variable assignment is checked for unquoted tilde-prefixes immediately
+following a @samp{:} or the first @samp{=}.
+In these cases, tilde expansion is also performed.
+Consequently, one may use file names with tildes in assignments to
+@env{PATH}, @env{MAILPATH}, and @env{CDPATH},
+and the shell assigns the expanded value.
+
+The following table shows how Bash treats unquoted tilde-prefixes:
+
+@table @code
+@item ~
+The value of @code{$HOME}
+@item ~/foo
+@file{$HOME/foo}
+
+@item ~fred/foo
+The subdirectory @code{foo} of the home directory of the user
+@code{fred}
+
+@item ~+/foo
+@file{$PWD/foo}
+
+@item ~-/foo
+@file{$@{OLDPWD-'~-'@}/foo}
+
+@item ~@var{N}
+The string that would be displayed by @samp{dirs +@var{N}}
+
+@item ~+@var{N}
+The string that would be displayed by @samp{dirs +@var{N}}
+
+@item ~-@var{N}
+The string that would be displayed by @samp{dirs -@var{N}}
+
+@end table
+
@node Shell Parameter Expansion
@subsection Shell Parameter Expansion
@cindex parameter expansion
characters immediately following it which could be
interpreted as part of the name.
+When braces are used, the matching ending brace is the first @samp{@}}
+not escaped by a backslash or within a quoted string, and not within an
+embedded arithmetic expansion, command substitution, or parameter
+expansion.
+
The basic form of parameter expansion is $@{@var{parameter}@}.
The value of @var{parameter} is substituted. The braces are required
when @var{parameter}
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},
-starting at @var{offset}.
+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{Arithmetic Evaluation}).
+(@pxref{Shell Arithmetic}).
This is referred to as Substring Expansion.
@var{length} must evaluate to a number greater than or equal to zero.
parameters beginning at @var{offset}.
If @var{parameter} is an array name indexed by @samp{@@} or @samp{*},
the result is the @var{length}
-members of the array beginning with $@{@var{parameter}[@var{offset}]@}.
-Substring indexing is zero-based unless the positional parameters are
-used, in which case the indexing starts at 1.
+members of the array beginning with @code{$@{@var{parameter}[@var{offset}]@}}.
+A negative @var{offset} is taken relative to one greater than the maximum
+index of the specified array.
+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.
+
+@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.
+
+@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 value of @var{parameter} is substituted.
-If @var{parameter}
-is @samp{*} or @samp{@@},
-the length substituted is the number of positional parameters.
-If @var{parameter}
-is an array name subscripted
-by @samp{*} or @samp{@@},
-the length substituted is the number of elements in the array.
+The length in characters of the expanded value of @var{parameter} is
+substituted.
+If @var{parameter} is @samp{*} or @samp{@@}, the value substituted
+is the number of positional parameters.
+If @var{parameter} is an array name subscripted by @samp{*} or @samp{@@},
+the value substituted is the number of elements in the array.
@item $@{@var{parameter}#@var{word}@}
@itemx $@{@var{parameter}##@var{word}@}
The @var{word}
is expanded to produce a pattern just as in filename
expansion (@pxref{Filename Expansion}). If the pattern matches
-the beginning of the value of @var{parameter},
-then the expansion is the value of @var{parameter}
+the beginning of the expanded value of @var{parameter},
+then the result of the expansion is the expanded value of @var{parameter}
with the shortest matching pattern (the @samp{#} case) or the
longest matching pattern (the @samp{##} case) deleted.
If @var{parameter} is @samp{@@} or @samp{*},
@itemx $@{@var{parameter}%%@var{word}@}
The @var{word} is expanded to produce a pattern just as in
filename expansion.
-If the pattern matches a trailing portion of the value of
-@var{parameter}, then the expansion is the value of @var{parameter}
-with the shortest matching pattern (the @samp{%} case) or the
-longest matching pattern (the @samp{%%} case) deleted.
+If the pattern matches a trailing portion of the expanded value of
+@var{parameter}, then the result of the expansion is the value of
+@var{parameter} with the shortest matching pattern (the @samp{%} case)
+or the longest matching pattern (the @samp{%%} case) deleted.
If @var{parameter} is @samp{@@} or @samp{*},
the pattern removal operation is applied to each positional
parameter in turn, and the expansion is the resultant list.
The second form causes all matches of @var{pattern} to be
replaced with @var{string}.
If @var{pattern} begins with @samp{#}, it must match at the beginning
-of @var{string}.
+of the expanded value of @var{parameter}.
If @var{pattern} begins with @samp{%}, it must match at the end
-of @var{string}.
+of the expanded value of @var{parameter}.
If @var{string} is null, matches of @var{pattern} are deleted
and the @code{/} following @var{pattern} may be omitted.
If @var{parameter} is @samp{@@} or @samp{*},
@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
$(@var{command})
@end example
Bash performs the expansion by executing @var{command} and
replacing the command substitution with the standard output of the
command, with any trailing newlines deleted.
+Embedded newlines are not deleted, but they may be removed during
+word splitting.
+The command substitution @code{$(cat @var{file})} can be
+replaced by the equivalent but faster @code{$(< @var{file})}.
When the old-style backquote form of substitution is used,
backslash retains its literal meaning except when followed by
-@samp{$}, @samp{`}, or @samp{\}.
+@samp{$}, @samp{`}, or @samp{\}.
+The first backquote not preceded by a backslash terminates the
+command substitution.
When using the @code{$(@var{command})} form, all characters between
the parentheses make up the command; none are treated specially.
-Command substitutions may be nested. To nest when using the old form,
-escape the inner backquotes with backslashes.
+Command substitutions may be nested. To nest when using the backquoted
+form, escape the inner backquotes with backslashes.
If the substitution appears within double quotes, word splitting and
filename expansion are not performed on the results.
+@node Arithmetic Expansion
+@subsection Arithmetic Expansion
+@cindex expansion, arithmetic
+@cindex arithmetic expansion
+
+Arithmetic expansion allows the evaluation of an arithmetic expression
+and the substitution of the result. The format for arithmetic expansion is:
+
+@example
+$(( @var{expression} ))
+@end example
+
+The expression is treated as if it were within double quotes, but
+a double quote inside the parentheses is not treated specially.
+All tokens in the expression undergo parameter expansion, command
+substitution, and quote removal.
+Arithmetic expansions may be nested.
+
+The evaluation is performed according to the rules listed below
+(@pxref{Shell Arithmetic}).
+If the expression is invalid, Bash prints a message indicating
+failure to the standard error and no substitution occurs.
+
@node Process Substitution
@subsection Process Substitution
@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.
-On systems that support it, process substitution is performed
-simultaneously with parameter and variable expansion,
-command substitution, and arithmetic expansion.
+When available, process substitution is performed simultaneously with
+parameter and variable expansion, command substitution, and arithmetic
+expansion.
@node Word Splitting
@subsection Word Splitting
and arithmetic expansion that did not occur within double quotes for
word splitting.
-The shell treats each character of @code{$IFS}
+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
-@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}
+@env{IFS} is unset, or its value is exactly @code{<space><tab><newline>},
+the default, then any sequence of @env{IFS}
+characters 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.
@node Filename Expansion
@subsection Filename Expansion
+@menu
+* Pattern Matching:: How the shell matches patterns.
+@end menu
@cindex expansion, filename
@cindex expansion, pathname
@cindex filename expansion
@cindex pathname expansion
-After word splitting,
-unless the @samp{-f}
-option has been set (@pxref{The Set Builtin}),
-Bash scans each word for the characters
+After word splitting, unless the @option{-f} option has been set
+(@pxref{The Set Builtin}), Bash scans each word for the characters
@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
file names matching the pattern. If no matching file names are found,
and the shell option @code{nullglob} is disabled, the word is left
-unchanged. If the option is set, and no matches are found, the word
-is removed. When a pattern is used for filename generation,
-the character @samp{.}
+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.
+
+When a pattern is used for filename generation, the character @samp{.}
at the start of a filename or immediately following a slash
-must be matched explicitly, unless the shell option @code{dotglob}
-is set. The slash character must always be matched explicitly.
+must be matched explicitly, unless the shell option @code{dotglob} is set.
+When matching a file name, the slash character must always be
+matched explicitly.
In other cases, the @samp{.} character is not treated specially.
+
See the description of @code{shopt} in @ref{Bash Builtins},
-for a description of the @code{nullglob} and @code{dotglob} options.
+for a description of the @code{nocaseglob}, @code{nullglob},
+@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
-@var{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
+@subsubsection Pattern Matching
+@cindex pattern matching
+@cindex matching, pattern
+
+Any character that appears in a pattern, other than the special pattern
+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 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} 1003.2 standard:
+@example
+alnum alpha ascii blank cntrl digit graph lower
+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 all characters with the same collation weight (as defined
+by the current locale) as the character @var{c}.
+
+Within @samp{[} and @samp{]}, the syntax @code{[.}@var{symbol}@code{.]}
+matches the collating symbol @var{symbol}.
+@end table
+
+If the @code{extglob} shell option is enabled using the @code{shopt}
+builtin, several extended pattern matching operators are recognized.
+In the following description, a @var{pattern-list} is a list of one
+or more patterns separated by a @samp{|}.
+Composite patterns may be formed using one or more of the following
+sub-patterns:
+
+@table @code
+@item ?(@var{pattern-list})
+Matches zero or one occurrence of the given patterns.
+
+@item *(@var{pattern-list})
+Matches zero or more occurrences of the given patterns.
+
+@item +(@var{pattern-list})
+Matches one or more occurrences of the given patterns.
+
+@item @@(@var{pattern-list})
+Matches one of the given patterns.
+
+@item !(@var{pattern-list})
+Matches anything except one of the given patterns.
@end table
@node Quote Removal
is @samp{>}, the redirection refers to the standard output (file
descriptor 1).
-The word that follows the redirection operator in the following
-descriptions is subjected to brace expansion, tilde expansion,
-parameter expansion, command substitution, arithmetic expansion,
-quote removal, and filename expansion. If it expands to more
-than one word, Bash reports an error.
+The word following the redirection operator in the following
+descriptions, unless otherwise noted, is subjected to brace expansion,
+tilde expansion, parameter expansion, command substitution, arithmetic
+expansion, quote removal, filename expansion, and word splitting.
+If it expands to more than one word, Bash reports an error.
Note that the order of redirections is significant. For example,
the command
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 @samp{-C} option to the
-@code{set} builtin has been enabled, the redirection will fail if the
-filename whose name results from the expansion of @var{word} exists.
-If the redirection operator is @samp{>|},
-then the value of the @samp{-C} option to the @code{set}
-builtin command is not tested, and the redirection is attempted even
-if the file named by @var{word} exists.
+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 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
+is attempted even if the file named by @var{word} exists.
@subsection Appending Redirected Output
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
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. Otherwise,
+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}
-is made to be a copy of that file descriptor. 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.
+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 @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.
-As a special case, if @code{n} is omitted, and @var{word} does not
+@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 @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
@section 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 Command Search and Execution
-@subsection Command Search and Execution
-@cindex command execution
-@cindex command search
+@node Simple Command Expansion
+@subsection Simple Command Expansion
+@cindex command expansion
+
+When a simple command is executed, the shell performs the following
+expansions, assignments, and redirections, from left to right.
+
+@enumerate
+@item
+The words that the parser has marked as variable assignments (those
+preceding the command name) and redirections are saved for later
+processing.
+
+@item
+The words that are not variable assignments or redirections are
+expanded (@pxref{Shell Expansions}).
+If any words remain after expansion, the first word
+is taken to be the name of the command and the remaining words are
+the arguments.
+
+@item
+Redirections are performed as described above (@pxref{Redirections}).
+
+@item
+The text after the @samp{=} in each variable assignment undergoes tilde
+expansion, parameter expansion, command substitution, arithmetic expansion,
+and quote removal before being assigned to the variable.
+@end enumerate
+
+If no command name results, the variable assignments affect the current
+shell environment. Otherwise, the variables are added to the environment
+of the executed command and do not affect the current shell environment.
+If any of the assignments attempts to assign a value to a readonly variable,
+an error occurs, and the command exits with a non-zero status.
+
+If no command name results, redirections are performed, but do not
+affect the current shell environment. A redirection error causes the
+command to exit with a non-zero status.
+
+If there is a command name left after expansion, execution proceeds as
+described below. Otherwise, the command exits. If one of the expansions
+contained a command substitution, the exit status of the command is
+the exit status of the last command substitution performed. If there
+were no command substitutions, the command exits with a status of zero.
+
+@node Command Search and Execution
+@subsection Command Search and Execution
+@cindex command execution
+@cindex command search
After a command has been split into words, if it results in a
simple command and an optional list of arguments, the following
@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
-filenames of executable files (see the description of
-@code{hash} in @ref{Bourne Shell Builtins}) to avoid multiple
-@code{PATH} searches.
-A full search of the directories in @code{$PATH}
+pathnames of executable files to avoid multiple @env{PATH} searches
+(see the description of @code{hash} in @ref{Bourne Shell Builtins}).
+A full search of the directories in @env{$PATH}
is performed only if the command is not found in the hash table.
If the search is unsuccessful, the shell prints an error
-message and returns a nonzero exit status.
+message and returns an exit status of 127.
@item
If the search is successful, or if the command name contains
-one or more slashes, the shell executes the named program.
+one or more slashes, the shell executes the named program in
+a separate execution environment.
Argument 0 is set to the name given, and the remaining arguments
to the command are set to the arguments supplied, if any.
@item
If this execution fails because the file is not in executable
-format, and the file is not a directory, it is assumed to be
-@var{shell script} (@pxref{Shell Scripts}).
+format, and the file is not a directory, it is assumed to be a
+@var{shell script} and the shell executes it as described in
+@ref{Shell Scripts}.
+
+@item
+If the command was not begun asynchronously, the shell waits for
+the command to complete and collects its exit status.
+
@end enumerate
+@node Command Execution Environment
+@subsection Command Execution Environment
+@cindex execution environment
+
+The shell has an @var{execution environment}, which consists of the
+following:
+
+@itemize @bullet
+@item
+open files inherited by the shell at invocation, as modified by
+redirections supplied to the @code{exec} builtin
+
+@item
+the current working directory as set by @code{cd}, @code{pushd}, or
+@code{popd}, or inherited by the shell at invocation
+
+@item
+the file creation mode mask as set by @code{umask} or inherited from
+the shell's parent
+
+@item
+current traps set by @code{trap}
+
+@item
+shell parameters that are set by variable assignment or with @code{set}
+or inherited from the shell's parent in the environment
+
+@item
+shell functions defined during execution or inherited from the shell's
+parent in the environment
+
+@item
+options enabled at invocation (either by default or with command-line
+arguments) or by @code{set}
+
+@item
+options enabled by @code{shopt}
+
+@item
+shell aliases defined with @code{alias} (@pxref{Aliases})
+
+@item
+various process @sc{id}s, including those of background jobs
+(@pxref{Lists}), the value of @code{$$}, and the value of
+@env{$PPID}
+
+@end itemize
+
+When a simple command other than a builtin or shell function
+is to be executed, it
+is invoked in a separate execution environment that consists of
+the following. Unless otherwise noted, the values are inherited
+from the shell.
+
+@itemize @bullet
+@item
+the shell's open files, plus any modifications and additions specified
+by redirections to the command
+
+@item
+the current working directory
+
+@item
+the file creation mode mask
+
+@item
+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
+shell's parent, and traps ignored by the shell are ignored
+
+@end itemize
+
+A command invoked in this separate environment cannot affect the
+shell's execution environment.
+
+Command substitution, commands grouped with parentheses,
+and asynchronous commands are invoked in a
+subshell environment that is a duplicate of the shell environment,
+except that traps caught by the shell are reset to the values
+that the shell inherited from its parent at invocation. Builtin
+commands that are invoked as part of a pipeline are also executed
+in a subshell environment. Changes made to the subshell environment
+cannot affect the shell's execution environment.
+
+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.
of the environment, replacing the old. The environment
inherited by any executed command consists of the shell's
initial environment, whose values may be modified in the shell,
-less any pairs removed by the @code{unset} command, plus any
-additions via the @code{export} and @samp{declare -x} commands.
+less any pairs removed by the @code{unset} and @samp{export -n}
+commands, plus any additions via the @code{export} and
+@samp{declare -x} commands.
The environment for any simple command
or function may be augmented temporarily by prefixing it with
These assignment statements affect only the environment seen
by that command.
-If the @samp{-k} flag 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
-For the purposes of the shell, a command which exits with a
+For the shell's purposes, a command which exits with a
zero exit status has succeeded.
A non-zero exit status indicates failure.
This seemingly counter-intuitive scheme is used so there
is one well-defined way to indicate success and a variety of
ways to indicate various failure modes.
-When a command terminates on a fatal signal whose number is @var{n},
-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
but is not executable, the return status is 126.
+If a command fails because of an error during expansion or redirection,
+the exit status is greater than zero.
+
The exit status is used by the Bash conditional commands
(@pxref{Conditional Constructs}) and some of the list
constructs (@pxref{Lists}).
All of the Bash builtins return an exit status of zero if they succeed
and a non-zero status on failure, so they may be used by the
conditional and list constructs.
+All builtins return an exit status of 2 to indicate incorrect usage.
@node Signals
@subsection Signals
@cindex signal handling
-When Bash is interactive, it ignores
+When Bash is interactive, in the absence of any traps, it ignores
@code{SIGTERM} (so that @samp{kill 0} does not kill an interactive shell),
and @code{SIGINT}
is caught and handled (so that the @code{wait} builtin is interruptible).
If job control is in effect (@pxref{Job Control}), Bash
ignores @code{SIGTTIN}, @code{SIGTTOU}, and @code{SIGTSTP}.
-Synchronous jobs started by Bash have signals set to the
-values inherited by the shell from its parent. When job control
-is not in effect, background jobs (commands terminated with @samp{&})
-ignore @code{SIGINT} and @code{SIGQUIT}.
