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+\input texinfo.tex @c -*- texinfo -*-
+@c %**start of header
+@setfilename bashref.info
+@settitle Bash Reference Manual
+
+@include version.texi
+@c %**end of header
+
+@copying
+This text is a brief description of the features that are present in
+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 @copyright{} 1988--2020 Free Software Foundation, Inc.
+
+@quotation
+Permission is granted to copy, distribute and/or modify this document
+under the terms of the GNU Free Documentation License, Version 1.3 or
+any later version published by the Free Software Foundation; with no
+Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
+A copy of the license is included in the section entitled
+``GNU Free Documentation License''.
+@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-MONTH}
+@author Chet Ramey, Case Western Reserve University
+@author Brian Fox, Free Software Foundation
+
+@page
+@vskip 0pt plus 1filll
+@insertcopying
+
+@end titlepage
+
+@contents
+
+@ifnottex
+@node Top, Introduction, (dir), (dir)
+@top Bash Features
+
+This text is a brief description of the features that are present in
+the Bash shell (version @value{VERSION}, @value{UPDATED}).
+The Bash home page is @url{http://www.gnu.org/software/bash/}.
+
+This is Edition @value{EDITION}, last updated @value{UPDATED},
+of @cite{The GNU Bash Reference Manual},
+for @code{Bash}, Version @value{VERSION}.
+
+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
+(@file{ksh}), and the C-shell (@file{csh} and its successor,
+@file{tcsh}).  The following menu breaks the features up into
+categories, noting which features were inspired by other shells and
+which are specific to Bash.
+
+This manual is meant as a brief introduction to features found in
+Bash.  The Bash manual page should be used as the definitive
+reference on shell behavior.
+
+@menu
+* Introduction::		An introduction to the shell.
+* Definitions::			Some definitions used in the rest of this
+				manual.
+* Basic Shell Features::	The shell "building blocks".
+* 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::			What job control is and how Bash allows you
+				to use it.
+* Command Line Editing::	Chapter describing the command line
+				editing features.
+* Using History Interactively::	Command History Expansion
+* Installing Bash::		How to build and install Bash on your system.
+* Reporting Bugs::		How to report bugs in Bash.
+* Major Differences From The Bourne Shell::	A terse list of the differences
+						between Bash and historical
+						versions of /bin/sh.
+* GNU Free Documentation License::	Copying and sharing this documentation.
+* Indexes::			Various indexes for this manual.
+@end menu
+@end 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
+
+@node What is Bash?
+@section What is Bash?
+
+Bash is the shell, or command language interpreter,
+for the @sc{gnu} operating system.
+The name is an acronym for the @samp{Bourne-Again SHell},
+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 largely compatible with @code{sh} and incorporates useful
+features from the Korn shell @code{ksh} and the C shell @code{csh}.
+It is intended to be a conformant implementation of the @sc{ieee}
+@sc{posix} Shell and Tools portion of the @sc{ieee} @sc{posix}
+specification (@sc{ieee} Standard 1003.1).
+It offers functional improvements over @code{sh} for both interactive and
+programming use.
+
+While the @sc{gnu} operating system provides other shells, including
+a version of @code{csh}, Bash is the default shell.
+Like other @sc{gnu} software, Bash is quite portable.  It currently runs
+on nearly every version of Unix and a few other operating systems @minus{}
+independently-supported ports exist for @sc{ms-dos}, @sc{os/2},
+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.  The term macro processor means functionality where text
+and symbols are expanded to create larger expressions.
+
+A Unix shell is both a command interpreter and a programming
+language.  As a command interpreter, the shell provides the user
+interface to the rich set of @sc{gnu} utilities.  The programming
+language features allow these utilities to be combined.
+Files containing commands can be created, and become
+commands themselves.  These new commands have the same status as
+system commands in directories 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
+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
+complexity) of shells is due to their embedded programming
+languages.  Like any high-level language, the shell provides
+variables, flow control constructs, quoting, and functions. 
+
+Shells offer features geared specifically for
+interactive use rather than to augment the programming language. 
+These interactive features include job control, command line
+editing, command history and aliases.  Each of these features is
+described in this manual.
+
+@node Definitions
+@chapter Definitions
+These definitions are used throughout the remainder of this manual.
+
+@table @code
+
+@item POSIX
+@cindex POSIX
+A family of open system standards based on Unix.  Bash
+is primarily concerned with the Shell and Utilities portion of the
+@sc{posix} 1003.1 standard. 
+
+@item blank
+A space or tab character.
+
+@item builtin
+@cindex builtin
+A command that is implemented internally by the shell itself, rather
+than by an executable program somewhere in the file system.
+
+@item control operator
+@cindex control operator
+A @code{token} that performs a control function.  It is a @code{newline}
+or one of the following:
+@samp{||}, @samp{&&}, @samp{&}, @samp{;}, @samp{;;}, @samp{;&}, @samp{;;&},
+@samp{|}, @samp{|&}, @samp{(}, or @samp{)}.
+
+@item exit status
+@cindex exit status
+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
+A unit of text that is the result of one of the shell expansions.  After
+expansion, when executing a command, the resulting fields are used as
+the command name and arguments.
+
+@item filename
+@cindex filename
+A string of characters used to identify a file.
+
+@item job
+@cindex job
+A set of processes comprising a pipeline, and any processes descended
+from it, that are all in the same process group.
+
+@item job control
+@cindex job control
+A mechanism by which users can selectively stop (suspend) and restart
+(resume) execution of processes.
+
+@item metacharacter
+@cindex metacharacter
+A character that, when unquoted, separates words.  A metacharacter is
+a @code{space}, @code{tab}, @code{newline}, or one of the following characters:
+@samp{|}, @samp{&}, @samp{;}, @samp{(}, @samp{)}, @samp{<}, or
+@samp{>}.
+
+@item name
+@cindex name
+@cindex identifier
+A @code{word} consisting solely of letters, numbers, and underscores,
+and beginning with a letter or underscore.  @code{Name}s are used as
+shell variable and function names.
+Also referred to as an @code{identifier}.
+
+@item operator
+@cindex operator, shell
+A @code{control operator} or a @code{redirection operator}.
+@xref{Redirections}, for a list of redirection operators.
+Operators contain at least one unquoted @code{metacharacter}.
+
+@item process group
+@cindex process group
+A collection of related processes each having the same process
+group @sc{id}.
+
+@item process group ID
+@cindex process group ID
+A unique identifier that represents a @code{process group}
+during its lifetime.
+
+@item reserved word
+@cindex reserved word
+A @code{word} that has a special meaning to the shell.  Most reserved
+words introduce shell flow control constructs, such as @code{for} and
+@code{while}.
+
+@item return status
+@cindex return status
+A synonym for @code{exit status}.