-Commands run as a result of command substitution ignore the
-keyboard-generated job control signals
+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} 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. To prevent the shell from
-sending the @code{SIGHUP} signal to a particular job, remove it
-from the jobs table with the @code{disown} builtin
-(@pxref{Job Control Builtins})
-or use @code{disown -h} to mark it to not receive @code{SIGHUP}.
+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
+particular job, it should be removed
+from the jobs table with the @code{disown}
+builtin (@pxref{Job Control Builtins}) or marked
+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
+an interactive login shell exits.
+
+If Bash is waiting for a command to complete and receives a signal
+for which a trap has been set, the trap will not be executed until
+the command completes.
+When Bash is waiting for an asynchronous
+command via the @code{wait} builtin, the reception of a signal for
+which a trap has been set will cause the @code{wait} builtin to return
+immediately with an exit status greater than 128, immediately after
+which the trap is executed.
@node Shell Scripts
@section Shell Scripts
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}
@noindent
if @code{filename} is an executable shell script.
This subshell reinitializes itself, so that the effect is as if a
-new shell had been invoked to interpret the script.
+new shell had been invoked to interpret the script, with the
+exception that the locations of commands remembered by the parent
+(see the description of @code{hash} 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.
+* The Set Builtin:: This builtin is so overloaded it
+ deserves its own section.
+* Special Builtins:: Builtin commands classified specially by
+ POSIX.2.
@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.
+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 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} 1003.2 standard.
@table @code
-@item :
+@item : @r{(a colon)}
@btindex :
@example
: [@var{arguments}]
@end example
Do nothing beyond expanding @var{arguments} and performing redirections.
+The return status is zero.
-@item .
+@item . @r{(a period)}
@btindex .
@example
-. @var{filename}
+. @var{filename} [@var{arguments}]
@end example
Read and execute commands from the @var{filename} argument in the
-current shell context.
+current shell context. If @var{filename} does not contain a slash,
+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{$PATH}.
+If any @var{arguments} are supplied, they become the positional
+parameters when @var{filename} is executed. Otherwise the positional
+parameters are unchanged.
+The return status is the exit status of the last command executed, or
+zero if no commands are executed. If @var{filename} is not found, or
+cannot be read, the return status is non-zero.
+This builtin is equivalent to @code{source}.
@item break
@btindex break
@end example
Exit from a @code{for}, @code{while}, @code{until}, or @code{select} loop.
If @var{n} is supplied, the @var{n}th enclosing loop is exited.
+@var{n} must be greater than or equal to 1.
+The return status is zero unless @var{n} is not greater than or equal to 1.
@item cd
@btindex cd
@example
-cd [-LP] [@var{directory}]
+cd [-L|-P] [@var{directory}]
@end example
-Change the current working directory to @var{directory}. If @var{directory}
-is not given, the value of the @code{HOME} shell variable is used. If the
-shell variable @code{CDPATH} exists, it is used as a search path. If
-@var{directory} begins with a slash, @code{CDPATH} is not used.
-The @samp{-P} option means
-to not follow symbolic links; symlinks are followed by default or with the
-@samp{-L} option.
+Change the current working directory to @var{directory}.
+If @var{directory} is not given, the value of the @env{HOME} shell
+variable is used.
+If the shell variable @env{CDPATH} exists, it is used as a search path.
+If @var{directory} begins with a slash, @env{CDPATH} is not used.
+
+The @option{-P} option means to not follow symbolic links; symbolic
+links are followed by default or with the @option{-L} option.
+If @var{directory} is @samp{-}, it is equivalent to @env{$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.
@item continue
@btindex continue
@end example
Resume the next iteration of an enclosing @code{for}, @code{while},
@code{until}, or @code{select} loop.
-If @var{n} is supplied, the execution of the
-@var{n}th enclosing loop is resumed.
+If @var{n} is supplied, the execution of the @var{n}th enclosing loop
+is resumed.
+@var{n} must be greater than or equal to 1.
+The return status is zero unless @var{n} is not greater than or equal to 1.
@item eval
@btindex eval
@example
eval [@var{arguments}]
@end example
-The arguments are concatenated together into a single
-command, which is then read and executed.
+The arguments are concatenated together into a single command, which is
+then read and executed, and its exit status returned as the exit status
+of @code{eval}.
+If there are no arguments or only empty arguments, the return status is
+zero.
@item exec
@btindex exec
@example
-exec [-cl] [-a @var{name}] [@var{command}] [@var{arguments}]
+exec [-cl] [-a @var{name}] [@var{command} [@var{arguments}]]
@end example
If @var{command}
-is supplied, it replaces the shell.
-If the @samp{-l} option is supplied,
-the shell places a dash in the zeroth arg passed to @var{command}.
+is supplied, it replaces the shell without creating a new process.
+If the @option{-l} option is supplied, the shell places a dash at the
+beginning of the zeroth arg 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 environment.
-If @samp{-a} is supplied, the shell passes @var{name}
-as the zeroth argument to @var{command}.
+The @option{-c} option causes @var{command} to be executed with an empty
+environment.
+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.
+the current shell environment. If there are no redirection errors, the
+return status is zero; otherwise the return status is non-zero.
@item exit
@btindex exit
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
@btindex 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
-refer to shell functions. 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
+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 @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 @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 @option{-f} is supplied
+with a name that is not a shell function.
@item getopts
@btindex 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
-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 reset between multiple
-calls to @code{getopts}
-within the same shell invocation if a new set of parameters
-is to be used.
+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 @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.
+@env{OPTIND} is set to the index of the first non-option argument,
+and @code{name} is set to @samp{?}.
+
+@code{getopts}
+normally parses the positional parameters, but if more arguments are
+given in @var{args}, @code{getopts} parses those instead.
@code{getopts} can report errors in two ways. If the first character of
@var{optstring} is a colon, @var{silent}
error reporting is used. In normal operation diagnostic messages
-are printed when illegal options or missing option arguments are
+are printed when invalid options or missing option arguments are
encountered.
-If the variable @code{OPTERR}
-is set to 0, no error message will be displayed, even if the first
+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 illegal option is seen,
+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.
-
-@code{getopts}
-normally parses the positional parameters, but if more arguments are
-given in @var{args}, @code{getopts} parses those instead.
+@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 filenames of commands specified as arguments,
-so they need not be searched for on subsequent invocations. The
-commands are found by searching through the directories listed in
-@code{$PATH}. The @samp{-p} option inhibits the path search, and
-@var{filename} is used as the location of @var{name}.
-The @samp{-r} option causes the shell to forget
-all remembered locations. If no arguments are given, information
-about remembered commands is printed.
+Remember the full pathnames of commands specified as @var{name} arguments,
+so they need not be searched for on subsequent invocations.
+The commands are found by searching through the directories listed in
+@env{$PATH}.
+The @option{-p} option inhibits the path search, and @var{filename} is
+used as the location of @var{name}.
+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.
@item pwd
@btindex pwd
@example
pwd [-LP]
@end example
-Print the current working directory. If the @samp{-P} option is supplied,
-the path printed will not contain symbolic links. If the @samp{-L} option
-is supplied, the path printed may contain symbolic links.
+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 @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
+is supplied.
@item readonly
@btindex readonly
@example
-readonly [-apf] [@var{name}] @dots{}
+readonly [-apf] [@var{name}[=@var{value}]] @dots{}
@end example
-Mark each @var{name} as unchangable. 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 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}
+Mark each @var{name} as readonly.
+The values of these names may not be changed by subsequent assignment.
+If the @option{-f} option is supplied, each @var{name} refers to a shell
+function.
+The @option{-a} option means each @var{name} refers to an 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 @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 @option{-f} option is supplied with a name that is not a shell function.
@item return
@btindex return
@example
return [@var{n}]
@end example
-Cause a shell function to exit with value @var{n}. This may also be used
-to terminate execution of a script being executed with the @code{.}
-builtin.
+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{.} (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
@example
shift [@var{n}]
@end example
-Shift positional parameters to the left by @var{n}.
-The positional parameters from @var{n}+1 @dots{}
-are renamed to
-@code{$1} @dots{} .
-Parameters represented by the numbers
-@code{$#} to @var{n}+1 are unset. @var{n}
-must be a non-negative number less than or equal to @code{$#}.
+Shift the positional parameters to the left by @var{n}.
+The positional parameters from @var{n}+1 @dots{} @code{$#} are
+renamed to @code{$1} @dots{} @code{$#}-@var{n}+1.
+Parameters represented by the numbers @code{$#} to @var{n}+1 are unset.
+@var{n} must be a non-negative number less than or equal to @code{$#}.
+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.
@item test
@itemx [
@btindex test
@btindex [
-Evaluate a conditional expression (@pxref{Bash Conditional Expressions}).
+Evaluate a conditional expression @var{expr}.
+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.
+
+@table @code
+@item ! @var{expr}
+True if @var{expr} is false.
+
+@item ( @var{expr} )
+Returns the value of @var{expr}.
+This may be used to override the normal precedence of operators.
+
+@item @var{expr1} -a @var{expr2}
+True if both @var{expr1} and @var{expr2} are true.
+
+@item @var{expr1} -o @var{expr2}
+True if either @var{expr1} or @var{expr2} is true.
+@end table
+
+The @code{test} and @code{[} builtins evaluate conditional
+expressions using a set of rules based on the number of arguments.
+
+@table @asis
+@item 0 arguments
+The expression is false.
+
+@item 1 argument
+The expression is true if and only if the argument is not null.
+
+@item 2 arguments
+If the first argument is @samp{!}, the expression is true if and
+only if the second argument is null.
+If the first argument is one of the unary conditional operators
+(@pxref{Bash Conditional Expressions}), the expression
+is true if the unary test is true.
+If the first argument is not a valid unary operator, the expression is
+false.
+
+@item 3 arguments
+If the second argument is one of the binary conditional
+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.
+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
+the three-argument expression composed of the remaining arguments.
+Otherwise, the expression is parsed and evaluated according to
+precedence using the rules listed above.
+
+@item 5 or more arguments
+The expression is parsed and evaluated according to precedence
+using the rules listed above.
+@end table
@item times
@btindex times
times
@end example
Print out the user and system times used by the shell and its children.
+The return status is zero.
@item trap
@btindex trap
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
-associated with each signal number.
-Each @var{sigspec} is either a signal name such as @code{SIGINT} (with
-or without the @code{SIG} prefix) or a signal number.
+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.
+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{Bash Builtins}) 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 @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.
+The return status is zero unless a @var{sigspec} does not specify a
+valid signal.
+
@item umask
@btindex umask
@example
-umask [-S] [@var{mode}]
+umask [-p] [-S] [@var{mode}]
@end example
Set the shell process's file creation mask to @var{mode}. If
@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 @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
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.
-Read-only variables and functions may not be unset.
-
+Readonly variables and functions may not be unset.
+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} 1003.2 standard.
-@item IFS
-A list of characters that separate fields; used when the shell splits
-words as part of expansion.
+@table @code
-@item PATH
-A colon-separated list of directories in which the shell looks for
-commands.
+@item alias
+@btindex alias
+@example
+alias [@code{-p}] [@var{name}[=@var{value}] @dots{}]
+@end example
-@item HOME
-The current user's home directory; the default for the @code{cd} builtin
-command.
+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 CDPATH
-A colon-separated list of directories used as a search path for
-the @code{cd} command.
+@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 files which the shell periodically checks
-for new mail. You can
-also specify what message is printed by separating the file name from
-the message with a @samp{?}. When used in the text of the message,
-@code{$_} stands for the name of the current mailfile.
+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
+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}.
+Options, if supplied, have the following meanings:
-@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.
+@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 PS1
-The primary prompt string. The default value is @samp{\s-\v\$ }.
+@item -l
+List the names of all Readline functions.
-@item PS2
-The secondary prompt string. The default value is @samp{> }.
+@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 OPTIND
-The index of the last option processed by the
-@code{getopts} builtin.
+@item -P
+List current Readline function names and bindings.
-@item OPTARG
-The value of the last option argument processed by the
-@code{getopts} builtin.
+@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.
-@end vtable
+@item -V
+List current Readline variable names and values.
-@node Other Bourne Shell Features
-@section Other Bourne Shell Features
+@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.
-@menu
-* Major Differences From The Bourne Shell:: Major differences between
- Bash and the Bourne shell.
-@end menu
+@item -S
+Display Readline key sequences bound to macros and the strings they output.
-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 the @sc{POSIX} standard; this section quickly details the differences
-of significance. A number of these differences are explained in greater
-depth in subsequent sections.
+@item -f @var{filename}
+Read key bindings from @var{filename}.
-@node Major Differences From The Bourne Shell
-@subsection Major Differences From The SVR4.2 Bourne Shell
+@item -q @var{function}
+Query about which keys invoke the named @var{function}.
-Bash is @sc{POSIX}-conformant, even where the @sc{POSIX} specification
-differs from traditional @code{sh} behavior.
+@item -u @var{function}
+Unbind all keys bound to the named @var{function}.
-Bash has multi-character invocation options (@pxref{Invoking Bash}).
+@item -r @var{keyseq}
+Remove any current binding for @var{keyseq}.
-Bash has command-line editing (@pxref{Command Line Editing}) and
-the @code{bind} builtin.
+@item -x @var{keyseq:shell-command}
+Cause @var{shell-command} to be executed whenever @var{keyseq} is
+entered.
-Bash has command history (@pxref{Bash History Facilities}) and the
-@code{history} and @code{fc} builtins to manipulate it.
+@end table
-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.
-Bash has one-dimensional array variables (@pxref{Arrays}), and the
-appropriate variable expansions and assignment syntax to use them.
-Some of the Bash builtins take options to act on arrays. Bash provides
-some 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.
-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.
+@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).
-Bash includes the @code{select} compound command, which allows the
-generation of simple menus (@pxref{Korn Shell Constructs}).
+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.
-Bash includes brace expansion (@pxref{Brace Expansion}) and tilde
-expansion (@pxref{Tilde Expansion}).
+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.
-Bash implements command aliases and the @code{alias} and @code{unalias}
-builtins (@pxref{Aliases}).
+@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.
-Bash provides shell arithmetic and arithmetic expansion
-(@pxref{Shell Arithmetic}).
+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.
-The @sc{POSIX} and @code{ksh}-style @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 declare
+@btindex declare
+@example
+declare [-afFirtx] [-p] [@var{name}[=@var{value}] @dots{}]
+@end example
-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.
+Declare variables and give them attributes. If no @var{name}s
+are given, then display the values of variables instead.
-Bash includes the @sc{POSIX} and @code{ksh}-style pattern removal
-@samp{%}, @samp{#}, @samp{%%} and @samp{##} constructs to remove
-leading or trailing substrings from variable values
-(@pxref{Shell Parameter Expansion}).
+The @option{-p} option will display the attributes and values of each
+@var{name}.
+When @option{-p} is used, additional options are ignored.
+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{Bash Builtins}), 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:
-The expansion @code{$@{#xx@}}, which returns the length of @code{$xx},
-is supported (@pxref{Shell Parameter Expansion}).
+@table @code
+@item -a
+Each @var{name} is an array variable (@pxref{Arrays}).
-The @code{$'@dots{}'} quoting syntax, which expands ANSI-C
-backslash-escaped characters in the text between the single quotes,
-is supported (@pxref{ANSI-C Quoting}).
+@item -f
+Use function names only.
-Bash supports the @code{$"@dots{}"} quoting syntax to do
-locale-specific translation of the characters between the double
-quotes. The @samp{-D} and @samp{--dump-strings} invocation options
-list the translatable strings found in a script
-(@pxref{Locale Translation}).
+@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.
-The expansion @code{$@{var:}@var{offset}@code{[:}@var{length}@code{]@}},
-which expands to the substring of @code{var}'s value of length
-@var{length}, optionally beginning at @var{offset}, is present
-(@pxref{Shell Parameter Expansion}).
+@item -r
+Make @var{name}s readonly. These names cannot then be assigned values
+by subsequent assignment statements or unset.
-The expansion
-@code{$@{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 -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.
-Bash has @var{indirect} variable expansion using @code{$@{!word@}}
-(@pxref{Shell Parameter Expansion}).
+@item -x
+Mark each @var{name} for export to subsequent commands via
+the environment.
+@end table
-Bash can expand positional parameters beyond @code{$9} using
-@code{$@{@var{num}@}}.
+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. 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 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}.
-Bash has process substitution (@pxref{Process Substitution}).
+@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.
-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.
+@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 \0@var{nnn}
+the eight-bit character whose value is the octal value @var{nnn}
+(zero to three octal digits)
+@item \@var{nnn}
+the eight-bit character whose value is the octal value @var{nnn}
+(one 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
-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 enable
+@btindex enable
+@example
+enable [-n] [-p] [-f @var{filename}] [-ads] [@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}.
-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.
-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}.
-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}).
-Bash performs filename expansion on filenames specified as operands
-to 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.
-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 [-s] [@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 @option{-s} option restricts the information displayed to a short
+usage synopsis.
+The return status is zero unless no command matches @var{pattern}.
-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}.
+@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.
-Bash interprets special backslash-escaped characters in the prompt
-strings when interactive (@pxref{Printing a Prompt}).
+@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.
-Bash allows you to write a function to override a builtin, and provides
-access to that builtin's functionality within the function via the
-@code{builtin} and @code{command} builtins (@pxref{Bash 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.
-The @code{command} builtin allows selective disabling of functions
-when command lookup is performed (@pxref{Bash Builtins}).
+@item printf
+@btindex printf
+@example
+@code{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.
+
+The @option{-v} option causes the output to be assigned to the variable
+@var{var} rather than being printed to the standard output.
+
+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.
-Individual builtins may be enabled or disabled using the @code{enable}
-builtin (@pxref{Bash Builtins}).
+@item read
+@btindex read
+@example
+read [-ers] [-a @var{aname}] [-d @var{delim}] [-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, or an invalid file descriptor is supplied as the argument to
+@option{-u}.
+Options, if supplied, have the following meanings:
-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}.
+@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.
-Shell functions may be exported to children via the environment
-(@pxref{Shell Functions}).
+@item -d @var{delim}
+The first character of @var{delim} is used to terminate the input line,
+rather than newline.
-Bash includes a @code{help} builtin for quick reference to shell
-facilities (@pxref{Bash Builtins}).
+@item -e
+Readline (@pxref{Command Line Editing}) is used to obtain the line.
-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 -n @var{nchars}
+@code{read} returns after reading @var{nchars} characters rather than
+waiting for a complete line of input.
-Bash includes the @code{shopt} builtin, for finer control of shell
-optional capabilities (@pxref{Bash Builtins}).
+@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.
-Bash has much more optional behavior controllable with the @code{set}
-builtin (@pxref{The Set Builtin}).
+@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.
-The @code{disown} builtin can remove a job from the internal shell
-job table (@pxref{Job Control Builtins}).
+@item -s
+Silent mode. If input is coming from a terminal, characters are
+not echoed.
-The @code{return} builtin may be used to abort execution of scripts
-executed with the @code{.} or @code{source} builtins
-(@pxref{Bourne Shell Builtins}).
+@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.
+This option has no effect if @code{read} is not reading input from the
+terminal or a pipe.
-The @code{test} builtin (@pxref{Bourne Shell Builtins})
-is slightly different, as it implements the
-@sc{POSIX} 1003.2 algorithm, which specifies the behavior based on the
-number of arguments.
+@item -u @var{fd}
+Read input from file descriptor @var{fd}.
-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.
+@end table
-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 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 @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:
-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 -s
+Enable (set) each @var{optname}.
-The Bash @code{type} builtin is more extensive and gives more information
-about the names it finds (@pxref{Bash Builtins}).
+@item -u
+Disable (unset) each @var{optname}.
-Bash implements a @code{csh}-like directory stack, and provides the
-@code{pushd}, @code{popd}, and @code{dirs} builtins to manipulate it
-(@pxref{C Shell Builtins}).
-Bash also makes the directory stack visible as the value of the
-@code{DIRSTACK} shell variable.
+@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 @option{-q},
+the return status is zero if all @var{optnames} are enabled;
+non-zero otherwise.
-The Bash restricted mode is more useful (@pxref{The Restricted Shell});
-the @sc{SVR4.2} shell restricted mode is too limited.
+@item -o
+Restricts the values of
+@var{optname} to be those defined for the @option{-o} option to the
+@code{set} builtin (@pxref{The Set Builtin}).
+@end table
-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.
+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 @sc{SVR4.2} shell has two privilege-related builtins
-(@code{mldmode} and @code{priv}) not present in Bash.
+Unless otherwise noted, the @code{shopt} options are disabled (off)
+by default.
-Bash does not have the @code{stop} or @code{newgrp} builtins.
+The return status when listing options is zero if all @var{optnames}
+are enabled, non-zero otherwise. When setting or unsetting options,
+the return status is zero unless an @var{optname} is not a valid shell
+option.
+
+The list of @code{shopt} options is:
+@table @code
+@item cdable_vars
+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.
+
+@item cdspell
+If set, minor errors in the spelling of a directory component in a
+@code{cd} command will be corrected.
+The errors checked for are transposed characters,
+a missing character, and a character too many.
+If a correction is found, the corrected path is printed,
+and the command proceeds.
+This option is only used by interactive shells.
+
+@item checkhash
+If this is set, Bash checks that a command found in the hash
+table exists before trying to execute it. If a hashed command no
+longer exists, a normal path search is performed.
-Bash does not use the @code{SHACCT} variable or perform shell accounting.
+@item checkwinsize
+If set, Bash checks the window size after each command
+and, if necessary, updates the values of
+@env{LINES} and @env{COLUMNS}.
-The @sc{SVR4.2} @code{sh} uses a @code{TIMEOUT} variable like Bash uses
-@code{TMOUT}.
+@item cmdhist
+If set, Bash
+attempts to save all lines of a multiple-line
+command in the same history entry. This allows
+easy re-editing of multi-line commands.
-More features unique to Bash may be found in
-@ref{Bash Features}.
+@item dotglob
+If set, Bash includes filenames beginning with a `.' in
+the results of filename expansion.
-@subsection Implementation Differences From The SVR4.2 Shell
+@item execfail
+If this is set, a non-interactive shell will not exit if
+it cannot execute the file specified as an argument to the @code{exec}
+builtin command. An interactive shell does not exit if @code{exec}
+fails.
-Since Bash is a completely new implementation, it does not suffer from
-many of the limitations of the @sc{SVR4.2} shell. For instance:
+@item expand_aliases
+If set, aliases are expanded as described below under Aliases,
+@ref{Aliases}.
+This option is enabled by default for interactive shells.
-@itemize @bullet
+@item extdebug
+If set, behavior intended for use by debuggers is enabled:
+@enumerate
@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.
+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
-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.
+If the command run by the @code{DEBUG} trap returns a non-zero value, the
+next command is skipped and not executed.
@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), the shell misbehaves badly.
+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
-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.
+@code{BASH_ARGC} and @code{BASH_ARGV} are updated as described in their
+descriptions (@pxref{Bash Variables}).
@item
-The @sc{SVR4.2} shell does not allow users to trap @code{SIGALRM} or
-@code{SIGCHLD}.
+Function tracing is enabled: command substitution, shell functions, and
+subshells invoked with @code{( @var{command} )} inherit the
+@code{DEBUG} and @code{RETURN} traps.
@item
-For some reason, the @sc{SVR4.2} shell does not allow the @code{MAILCHECK}
-variable to be unset.
+Error tracing is enabled: command substitution, shell functions, and
+subshells invoked with @code{( @var{command} )} inherit the
+@code{ERROR} trap.
+@end enumerate
-@item
-The @sc{SVR4.2} shell treats @samp{^} as the undocumented equivalent of
-@samp{|}.
+@item extglob
+If set, the extended pattern matching features described above
+(@pxref{Pattern Matching}) are enabled.
-@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 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
-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 failglob
+If set, patterns which fail to match filenames during pathname expansion
+result in an expansion error.
-@item
-The @sc{SVR4.2} shell behaves differently when invoked as @code{jsh}
-(it turns on job control).
-@end itemize
+@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.
-@node Csh Features
-@chapter C-Shell Style Features
+@item gnu_errfmt
+If set, shell error messages are written in the standard @sc{gnu} error
+message format.
-The C-Shell (@dfn{@code{csh}}) was created by Bill Joy at The
-University of California at Berkeley. It
-is generally considered to have better features for interactive use than
-the original Bourne shell. Some of the @code{csh} features present in
-Bash include job control, history expansion, `protected' redirection, and
-several variables to control the interactive behaviour of the shell
-(e.g., @code{IGNOREEOF}).
+@item histappend
+If set, the history list is appended to the file named by the value
+of the @env{HISTFILE}
+variable when the shell exits, rather than overwriting the file.
-@xref{Using History Interactively}, for details on history expansion.
+@item histreedit
+If set, and Readline
+is being used, a user is given the opportunity to re-edit a
+failed history substitution.
-@menu
-* Brace Expansion:: Expansion of expressions within braces.
-* Tilde Expansion:: Expansion of the ~ character.
-* C Shell Builtins:: Builtin commands adopted from the C Shell.
-* C Shell Variables:: Variables which Bash uses in essentially
- the same way as the C Shell.
-@end menu
+@item histverify
+If set, and Readline
+is being used, the results of history substitution are not immediately
+passed to the shell parser. Instead, the resulting line is loaded into
+the Readline editing buffer, allowing further modification.
-@node Brace Expansion
-@section Brace Expansion
-@cindex brace expansion
-@cindex expansion, brace
+@item hostcomplete
+If set, and Readline is being used, Bash will attempt to perform
+hostname completion when a word containing a @samp{@@} is being
+completed (@pxref{Commands For Completion}). This option is enabled
+by default.
-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{postamble}.
-The preamble is prepended to each string contained
-within the braces, and the postamble 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
+@item huponexit
+If set, Bash will send @code{SIGHUP} to all jobs when an interactive
+login shell exits (@pxref{Signals}).
-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.
+@item interactive_comments
+Allow a word beginning with @samp{#}
+to cause that word and all remaining characters on that
+line to be ignored in an interactive shell.
+This option is enabled by default.
-A correctly-formed brace expansion must contain unquoted opening
-and closing braces, and at least one unquoted comma.
-Any incorrectly formed brace expansion is left unchanged.
+@item lithist
+If enabled, and the @code{cmdhist}
+option is enabled, multi-line commands are saved to the history with
+embedded newlines rather than using semicolon separators where possible.
-This construct is typically used as shorthand when the common
-prefix of the strings to be generated is longer than in the
-above example:
-@example
-mkdir /usr/local/src/bash/@{old,new,dist,bugs@}
-@end example
-or
-@example
-chown root /usr/@{ucb/@{ex,edit@},lib/@{ex?.?*,how_ex@}@}
-@end example
+@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.
-@node Tilde Expansion
-@section Tilde Expansion
-@cindex tilde expansion
-@cindex expansion, tilde
+@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.
-Bash has tilde (~) expansion, similar, but not identical, to that of
-@code{csh}. The following table shows what unquoted words beginning
-with a tilde expand to.
+@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.
-@table @code
-@item ~
-The current value of @code{$HOME}.
-@item ~/foo
-@file{$HOME/foo}
+@item nocaseglob
+If set, Bash matches filenames in a case-insensitive fashion when
+performing filename expansion.
-@item ~fred/foo
-The subdirectory @code{foo} of the home directory of the user
-@code{fred}.
+@item nocasematch
+If set, Bash matches patterns in a case-insensitive fashion when
+performing matching while executing @code{case} or @code{[[}
+conditional commands.
-@item ~+/foo
-@file{$PWD/foo}
+@item nullglob
+If set, Bash allows filename patterns which match no
+files to expand to a null string, rather than themselves.
-@item ~-/foo
-@file{$OLDPWD/foo}
-@end table
+@item progcomp
+If set, the programmable completion facilities
+(@pxref{Programmable Completion}) are enabled.
+This option is enabled by default.
-Bash will also tilde expand words following redirection operators
-and words following @samp{=} in assignment statements.
+@item promptvars
+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.
-@node C Shell Builtins
-@section C Shell Builtins
+@item restricted_shell
+The shell sets this option if it is started in restricted mode
+(@pxref{The Restricted Shell}).
+The value may not be changed.
+This is not reset when the startup files are executed, allowing
+the startup files to discover whether or not a shell is restricted.
-Bash has several builtin commands whose definition is very similar
-to @code{csh}.
+@item shift_verbose
+If this is set, the @code{shift}
+builtin prints an error message when the shift count exceeds the
+number of positional parameters.
-@table @code
-@btindex pushd
-@item pushd
-@example
-pushd [@var{dir} | @var{+N} | @var{-N}] [-n]
-@end example
+@item sourcepath
+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.
-Save the current directory on a list and then @code{cd} to
-@var{dir}. With no
-arguments, exchanges the top two directories.
+@item xpg_echo
+If set, the @code{echo} builtin expands backslash-escape sequences
+by default.
-@table @code
-@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
-the list by rotating the stack.
-@item -@var{N}
-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
-@code{cd}s to @var{dir}. You can see the saved directory list
-with the @code{dirs} command.
@end table
-@item popd
-@btindex popd
+@noindent
+The return status when listing options is zero if all @var{optnames}
+are enabled, non-zero otherwise.
+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
-popd [+@var{N} | -@var{N}] [-n]
+source @var{filename}
@end example
+A synonym for @code{.} (@pxref{Bourne Shell Builtins}).
-Pop the directory stack, and @code{cd} to the new top directory. When
-no arguments are given, @code{popd}
-removes the top directory from the stack and
-performs a @code{cd} to the new top directory. The
-elements are numbered from 0 starting at the first directory listed with
-@code{dirs}; i.e., @code{popd} is equivalent to @code{popd +0}.
-@table @code
-@item +@var{N}
-Removes the @var{N}th directory (counting from the left of the
-list printed by @code{dirs}), starting with zero.
-@item -@var{N}
-Removes the @var{N}th directory (counting from the right of the
-list printed by @code{dirs}), starting with zero.
-@item -n
-Suppresses the normal change of directory when removing directories
-from the stack, so that only the stack is manipulated.
-@end table
-
-@item dirs
-@btindex dirs
+@item type
+@btindex type
@example
-dirs [+@var{N} | -@var{N}] [-clvp]
+type [-afptP] [@var{name} @dots{}]
@end example
-Display the list of currently remembered directories. Directories
-find their way onto the list with the @code{pushd} command; you can get
-back up through the list with the @code{popd} command.
-@table @code
-@item +@var{N}
-Displays the @var{N}th directory (counting from the left of the
-list printed by @code{dirs} when invoked without options), starting
-with zero.
-@item -@var{N}
-Displays the @var{N}th directory (counting from the right of the
-list printed by @code{dirs} when invoked without options), starting
-with zero.
-@item -c
-Clears the directory stack by deleting all of the elements.
-@item -l
-Produces a longer listing; the default listing format uses a
-tilde to denote the home directory.
-@item -p
-Causes @code{dirs} to print the directory stack with one entry per
-line.
-@item -v
-Causes @code{dirs} to print the directory stack with one entry per
-line, prepending each entry with its index in the stack.
-@end table
+For each @var{name}, indicate how it would be interpreted if used as a
+command name.
-@item history
-@btindex history
+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.
+
+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}.
+
+The @option{-P} option forces a path search for each @var{name}, even if
+@option{-t} would not return @samp{file}.
+
+If a command is hashed, @option{-p} and @option{-P} print the hashed value,
+not necessarily the file that appears first in @code{$PATH}.
+
+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.
+
+If the @option{-f} option is used, @code{type} does not attempt to find
+shell functions, as with the @code{command} builtin.
+
+The return status is zero if any of the @var{names} are found, non-zero
+if none are found.
+
+@item typeset
+@btindex typeset
@example
-history [-c] [@var{n}]
-history [-anrw] [@var{filename}]
-history -ps @var{arg}
+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.
-Display the history list with line numbers. Lines prefixed with
-with a @samp{*} have been modified. An argument of @var{n} says
-to list only the last @var{n} lines. Options, if supplied, have
-the following meanings:
-
+@item ulimit
+@btindex ulimit
+@example
+ulimit [-acdflmnpstuvSH] [@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 -w
-Write out the current history to the history file.
+@item -S
+Change and report the soft limit associated with a resource.
-@item -r
-Read the current history file and append its contents to
-the history list.
+@item -H
+Change and report the hard limit associated with a resource.
@item -a
-Append the new
-history lines (history lines entered since the beginning of the
-current Bash session) to the history file.
-
-@item -n
-Append the history lines not already read from the history file
-to the current history list. These are lines appended to the history
-file since the beginning of the current Bash session.
+All current limits are reported.
@item -c
-Clear the history list. This may be combined
-with the other options to replace the history list completely.
-
-@item -s
-The @var{arg}s are added to the end of
-the history list as a single entry.
-
-@item -p
-Perform history substitution on the @var{arg}s and display the result
-on the standard output, without storing the results in the history list.
-@end table
+The maximum size of core files created.
-When the @samp{-w}, @samp{-r}, @samp{-a}, or @samp{-n} option is
-used, if @var{filename}
-is given, then it is used as the history file. If not, then
-the value of the @code{HISTFILE} variable is used.
+@item -d
+The maximum size of a process's data segment.
-@item logout
-@btindex logout
-Exit a login shell.
+@item -f
+The maximum size of files created by the shell.
-@item source
-@btindex source
-A synonym for @code{.} (@pxref{Bourne Shell Builtins}).
+@item -l
+The maximum size that may be locked into memory.
-@end table
+@item -m
+The maximum resident set size.
-@node C Shell Variables
-@section C Shell Variables
+@item -n
+The maximum number of open file descriptors.
-@vtable @code
+@item -p
+The pipe buffer size.
-@item IGNOREEOF
-If this variable is set, its value is used the number of consecutive
-@code{EOF}s Bash will read before exiting. By default, Bash will exit
-upon reading a single @code{EOF}. If @code{IGNOREEOF} is not set to
-a numeric value, Bash acts as if its value were 10.
+@item -s
+The maximum stack size.
-@end vtable
+@item -t
+The maximum amount of cpu time in seconds.
-@node Korn Shell Features
-@chapter Korn Shell Style Features
+@item -u
+The maximum number of processes available to a single user.
-This section describes features primarily inspired by the
-Korn Shell (@code{ksh}). In some cases, the @sc{POSIX} 1003.2
-standard has adopted these commands and variables from the
-Korn Shell; Bash implements those features using the @sc{POSIX}
-standard as a guide.
+@item -v
+The maximum amount of virtual memory available to the process.
-@menu
-* Korn Shell Constructs:: Shell grammar constructs adopted from the
- Korn Shell
-* Korn Shell Builtins:: Builtin commands adopted from the Korn Shell.
-* Korn Shell Variables:: Variables which Bash uses in essentially
- the same way as the Korn Shell.
-* Aliases:: Substituting one command for another.
-@end menu
+@end table
-@node Korn Shell Constructs
-@section Korn Shell Constructs
+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.
+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.
-Bash includes the Korn Shell @code{select} construct. This construct
-allows the easy generation of menus. It has almost the same syntax as
-the @code{for} command.
+The return status is zero unless an invalid option or argument is supplied,
+or an error occurs while setting a new limit.
-The syntax of the @code{select} command is:
-@rwindex select
+@item unalias
+@btindex unalias
@example
-select @var{name} [in @var{words} @dots{}]; do @var{commands}; done
+unalias [-a] [@var{name} @dots{} ]
@end example
-The list of words following @code{in} is expanded, generating a list
-of items. The set of expanded words is printed on the standard
-error, each preceded by a number. If the @samp{in @var{words}}
-is omitted, the positional parameters are printed. The
-@code{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}.