+
+@item signal
+@cindex signal
+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} standard.
+
+@item token
+@cindex token
+A sequence of characters considered a single unit by the shell.
+It is either a @code{word} or an @code{operator}.
+
+@item word
+@cindex word
+A sequence of characters treated as a unit by the shell.
+Words may not include unquoted @code{metacharacters}.
+@end table
+
+@node Basic Shell Features
+@chapter Basic Shell Features
+@cindex Bourne shell
+
+Bash is an acronym for @samp{Bourne-Again SHell}.
+The Bourne shell is
+the traditional Unix shell originally written by Stephen Bourne.
+All of the Bourne shell builtin commands are available in Bash,
+The rules for evaluation and quoting are taken from the @sc{posix}
+specification for the `standard' Unix shell.
+
+This chapter briefly summarizes the shell's `building blocks':
+commands, control structures, shell functions, shell @i{parameters},
+shell expansions,
+@i{redirections}, which are a way to direct input and output from
+and to named files, and how the shell executes commands.
+
+@menu
+* Shell Syntax::		What your input means to the shell.
+* Shell Commands::		The types of commands you can use.
+* Shell Functions::		Grouping commands by name.
+* Shell Parameters::		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.
+* Shell Scripts::		Executing files of shell commands.
+@end menu
+
+@node Shell Syntax
+@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
+
+The following is a brief description of the shell's operation when it
+reads and executes a command.  Basically, the shell does the
+following:
+
+@enumerate
+@item
+Reads its input from a file (@pxref{Shell Scripts}), from a string
+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}.  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
+(@pxref{Shell Commands}).
+
+@item
+Performs the various shell expansions (@pxref{Shell Expansions}), breaking
+the expanded tokens into lists of filenames (@pxref{Filename Expansion})
+and commands and arguments.
+
+@item
+Performs any necessary redirections (@pxref{Redirections}) and removes
+the redirection operators and their operands from the argument list.
+
+@item
+Executes the command (@pxref{Executing Commands}).
+
+@item
+Optionally waits for the command to complete and collects its exit
+status (@pxref{Exit Status}).
+
+@end enumerate
+
+@node Quoting
+@subsection Quoting
+@cindex quoting
+@menu
+* Escape Character::	How to remove the special meaning from a single
+			character.
+* Single Quotes::	How to inhibit all interpretation of a sequence
+			of characters.
+* 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
+
+Quoting is used to remove the special meaning of certain
+characters or words to the shell.  Quoting can be used to
+disable special treatment for special characters, to prevent
+reserved words from being recognized as such, and to prevent
+parameter expansion.
+
+Each of the shell metacharacters (@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
+@subsubsection 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 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 (@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 (@samp{"}) preserves the literal value
+of all characters within the quotes, with the exception of
+@samp{$}, @samp{`}, @samp{\},
+and, when history expansion is enabled, @samp{!}.
+When the shell is in
+@sc{posix} mode (@pxref{Bash POSIX Mode}),
+the @samp{!} has no special meaning
+within double quotes, even when history expansion is enabled.
+The characters @samp{$} and @samp{`}
+retain their special meaning within double quotes (@pxref{Shell Expansions}).
+The backslash retains its special meaning only when followed by one of
+the following characters:
+@samp{$}, @samp{`}, @samp{"}, @samp{\}, or @code{newline}.
+Within double quotes, backslashes that are followed by one of these
+characters are removed.  Backslashes preceding characters without a
+special meaning are left unmodified.
+A double quote may be quoted within double quotes by preceding it with
+a backslash.
+If enabled, history expansion will be performed unless an @samp{!}
+appearing in double quotes is escaped using a backslash.
+The backslash preceding the @samp{!} is not removed.
+
+The special parameters @samp{*} and @samp{@@} have special meaning
+when in double quotes (@pxref{Shell Parameter Expansion}).
+
+@node ANSI-C Quoting
+@subsubsection ANSI-C Quoting
+@cindex quoting, ANSI
+
+Words of the form @code{$'@var{string}'} are treated specially.  The
+word expands to @var{string}, with backslash-escaped characters replaced
+as specified by the ANSI C standard.  Backslash escape sequences, if
+present, are decoded as follows:
+
+@table @code
+@item \a
+alert (bell)
+@item \b
+backspace
+@item \e
+@itemx \E
+an escape character (not ANSI C)
+@item \f
+form feed
+@item \n
+newline
+@item \r
+carriage return
+@item \t
+horizontal tab
+@item \v
+vertical tab
+@item \\
+backslash
+@item \'
+single quote
+@item \"
+double quote
+@item \?
+question mark
+@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)
+@item \u@var{HHHH}
+the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value
+@var{HHHH} (one to four hex digits)
+@item \U@var{HHHHHHHH}
+the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value
+@var{HHHHHHHH} (one to eight hex digits)
+@item \c@var{x}
+a control-@var{x} character
+@end table
+
+@noindent
+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.
+The @var{gettext} infrastructure performs the message catalog lookup and 
+translation, using the @code{LC_MESSAGES} and @code{TEXTDOMAIN} shell
+variables, as explained below. See the gettext documentation for additional
+details.
+If the current locale is @code{C} or @code{POSIX},
+or if there are no translations available,
+the dollar sign is ignored.
+If the string is translated and replaced, the replacement is
+double-quoted.
+
+@vindex LC_MESSAGES
+@vindex TEXTDOMAIN
+@vindex TEXTDOMAINDIR
+Some systems use the message catalog selected by the @env{LC_MESSAGES}
+shell variable.  Others create the name of the message catalog from the
+value of the @env{TEXTDOMAIN} shell variable, possibly adding a
+suffix of @samp{.mo}.  If you use the @env{TEXTDOMAIN} variable, you
+may need to set the @env{TEXTDOMAINDIR} variable to the location of
+the message catalog files.  Still others use both variables in this
+fashion:
+@env{TEXTDOMAINDIR}/@env{LC_MESSAGES}/LC_MESSAGES/@env{TEXTDOMAIN}.mo.
+
+@node Comments
+@subsection Comments
+@cindex comments, shell
+
+In a non-interactive shell, or an interactive shell in which the
+@code{interactive_comments} option to the @code{shopt}
+builtin is enabled (@pxref{The Shopt Builtin}),
+a word beginning with @samp{#}
+causes that word and all remaining characters on that line to
+be ignored.  An interactive shell without the @code{interactive_comments}
+option enabled does not allow comments.  The @code{interactive_comments}
+option is on by default in interactive shells.
+@xref{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
+* Reserved Words::		Words that have special meaning 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.
+* Compound Commands::		Shell commands for control flow.
+* Coprocesses::			Two-way communication between commands.
+* GNU Parallel::		Running commands in parallel.