+Remove each @var{name} from the list of aliases. If @option{-a} is
+supplied, all aliases are removed.
+Aliases are described in @ref{Aliases}.
-The @var{commands} are executed after each selection until a
-@code{break} or @code{return} command is executed, at which
-point the @code{select} command completes.
+@end table
-Bash also has adopted command timing from the Korn shell. If the
-@code{time} reserved word precedes a pipeline, which may consist
-of a single command, timing statistics for the pipeline are displayed
-when it completes.
-The statistics currently consist of elapsed (wall-clock) time and
-user and system time consumed by the command's execution.
+@node The Set Builtin
+@section The Set Builtin
-The use of @code{time} as a reserved word permits the timing of
-shell builtins, shell functions, and pipelines. An external
-@code{time} command cannot time these easily.
+This builtin is so complicated that it deserves its own section.
+
+@table @code
+@item set
+@btindex set
+@example
+set [--abefhkmnptuvxBCHP] [-o @var{option}] [@var{argument} @dots{}]
+@end example
-@node Korn Shell Builtins
-@section Korn Shell Builtins
+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.
-This section describes Bash builtin commands taken from @code{ksh}.
+When options are supplied, they set or unset shell attributes.
+Options, if specified, have the following meanings:
@table @code
+@item -a
+Mark variables and function which are modified or created for export
+to the environment of subsequent commands.
-@item fc
-@btindex fc
-@example
-@code{fc [-e @var{ename}] [-nlr] [@var{first}] [@var{last}]}
-@code{fc -s [@var{pat}=@var{rep}] [@var{command}]}
-@end example
+@item -b
+Cause the status of terminated background jobs to be reported
+immediately, rather than before printing the next primary prompt.
-Fix Command. In the first form, a range of commands from @var{first} to
-@var{last} is selected from the history list. Both @var{first} and
-@var{last} may be specified as a string (to locate the most recent
-command beginning with that string) or as a number (an index into the
-history list, where a negative number is used as an offset from the
-current command number). If @var{last} is not specified it is set to
-@var{first}. If @var{first} is not specified it is set to the previous
-command for editing and @minus{}16 for listing. If the @samp{-l} flag is
-given, the commands are listed on standard output. The @samp{-n} flag
-suppresses the command numbers when listing. The @samp{-r} flag
-reverses the order of the listing. Otherwise, the editor given by
-@var{ename} is invoked on a file containing those commands. If
-@var{ename} is not given, the value of the following variable expansion
-is used: @code{$@{FCEDIT:-$@{EDITOR:-vi@}@}}. This says to use the
-value of the @code{FCEDIT} variable if set, or the value of the
-@code{EDITOR} variable if that is set, or @code{vi} if neither is set.
-When editing is complete, the edited commands are echoed and executed.
-
-In the second form, @var{command} is re-executed after each instance
-of @var{pat} in the selected command is replaced by @var{rep}.
-
-A useful alias to use with the @code{fc} command is @code{r='fc -s'}, so
-that typing @samp{r cc} runs the last command beginning with @code{cc}
-and typing @samp{r} re-executes the last command (@pxref{Aliases}).
+@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 @code{&&} or @code{||} list, or if the command's return
+status is being inverted using @code{!}.
+A trap on @code{ERR}, if set, is executed before the shell exits.
-@item let
-@btindex let
-The @code{let} builtin allows arithmetic to be performed on shell variables.
-For details, refer to @ref{Arithmetic Builtins}.
+@item -f
+Disable file name generation (globbing).
-@item typeset
-@btindex typeset
-The @code{typeset} command is supplied for compatibility with the Korn
-shell; however, it has been deprecated in favor of the
-@code{declare} command (@pxref{Bash Builtins}).
+@item -h
+Locate and remember (hash) commands as they are looked up for execution.
+This option is enabled by default.
-@end table
+@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 Korn Shell Variables
-@section Korn Shell Variables
+@item -m
+Job control is enabled (@pxref{Job Control}).
-@vtable @code
+@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 REPLY
-The default variable for the @code{read} builtin.
+@item -o @var{option-name}
-@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.
+Set the option corresponding to @var{option-name}:
-@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.
+@table @code
+@item allexport
+Same as @code{-a}.
-@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 braceexpand
+Same as @code{-B}.
-@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 default is @samp{+ }.
+@item emacs
+Use an @code{emacs}-style line editing interface (@pxref{Command Line Editing}).
-@item PWD
-The current working directory as set by the @code{cd} builtin.
+@item errexit
+Same as @code{-e}.
-@item OLDPWD
-The previous working directory as set by the @code{cd} builtin.
+@item errtrace
+Same as @code{-E}.
-@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.
+@item functrace
+Same as @code{-T}.
-@item LINENO
-The line number in the script or shell function currently executing.
+@item hashall
+Same as @code{-h}.
-@item FCEDIT
-The editor used as a default by the @code{fc} builtin command.
+@item histexpand
+Same as @code{-H}.
-@end vtable
+@item history
+Enable command history, as described in @ref{Bash History Facilities}.
+This option is on by default in interactive shells.
-@node Aliases
-@section Aliases
-@cindex alias expansion
+@item ignoreeof
+An interactive shell will not exit upon reading EOF.
-@menu
-* Alias Builtins:: Builtins commands to maniuplate aliases.
-@end menu
+@item keyword
+Same as @code{-k}.
-The shell maintains a list of @var{aliases}
-that may be set and unset with the @code{alias} and
-@code{unalias} builtin commands.
+@item monitor
+Same as @code{-m}.
-The first word of each 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 @key{=}.
-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 noclobber
+Same as @code{-C}.
-Aliases are created and listed with the @code{alias}
-command, and removed with the @code{unalias} command.
+@item noexec
+Same as @code{-n}.
-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 noglob
+Same as @code{-f}.
-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 nolog
+Currently ignored.
-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 the 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 notify
+Same as @code{-b}.
-Note that for almost every purpose, aliases are superseded by
-shell functions.
+@item nounset
+Same as @code{-u}.
-@node Alias Builtins
-@subsection Alias Builtins
+@item onecmd
+Same as @code{-t}.
-@table @code
+@item physical
+Same as @code{-P}.
-@item alias
-@btindex alias
-@example
-alias [@code{-p}] [@var{name}[=@var{value}] @dots{}]
-@end example
+@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.
-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.
+@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 unalias
-@btindex unalias
-@example
-unalias [-a] [@var{name} @dots{} ]
-@end example
+@item privileged
+Same as @code{-p}.
-Remove each @var{name} from the list of aliases. If @samp{-a} is
-supplied, all aliases are removed.
+@item verbose
+Same as @code{-v}.
+
+@item vi
+Use a @code{vi}-style line editing interface.
+
+@item xtrace
+Same as @code{-x}.
@end table
-@node Bash Features
-@chapter Bash Features
+@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} 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.
-This section describes features unique to Bash.
+@item -t
+Exit after reading and executing one command.
-@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.
-* Arrays:: Array Variables
-* 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 -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.
-@node Invoking Bash
-@section Invoking Bash
+@item -v
+Print shell input lines as they are read.
-@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 -x
+Print a trace of simple commands, \fBfor\fP commands, \fBcase\fP
+commands, \fBselect\fP commands, and arithmetic \fBfor\fP 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.
-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 -B
+The shell will perform brace expansion (@pxref{Brace Expansion}).
+This option is on by default.
-@table @code
-@item --dump-strings
-Equivalent to @samp{-D}.
+@item -C
+Prevent output redirection using @samp{>}, @samp{>&}, and @samp{<>}
+from overwriting existing files.
-@item --help
-Display a usage message on standard output and exit sucessfully.
+@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 --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}. If you wanted to replace your
-current login shell with a Bash login shell, you would say
-@samp{exec bash --login}.
+@item -H
+Enable @samp{!} style history substitution (@pxref{History Interaction}).
+This option is on by default for interactive shells.
-@item --noediting
-Do not use the @sc{GNU} Readline library (@pxref{Command Line Editing})
-to read interactive command lines.
+@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 --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.
+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 --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}.
+@noindent
+If @code{set -P} is on, then:
+@example
+$ cd /usr/sys; echo $PWD
+/usr/local/sys
+$ cd ..; pwd
+/usr/local
+@end example
-@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
+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.
-@item --rcfile @var{filename}
-Execute commands from @var{filename} (instead of @file{~/.bashrc})
-in an interactive shell.
+@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 --restricted
-Make the shell a restricted shell (@pxref{The Restricted Shell}).
+@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 --verbose
-Equivalent to @samp{-v}.
+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 --version
-Show version information for this instance of
-Bash on the standard output and exit successfully.
+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
-There are several single-character options you can give which are
-not available with the @code{set} builtin.
+@node Special Builtins
+@section Special Builtins
+@cindex special builtin
-@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{$0}.
+For historical reasons, the @sc{posix} 1003.2 standard has classified
+several builtin commands as @emph{special}.
+When Bash is executing in @sc{posix} mode, the special builtins
+differ from other builtin commands in three respects:
-@item -i
-Force the shell to run interactively.
+@enumerate
+@item
+Special builtins are found before shell functions during command lookup.
-@item -r
-Make the shell restricted.
-
-@item -s
-If this flag is present, or if no arguments remain after option
-processing, then commands are read from the standard input.
-This option allows the positional parameters to be set
-when invoking an interactive shell.
-
-@item -D
-A list of all double-quoted strings preceded by @samp{$}
-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
+If a special builtin returns an error status, a non-interactive shell exits.
-@end table
+@item
+Assignment statements preceding the command stay in effect in the shell
+environment after the command completes.
+@end enumerate
-@cindex interactive shell
-An @emph{interactive} shell is one whose input and output are both
-connected to terminals (as determined by @code{isatty()}), or one
-started with the @samp{-i} option.
+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}.
-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.
+These are the @sc{posix} special builtins:
+@example
+@w{break : . continue eval exec exit export readonly return set}
+@w{shift trap unset}
+@end example
-@node Bash Startup Files
-@section Bash Startup Files
-@cindex startup files
+@node Shell Variables
+@chapter Shell Variables
-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}).
+@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
-When Bash is invoked as an interactive login shell, 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.
+This chapter describes the shell variables that Bash uses.
+Bash automatically assigns default values to a number of variables.
-When a login shell exits, Bash reads and executes commands from
-the file @file{~/.bash_logout}, if it exists.
+@node Bourne Shell Variables
+@section Bourne Shell Variables
-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}.
+Bash uses certain shell variables in the same way as the Bourne shell.
+In some cases, Bash assigns a default value to the variable.
-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.
+@vtable @code
-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 CDPATH
+A colon-separated list of directories used as a search path for
+the @code{cd} builtin command.
-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.
-
-When invoked as a login shell, 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},
-@code{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 startup files.
+@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}).
-When invoked as @code{sh}, Bash enters @sc{POSIX} mode after
-the startup files are read.
+@item IFS
+A list of characters that separate fields; used when the shell splits
+words as part of expansion.
-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, the @code{ENV} variable is expanded and commands are read
-and executed from the file whose name is the expanded value.
-No other startup files are read.
-This is done by interactive shells only.
+@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.
-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
-rshd does not generally invoke the shell with those options or allow
-them to be specified.
+@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.
-@node Is This Shell Interactive?
-@section Is This Shell Interactive?
-@cindex interactive shell
+@item OPTARG
+The value of the last option argument processed by the @code{getopts} builtin.
-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 OPTIND
+The index of the last option argument processed by the @code{getopts} builtin.
-You may wish to determine within a startup script whether Bash is
-running interactively or not. To do this, examine the variable
-@code{$PS1}; it is unset in non-interactive shells, and set in
-interactive shells. Thus:
+@item PATH
+A colon-separated list of directories in which the shell looks for
+commands.
+A zero-length (null) directory name in the value of @code{PATH} indicates the
+current directory.
+A null directory name may appear as two adjacent colons, or as an initial
+or trailing colon.
-@example
-if [ -z "$PS1" ]; then
- echo This shell is not interactive
-else
- echo This shell is interactive
-fi
-@end example
-Alternatively, you may test the value of the @samp{-} special parameter.
-It contains @code{i} when the shell is interactive. For example:
+@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.
-@example
-case "$-" in
-*i*) echo This shell is interactive ;;
-*) echo This shell is not interactive ;;
-esac
-@end example
+@item PS2
+The secondary prompt string. The default value is @samp{> }.
-@node Bash Builtins
-@section Bash Builtin Commands
+@end vtable
-This section describes builtin commands which are unique to
-or have been extended in Bash.
+@node Bash Variables
+@section Bash Variables
-@table @code
+These variables are set or used by Bash, but other shells
+do not normally treat them specially.
-@item bind
-@btindex bind
-@example
-bind [-m @var{keymap}] [-lpsvPSV] [-q @var{name}] [-r @var{keyseq}]
-bind [-m @var{keymap}] -f @var{filename}
-bind [-m @var{keymap}] @var{keyseq:function-name}
-@end example
+A few variables used by Bash are described in different chapters:
+variables for controlling the job control facilities
+(@pxref{Job Control Variables}).
-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:
+@vtable @code
-@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 BASH
+The full pathname used to execute the current instance of Bash.
+
+@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{Bash Builtins}
+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{Bash Builtins}
+for a description of the @code{extdebug} option to the @code{shopt}
+builtin).
+
+@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 -l
-List the names of all Readline functions
+@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 -p
-Display Readline function names and bindings in such a way that they
-can be re-read
+@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[$i]@}} was called.
+The corresponding source file name is @code{$@{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 BASH_SOURCE
+An array variable whose members are the source filenames corresponding
+to the elements in the @code{FUNCNAME} array variable.
+
+@item BASH_SUBSHELL
+Incremented by one each time a subshell or subshell environment is spawned.
+The initial value is 0.
-@item -P
-List current Readline function names and bindings
+@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:
-@item -v
-Display Readline variable names and values in such a way that they
-can be re-read
+@table @code
-@item -V
-List current Readline variable names and values
+@item BASH_VERSINFO[0]
+The major version number (the @var{release}).
-@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 BASH_VERSINFO[1]
+The minor version number (the @var{version}).
-@item -S
-Display Readline key sequences bound to macros and the strings they output
+@item BASH_VERSINFO[2]
+The patch level.
-@item -f @var{filename}
-Read key bindings from @var{filename}
+@item BASH_VERSINFO[3]
+The build version.
-@item -q
-Query about which keys invoke the named @var{function}
+@item BASH_VERSINFO[4]
+The release status (e.g., @var{beta1}).
-@item -r @var{keyseq}
-Remove any current binding for @var{keyseq}
+@item BASH_VERSINFO[5]
+The value of @env{MACHTYPE}.
@end table
-@item builtin
-@btindex builtin
-@example
-builtin [@var{shell-builtin} [@var{args}]]
-@end example
-Run a shell builtin. This is useful when you wish to define a
-shell function with the same name as a shell builtin, but need the
-functionality of the builtin within the function itself.
+@item BASH_VERSION
+The version number of the current instance of Bash.
-@item command
-@btindex command
-@example
-command [-pVv] @var{command} [@var{args} @dots{}]
-@end example
-Runs @var{command} with @var{arg} ignoring shell functions. If
-you have a shell function called @code{ls}, and you wish to call
-the command @code{ls}, you can say @samp{command ls}. The
-@samp{-p} option means to use a default value for @code{$PATH}
-that is guaranteed to find all of the standard utilities.
+@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_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.
-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 printed; the @samp{-V} option produces
-a more verbose description.
+@item COMP_WORDS
+An array variable consisting of the individual
+words in the current command line.
+This variable is available only in shell functions invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
-@item declare
-@btindex declare
-@example
-declare [-afFrxi] [-p] [@var{name}[=@var{value}]]
-@end example
+@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}).
-Declare variables and give them attributes. If no @var{name}s
-are given, then display the values of variables instead.
+@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.
-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 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.
-@table @code
-@item -a
-Each @var{name} is an array variable (@pxref{Arrays}).
+@item EUID
+The numeric effective user id of the current user. This variable
+is readonly.
-@item -f
-Use function names only.
+@item FCEDIT
+The editor used as a default by the @option{-e} option to the @code{fc}
+builtin command.
-@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 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 -r
-Make @var{name}s readonly. These names cannot then be assigned values
-by subsequent assignment statements.
+@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 "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 -x
-Mark each @var{name} for export to subsequent commands via
-the environment.
-@end table
+@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.
-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.
+@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 echo
-@btindex echo
-@example
-echo [-neE] [arg @dots{}]
-@end example
-Output the @code{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 \nnn
-the character whose ASCII code is @code{nnn} (octal)
-@end table
-
-@item enable
-@btindex enable
-@example
-enable [-n] [-p] [-f @var{filename}] [-ads] [@var{name} @dots{}]
-@end example
-Enable and disable builtin shell commands. This allows you to
-use a disk command which has the same name as a shell builtin.
-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}.
+@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.
-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.
+@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.
-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.2} special
-builtins. If @samp{-s} is used with @samp{-f}, the new builtin becomes
-a special builtin.
+@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 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.
+@item HISTFILE
+The name of the file to which the command history is saved. The
+default value is @file{~/.bash_history}.
-@item local
-@btindex local
-@example
-local @var{name}[=@var{value}]
-@end example
-For each argument, create a local variable called @var{name}, and
-give it @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.
+@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 history file is also truncated to this size after
+writing it when an interactive shell exits.
+The default value is 500.
-@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 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 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 assigned to the last @var{name}.
-Only the characters in the value of the @code{IFS} variable
-are recognized as word delimiters. 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:
+@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}.
-@table @code
-@item -r
-If this option is given, a backslash-newline pair is not ignored, and
-the backslash is considered to be part of the line.
+@item HISTSIZE
+The maximum number of commands to remember on the history list.
+The default value is 500.
-@item -p @var{prompt}
-Display @code{prompt}, without a
-trailing newline, before attempting to read any input. The prompt
-is displayed only if input is coming from a terminal.
+@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.
-@item -a @var{aname}
-The words are assigned to
-sequential indices of the array variable @var{aname}, starting at 0.
+@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.
-@item -e
-Readline (@pxref{Command Line Editing})
-is used to obtain the line.
-@end table
+@item HOSTNAME
+The name of the current host.
-@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. Other options have
-the following meanings:
+@item HOSTTYPE
+A string describing the machine Bash is running on.
-@table @code
-@item -s
-Enable (set) each @var{optname}
+@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.
-@item -u
-Disable (unset) each @var{optname}.
+@item INPUTRC
+The name of the Readline initialization file, overriding the default
+of @file{~/.inputrc}.
-@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},
-the return status is zero if all @var{optnames} are enabled;
-non-zero otherwise.
+@item LANG
+Used to determine the locale category for any category not specifically
+selected with a variable starting with @code{LC_}.
-@item -o
-Restricts the values of
-@var{optname} to be those defined for the @samp{-o} option to the
-@code{set} builtin (@pxref{The Set Builtin}).
-@end table
+@item LC_ALL
+This variable overrides the value of @env{LANG} and any other
+@code{LC_} variable specifying a locale category.
-If either of
-@samp{-s} or @samp{-u}
-is used with no @var{optname} arguments, the display is limited to
-those options which are set or unset, respectively.
+@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}).
-Unless otherwise noted, the @code{shopt} options are disabled (off)
-by default.
+@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}).
-The return status when listing options is zero if all @var{optnames}
-are enabled, non-zero otherwise. When setting or unsetting options,
-the return status is zero unless an @var{optname} is not a legal shell
-option.
+@item LC_MESSAGES
+This variable determines the locale used to translate double-quoted
+strings preceded by a @samp{$} (@pxref{Locale Translation}).
-The list of @code{shopt} options is:
-@table @code
-@item cdable_vars
-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.
+@item LC_NUMERIC
+This variable determines the locale category used for number formatting.
-@item cdspell
-If set, minor errors in the spelling of a directory component in a
-@code{cd} command will be corrected.
-The errors checked for are transposed characters,
-a missing character, and a character too many.
-If a correction is found, the corrected path is printed,
-and the command proceeds.
-This option is only used by interactive shells.
+@item LINENO
+The line number in the script or shell function currently executing.
-@item checkhash
-If this is set, Bash checks that a command found in the hash
-table exists before trying to execute it. If a hashed command no
-longer exists, a normal path search is performed.
+@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 checkwinsize
-If set, Bash checks the window size after each command
-and, if necessary, updates the values of
-@code{LINES} and @code{COLUMNS}.
+@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 cmdhist
-If set, Bash
-attempts to save all lines of a multiple-line
-command in the same history entry. This allows
-easy re-editing of multi-line commands.
+@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 dotglob
-If set, Bash includes filenames beginning with a `.' in
-the results of filename expansion.
+@item OLDPWD
+The previous working directory as set by the @code{cd} builtin.
-@item execfail
-If this is set, a non-interactive shell will not exit if
-it cannot execute the file specified as an argument to the @code{exec}
-builtin command. An interactive shell does not exit if @code{exec}
-fails.
+@item OPTERR
+If set to the value 1, Bash displays error messages
+generated by the @code{getopts} builtin command.
-@item histappend
-If set, the history list is appended to the file named by the value
-of the @code{HISTFILE}
-variable when the shell exits, rather than overwriting the file.
+@item OSTYPE
+A string describing the operating system Bash is running on.
-@item histreedit
-If set, and Readline
-is being used, a user is given the opportunity to re-edit a
-failed history substitution.
+@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 histverify
-If set, and Readline
-is being used, the results of history substitution are not immediately
-passed to the shell parser. Instead, the resulting line is loaded into
-the Readline editing buffer, allowing further modification.
+@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 hostcomplete
-If set, and Readline is being used, Bash will attempt to perform
-hostname completion when a word beginning with @samp{@@} is being
-completed (@pxref{Commands For Completion}). This option is enabled
-by default.
+@item PPID
+The process @sc{id} of the shell's parent process. This variable
+is readonly.
-@item interactive_comments
-Allow a word beginning with @samp{#}
-to cause that word and all remaining characters on that
-line to be ignored in an interactive shell.
-This option is enabled by default.
+@item PROMPT_COMMAND
+If set, the value is interpreted as a command to execute
+before the printing of each primary prompt (@env{$PS1}).
-@item lithist
-If enabled, and the @code{cmdhist}
-option is enabled, multi-line commands are saved to the history with
-embedded newlines rather than using semicolon separators where possible.
+@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 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 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 nullglob
-If set, Bash allows filename patterns which match no
-files to expand to a null string, rather than themselves.
+@item PWD
+The current working directory as set by the @code{cd} builtin.
-@item promptvars
-If set, prompt strings undergo variable and parameter expansion after
-being expanded (@pxref{Printing a Prompt}).
-This option is enabled by default.
+@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 shift_verbose
-If this is set, the @code{shift}
-builtin prints an error message when the shift count exceeds the
-number of positional parameters.
+@item REPLY
+The default variable for the @code{read} builtin.
-@item sourcepath
-If set, the @code{source} builtin uses the value of @code{PATH}
-to find the directory containing the file supplied as an argument.
-This is enabled by default.
-@end table
-
-@item type
-@btindex type
-@example
-type [-all] [-type | -path] [@var{name} @dots{}]
-@end example
-For each @var{name}, indicate how it would be interpreted if used as a
-command name.
+@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.
-If the @samp{-type} flag is used, @code{type} returns 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.
+@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.
-If the @samp{-path} flag is used, @code{type} either returns the name
-of the disk file that would be executed, or nothing if @samp{-type}
-would not return @samp{file}.
+@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.
-If the @samp{-all} flag is used, returns all of the places that contain
-an executable named @var{file}. This includes aliases and functions,
-if and only if the @samp{-path} flag is not also used.
+@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.
-@code{type} accepts @samp{-a}, @samp{-t}, and @samp{-p} as equivalent to
-@samp{-all}, @samp{-type}, and @samp{-path}, respectively.
+@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 ulimit
-@btindex ulimit
-@example
-ulimit [-acdflmnpstuvSH] [@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 -H
-change and report the hard limit associated with a resource.
-@item -a
-all current limits are reported.
+@item %%
+A literal @samp{%}.
-@item -c
-the maximum size of core files created.
+@item %[@var{p}][l]R
+The elapsed time in seconds.
-@item -d
-the maximum size of a process's data segment.
+@item %[@var{p}][l]U
+The number of CPU seconds spent in user mode.
-@item -f
-the maximum size of files created by the shell.
+@item %[@var{p}][l]S
+The number of CPU seconds spent in system mode.
-@item -l
-The maximum size that may be locked into memory.
+@item %P
+The CPU percentage, computed as (%U + %S) / %R.
+@end table
-@item -m
-the maximum resident set size.
+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 -n
-the maximum number of open file descriptors.
+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 -p
-the pipe buffer size.
+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 -s
-the maximum stack size.
+@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.
-@item -t
-the maximum amount of cpu time in seconds.
+In an interative 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 -u
-the maximum number of processes available to a single user.
+@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 -v
-the maximum amount of virtual memory available to the process.
+@item UID
+The numeric real user id of the current user. This variable is readonly.
-@end table
+@end vtable
-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.
+@node Bash Features
+@chapter Bash Features
-@end table
+This section describes features unique to Bash.
-@node The Set Builtin
-@section The Set Builtin
+@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
-This builtin is so overloaded that it deserves its own section.
+@node Invoking Bash
+@section Invoking Bash
-@table @code
-@item set
-@btindex set
@example
-set [-abefhkmnptuvxdBCHP] [-o @var{option}] [@var{argument} @dots{}]
+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
-@table @code
-@item -a
-Mark variables which are modified or created for export.
-
-@item -b
-Cause the status of terminated background jobs to be reported
-immediately, rather than before printing the next primary prompt.
+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 -e
-Exit immediately if a simple command exits with a non-zero status.
+@table @code
+@item --debugger
+Arrange for the debugger profile to be executed before the shell
+starts. Turns on extended debugging mode (see @ref{Bash Builtins}
+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 --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 -f
-Disable file name generation (globbing).
+@item --dump-strings
+Equivalent to @option{-D}.
-@item -h
-Locate and remember (hash) commands as they are looked up for execution.
+@item --help
+Display a usage message on standard output and exit sucessfully.
-@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 --init-file @var{filename}
+@itemx --rcfile @var{filename}
+Execute commands from @var{filename} (instead of @file{~/.bashrc})
+in an interactive shell.
-@item -m
-Job control is enabled (@pxref{Job Control}).
+@item --login
+Equivalent to @option{-l}.
-@item -n
-Read commands but do not execute them.
+@item --noediting
+Do not use the @sc{gnu} Readline library (@pxref{Command Line Editing})
+to read command lines when the shell is interactive.
-@item -o @var{option-name}
+@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.
-Set the flag corresponding to @var{option-name}:
+@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}.
-@table @code
-@item allexport
-same as @code{-a}.
+@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 braceexpand
-same as @code{-B}.
+@item --restricted
+Make the shell a restricted shell (@pxref{The Restricted Shell}).
-@item emacs
-use an @code{emacs}-style line editing interface (@pxref{Command Line Editing}).
+@item --verbose
+Equivalent to @option{-v}. Print shell input lines as they're read.
-@item errexit
-same as @code{-e}.
+@item --version
+Show version information for this instance of
+Bash on the standard output and exit successfully.
-@item hashall
-same as @code{-h}.
+@end table
-@item histexpand
-same as @code{-H}.
+There are several single-character options that may be supplied at
+invocation which are not available with the @code{set} builtin.
-@item history
-Enable command history, as described in @ref{Bash History Facilities}.
-This option is on by default in 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{$0}.
-@item ignoreeof
-the shell will not exit upon reading EOF.
+@item -i
+Force the shell to run interactively. Interactive shells are
+described in @ref{Interactive Shells}.
-@item keyword
-same as @code{-k}.
+@item -l
+Make this shell act as if it had been directly invoked by login.
+When the shell is interactive, this is equivalent to starting a
+login shell with @samp{exec -l bash}.
+When the shell is not interactive, the login shell startup files will
+be executed.
+@samp{exec bash -l} or @samp{exec bash --login}
+will replace the current shell with a Bash login shell.
+@xref{Bash Startup Files}, for a description of the special behavior
+of a login shell.
-@item monitor
-same as @code{-m}.
+@item -r
+Make the shell a restricted shell (@pxref{The Restricted Shell}).
-@item noclobber
-same as @code{-C}.
+@item -s
+If this option is present, or if no arguments remain after option
+processing, then commands are read from the standard input.
+This option allows the positional parameters to be set
+when invoking an interactive shell.
-@item noexec
-same as @code{-n}.
+@item -D
+A list of all double-quoted strings preceded by @samp{$}
+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{Shell Builtin Commands}).
+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 noglob
-same as @code{-f}.
+@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 notify
-same as @code{-b}.
+@end table
-@item nounset
-same as @code{-u}.
+@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 onecmd
-same as @code{-t}.
+@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 physical
-same as @code{-P}.
+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{$0}
+is set to the name of the file, and the positional parameters
+are set to the remaining arguments.
+Bash reads and executes commands from this file, then exits.
+Bash's exit status is the exit status of the last command executed
+in the script. If no commands are executed, the exit status is 0.
-@item posix
-change the behavior of Bash where the default operation differs
-from the @sc{POSIX} 1003.2 standard to match the standard. This
-is intended to make Bash behave as a strict superset of that
-standard.
+@node Bash Startup Files
+@section Bash Startup Files
+@cindex startup files
-@item privileged
-same as @code{-p}.
+This section describs how Bash executes its startup files.
+If any of the files exist but cannot be read, Bash reports an error.
+Tildes are expanded in file names as described above under
+Tilde Expansion (@pxref{Tilde Expansion}).
-@item verbose
-same as @code{-v}.
+Interactive shells are described in @ref{Interactive Shells}.
-@item vi
-use a @code{vi}-style line editing interface.
+@subsubheading Invoked as an interactive login shell, or with @option{--login}
-@item xtrace
-same as @code{-x}.
-@end table
+When Bash is invoked as an interactive login shell, or as a
+non-interactive shell with the @option{--login} option, it first reads and
+executes commands from the file @file{/etc/profile}, if that file exists.
+After reading that file, it looks for @file{~/.bash_profile},
+@file{~/.bash_login}, and @file{~/.profile}, in that order, and reads
+and executes commands from the first one that exists and is readable.
+The @option{--noprofile} option may be used when the shell is started to
+inhibit this behavior.
-@item -p
-Turn on privileged mode.
-In this mode, the @code{$BASH_ENV}
-file is not processed, and shell functions
-are not inherited from the environment. This is enabled automatically
-on startup if the effective user (group) id is not equal to the real
-user (group) id. Turning this option off causes the effective user
-and group ids to be set to the real user and group ids.
+When a login shell exits, Bash reads and executes commands from
+the file @file{~/.bash_logout}, if it exists.
-@item -t
-Exit after reading and executing one command.
+@subsubheading Invoked as an interactive non-login shell
-@item -u
-Treat unset variables as an error when substituting.
+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 -v
-Print shell input lines as they are read.
+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 -x
-Print commands and their arguments as they are executed.
+@subsubheading Invoked non-interactively
-@item -B
-The shell will perform brace expansion (@pxref{Brace Expansion}).
-This option is on by default.
+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 -C
-Disallow output redirection to existing files.
+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 -H
-Enable @samp{!} style history substitution (@pxref{History Interaction}).
-This flag is on by default for interactive shells.
+@subsubheading Invoked with name @code{sh}
-@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.
+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.
+
+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.
+
+When invoked as @code{sh}, Bash enters @sc{posix} mode after
+the startup files are read.
+
+@subsubheading Invoked in @sc{posix} 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.
+
+@subsubheading Invoked by remote shell daemon
+
+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 @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.
+
+@subsubheading Invoked with unequal effective and real @sc{uid/gid}s
+
+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.
+
+@node Interactive Shells
+@section Interactive Shells
+@cindex interactive shell
+@cindex shell, interactive
+
+@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
+
+@node What is an Interactive Shell?
+@subsection What is an Interactive Shell?
+
+An interactive shell
+is one started without non-option arguments, unless @option{-s} is
+specified, without specifiying 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.
+
+An interactive shell generally reads from and writes to a user's
+terminal.
+
+The @option{-s} invocation option may be used to set the positional parameters
+when an interactive shell is started.
+
+@node Is this Shell Interactive?
+@subsection Is this Shell Interactive?
+
+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:
-For example, if @file{/usr/sys} is a link to @file{/usr/local/sys} then:
@example
-$ cd /usr/sys; echo $PWD
-/usr/sys
-$ cd ..; pwd
-/usr
+case "$-" in
+*i*) echo This shell is interactive ;;
+*) echo This shell is not interactive ;;
+esac
@end example
-@noindent
-If @code{set -P} is on, then:
+Alternatively, startup scripts may examine the variable
+@env{PS1}; it is unset in non-interactive shells, and set in
+interactive shells. Thus:
+
@example
-$ cd /usr/sys; echo $PWD
-/usr/local/sys
-$ cd ..; pwd
-/usr/local
+if [ -z "$PS1" ]; then
+ echo This shell is not interactive
+else
+ echo This shell is interactive
+fi
@end example
-@item --
-If no arguments follow this flag, then the positional parameters are
-unset. Otherwise, the positional parameters are set to the
-@var{arguments}, even if some of them begin with a @samp{-}.
+@node Interactive Shell Behavior
+@subsection Interactive Shell Behavior
-@item -
-Signal the end of options, cause all remaining @var{arguments}
-to be assigned to the positional parameters. The @samp{-x}
-and @samp{-v} options are turned off.
-If there are no arguments, the positional parameters remain unchanged.
-@end table
+When the shell is running interactively, it changes its behavior in
+several ways.
+
+@enumerate
+@item
+Startup files are read and executed as described in @ref{Bash Startup Files}.
-Using @samp{+} rather than @samp{-} causes these flags to be
-turned off. The flags can also be used upon invocation of the
-shell. The current set of flags may be found in @code{$-}.
+@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}.
-The remaining N @var{arguments} are positional parameters and are
-assigned, in order, to @code{$1}, @code{$2}, @dots{} @code{$N}. If
-no arguments are given, all shell variables are printed.
-@end table
+@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
+Bash executes the value of the @env{PROMPT_COMMAND} variable as a command
+before printing the primary prompt, @env{$PS1}
+(@pxref{Bash Variables}).
+
+@item
+Readline (@pxref{Command Line Editing}) is used to read commands from
+the user's terminal.
+
+@item
+Bash inspects the value of the @code{ignoreeof} option to @code{set -o}
+instead of exiting immediately when it receives an @code{EOF} on its
+standard input when reading a command (@pxref{The Set Builtin}).
+
+@item
+Command history (@pxref{Bash History Facilities})
+and history expansion (@pxref{History Interaction})
+are enabled by default.
+Bash will save the command history to the file named by @env{$HISTFILE}
+when an interactive shell exits.
+
+@item
+Alias expansion (@pxref{Aliases}) is performed by default.
+
+@item
+In the absence of any traps, Bash ignores @code{SIGTERM}
+(@pxref{Signals}).
+
+@item
+In the absence of any traps, @code{SIGINT} is caught and handled
+((@pxref{Signals}).
+@code{SIGINT} will interrupt some shell builtins.
+
+@item
+An interactive login shell sends a @code{SIGHUP} to all jobs on exit
+if the @code{hupoxexit} shell option has been enabled (@pxref{Signals}).
+
+@item
+The @option{-n} invocation option is ignored, and @samp{set -n} has
+no effect (@pxref{The Set Builtin}).
+
+@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}).
+
+@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}).
+
+@item
+The shell will not exit on expansion errors caused by @var{var} being unset
+or null in @code{$@{@var{var}:?@var{word}@}} expansions
+(@pxref{Shell Parameter Expansion}).