+@end menu
+
+@node Reserved Words
+@subsection Reserved Words
+@cindex reserved words
+
+Reserved words are words that have special meaning to the shell.
+They are used to begin and end the shell's compound commands.
+
+The following words are recognized as reserved when unquoted and 
+the first word of a command (see below for exceptions):
+
+@multitable @columnfractions .1 .1 .1 .1 .12 .1
+@item @code{if} @tab @code{then} @tab @code{elif}
+@tab @code{else} @tab @code{fi} @tab @code{time}
+@item @code{for} @tab @code{in} @tab @code{until}
+@tab @code{while} @tab @code{do} @tab @code{done}
+@item @code{case} @tab @code{esac} @tab @code{coproc}
+@tab @code{select} @tab @code{function}
+@item @code{@{} @tab @code{@}} @tab @code{[[} @tab @code{]]} @tab @code{!}
+@end multitable
+
+@noindent
+@code{in} is recognized as a reserved word if it is the third word of a
+@code{case} or @code{select} command.
+@code{in} and @code{do} are recognized as reserved
+words if they are the third word in a @code{for} command.
+
+@node Simple Commands
+@subsection Simple Commands
+@cindex commands, simple
+
+A simple command is the kind of command encountered most often.
+It's just a sequence of words separated by @code{blank}s, terminated
+by one of the shell's control operators (@pxref{Definitions}).  The
+first word generally specifies a command to be executed, 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} 1003.1 @code{waitpid} function, or 128+@var{n} if
+the command was terminated by signal @var{n}.
+
+@node Pipelines
+@subsection Pipelines
+@cindex pipeline
+@cindex commands, pipelines
+
+A @code{pipeline} is a sequence of one or more commands separated by
+one of the control operators @samp{|} or @samp{|&}.
+
+@rwindex time
+@rwindex !
+@cindex command timing
+The format for a pipeline is
+@example
+[time [-p]] [!] @var{command1} [ | or |& @var{command2} ] @dots{}
+@end example
+
+@noindent
+The output of each command in the pipeline is connected via a pipe
+to the input of the next command.
+That is, each command reads the previous command's output.  This
+connection is performed before any redirections specified by the
+command.
+
+If @samp{|&} is used, @var{command1}'s standard error, in addition to
+its standard output, is connected to
+@var{command2}'s standard input through the pipe;
+it is shorthand for @code{2>&1 |}.
+This implicit redirection of the standard error to the standard output is
+performed after any redirections specified by the command.
+
+The reserved word @code{time} causes timing statistics
+to be printed for the pipeline once it finishes.
+The statistics currently consist of elapsed (wall-clock) time and
+user and system time consumed by the command's execution.
+The @option{-p} option changes the output format to that specified
+by @sc{posix}.
+When the shell is in @sc{posix} mode (@pxref{Bash POSIX Mode}),
+it does not recognize @code{time} as a reserved word if the next
+token begins with a @samp{-}.
+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.
+
+When the shell is in @sc{posix} mode (@pxref{Bash POSIX Mode}), @code{time}
+may be followed by a newline.  In this case, the shell displays the
+total user and system time consumed by the shell and its children.
+The @env{TIMEFORMAT} variable may be used to specify the format of
+the time information.
+
+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, which is a
+separate process (@pxref{Command Execution Environment}).
+If the @code{lastpipe} option is enabled using the @code{shopt} builtin
+(@pxref{The Shopt Builtin}),
+the last element of a pipeline may be run by the shell process.
+
+The exit
+status of a pipeline is the exit status of the last command in the
+pipeline, unless the @code{pipefail} option is enabled
+(@pxref{The Set Builtin}).
+If @code{pipefail} is enabled, the pipeline's return status is the
+value of the last (rightmost) command to exit with a non-zero status,
+or zero if all commands exit successfully.
+If the reserved word @samp{!} precedes the pipeline, the
+exit status is the logical negation of the exit status as described
+above.
+The shell waits for all commands in the pipeline to terminate before
+returning a value.
+
+@node Lists
+@subsection Lists of Commands
+@cindex commands, lists
+
+A @code{list} is a sequence of one or more pipelines separated by one
+of the operators @samp{;}, @samp{&}, @samp{&&}, or @samp{||},
+and optionally terminated by one of @samp{;}, @samp{&}, or a
+@code{newline}.
+
+Of these list operators, @samp{&&} and @samp{||}
+have equal precedence, followed by @samp{;} and @samp{&},
+which have equal precedence.
+
+A sequence of one or more newlines may appear in a @code{list}
+to delimit commands, equivalent to a semicolon.
+
+If a command is terminated by the control operator @samp{&},
+the shell executes the command asynchronously in a subshell.
+This is known as executing the command in the @var{background},
+and these are referred to as @var{asynchronous} commands.
+The shell does not wait for the command to finish, and the return
+status is 0 (true).
+When job control is not active (@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.
+
+@sc{and} and @sc{or} lists are sequences of one or more pipelines
+separated by the control operators @samp{&&} and @samp{||},
+respectively.  @sc{and} and @sc{or} lists are executed with left
+associativity.
+
+An @sc{and} list has the form
+@example
+@var{command1} && @var{command2}
+@end example
+
+@noindent
+@var{command2} is executed if, and only if, @var{command1}
+returns an exit status of zero (success).
+
+An @sc{or} list has the form
+@example
+@var{command1} || @var{command2}
+@end example
+
+@noindent
+@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
+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 language 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.
+
+In most cases a list of commands in a compound command's description may be
+separated from the rest of the command by one or more newlines, and may be
+followed by a newline in place of a semicolon.
+
+Bash provides looping constructs, conditional commands, and mechanisms
+to group commands and execute them as a unit.
+
+@node Looping Constructs
+@subsubsection Looping Constructs
+@cindex commands, looping
+
+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
+@rwindex do
+@rwindex done
+The syntax of the @code{until} command is:
+
+@example
+until @var{test-commands}; do @var{consequent-commands}; done
+@end example
+
+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
+The syntax of the @code{while} command is:
+
+@example
+while @var{test-commands}; do @var{consequent-commands}; done
+@end example
+
+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
+The syntax of the @code{for} command is:
+
+@example
+for @var{name} [ [in [@var{words} @dots{}] ] ; ] do @var{commands}; done
+@end example
+
+Expand @var{words} (@pxref{Shell Expansions}), 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{commands}
+that is executed, or false if any of the expressions is invalid.
+@end table
+
+The @code{break} and @code{continue} builtins (@pxref{Bourne Shell Builtins})
+may be used to control loop execution.
+
+@node Conditional Constructs
+@subsubsection Conditional Constructs
+@cindex commands, conditional
+
+@table @code
+@item if
+@rwindex if
+@rwindex then
+@rwindex else
+@rwindex elif
+@rwindex fi
+The syntax of the @code{if} command is:
+
+@example
+if @var{test-commands}; then
+  @var{consequent-commands};
+[elif @var{more-test-commands}; then
+  @var{more-consequents};]
+[else @var{alternate-consequents};]
+fi
+@end example
+
+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 @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
+@rwindex in
+@rwindex esac
+The syntax of the @code{case} command is:
+
+@example
+case @var{word} in
+    [ [(] @var{pattern} [| @var{pattern}]@dots{}) @var{command-list} ;;]@dots{}
+esac
+@end example
+
+@code{case} will selectively execute the @var{command-list} corresponding to
+the first @var{pattern} that matches @var{word}.
+The match is performed according
+to the rules described below in @ref{Pattern Matching}.
+If the @code{nocasematch} shell option
+(see the description of @code{shopt} in @ref{The Shopt Builtin})
+is enabled, the match is performed without regard to the case
+of alphabetic characters.
+The @samp{|} is used to separate multiple patterns, and the @samp{)}
+operator terminates a pattern list.
+A list of patterns and an associated command-list is known
+as a @var{clause}.
+
+Each clause must be terminated with @samp{;;}, @samp{;&}, or @samp{;;&}.
+The @var{word} undergoes tilde expansion, parameter expansion, command
+substitution, arithmetic expansion, and quote removal
+(@pxref{Shell Parameter Expansion})
+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{;;}, @samp{;&}, or @samp{;;&}.
+The first pattern that matches determines the
+command-list that is executed.
+It's a common idiom to use @samp{*} as the final pattern to define the
+default case, since that pattern will always match.
+
+Here is an example using @code{case} in a script that could be used to
+describe one interesting feature of an animal:
+
+@example
+echo -n "Enter the name of an animal: "
+read ANIMAL
+echo -n "The $ANIMAL has "
+case $ANIMAL in
+  horse | dog | cat) echo -n "four";;
+  man | kangaroo ) echo -n "two";;
+  *) echo -n "an unknown number of";;
+esac
+echo " legs."
+@end example
+
+@noindent
+
+If the @samp{;;} operator is used, no subsequent matches are attempted after
+the first pattern match.
+Using @samp{;&}  in place of @samp{;;} causes execution to continue with
+the @var{command-list} associated with the next clause, if any.
+Using @samp{;;&} in place of @samp{;;} causes the shell to test the patterns
+in the next clause, if any, and execute any associated @var{command-list}
+on a successful match,
+continuing the case statement execution as if the pattern list had not matched.
+
+The return status is zero if no @var{pattern} is matched.  Otherwise, the
+return status is the exit status of the @var{command-list} executed.
+
+@item select
+@rwindex select
+
+The @code{select} construct allows the easy generation of menus.
+It has almost the same syntax as the @code{for} command:
+
+@example
+select @var{name} [in @var{words} @dots{}]; do @var{commands}; done
+@end example
+
+The list of words following @code{in} is expanded, generating a list
+of items.  The set of expanded words is printed on the standard
+error output stream, each preceded by a number.  If the
+@samp{in @var{words}} is omitted, the positional parameters are printed,
+as if @samp{in "$@@"} had been specified.
+The @env{PS3} prompt is then displayed and a line is read from the
+standard input.
+If the line consists of a number corresponding to one of the displayed
+words, then the value of @var{name} is set to that word.
+If the line is empty, the words and prompt are displayed again.
+If @code{EOF} is read, the @code{select} command completes.
+Any other value read causes @var{name} to be set to null.
+The line read is saved in the variable @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 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 @code{[[} and @code{]]}; 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 used with @code{[[}, the @samp{<} and @samp{>} operators sort
+lexicographically using the current locale.
+
+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},
+as if the @code{extglob} shell option were enabled.
+The @samp{=} operator is identical to @samp{==}.
+If the @code{nocasematch} shell option
+(see the description of @code{shopt} in @ref{The Shopt Builtin})
+is enabled, the match is performed without regard to the case
+of alphabetic characters.
+The return value is 0 if the string matches (@samp{==}) or does not
+match (@samp{!=}) the pattern, and 1 otherwise.
+Any part of the pattern may be quoted to force the quoted portion
+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
+a @sc{posix} extended regular expression and matched accordingly
+(using the @sc{posix} @code{regcomp} and @code{regexec} interfaces
+usually described 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 @code{nocasematch} shell option
+(see the description of @code{shopt} in @ref{The Shopt Builtin})
+is enabled, the match is performed without regard to the case
+of alphabetic characters.
+Any part of the pattern may be quoted to force the quoted portion
+to be matched as a string.
+Bracket expressions in regular expressions must be treated carefully,
+since normal quoting characters lose their meanings between brackets.
+If the pattern is stored in a shell variable, quoting the variable
+expansion forces the entire pattern to be matched as a string.
+
+The pattern will match if it matches any part of the string.
+Anchor the pattern using the @samp{^} and @samp{$} regular expression
+operators to force it to match the entire string.
+The array variable @code{BASH_REMATCH} records which parts of the string
+matched the pattern.
+The element of @code{BASH_REMATCH} with index 0 contains the portion of
+the string matching the entire regular expression.
+Substrings matched by parenthesized subexpressions within the regular
+expression are saved in the remaining @code{BASH_REMATCH} indices.
+The element of @code{BASH_REMATCH} with index @var{n} is the portion of the
+string matching the @var{n}th parenthesized subexpression.
+
+For example, the following will match a line
+(stored in the shell variable @var{line})
+if there is a sequence of characters anywhere in the value consisting of
+any number, including zero, of 
+characters in the @code{space} character class,
+zero or one instances of @samp{a}, then a @samp{b}:
+@example
+[[ $line =~ [[:space:]]*(a)?b ]]
+@end example
+
+@noindent
+That means values like @samp{aab} and @samp{  aaaaaab} will match, as
+will a line containing a @samp{b} anywhere in its value.
+
+Storing the regular expression in a shell variable is often a useful
+way to avoid problems with quoting characters that are special to the
+shell.
+It is sometimes difficult to specify a regular expression literally
+without using quotes, or to keep track of the quoting used by regular
+expressions while paying attention to the shell's quote removal.
+Using a shell variable to store the pattern decreases these problems.
+For example, the following is equivalent to the above:
+@example
+pattern='[[:space:]]*(a)?b'
+[[ $line =~ $pattern ]]
+@end example
+
+@noindent
+If you want to match a character that's special to the regular expression
+grammar, it has to be quoted to remove its special meaning.
+This means that in the pattern @samp{xxx.txt}, the @samp{.} matches any
+character in the string (its usual regular expression meaning), but in the
+pattern @samp{"xxx.txt"} it can only match a literal @samp{.}.