+
+@item
+Redirection errors encountered by shell builtins will not cause the
+shell to exit.
+
+@item
+When running in @sc{posix} mode, a special builtin returning an error
+status will not cause the shell to exit (@pxref{Bash POSIX Mode}).
+
+@item
+A failed @code{exec} will not cause the shell to exit
+(@pxref{Bourne Shell Builtins}).
+
+@item
+Parser syntax errors will not cause the shell to exit.
+
+@item
+Simple spelling correction for directory arguments to the @code{cd}
+builtin is enabled by default (see the description of the @code{cdspell}
+option to the @code{shopt} builtin in @ref{Bash Builtins}).
+
+@item
+The shell will check the value of the @env{TMOUT} variable and exit
+if a command is not read within the specified number of seconds after
+printing @env{$PS1} (@pxref{Bash Variables}).
+
+@end enumerate
@node Bash Conditional Expressions
@section Bash Conditional Expressions
@cindex expressions, conditional
-Conditional expressions are used by the @code{test} and @code{[} builtins.
+Conditional expressions are used by the @code{[[} compound command
+and the @code{test} and @code{[} builtin commands.
+
+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.
-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. Each
-operator and operand must be a separate argument. If @var{file}
-is of the form @file{/dev/fd/@var{N}}, then file descriptor @var{N} is
-checked. Expressions are composed of the following primaries:
+Unless otherwise specified, primaries that operate on files follow symbolic
+links and operate on the target of the link, rather than the link itself.
@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.
True if @var{file} exists and is a regular file.
@item -g @var{file}
-True if @var{file} exists and is set-group-id.
+True if @var{file} exists and its set-group-id bit is set.
-@item -k @var{file}
-True if @var{file} has its "sticky" bit set.
-
-@item -L @var{file}
+@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.
+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 -S @var{file}
-True if @var{file} exists and is a socket.
-
@item -t @var{fd}
-True if @var{fd} is opened on a terminal.
+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 -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}.
+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}.
+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} have the same device and
+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 @samp{-o}
+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}
@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{=}.
+@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.
+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.
-
-@item ! @var{expr}
-True if @var{expr} is false.
-
-@item @var{expr1} -a @var{expr2}
-True if both @var{expr1} and @var{expr2} are true.
-
-@item @var{expr1} -o @var{expr2}
-True if either @var{expr1} and @var{expr2} is true.
+True if @var{string1} sorts after @var{string2} lexicographically
+in the current locale.
@item @var{arg1} OP @var{arg2}
@code{OP} is one of
@end table
-The Bash @code{test} and @code{[} builtins evaluate conditional
-expressions using a set of rules based on the number of arguments.
-These are the rules:
+@node Shell Arithmetic
+@section Shell Arithmetic
+@cindex arithmetic, shell
+@cindex shell arithmetic
+@cindex expressions, arithmetic
+@cindex evaluation, arithmetic
+@cindex arithmetic evaluation
-@table @asis
-@item 0 arguments
-The expression is false.
-@item 1 argument
-The expression is true if and only if the argument is not null.
-@item 2 arguments
-If the first argument is @samp{!}, the expression is true if and
-only if the second argument is null. If the first argument is
-one of the listed unary operators, the expression is true if the
-unary test is true. If the first argument is not a legal unary
-operator, the expression is false.
-@item 3 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 second argument is one of the binary operators, the result
-of the expression is the result of the binary test using the first
-and third arguments as operands.
-If the first argument is 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
-the three-argument expression composed of the remaining arguments.
-Otherwise, the expression is parsed and evaluated according to
-precedence. @samp{-a} has a higher precedence than @samp{-o}.
-@item 5 or more arguments
-The expression is parsed and evaluated according to precedence,
-with @samp{-a} having a higher precedence than @samp{-o}.
-@end table
+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.
-@node Bash Variables
-@section Bash Variables
+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.
-These variables are set or used by Bash, but other shells
-do not normally treat them specially.
+@table @code
-@vtable @code
+@item @var{id}++ @var{id}--
+variable post-increment and post-decrement
-@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 ++@var{id} --@var{id}
+variable pre-increment and pre-decrement
-@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 - +
+unary minus and plus
-@table @code
+@item ! ~
+logical and bitwise negation
-@item %%
-A literal @samp{%}.
+@item **
+exponentiation
-@item %[@var{p}][l]R
-The elapsed time in seconds.
+@item * / %
+multiplication, division, remainder
-@item %[@var{p}][l]U
-The number of CPU seconds spent in user mode.
+@item + -
+addition, subtraction
-@item %[@var{p}][l]S
-The number of CPU seconds spent in system mode.
+@item << >>
+left and right bitwise shifts
-@item %P
-The CPU percentage, computed as (%U + %S) / %R.
-@end table
+@item <= >= < >
+comparison
-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 == !=
+equality and inequality
-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 &
+bitwise AND
-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 ^
+bitwise exclusive OR
-@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.
+@item |
+bitwise OR
-@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.
+@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{Bash Builtins}).
+
+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.
+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.
+
+An array is created automatically if any variable is assigned to using
+the syntax
+@example
+name[@var{subscript}]=@var{value}
+@end example
+
+@noindent
+The @var{subscript}
+is treated as an arithmetic expression that must evaluate to a number
+greater than or equal to zero. To explicitly declare an array, use
+@example
+declare -a @var{name}
+@end example
+@noindent
+The syntax
+@example
+declare -a @var{name}[@var{subscript}]
+@end example
+@noindent
+is also accepted; the @var{subscript} is ignored. 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.
+
+Arrays are assigned to using compound assignments of the form
+@example
+name=(value@var{1} @dots{} value@var{n})
+@end example
+@noindent
+where each
+@var{value} is of the form @code{[[@var{subscript}]=]}@var{string}. If
+the optional subscript is supplied, that index is assigned to;
+otherwise the index of the element assigned is the last index assigned
+to by the statement plus one. Indexing starts at zero.
+This syntax is also accepted by the @code{declare}
+builtin. Individual array elements may be assigned to using the
+@code{name[}@var{subscript}@code{]=}@var{value} syntax introduced above.
+
+Any element of an array may be referenced using
+@code{$@{name[}@var{subscript}@code{]@}}.
+The braces are required to avoid
+conflicts with the shell's filename expansion operators. If the
+@var{subscript} is @samp{@@} or @samp{*}, the word expands to all members
+of the array @var{name}. These subscripts differ only when the word
+appears within double quotes.
+If the word is double-quoted,
+@code{$@{name[*]@}} expands to a single word with
+the value of each array member separated by the first character of the
+@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.
+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.
+
+The @code{unset} builtin is used to destroy arrays.
+@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 @option{-a}
+option to specify an 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}
+builtins display array values in a way that allows them to be
+reused as input.
+
+@node The Directory Stack
+@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
+directories from the stack and changes the current directory to
+the directory removed. The @code{dirs} builtin displays the contents
+of the directory stack.
+
+The contents of the directory stack are also visible
+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}] [-clpv]
+@end example
+Display the list of currently remembered directories. Directories
+are added to the list with the @code{pushd} command; the
+@code{popd} command removes directories from the list.
+@table @code
+@item +@var{N}
+Displays the @var{N}th directory (counting from the left of the
+list printed by @code{dirs} when invoked without options), starting
+with zero.
+@item -@var{N}
+Displays the @var{N}th directory (counting from the right of the
+list printed by @code{dirs} when invoked without options), starting
+with zero.
+@item -c
+Clears the directory stack by deleting all of the elements.
+@item -l
+Produces a longer listing; the default listing format uses a
+tilde to denote the home directory.
+@item -p
+Causes @code{dirs} to print the directory stack with one entry per
+line.
+@item -v
+Causes @code{dirs} to print the directory stack with one entry per
+line, prefixing each entry with its index in the stack.
+@end table
+
+@item popd
+@btindex popd
+@example
+popd [+@var{N} | -@var{N}] [-n]
+@end example
+
+Remove the top entry from the directory stack, and @code{cd}
+to the new top directory.
+When no arguments are given, @code{popd}
+removes the top directory from the stack and
+performs a @code{cd} to the new top directory. The
+elements are numbered from 0 starting at the first directory listed with
+@code{dirs}; i.e., @code{popd} is equivalent to @code{popd +0}.
+@table @code
+@item +@var{N}
+Removes the @var{N}th directory (counting from the left of the
+list printed by @code{dirs}), starting with zero.
+@item -@var{N}
+Removes the @var{N}th directory (counting from the right of the
+list printed by @code{dirs}), starting with zero.
+@item -n
+Suppresses the normal change of directory when removing directories
+from the stack, so that only the stack is manipulated.
+@end table
+
+@btindex pushd
+@item pushd
+@example
+pushd [@var{dir} | @var{+N} | @var{-N}] [-n]
+@end example
+
+Save the current directory on the top of the directory stack
+and then @code{cd} to @var{dir}.
+With no arguments, @code{pushd} exchanges the top two directories.
+
+@table @code
+@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
+the list by rotating the stack.
+@item -@var{N}
+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}'.
+@code{cd}s to @var{dir}.
+@end table
+
+@end table
+
+@node Printing a Prompt
+@section Controlling the Prompt
+@cindex prompting
+
+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
+can appear in the prompt variables:
+
+@table @code
+@item \a
+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
+A carriage return.
+@item \s
+The name of the shell, the basename of @code{$0} (the portion
+following the final slash).
+@item \t
+The time, in 24-hour HH:MM:SS format.
+@item \T
+The time, in 12-hour HH:MM:SS format.
+@item \@@
+The time, in 12-hour am/pm format.
+@item \A
+The time, in 24-hour HH:MM format.
+@item \u
+The username of the current user.
+@item \v
+The version of Bash (e.g., 2.00)
+@item \V
+The release of Bash, version + patchlevel (e.g., 2.00.0)
+@item \w
+The current working directory, with @env{$HOME} abbreviated with a tilde.
+@item \W
+The basename of @env{$PWD}, with @env{$HOME} abbreviated with a tilde.
+@item \!
+The history number of this command.
+@item \#
+The command number of this command.
+@item \$
+If the effective uid is 0, @code{#}, otherwise @code{$}.
+@item \@var{nnn}
+The character whose ASCII code is the octal value @var{nnn}.
+@item \\
+A backslash.
+@item \[
+Begin a sequence of non-printing characters. This could be used to
+embed a terminal control sequence into the prompt.
+@item \]
+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
+@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 or not performed:
+
+@itemize @bullet
+@item
+Changing directories with the @code{cd} builtin.
+@item
+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 @env{SHELLOPTS} from the shell environment at startup.
+@item
+Redirecting output using the @samp{>}, @samp{>|}, @samp{<>}, @samp{>&},
+@samp{&>}, and @samp{>>} redirection operators.
+@item
+Using the @code{exec} builtin to replace the shell with another command.
+@item
+Adding or deleting builtin commands with the
+@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 @option{-p} option to the @code{command} builtin.
+@item
+Turning off restricted mode with @samp{set +r} or @samp{set +o restricted}.
+@end itemize
-@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}.
+These restrictions are enforced after any startup files are read.
-@item HISTFILE
-The name of the file to which the command history is saved. The
-default is @file{~/.bash_history}.
+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.
-@item HISTSIZE
-If set, this is the maximum number of commands to remember in the
-history.
+@node Bash POSIX Mode
+@section Bash POSIX Mode
+@cindex POSIX Mode
-@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.
+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} 1003.2 standard by changing the behavior to
+match that specified by @sc{posix} in areas where the Bash default differs.
-@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 signifies 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.
+When invoked as @code{sh}, Bash enters @sc{posix} mode after reading the
+startup files.
-@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.
+The following list is what's changed when `@sc{posix} mode' is in effect:
-@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.
+@enumerate
+@item
+When a command in the hash table no longer exists, Bash will re-search
+@env{$PATH} to find the new location. This is also available with
+@samp{shopt -s checkhash}.
-@item MAILCHECK
-How often (in seconds) that the shell should check for mail
-in the files specified in @code{MAILPATH}.
+@item
+The message printed by the job control code and builtins when a job
+exits with a non-zero status is `Done(status)'.
-@item PROMPT_COMMAND
-If present, this contains a string which is a command to execute
-before the printing of each primary prompt (@code{$PS1}).
+@item
+The message printed by the job control code and builtins when a job
+is stopped is `Stopped(@var{signame})', where @var{signame} is, for
+example, @code{SIGTSTP}.
-@item UID
-The numeric real user id of the current user.
+@item
+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 EUID
-The numeric effective user id of the current user.
+@item
+Reserved words appearing in a context where reserved words are recognized
+do not undergo alias expansion.
-@item GROUPS
-An array variable containing the list of groups of which the current
-user is a member.
+@item
+The @sc{posix} 1003.2 @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 PPID
-The process id of the shell's parent process.
+@item
+The @sc{posix} 1003.2 startup files are executed (@env{$ENV}) rather than
+the normal Bash files.
-@item HOSTNAME
-The name of the current host.
+@item
+Tilde expansion is only performed on assignments preceding a command
+name, rather than on all assignment statements on the line.
-@item HOSTTYPE
-A string describing the machine Bash is running on.
+@item
+The default history file is @file{~/.sh_history} (this is the
+default value of @env{$HISTFILE}).
-@item OSTYPE
-A string describing the operating system Bash is running on.
+@item
+The output of @samp{kill -l} prints all the signal names on a single line,
+separated by spaces, without the @samp{SIG} prefix.
-@item MACHTYPE
-A string that fully describes the system type on which Bash
-is executing, in the standard GNU @var{cpu-company-system} format.
+@item
+The @code{kill} builtin does not accept signal names with a @samp{SIG}
+prefix.
-@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.
+@item
+Non-interactive shells exit if @var{filename} in @code{.} @var{filename}
+is not found.
-@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
+Non-interactive shells exit if a syntax error in an arithmetic expansion
+results in an invalid expression.
-@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
+Redirection operators do not perform filename expansion on the word
+in the redirection unless the shell is interactive.
-@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.
+@item
+Redirection operators do not perform word splitting on the word in the
+redirection.
-@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
+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 INPUTRC
-The name of the Readline startup file, overriding the default
-of @file{~/.inputrc}.
+@item
+@sc{posix} 1003.2 special builtins are found before shell functions
+during command lookup.
-@item BASH
-The full filename used to execute the current instance of Bash.
+@item
+If a @sc{posix} 1003.2 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,
+redirection errors, variable assignment errors for assignments preceding
+the command name, and so on.
+
+@item
+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 @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.
+
+@item
+A non-interactive shell exits with an error status if a variable
+assignment error occurs when no command name follows the assignment
+statements.
+A variable assignment error occurs, for example, when trying to assign
+a value to a readonly variable.
+
+@item
+A non-interactive shell exits with an error status if the iteration
+variable in a @code{for} statement or the selection variable in a
+@code{select} statement is a readonly variable.
+
+@item
+Process substitution is not available.
+
+@item
+Assignment statements preceding @sc{posix} 1003.2 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} 1003.2.
+
+@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{$FCEDIT} and
+@code{$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.
+
+@end enumerate
+
+There is other @sc{posix} 1003.2 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
+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
+
+This chapter discusses what job control is, how it works, and how
+Bash allows you to access its facilities.
+
+@menu
+* Job Control Basics:: How job control works.
+* Job Control Builtins:: Bash builtin commands used to interact
+ with job control.
+* Job Control Variables:: Variables Bash uses to customize job
+ control.
+@end menu
+
+@node Job Control Basics
+@section Job Control Basics
+@cindex job control
+@cindex foreground
+@cindex background
+@cindex suspending jobs
+
+Job control
+refers to the ability to selectively stop (suspend)
+the execution of processes and continue (resume)
+their execution at a later point. A user typically employs
+this facility via an interactive interface supplied jointly
+by the system's terminal driver and Bash.
+
+The shell associates a @var{job} with each pipeline. It keeps a
+table of currently executing jobs, which may be listed with the
+@code{jobs} command. When Bash starts a job
+asynchronously, it prints a line that looks
+like:
+@example
+[1] 25647
+@end example
+@noindent
+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 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
+terminal's; such processes are immune to keyboard-generated
+signals. Only foreground processes are allowed to read from or
+write to the terminal. Background processes which attempt to
+read from (write to) the terminal are sent a @code{SIGTTIN}
+(@code{SIGTTOU}) signal by the terminal driver, which, unless
+caught, suspends the process.
-@item BASH_VERSION
-The version number of the current instance of Bash.
+If the operating system on which Bash is running supports
+job control, Bash contains facilities to use it. Typing the
+@var{suspend} character (typically @samp{^Z}, Control-Z) while a
+process is running causes that process to be stopped and returns
+control to Bash. Typing the @var{delayed suspend} character
+(typically @samp{^Y}, Control-Y) causes the process to be stopped
+when it attempts to read input from the terminal, and control to
+be returned to Bash. The user then manipulates the state of
+this job, using the @code{bg} command to continue it in the
+background, the @code{fg} command to continue it in the
+foreground, or the @code{kill} command to kill it. A @samp{^Z}
+takes effect immediately, and has the additional side effect of
+causing pending output and typeahead to be discarded.
-@item BASH_VERSINFO
-An array variable whose members hold version information for this
-instance of Bash.
-The values assigned to the array members are as follows:
+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}.
+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{%-}. 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{-}.
-@table @code
+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.
-@item BASH_VERSINFO[0]
-The major version number (the @var{release}).
+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}
-@item BASH_VERSINFO[1]
-The minor version number (the @var{version}).
+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.
-@item BASH_VERSINFO[2]
-The patch level.
+If an attempt to exit Bash is made 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 BASH_VERSINFO[3]
-The build version.
+@node Job Control Builtins
+@section Job Control Builtins
-@item BASH_VERSINFO[4]
-The release status (e.g., @var{beta1}).
+@table @code
-@item BASH_VERSINFO[5]
-The value of @code{MACHTYPE}.
+@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.