+Shell programmers should take special care with backslashes, since backslashes
+are used both by the shell and regular expressions to remove the special
+meaning from the following character.
+The following two sets of commands are @emph{not} equivalent:
+@example
+pattern='\.'
+
+[[ . =~ $pattern ]]
+[[ . =~ \. ]]
+
+[[ . =~ "$pattern" ]]
+[[ . =~ '\.' ]]
+@end example
+
+@noindent
+The first two matches will succeed, but the second two will not, because
+in the second two the backslash will be part of the pattern to be matched.
+In the first two examples, the backslash removes the special meaning from
+@samp{.}, so the literal @samp{.} matches.
+If the string in the first examples were anything other than @samp{.}, say
+@samp{a}, the pattern would not match, because the quoted @samp{.} in the
+pattern loses its special meaning of matching any single character.
+
+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.
+@end table
+
+@node Command Grouping
+@subsubsection Grouping Commands
+@cindex commands, grouping
+
+Bash provides two ways to group a list of commands to be executed
+as a unit.  When commands are grouped, redirections may be applied
+to the entire command list.  For example, the output of all the
+commands in the list may be redirected to a single stream.
+
+@table @code
+@item ()
+@example
+( @var{list} )
+@end example
+
+Placing a list of commands between parentheses causes a subshell
+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 @{
+@rwindex @}
+@example
+@{ @var{list}; @}
+@end example
+
+Placing a list of commands between curly braces causes the list to
+be executed in the current shell context.  No subshell is created.
+The semicolon (or newline) following @var{list} is required.
+@end table
+
+In addition to the creation of a subshell, there is a subtle difference
+between these two constructs due to historical reasons.  The braces
+are @code{reserved words}, so they must be separated from the @var{list}
+by @code{blank}s or other shell metacharacters.
+The parentheses are @code{operators}, and are
+recognized as separate tokens by the shell even if they are not separated
+from the @var{list} by whitespace.
+
+The exit status of both of these constructs is the exit status of
+@var{list}.
+
+@node Coprocesses
+@subsection Coprocesses
+@cindex coprocess
+
+A @code{coprocess} is a shell command preceded by the @code{coproc}
+reserved word.
+A coprocess is executed asynchronously in a subshell, as if the command
+had been terminated with the @samp{&} control operator, with a two-way pipe
+established between the executing shell and the coprocess.
+
+The format for a coprocess is:
+@example
+coproc [@var{NAME}] @var{command} [@var{redirections}]
+@end example
+
+@noindent
+This creates a coprocess named @var{NAME}.
+If @var{NAME} is not supplied, the default name is @var{COPROC}.
+@var{NAME} must not be supplied if @var{command} is a simple
+command (@pxref{Simple Commands}); otherwise, it is interpreted as
+the first word of the simple command.
+
+When the coprocess is executed, the shell creates an array variable
+(@pxref{Arrays})
+named @env{NAME} in the context of the executing shell.
+The standard output of @var{command}
+is connected via a pipe to a file descriptor in the executing shell,
+and that file descriptor is assigned to @env{NAME}[0].
+The standard input of @var{command}
+is connected via a pipe to a file descriptor in the executing shell,
+and that file descriptor is assigned to @env{NAME}[1].
+This pipe is established before any redirections specified by the
+command (@pxref{Redirections}).
+The file descriptors can be utilized as arguments to shell commands
+and redirections using standard word expansions.
+Other than those created to execute command and process substitutions,
+the file descriptors are not available in subshells.
+
+The process ID of the shell spawned to execute the coprocess is
+available as the value of the variable @env{NAME}_PID.
+The @code{wait}
+builtin command may be used to wait for the coprocess to terminate.
+
+Since the coprocess is created as an asynchronous command,
+the @code{coproc} command always returns success.
+The return status of a coprocess is the exit status of @var{command}.
+
+@node GNU Parallel
+@subsection GNU Parallel
+
+There are ways to run commands in parallel that are not built into Bash.
+GNU Parallel is a tool to do just that.
+
+GNU Parallel, as its name suggests, can be used to build and run commands
+in parallel.  You may run the same command with different arguments, whether
+they are filenames, usernames, hostnames, or lines read from files.  GNU
+Parallel provides shorthand references to many of the most common operations
+(input lines, various portions of the input line, different ways to specify
+the input source, and so on).  Parallel can replace @code{xargs} or feed
+commands from its input sources to several different instances of Bash.
+
+For a complete description, refer to the GNU Parallel documentation.  A few
+examples should provide a brief introduction to its use.
+
+For example, it is easy to replace @code{xargs} to gzip all html files in the
+current directory and its subdirectories:
+@example
+find . -type f -name '*.html' -print | parallel gzip
+@end example
+@noindent
+If you need to protect special characters such as newlines in file names,
+use find's @option{-print0} option and parallel's @option{-0} option.
+
+You can use Parallel to move files from the current directory when the
+number of files is too large to process with one @code{mv} invocation:
+@example
+printf '%s\n' * | parallel mv @{@} destdir
+@end example
+
+As you can see, the @{@} is replaced with each line read from standard input.
+While using @code{ls} will work in most instances, it is not sufficient to
+deal with all filenames. @code{printf} is a shell builtin, and therefore is
+not subject to the kernel's limit on the number of arguments to a program,
+so you can use @samp{*} (but see below about the @code{dotglob} shell option).
+If you need to accommodate special characters in filenames, you can use
+
+@example
+printf '%s\0' * | parallel -0 mv @{@} destdir
+@end example
+
+@noindent
+as alluded to above.
+
+This will run as many @code{mv} commands as there are files in the current
+directory.
+You can emulate a parallel @code{xargs} by adding the @option{-X} option:
+@example
+printf '%s\0' * | parallel -0 -X mv @{@} destdir
+@end example
+
+(You may have to modify the pattern if you have the @code{dotglob} option
+enabled.)
+
+GNU Parallel can replace certain common idioms that operate on lines read
+from a file (in this case, filenames listed one per line):
+@example
+	while IFS= read -r x; do
+		do-something1 "$x" "config-$x"
+		do-something2 < "$x"
+	done < file | process-output
+@end example
+
+@noindent
+with a more compact syntax reminiscent of lambdas:
+@example
+cat list | parallel "do-something1 @{@} config-@{@} ; do-something2 < @{@}" |
+           process-output
+@end example
+
+Parallel provides a built-in mechanism to remove filename extensions, which
+lends itself to batch file transformations or renaming:
+@example
+ls *.gz | parallel -j+0 "zcat @{@} | bzip2 >@{.@}.bz2 && rm @{@}"
+@end example
+@noindent
+This will recompress all files in the current directory with names ending
+in .gz using bzip2, running one job per CPU (-j+0) in parallel.
+(We use @code{ls} for brevity here; using @code{find} as above is more
+robust in the face of filenames containing unexpected characters.)
+Parallel can take arguments from the command line; the above can also be
+written as
+
+@example
+parallel "zcat @{@} | bzip2 >@{.@}.bz2 && rm @{@}" ::: *.gz
+@end example
+
+If a command generates output, you may want to preserve the input order in
+the output.  For instance, the following command
+@example
+@{
+    echo foss.org.my ;
+    echo debian.org ;
+    echo freenetproject.org ;
+@} | parallel traceroute
+@end example
+@noindent
+will display as output the traceroute invocation that finishes first.
+Adding the @option{-k} option 
+@example
+@{
+    echo foss.org.my ;
+    echo debian.org ;
+    echo freenetproject.org ;
+@} | parallel -k traceroute
+@end example
+@noindent
+will ensure that the output of @code{traceroute foss.org.my} is displayed first.
+
+Finally, Parallel can be used to run a sequence of shell commands in parallel,
+similar to @samp{cat file | bash}.
+It is not uncommon to take a list of filenames, create a series of shell
+commands to operate on them, and feed that list of commands to a shell.
+Parallel can speed this up.  Assuming that @file{file} contains a list of
+shell commands, one per line,
+
+@example
+parallel -j 10 < file
+@end example
+
+@noindent
+will evaluate the commands using the shell (since no explicit command is
+supplied as an argument), in blocks of ten shell jobs at a time.
+
+@node Shell Functions
+@section Shell Functions
+@cindex shell function
+@cindex functions, shell
+
+Shell functions are a way to group commands for later execution
+using a single name for the group.  They are executed just like
+a "regular" command.
+When the name of a shell function is used as a simple command name,
+the list of commands associated with that function name is executed.
+Shell functions are executed in the current
+shell context; no new process is created to interpret them.
+
+Functions are declared using this syntax:
+@rwindex function
+@example
+@var{fname} () @var{compound-command} [ @var{redirections} ]
+@end example
+
+or
+
+@example
+function @var{fname} [()] @var{compound-command} [ @var{redirections} ]
+@end example
+
+This defines a shell function named @var{fname}.  The reserved
+word @code{function} is optional.
+If the @code{function} reserved
+word is supplied, the parentheses are optional.
+The @var{body} of the function is the 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,
+with one exception: If the @code{function} reserved word is used, but the
+parentheses are not supplied, the braces are required.                   
+@var{compound-command} is executed whenever @var{fname} is specified as the
+name of a command.
+When the shell is in @sc{posix} mode (@pxref{Bash POSIX Mode}),
+@var{fname} must be a valid shell @var{name} and
+may not be the same as one of the special builtins
+(@pxref{Special Builtins}).
+In default mode, a function name can be any unquoted shell word that does
+not contain @samp{$}.
+Any redirections (@pxref{Redirections}) associated with the shell function
+are performed when the function is executed.
+A function definition may be deleted using the @option{-f} option to the
+@code{unset} builtin (@pxref{Bourne Shell Builtins}).
+
+The exit status of a function definition is zero unless a syntax error
+occurs or a readonly function with the same name already exists.
+When executed, the exit status of a function is the exit status of the
+last command executed in the body.
+
+Note that for historical reasons, in the most common usage the curly braces
+that surround the body of the function must be separated from the body by
+@code{blank}s or newlines.
+This is because the braces are reserved words and are only recognized
+as such when they are separated from the command list
+by whitespace or another shell metacharacter.
+Also, when using the braces, the @var{list} must be terminated by a semicolon,
+a @samp{&}, or a newline.
+
+When a function is executed, the arguments to the
+function become the positional parameters
+during its execution (@pxref{Positional Parameters}).
+The special parameter @samp{#} that expands to the number of
+positional parameters is updated to reflect the change.
+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 these exceptions:
+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),
+and the @env{ERR} trap is not inherited unless the @code{-o errtrace}
+shell option has been enabled.
+@xref{Bourne Shell Builtins}, for the description of the
+@code{trap} builtin.
+
+The @env{FUNCNEST} variable, if set to a numeric value greater
+than 0, defines a maximum function nesting level.  Function
+invocations that exceed the limit cause the entire command to
+abort.
+
+If the builtin command @code{return}
+is executed in a function, the function completes and
+execution resumes with the next command after the function
+call.
+Any command associated with the @code{RETURN} trap is executed
+before execution resumes.
+When a function completes, the values of the
+positional parameters and the special parameter @samp{#}
+are restored to the values they had prior to the function's
+execution.  If a numeric argument is given to @code{return},
+that is the function's return status; otherwise the 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.  This is particularly
+important when a shell function calls other functions.
+
+Local variables "shadow" variables with the same name declared at
+previous scopes.  For instance, a local variable declared in a function
+hides a global variable of the same name: references and assignments
+refer to the local variable, leaving the global variable unmodified.
+When the function returns, the global variable is once again visible.
+
+The shell uses @var{dynamic scoping} to control a variable's visibility
+within functions.
+With dynamic scoping, visible variables and their values
+are a result of the sequence of function calls that caused execution
+to reach the current function.
+The value of a variable that a function sees depends
+on its value within its caller, if any, whether that caller is
+the "global" scope or another shell function.
+This is also the value that a local variable
+declaration "shadows", and the value that is restored when the function
+returns.
+
+For example, if a variable @var{var} is declared as local in function
+@var{func1}, and @var{func1} calls another function @var{func2},
+references to @var{var} made from within @var{func2} will resolve to the
+local variable @var{var} from @var{func1}, shadowing any global variable
+named @var{var}.
+
+The following script demonstrates this behavior.
+When executed, the script displays
+
+@example
+In func2, var = func1 local
+@end example
+
+@example
+func1()
+@{
+    local var='func1 local'
+    func2
+@}
+
+func2()
+@{
+    echo "In func2, var = $var"
+@}
+
+var=global
+func1
+@end example
+
+The @code{unset} builtin also acts using the same dynamic scope: if a  
+variable is local to the current scope, @code{unset} will unset it;         
+otherwise the unset will refer to the variable found in any calling scope 
+as described above.
+If a variable at the current local scope is unset, it will remain so
+until it is reset in that scope or until the function returns.
+Once the function returns, any instance of the variable at a previous
+scope will become visible.
+If the unset acts on a variable at a previous scope, any instance of a   
+variable with that name that had been shadowed will become visible.
+
+Function names and definitions may be listed with the
+@option{-f} option to the @code{declare} (@code{typeset})
+builtin command (@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}).
+
+Functions may be recursive.
+The @code{FUNCNEST} variable may be used to limit the depth of the
+function call stack and restrict the number of function invocations.