-@end table
+@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 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 jobs
+@btindex jobs
+@example
+jobs [-lnprs] [@var{jobspec}]
+jobs -x @var{command} [@var{arguments}]
+@end example
-@item OPTERR
-If set to the value 1, Bash displays error messages
-generated by the @code{getopts} builtin command.
+The first form lists the active jobs. The options have the
+following meanings:
-@item LANG
-Used to determine the locale category for any category not specifically
-selected with a variable starting with @code{LC_}.
+@table @code
+@item -l
+List process @sc{id}s in addition to the normal information.
-@item LC_ALL
-This variable overrides the value of @code{LANG} and any other
-@code{LC_} variable specifying a locale category.
+@item -n
+Display information only about jobs that have changed status since
+the user was last notified of their status.
-@item LC_COLLATE
-This variable determines the collation order used when sorting the
-results of filename expansion (@pxref{Filename Expansion}).
+@item -p
+List only the process @sc{id} of the job's process group leader.
-@item LC_MESSAGES
-This variable determines the locale used to translate double-quoted
-strings preceded by a @samp{$} (@pxref{Locale Translation}).
+@item -r
+Restrict output to running jobs.
-@item IGNOREEOF
-Controls the action of the shell on receipt of an @code{EOF} character
-as the sole input. If set, then the value of it is 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.
+@item -s
+Restrict output to stopped jobs.
+@end table
-@end vtable
+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.
-@node Shell Arithmetic
-@section Shell Arithmetic
-@cindex arithmetic, shell
+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.
-@menu
-* Arithmetic Evaluation:: How shell arithmetic works.
-* Arithmetic Expansion:: How to use arithmetic in shell expansions.
-* Arithmetic Builtins:: Builtin commands that use shell arithmetic.
-@end menu
+@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.
-Bash includes several mechanisms to evaluate arithmetic expressions
-and display the result or use it as part of a command.
+@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.
-@node Arithmetic Evaluation
-@subsection Arithmetic Evaluation
-@cindex expressions, arithmetic
-@cindex evaluation, arithmetic
-@cindex arithmetic evaluation
+@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.
-The shell allows arithmetic expressions to be evaluated, as one of
-the shell expansions or by the @code{let} builtin.
+@item suspend
+@btindex suspend
+@example
+suspend [-f]
+@end example
+Suspend the execution of this shell until it receives a
+@code{SIGCONT} signal. The @option{-f} option means to suspend
+even if the shell is a login shell.
-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.
+@end table
-@table @code
-@item - +
-unary minus and plus
+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 ! ~
-logical and bitwise negation
+@node Job Control Variables
+@section Job Control Variables
-@item * / %
-multiplication, division, remainder
+@vtable @code
-@item + -
-addition, subtraction
+@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 << >>
-left and right bitwise shifts
+@end vtable
-@item <= >= < >
-comparison
+@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
-@item == !=
-equality and inequality
+@node Installing Bash
+@chapter Installing Bash
-@item &
-bitwise AND
+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.
-@item ^
-bitwise exclusive OR
+@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
-@item |
-bitwise OR
+@node Basic Installation
+@section Basic Installation
+@cindex installation
+@cindex configuration
+@cindex Bash installation
+@cindex Bash configuration
-@item &&
-logical AND
+These are installation instructions for Bash.
-@item ||
-logical OR
+The simplest way to compile Bash is:
-@item expr ? expr : expr
-conditional evaluation
+@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.
-@item = *= /= %= += -= <<= >>= &= ^= |=
-assignment
-@end table
+Running @code{configure} takes some time.
+While running, it prints messages telling which features it is
+checking for.
-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
+Type @samp{make} to compile Bash and build the @code{bashbug} bug
+reporting script.
-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
+Optionally, type @samp{make tests} to run the Bash test suite.
-Operators are evaluated in order of precedence. Sub-expressions in
-parentheses are evaluated first and may override the precedence
-rules above.
+@item
+Type @samp{make install} to install @code{bash} and @code{bashbug}.
+This will also install the manual pages and Info file.
-@node Arithmetic Expansion
-@subsection Arithmetic Expansion
-@cindex expansion, arithmetic
-@cindex arithmetic expansion
+@end enumerate
-Arithmetic expansion allows the evaluation of an arithmetic expression
-and the substitution of the result. The format for arithmetic expansion is:
+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
-$(( @var{expression} ))
+bash-2.04$ ./configure --help
@end example
-The expression is treated as if it were within double quotes, but
-a double quote inside the braces or parentheses is not treated
-specially. All tokens in the expression undergo parameter
-expansion, command substitution, and quote removal. Arithmetic
-substitutions may be nested.
-
-The evaluation is performed according to the rules listed above.
-If the expression is invalid, Bash
-prints a message indicating failure and no substitution occurs.
+@noindent
+at the Bash prompt in your Bash source directory.
-@node Arithmetic Builtins
-@subsection Arithmetic Builtins
+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.
-@table @code
+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.
-@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 previously (@pxref{Arithmetic Evaluation}). If the
-last @var{expression} evaluates to 0, @code{let} returns 1;
-otherwise 0 is returned.
-@end table
+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 Arrays
-@section Arrays
-@cindex arrays
+@node Compilers and Options
+@section Compilers and Options
-Bash provides one-dimensional array variables. Any variable may be used as
-an 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.
+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:
-An array is created automatically if any variable is assigned to using
-the syntax
@example
-name[@var{subscript}]=@var{value}
+CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure
@end example
-@noindent
-The @var{subscript}
-is treated as an arithmetic expression that must evaluate to a number
-greater than or equal to zero. To explicitly declare an array, use
-@example
-declare -a @var{name}
-@end example
-@noindent
-The syntax
-@example
-declare -a @var{name}[@var{subscript}]
-@end example
-@noindent
-is also accepted; the @var{subscript} is ignored. 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.
+On systems that have the @code{env} program, you can do it like this:
-Arrays are assigned to using compound assignments of the form
@example
-name=(value@var{1} @dots{} value@var{n})
+env CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure
@end example
-@noindent
-where each
-@var{value} is of the form @code{[[@var{subscript}]=]}@var{string}. If
-the optional subscript is supplied, that index is assigned to;
-otherwise the index of the element assigned is the last index assigned
-to by the statement plus one. Indexing starts at zero.
-This syntax is also accepted by the @code{declare}
-builtin. Individual array elements may be assigned to using the
-@code{name[}@var{subscript}@code{]=}@var{value} syntax introduced above.
-
-Any element of an array may be referenced using
-@code{$@{name[}@var{subscript}@code{]@}}.
-The braces are required to avoid
-conflicts with the shell's filename expansion operators. If the
-@var{subscript} is @samp{@@} or @samp{*}, the word expands to all members
-of the array @var{name}. These subscripts differ only when the word
-appears within double quotes. If the word is double-quoted,
-@code{$@{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{$@{name[@@]@}} expands each element of
-@var{name} to a separate word. When there are no array members,
-@code{$@{name[@@]@}} expands to nothing. 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.
-
-The @code{unset} builtin is used to destroy arrays.
-@code{unset} @var{name[subscript]}
-destroys the array element at index @var{subscript}.
-@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}
-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}
-builtins display array values in a way that allows them to be
-reused as input.
+The configuration process uses GCC to build Bash if it
+is available.
-@node Printing a Prompt
-@section Controlling the Prompt
-@cindex prompting
+@node Compiling For Multiple Architectures
+@section Compiling For Multiple Architectures
-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
-value is executed just as if you had typed it on the command line.
+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 `..'.
-In addition, the following table describes the special characters which
-can appear in the prompt variables:
+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.
-@table @code
-@item \a
-a bell character.
-@item \d
-the date, in "Weekday Month Date" format (e.g., "Tue May 26").
-@item \e
-an escape character.
-@item \h
-the hostname, up to the first `.'.
-@item \H
-the hostname.
-@item \n
-newline.
-@item \s
-the name of the shell, the basename of @code{$0} (the portion
-following the final slash).
-@item \t
-the time, in 24-hour HH:MM:SS format.
-@item \T
-the time, in 12-hour HH:MM:SS format.
-@item \@@
-the time, in 12-hour am/pm format.
-@item \v
-the version of Bash (e.g., 2.00)
-@item \V
-the release of Bash, version + patchlevel (e.g., 2.00.0)
-@item \w
-the current working directory.
-@item \W
-the basename of @code{$PWD}.
-@item \u
-your username.
-@item \!
-the history number of this command.
-@item \#
-the command number of this command.
-@item \$
-if the effective uid is 0, @code{#}, otherwise @code{$}.
-@item \nnn
-the character corresponding to the octal number @code{nnn}.
-@item \\
-a backslash.
-@item \[
-begin a sequence of non-printing characters. This could be used to
-embed a terminal control sequence into the prompt.
-@item \]
-end a sequence of non-printing characters.
-@end table
+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}:
-@node The Restricted Shell
-@section The Restricted Shell
-@cindex restricted shell
+@example
+bash /usr/gnu/src/bash-2.0/support/mkclone -s /usr/gnu/src/bash-2.0 .
+@end example
-If Bash is started with the name @code{rbash}, or the
-@samp{--restricted}
-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:
-@itemize @bullet
-@item
-Changing directories with the @code{cd} builtin.
-@item
-Setting or unsetting the values of the @code{SHELL} or @code{PATH}
-variables.
-@item
-Specifying command names containing slashes.
-@item
-Specifying a filename containing a slash as an argument to the @code{.}
-builtin command.
-@item
-Importing function definitions from the shell environment at startup.
-@item
-Redirecting output using the @samp{>}, @samp{>|}, @samp{<>}, @samp{>&},
-@samp{&>}, and @samp{>>} redirection operators.
-@item
-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.
-@item
-Specifying the @samp{-p} option to the @code{command} builtin.
-@item
-Turning off restricted mode with @samp{set +r}.
-@end itemize
+@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 Bash POSIX Mode
-@section Bash POSIX Mode
-@cindex POSIX Mode
+@node Installation Names
+@section Installation Names
-Starting Bash with the @samp{--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.
+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}.
-The following list is what's changed when `@sc{POSIX} mode' is in effect:
+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.
-@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
-@samp{shopt -s checkhash}.
+@node Specifying the System Type
+@section Specifying the System Type
-@item
-The @samp{>&} redirection does not redirect stdout and stderr.
+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}).
-@item
-The message printed by the job control code and builtins when a job
-exits with a non-zero status is `Done(status)'.
+See the file @file{support/config.sub} for the possible
+values of each field.
-@item
-Reserved words may not be aliased.
+@node Sharing Defaults
+@section Sharing Defaults
-@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 value regardless of the setting of the @code{promptvars} option.
+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
-Interactive comments are enabled by default. (Note that Bash has
-them on by default anyway.)
+@node Operation Controls
+@section Operation Controls
-@item
-The @sc{POSIX.2} startup files are executed (@code{$ENV}) rather than
-the normal Bash files.
+@code{configure} recognizes the following options to control how it
+operates.
-@item
-Tilde expansion is only performed on assignments preceding a command
-name, rather than on all assignment statements on the line.
+@table @code
-@item
-The default history file is @file{~/.sh_history} (this is the
-default value of @code{$HISTFILE}).
+@item --cache-file=@var{file}
+Use and save the results of the tests in
+@var{file} instead of @file{./config.cache}. Set @var{file} to
+@file{/dev/null} to disable caching, for debugging
+@code{configure}.
-@item
-The output of @samp{kill -l} prints all the signal names on a single line,
-separated by spaces.
+@item --help
+Print a summary of the options to @code{configure}, and exit.
-@item
-Non-interactive shells exit if @var{filename} in @code{.} @var{filename}
-is not found.
+@item --quiet
+@itemx --silent
+@itemx -q
+Do not print messages saying which checks are being made.
-@item
-Redirection operators do not perform filename expansion on the word
-in the redirection unless the shell is interactive.
+@item --srcdir=@var{dir}
+Look for the Bash source code in directory @var{dir}. Usually
+@code{configure} can determine that directory automatically.
-@item
-Function names must be valid shell @code{name}s. That is, they may not
-contain characters other than letters, digits, and underscores, and
-may not start with a digit. Declaring a function with an illegal name
-causes a fatal syntax error in non-interactive shells.
+@item --version
+Print the version of Autoconf used to generate the @code{configure}
+script, and exit.
+@end table
-@item
-@sc{POSIX.2} `special' builtins are found before shell functions
-during command lookup.
+@code{configure} also accepts some other, not widely used, boilerplate
+options. @samp{configure --help} prints the complete list.
-@item
-If a @sc{POSIX.2} special builtin returns an error status, a
-non-interactive shell exits. The fatal errors are those listed in
-the POSIX.2 standard, and include things like passing incorrect options,
-redirection errors, variable assignment errors for assignments preceding
-the command name, and so on.
+@node Optional Features
+@section Optional Features
-@item
-If the @code{cd} builtin finds a directory to change to
-using @code{$CDPATH}, the
-value it assigns to the @code{PWD} variable does not contain any
-symbolic links, as if @samp{cd -P} had been executed.
+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}}.
-@item
-A non-interactive shell exits with an error status if a variable
-assignment error occurs when no command name follows the assignment
-statements.
-A variable assignment error occurs, for example, when trying to assign
-a value to a read-only variable.
+Here is a complete list of the @option{--enable-} and
+@option{--with-} options that the Bash @code{configure} recognizes.
-@item
-A non-interactive shell exits with an error status if the iteration
-variable in a @code{for} statement or the selection variable in a
-@code{select} statement is a read-only variable.
+@table @code
+@item --with-afs
+Define if you are using the Andrew File System from Transarc.
-@item
-Process substitution is not available.
+@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
-Assignment statements preceding @sc{POSIX.2} @code{special} builtins
-persist in the shell environment after the builtin completes.
+@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{export} and @code{readonly} builtin commands display their
-output in the format required by @sc{POSIX.2}.
+@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}).
-@end enumerate
+@item --with-purify
+Define this to use the Purify memory allocation checker from Rational
+Software.
-There is other @sc{POSIX.2} behavior that Bash does not implement.
-Specifically:
+@item --enable-minimal-config
+This produces a shell with minimal features, close to the historical
+Bourne shell.
+@end table
-@enumerate
-@item
-Assignment statements affect the execution environment of all
-builtins, not just special ones.
-@end enumerate
+There are several @option{--enable-} options that alter how Bash is
+compiled and linked, rather than changing run-time features.
-@node Job Control
-@chapter Job Control
+@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
-This chapter disusses what job control is, how it works, and how
-Bash allows you to access its facilities.
+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}}.
-@menu
-* Job Control Basics:: How job control works.
-* Job Control Builtins:: Bash builtin commands used to interact
- with job control.
-* Job Control Variables:: Variables Bash uses to customize job
- control.
-@end menu
+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.
-@node Job Control Basics
-@section Job Control Basics
-@cindex job control
-@cindex foreground
-@cindex background
-@cindex suspending jobs
+@table @code
+@item --enable-alias
+Allow alias expansion and include the @code{alias} and @code{unalias}
+builtins (@pxref{Aliases}).
-Job control
-refers to the ability to selectively stop (suspend)
-the execution of processes and continue (resume)
-their execution at a later point. A user typically employs
-this facility via an interactive interface supplied jointly
-by the system's terminal driver and Bash.
+@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}).
-The shell associates a @var{job} with each pipeline. It keeps a
-table of currently executing jobs, which may be listed with the
-@code{jobs} command. When Bash starts a job
-asynchronously (in the background), it prints a line that looks
-like:
-@example
-[1] 25647
-@end example
-@noindent
-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.
+@item --enable-array-variables
+Include support for one-dimensional array shell variables
+(@pxref{Arrays}).
-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}.
-These processes are said to be in the foreground. Background
-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
-read from (write to) the terminal are sent a @code{SIGTTIN}
-(@code{SIGTTOU}) signal by the terminal driver, which, unless
-caught, suspends the process.
+@item --enable-bang-history
+Include support for @code{csh}-like history substitution
+(@pxref{History Interaction}).
-If the operating system on which Bash is running supports
-job control, Bash allows you to use it. Typing the
-@var{suspend} character (typically @samp{^Z}, Control-Z) while a
-process is running causes that process to be stopped and returns
-you to Bash. Typing the @var{delayed suspend} character
-(typically @samp{^Y}, Control-Y) causes the process to be stopped
-when it attempts to read input from the terminal, and control to
-be returned to Bash. You may then manipulate the state of
-this job, using the @code{bg} command to continue it in the
-background, the @code{fg} command to continue it in the
-foreground, or the @code{kill} command to kill it. A @samp{^Z}
-takes effect immediately, and has the additional side effect of
-causing pending output and typeahead to be discarded.
+@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.
-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. 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{-}.
+@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.
-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}
+@item --enable-cond-command
+Include support for the @code{[[} conditional command.
+(@pxref{Conditional Constructs}).
-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 set,
-Bash reports such changes immediately (@pxref{The Set Builtin}).
+@item --enable-cond-regexp
+Include support for matching POSIX regular expressions using the
+@samp{=~} binary operator in the @code{[[} conditional command.
+(@pxref{Conditional Constructs}).
-If you attempt to exit Bash while jobs are stopped, the
-shell prints a message warning you that you have stopped jobs.
-You may then use the
-@code{jobs} command to inspect their status. If you do this, or
-try to exit again immediately, you are not warned again, and the
-stopped jobs are terminated.
+@item --enable-debugger
+Include support for the bash debugger (distributed separately).
-@node Job Control Builtins
-@section Job Control Builtins
+@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}).
-@table @code
+@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 bg
-@btindex bg
-@example
-bg [@var{jobspec}]
-@end example
-Place @var{jobspec} into the background, as if it had been started
-with @samp{&}. If @var{jobspec} is not supplied, the current job
-is used.
+@item --enable-dparen-arithmetic
+Include support for the @code{((@dots{}))} command
+(@pxref{Conditional Constructs}).
-@item fg
-@btindex fg
-@example
-fg [@var{jobspec}]
-@end example
-Bring @var{jobspec} into the foreground and make it the current job.