+By default, no limit is placed on the number of recursive  calls.
+
+@node Shell Parameters
+@section Shell Parameters
+@cindex parameters
+@cindex variable, shell
+@cindex shell variable
+
+@menu
+* Positional Parameters::	The shell's command-line arguments.
+* 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.
+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
+the @code{unset} builtin command.
+
+A variable may be assigned to by a statement of the form
+@example
+@var{name}=[@var{value}]
+@end example
+@noindent
+If @var{value}
+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 @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 (@var{declaration} commands).
+When in @sc{posix} mode (@pxref{Bash POSIX Mode}), these builtins may appear
+in a command after one or more instances of the @code{command} builtin
+and retain these assignment statement properties.
+
+In the context where an assignment statement is assigning a value  
+to a shell variable or array index (@pxref{Arrays}), the @samp{+=}
+operator can be used to   
+append to or add to the variable's previous value.
+This includes arguments to builtin commands such as @code{declare} that
+accept assignment statements (@var{declaration} commands).
+When @samp{+=} is applied to a variable for which the @var{integer} attribute
+has been set, @var{value} is evaluated as an arithmetic expression and
+added to the variable's current value, which is also evaluated.
+When @samp{+=} is applied to an array variable using compound assignment
+(@pxref{Arrays}), the
+variable's value is not unset (as it is when using @samp{=}), and new
+values are appended to the array beginning at one greater than the array's
+maximum index (for indexed arrays),  or added as additional key-value pairs
+in an associative array.
+When applied to a string-valued variable, @var{value} is expanded and
+appended to the variable's value.
+
+A variable can be assigned the @var{nameref} attribute using the
+@option{-n} option to the @code{declare} or @code{local} builtin commands
+(@pxref{Bash Builtins})
+to create a @var{nameref}, or a reference to another variable.
+This allows variables to be manipulated indirectly.
+Whenever the nameref variable is referenced, assigned to, unset, or has
+its attributes modified (other than using or changing the nameref
+attribute itself), the
+operation is actually performed on the variable specified by the nameref
+variable's value.
+A nameref is commonly used within shell functions to refer to a variable
+whose name is passed as an argument to the function.
+For instance, if a variable name is passed to a shell function as its first
+argument, running
+@example
+declare -n ref=$1
+@end example
+@noindent
+inside the function creates a nameref variable @var{ref} whose value is
+the variable name passed as the first argument.
+References and assignments to @var{ref}, and changes to its attributes,
+are treated as references, assignments, and attribute modifications
+to the variable whose name was passed as @code{$1}.
+
+If the control variable in a @code{for} loop has the nameref attribute,
+the list of words can be a list of shell variables, and a name reference
+will be established for each word in the list, in turn, when the loop is
+executed.
+Array variables cannot be given the nameref attribute.
+However, nameref variables can reference array variables and subscripted
+array variables.
+Namerefs can be unset using the @option{-n} option to the @code{unset} builtin
+(@pxref{Bourne Shell Builtins}).
+Otherwise, if @code{unset} is executed with the name of a nameref variable
+as an argument, the variable referenced by the nameref variable will be unset.
+
+@node Positional Parameters
+@subsection Positional Parameters
+@cindex parameters, positional
+
+A @var{positional parameter} is a parameter denoted by one or more
+digits, other than the single digit @code{0}.  Positional parameters are
+assigned from the shell's arguments when it is invoked,
+and may be reassigned using the @code{set} builtin command.
+Positional parameter @code{N} may be referenced as @code{$@{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}).
+
+When a positional parameter consisting of more than a single
+digit is expanded, it must be enclosed in braces.
+
+@node Special Parameters
+@subsection Special Parameters
+@cindex parameters, special
+
+The shell treats several parameters specially.  These parameters may
+only be referenced; assignment to them is not allowed.
+
+@vtable @code
+
+@item *
+@vindex $*
+($*) Expands to the positional parameters, starting from one.
+When the expansion is not within double quotes, each positional parameter
+expands to a separate word.
+In contexts where it is performed, those words
+are subject to further word splitting and filename expansion.
+When the expansion occurs within double quotes, it expands to a single word
+with the value of each parameter separated by the first character of the
+@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 @env{IFS} is unset, the parameters are separated by spaces.
+If @env{IFS} is null, the parameters are joined without intervening
+separators.
+
+@item @@
+@vindex $@@
+($@@) Expands to the positional parameters, starting from one.
+In contexts where word splitting is performed, this expands each
+positional parameter to a separate word; if not within double
+quotes, these words are subject to word splitting.
+In contexts where word splitting is not performed,
+this expands to a single word
+with each positional parameter separated by a space.
+When the
+expansion occurs within double quotes, and word splitting is performed,
+each parameter expands to a
+separate word.  That is, @code{"$@@"} 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).
+
+@item #
+@vindex $#
+($#) Expands to the number of positional parameters in decimal.
+
+@item ?
+@vindex $?
+($?) Expands to the exit status of the most recently executed foreground
+pipeline.
+
+@item -
+@vindex $-
+($-, 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 @option{-i} option).
+
+@item $
+@vindex $$
+($$) 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 !
+@vindex $!
+($!) Expands to the process @sc{id} of the job most recently placed into the
+background, whether executed as an asynchronous command or using
+the @code{bg} builtin (@pxref{Job Control Builtins}).
+
+@item 0
+@vindex $0
+($0) Expands to the name of the shell or shell script.  This is set at
+shell initialization.  If Bash is invoked with a file of commands
+(@pxref{Shell Scripts}), @code{$0} is set to the name of that file.
+If Bash is started with the @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.
+@end vtable
+
+@node Shell Expansions
+@section Shell Expansions
+@cindex expansion
+
+Expansion is performed on the command line after it has been split into
+@code{token}s.  There are seven kinds of expansion performed:
+
+@itemize @bullet
+@item brace expansion
+@item tilde expansion
+@item parameter and variable expansion
+@item command substitution
+@item arithmetic expansion
+@item word splitting
+@item filename expansion
+@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
+			arguments.
+* Filename Expansion::	A shorthand for specifying filenames matching patterns.
+* Quote Removal::	How and when quote characters are removed from
+			words.
+@end menu
+
+The order of expansions is:
+brace expansion;
+tilde expansion, parameter and variable expansion, arithmetic expansion,
+and command substitution (done in a left-to-right fashion);
+word splitting;
+and filename expansion.
+
+On systems that can support it, there is an additional expansion
+available: @var{process substitution}.
+This is performed at the
+same time as tilde, parameter, variable, and arithmetic expansion and
+command substitution.
+
+After these expansions are performed, quote characters present in the
+original word are removed unless they have been quoted themselves
+(@var{quote removal}).