-If @var{jobspec} is not supplied, the current job is used.
+@item --enable-extended-glob
+Include support for the extended pattern matching features described
+above under @ref{Pattern Matching}.
-@item jobs
-@btindex jobs
-@example
-jobs [-lpnrs] [@var{jobspec}]
-jobs -x @var{command} [@var{jobspec}]
-@end example
+@item --enable-help-builtin
+Include the @code{help} builtin, which displays help on shell builtins and
+variables (@pxref{Bash Builtins}).
-The first form lists the active jobs. The options have the
-following meanings:
+@item --enable-history
+Include command history and the @code{fc} and @code{history}
+builtin commands (@pxref{Bash History Facilities}).
-@table @code
-@item -l
-List process @sc{ID}s in addition to the normal information
+@item --enable-job-control
+This enables the job control features (@pxref{Job Control}),
+if the operating system supports them.
-@item -n
-Display information only about jobs that have changed status since
-you were last notified of their status.
+@item --enable-multibyte
+This enables support for multibyte characters if the operating
+system provides the necessary support.
-@item -p
-List only the process @sc{ID} of the job's process group
-leader.
+@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}).
-@item -r
-Restrict output to running jobs.
+@item --enable-process-substitution
+This enables process substitution (@pxref{Process Substitution}) if
+the operating system provides the necessary support.
-@item -s
-Restrict output to stopped jobs.
-@end table
+@item --enable-progcomp
+Enable the programmable completion facilities
+(@pxref{Programmable Completion}).
+If Readline is not enabled, this option has no effect.
-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-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.
-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-readline
+Include support for command-line editing and history with the Bash
+version of the Readline library (@pxref{Command Line Editing}).
-@item kill
-@btindex kill
-@example
-kill [-s @var{sigspec}] [-n @var{signum}] [-@var{sigspec}] @var{jobspec}
-kill -l [@var{sigspec}]
-@end example
-Send a signal specified by @var{sigspec} or @var{signum} to the process
-named by @var{jobspec}.
-@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, or the signal name
-corresponding to @var{sigspec}.
+@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.
-@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 report its exit status. 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.
+@item --enable-select
+Include the @code{select} builtin, which allows the generation of simple
+menus (@pxref{Conditional Constructs}).
-@item disown
-@btindex disown
-@example
-disown [-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, the current job is used.
+@item --enable-separate-helpfiles
+Use external files for the documentation displayed by the @code{help} builtin
+instead of storing the text internally.
-@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-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.
-@end table
+@item --enable-strict-posix-default
+Make Bash @sc{posix}-conformant by default (@pxref{Bash POSIX Mode}).
-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-usg-echo-default
+A synonym for @code{--enable-xpg-echo-default}.
-@node Job Control Variables
-@section Job Control Variables
+@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.
-@vtable @code
+@end table
-@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 redirects 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}.
+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.
-@end vtable
+@node Reporting Bugs
+@appendix Reporting Bugs
-@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
+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/}.
-@node Installing Bash
-@chapter Installing Bash
+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}.
-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{OS/2}, Windows 95, and Windows @sc{NT}.
+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
-@menu
-* Basic Installation:: Installation instructions.
+@noindent
+@code{bashbug} inserts the first three items automatically into
+the template it provides for filing a bug report.
-* Compilers and Options:: How to set special options for various
- systems.
+Please send all reports concerning this manual to
+@email{chet@@po.CWRU.Edu}.
-* Compiling For Multiple Architectures:: How to compile Bash for more
- than one kind of system from
- the same source tree.
+@node Major Differences From The Bourne Shell
+@appendix Major Differences From The Bourne Shell
+
+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
+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.
-* Installation Names:: How to set the various paths used by the installation.
+@itemize @bullet
-* Specifying the System Type:: How to configure Bash for a particular system.
+@item
+Bash is @sc{posix}-conformant, even where the @sc{posix} specification
+differs from traditional @code{sh} behavior (@pxref{Bash POSIX Mode}).
-* Sharing Defaults:: How to share default configuration values among GNU
- programs.
+@item
+Bash has multi-character invocation options (@pxref{Invoking Bash}).
-* Operation Controls:: Options recognized by the configuration program.
+@item
+Bash has command-line editing (@pxref{Command Line Editing}) and
+the @code{bind} builtin.
-* Optional Features:: How to enable and disable optional features when
- building Bash.
-@end menu
+@item
+Bash provides a programmable word completion mechanism
+(@pxref{Programmable Completion}), and two builtin commands,
+@code{complete} and @code{compgen}, to manipulate it.
-@node Basic Installation
-@section Basic Installation
-@cindex installation
-@cindex configuration
-@cindex Bash installation
-@cindex Bash configuration
+@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.
-These are installation instructions for Bash.
+@item
+Bash implements @code{csh}-like history expansion
+(@pxref{History Interaction}).
-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.
+@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.
-If you need to do unusual things to compile the package, please
-try to figure out how @code{configure} could check whether or not
-to do them, and mail diffs or instructions to
-@code{bash-maintainers@@prep.ai.mit.edu} so they can be
-considered for the next release.
+@item
+The @code{$'@dots{}'} quoting syntax, which expands ANSI-C
+backslash-escaped characters in the text between the single quotes,
+is supported (@pxref{ANSI-C Quoting}).
-The file @file{configure.in} is used to create @code{configure}
-by a program called Autoconf. You only need
-@file{configure.in} if you want to change it or regenerate
-@code{configure} using a newer version of Autoconf. If
-you do this, make sure you are using Autoconf version 2.10 or
-newer.
+@item
+Bash supports the @code{$"@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}).
-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 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.
-The simplest way to compile Bash is:
+@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.
-@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 implements the @code{for (( @var{expr1} ; @var{expr2} ; @var{expr3} ))}
+arithmetic for command, similar to the C language (@pxref{Looping Constructs}).
-Running @code{configure} takes awhile. While running, it prints some
-messages telling which features it is checking for.
+@item
+Bash includes the @code{select} compound command, which allows the
+generation of simple menus (@pxref{Conditional Constructs}).
@item
-Type @samp{make} to compile Bash and build the @code{bashbug} bug
-reporting script.
+Bash includes the @code{[[} compound command, which makes conditional
+testing part of the shell grammar (@pxref{Conditional Constructs}), including
+optional regular expression matching.
@item
-Optionally, type @samp{make tests} to run the Bash test suite.
+Bash provides optional case-insensitive matching for the @code{case} and
+@code{[[} constructs.
@item
-Type @samp{make install} to install @code{bash} and @code{bashbug}.
-This will also install the manual pages and Info file.
+Bash includes brace expansion (@pxref{Brace Expansion}) and tilde
+expansion (@pxref{Tilde Expansion}).
-@end enumerate
+@item
+Bash implements command aliases and the @code{alias} and @code{unalias}
+builtins (@pxref{Aliases}).
-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 provides shell arithmetic, the @code{((} compound command
+(@pxref{Conditional Constructs}),
+and arithmetic expansion (@pxref{Shell Arithmetic}).
-@node Compilers and Options
-@section Compilers and Options
+@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.
-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 supports the @samp{+=} assignment operator, which appends to the value
+of the variable named on the left hand side.
-@example
-CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure
-@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}).
-On systems that have the @code{env} program, you can do it like this:
+@item
+The expansion @code{$@{#xx@}}, which returns the length of @code{$@{xx@}},
+is supported (@pxref{Shell Parameter Expansion}).
-@example
-env CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure
-@end example
+@item
+The expansion @code{$@{var:}@var{offset}@code{[:}@var{length}@code{]@}},
+which expands to the substring of @code{var}'s value of length
+@var{length}, beginning at @var{offset}, is present
+(@pxref{Shell Parameter Expansion}).
-The configuration process uses GCC to build Bash if it
-is available.
+@item
+The expansion
+@code{$@{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}).
-@node Compiling For Multiple Architectures
-@section Compiling For Multiple Architectures
+@item
+The expansion @code{$@{!@var{prefix@}*}} expansion, which expands to
+the names of all shell variables whose names begin with @var{prefix},
+is available (@pxref{Shell Parameter Expansion}).
-You can compile Bash for more than one kind of computer at the
-same time, by placing the object files for each architecture in their
-own directory. To do this, you must use a version of @code{make} that
-supports the @code{VPATH} variable, such as GNU @code{make}.
-@code{cd} to the
-directory where you want the object files and executables to go and run
-the @code{configure} script from the source directory. You may need to
-supply the @samp{--srcdir=PATH} argument to tell @code{configure} where the
-source files are. @code{configure} automatically checks for the
-source code in the directory that @code{configure} is in and in `..'.
+@item
+Bash has @var{indirect} variable expansion using @code{$@{!word@}}
+(@pxref{Shell Parameter Expansion}).
-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
+Bash can expand positional parameters beyond @code{$9} using
+@code{$@{@var{num}@}}.
-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
+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).
-@example
-bash /usr/gnu/src/bash-2.0/support/mkclone -s /usr/gnu/src/bash-2.0 .
-@end example
+@item
+Bash has process substitution (@pxref{Process Substitution}).
-@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
+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 Installation Names
-@section Installation Names
+@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.
-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
+Bash implements the full set of @sc{posix} 1003.2 filename expansion operators,
+including @var{character classes}, @var{equivalence classes}, and
+@var{collating symbols} (@pxref{Filename Expansion}).
+
+@item
+Bash implements extended pattern matching features when the @code{extglob}
+shell option is enabled (@pxref{Pattern Matching}).
+
+@item
+It is possible to have a variable and a function with the same name;
+@code{sh} does not separate the two name spaces.
-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}, the package will use @samp{PATH} as the
-prefix for installing programs and libraries. Documentation and
-other data files will still use the regular prefix.
+@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}).
-@node Specifying the System Type
-@section Specifying the System Type
+@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.
-There may be some features @code{configure} can not figure out
-automatically, but needs to determine by the type of host the
-package 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 performs filename expansion on filenames specified as operands
+to input and output redirection operators (@pxref{Redirections}).
-@noindent See the file @file{support/config.sub} for the possible
-values of each field.
+@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}).
-@node Sharing Defaults
-@section Sharing Defaults
+@item
+Bash includes the @samp{<<<} redirection operator, allowing a string to
+be used as the standard input to a command.
-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 implements the @samp{[n]<&@var{word}} and @samp{[n]>&@var{word}}
+redirection operators, which move one file descriptor to another.
-@node Operation Controls
-@section Operation Controls
+@item
+Bash treats a number of filenames specially when they are
+used in redirection operators (@pxref{Redirections}).
-@code{configure} recognizes the following options to control how it
-operates.
+@item
+Bash can open network connections to arbitrary machines and services
+with the redirection operators (@pxref{Redirections}).
-@table @code
+@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}.
-@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
+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.
-@item --help
-Print a summary of the options to @code{configure}, and exit.
+@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 --quiet
-@itemx --silent
-@itemx -q
-Do not print messages saying which checks are being made.
+@item
+The @code{command} builtin allows selective disabling of functions
+when command lookup is performed (@pxref{Bash Builtins}).
-@item --srcdir=@var{DIR}
-Look for the Bash source code in directory @var{DIR}. Usually
-@code{configure} can determine that directory automatically.
+@item
+Individual builtins may be enabled or disabled using the @code{enable}
+builtin (@pxref{Bash Builtins}).
-@item --version
-Print the version of Autoconf used to generate the @code{configure}
-script, and exit.
-@end table
+@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}).
-@code{configure} also accepts some other, not widely used, boilerplate
-options.
+@item
+Shell functions may be exported to children via the environment
+using @code{export -f} (@pxref{Shell Functions}).
-@node Optional Features
-@section Optional Features
+@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.
-The Bash @code{configure} has a number of @samp{--enable-@var{FEATURE}}
-options, where @var{FEATURE} indicates an optional part of the
-package. There are also several @samp{--with-@var{PACKAGE}} options,
-where @var{PACKAGE} is something like @samp{gnu-malloc} or
-@samp{purify} (for the Purify memory allocation checker). 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 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}).
-Here is a complete list of the @samp{--enable-} and
-@samp{--with-} options that the Bash @code{configure} recognizes.
+@item
+Bash includes a @code{help} builtin for quick reference to shell
+facilities (@pxref{Bash Builtins}).
-@table @code
-@item --with-afs
-Define if you are using the Andrew File System from Transarc.
+@item
+The @code{printf} builtin is available to display formatted output
+(@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 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.
-@item --with-glibc-malloc
-Use the @sc{GNU} libc version of @code{malloc} in
-@file{lib/malloc/gmalloc.c}. This is somewhat slower than the
-default @code{malloc}, but wastes considerably less space.
+@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}).
-@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 a lot of space. 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
+Bash includes the @code{shopt} builtin, for finer control of shell
+optional capabilities (@pxref{Bash Builtins}), and allows these options
+to be set and unset at shell invocation (@pxref{Invoking Bash}).
-@item --with-purify
-Define this to use the Purify memory allocation checker from Pure
-Software.
+@item
+Bash has much more optional behavior controllable with the @code{set}
+builtin (@pxref{The Set Builtin}).
-@item --enable-minimal-config
-This produces a shell with minimal features, close to the historical
-Bourne shell.
-@end table
+@item
+The @samp{-x} (@code{xtrace}) option displays commands other than
+simple commands when performing an execution trace
+(@pxref{The Set Builtin}).
-@noindent
-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{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.
-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{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.
-@table @code
-@item --enable-alias
-Allow alias expansion and include the @code{alias} and @code{unalias}
-builtins.
+@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-array-variables
-Include support for one-dimensional array shell variables.
+@item
+The Bash @code{type} builtin is more extensive and gives more information
+about the names it finds (@pxref{Bash Builtins}).
-@item --enable-bang-history
-Include support for @code{csh}-like history substitution.
+@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-brace-expansion
-Include @code{csh}-like brace expansion
-( @code{b@{a,b@}c} @expansion{} @code{bac bbc} ).
+@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-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
+Bash interprets special backslash-escaped characters in the prompt
+strings when interactive (@pxref{Printing a Prompt}).
-@item --enable-directory-stack
-Include support for a @code{csh}-like directory stack and the
-@code{pushd}, @code{popd}, and @code{dirs} builtins.
+@item
+The Bash restricted mode is more useful (@pxref{The Restricted Shell});
+the SVR4.2 shell restricted mode is too limited.
-@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
+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-dparen-arithmetic
-Include support for the @code{ksh} @code{((@dots{}))} command.
+@item
+Bash includes a number of features to support a separate debugger for
+shell scripts.
-@item --enable-help-builtin
-Include the @code{help} builtin, which displays help on shell builtins and
-variables.
+@item
+The SVR4.2 shell has two privilege-related builtins
+(@code{mldmode} and @code{priv}) not present in Bash.
-@item --enable-history
-Include command history and the @code{fc} and @code{history}
-builtin commands.
+@item
+Bash does not have the @code{stop} or @code{newgrp} builtins.
-@item --enable-job-control
-This enables job control features, if the @sc{OS} supports them.
+@item
+Bash does not use the @env{SHACCT} variable or perform shell accounting.
-@item --enable-process-substitution
-This enables process substitution (@pxref{Process Substitution}) if
-the @sc{OS} provides the necessary support.
+@item
+The SVR4.2 @code{sh} uses a @env{TIMEOUT} variable like Bash uses
+@env{TMOUT}.
-@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.
+@end itemize
-@item --enable-readline
-Include support for command-line editing and history with the Bash
-version of the Readline library.
+@noindent
+More features unique to Bash may be found in @ref{Bash Features}.
-@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.
-@item --enable-select
-Include the @code{ksh} @code{select} builtin, which allows the
-generation of simple menus.
+@appendixsec Implementation Differences From The SVR4.2 Shell
-@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.
+Since Bash is a completely new implementation, it does not suffer from
+many of the limitations of the SVR4.2 shell. For instance:
-@end table
+@itemize @bullet
-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.
+@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.
-@node Reporting Bugs
-@appendix Reporting Bugs
+@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.
-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
+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.
-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 @code{bug-bash@@prep.ai.MIT.Edu} or posted to the Usenet
-newsgroup @code{gnu.bash.bug}.
+@item
+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.
-All bug reports should include:
-@itemize @bullet
@item
-The version number of Bash.
+The SVR4.2 shell does not allow users to trap @code{SIGSEGV},
+@code{SIGALRM}, or @code{SIGCHLD}.
+
@item
-The hardware and operating system.
+The SVR4.2 shell does not allow the @env{IFS}, @env{MAILCHECK},
+@env{PATH}, @env{PS1}, or @env{PS2} variables to be unset.
+
@item
-The compiler used to compile Bash.
+The SVR4.2 shell treats @samp{^} as the undocumented equivalent of
+@samp{|}.
+
@item
-A description of the bug behaviour.
+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
-A short script or `recipe' which exercises the bug and may be used
-to reproduce it.
+The SVR4.2 shell exits a script if any builtin fails; Bash exits
+a script only if one of the @sc{posix} 1003.2 special builtins fails, and
+only for certain failures, as enumerated in the @sc{posix} 1003.2 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 Copying This Manual
+@appendix Copying This Manual
-Please send all reports concerning this manual to
-@code{chet@@ins.CWRU.Edu}.
+@menu
+* GNU Free Documentation License:: License for copying this manual.
+@end menu
+
+@include fdl.texi
@node Builtin Index
-@appendix Index of Shell Builtin Commands
+@unnumbered Index of Shell Builtin Commands
@printindex bt
@node Reserved Word Index
-@appendix Shell Reserved Words
+@unnumbered Index of Shell Reserved Words
@printindex rw
@node Variable Index
-@appendix Parameter and Variable Index
+@unnumbered Parameter and Variable Index
@printindex vr
@node Function Index
-@appendix Function Index
+@unnumbered Function Index
@printindex fn
@node Concept Index
-@appendix Concept Index
+@unnumbered Concept Index
@printindex cp
-@contents
@bye
projects / platform / upstream / bash.git / blobdiff