+
+Only brace expansion, word splitting, and filename expansion
+can increase the number of words of the expansion; other expansions
+expand a single word to a single word.
+The only exceptions to this are the expansions of
+@code{"$@@"} and @code{$*} (@pxref{Special Parameters}), and
+@code{"$@{@var{name}[@@]@}"} and @code{$@{@var{name}[*]@}}
+(@pxref{Arrays}).
+
+After all expansions, @code{quote removal} (@pxref{Quote Removal})
+is performed.
+
+@node Brace Expansion
+@subsection Brace Expansion
+@cindex brace expansion
+@cindex expansion, brace
+
+Brace expansion is a mechanism by which arbitrary strings may be generated.
+This mechanism is similar to
+@var{filename expansion} (@pxref{Filename Expansion}),
+but the filenames generated need not exist.
+Patterns to be brace expanded take the form of an optional @var{preamble},
+followed by either a series of comma-separated strings or a sequence expression
+between a pair of braces,
+followed by an optional @var{postscript}.
+The preamble is prefixed to each string contained within the braces, and
+the postscript is then appended to each resulting string, expanding left
+to right.
+
+Brace expansions may be nested.
+The results of each expanded string are not sorted; left to right order
+is preserved.
+For example,
+@example
+bash$ echo a@{d,c,b@}e
+ade ace abe
+@end example
+
+A sequence expression takes the form @code{@{@var{x}..@var{y}[..@var{incr}]@}},
+where @var{x} and @var{y} are either integers or single characters,
+and @var{incr}, an optional increment, is an integer.
+When integers are supplied, the expression expands to each number between
+@var{x} and @var{y}, inclusive.
+Supplied integers may be prefixed with @samp{0} to force each term to have the
+same width.
+When either @var{x} or @var{y} begins with a zero, the shell
+attempts to force all generated terms to contain the same number of digits,
+zero-padding where necessary.
+When characters are supplied, the expression expands to each character
+lexicographically between @var{x} and @var{y}, inclusive,
+using the default C locale.
+Note that both @var{x} and @var{y} must be of the same type.
+When the increment is supplied, it is used as the difference between
+each term.  The default increment is 1 or -1 as appropriate.
+
+Brace expansion is performed before any other expansions,
+and any characters special to other expansions are preserved
+in the result.  It is strictly textual.  Bash
+does not apply any syntactic interpretation to the context of the
+expansion or the text between the braces.
+
+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,
+and inhibits brace expansion until the closing @samp{@}}.
+
+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 filenames 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{$@{OLDPWD-'~-'@}/foo}
+
+@item ~@var{N}
+The string that would be displayed by @samp{dirs +@var{N}}
+
+@item ~+@var{N}
+The string that would be displayed by @samp{dirs +@var{N}}
+
+@item ~-@var{N}
+The string that would be displayed by @samp{dirs -@var{N}}
+@end table
+
+Bash also performs tilde expansion on words satisfying the conditions of
+variable assignments (@pxref{Shell Parameters})
+when they appear as arguments to simple commands.
+Bash does not do this, except for the @var{declaration} commands listed
+above, when in @sc{posix} mode.
+
+@node Shell Parameter Expansion
+@subsection Shell Parameter Expansion
+@cindex parameter expansion
+@cindex expansion, parameter
+
+The @samp{$} character introduces parameter expansion,
+command substitution, or arithmetic expansion.  The parameter name
+or symbol to be expanded may be enclosed in braces, which
+are optional but serve to protect the variable to be expanded from
+characters immediately following it which could be
+interpreted as part of the name.
+
+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 @var{parameter} is a shell parameter as described above
+(@pxref{Shell Parameters}) or an array reference (@pxref{Arrays}).
+The braces are required when @var{parameter}
+is a positional parameter with more than one digit,
+or when @var{parameter} is followed by a character that is not to be
+interpreted as part of its name.
+
+If the first character of @var{parameter} is an exclamation point (!),
+and @var{parameter} is not a @var{nameref},
+it introduces a level of indirection.
+Bash uses the value formed by expanding the rest of
+@var{parameter} as the new @var{parameter}; this is then
+expanded and that value is used in the rest of the expansion, rather
+than the expansion of the original @var{parameter}.
+This is known as @code{indirect expansion}.
+The value is subject to tilde expansion,
+parameter expansion, command substitution, and arithmetic expansion.
+If @var{parameter} is a nameref, this expands to the name of the
+variable referenced by @var{parameter} instead of performing the
+complete 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, using the form described
+below (e.g., @samp{:-}), Bash tests for a parameter that is unset or null.
+Omitting the colon results in a test only for a parameter that is unset.
+Put another way, if the colon is included,
+the operator tests for both @var{parameter}'s existence and that its value
+is not null; if the colon is omitted, the operator tests only for existence.
+
+@table @code
+
+@item $@{@var{parameter}:@minus{}@var{word}@}
+If @var{parameter} is unset or null, the expansion of
+@var{word} is substituted.  Otherwise, the value of
+@var{parameter} is substituted.
+
+@item $@{@var{parameter}:=@var{word}@}
+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.
+
+@item $@{@var{parameter}:?@var{word}@}
+If @var{parameter}
+is null or unset, the expansion of @var{word} (or a message
+to that effect if @var{word}
+is not present) is written to the standard error and the shell, if it
+is not interactive, exits.  Otherwise, the value of @var{parameter} is
+substituted.
+
+@item $@{@var{parameter}:+@var{word}@}
+If @var{parameter}
+is null or unset, nothing is substituted, otherwise the expansion of
+@var{word} is substituted.
+
+@item $@{@var{parameter}:@var{offset}@}
+@itemx $@{@var{parameter}:@var{offset}:@var{length}@}
+This is referred to as Substring Expansion.
+It expands to up to @var{length} characters of the value of @var{parameter}
+starting at the character specified by @var{offset}.
+If @var{parameter} is @samp{@@}, an indexed array subscripted by
+@samp{@@} or @samp{*}, or an associative array name, the results differ as
+described below.
+If @var{length} is omitted, it expands to the substring of the value of
+@var{parameter} starting at the character specified by @var{offset}
+and extending to the end of the value.
+@var{length} and @var{offset} are arithmetic expressions
+(@pxref{Shell Arithmetic}).
+
+If @var{offset} evaluates to a number less than zero, the value
+is used as an offset in characters
+from the end of the value of @var{parameter}.
+If @var{length} evaluates to a number less than zero,
+it is interpreted as an offset in characters
+from the end of the value of @var{parameter} rather than
+a number of characters, and the expansion is the characters between
+@var{offset} and that result.
+Note that a negative offset must be separated from the colon by at least
+one space to avoid being confused with the @samp{:-} expansion.
+
+Here are some examples illustrating substring expansion on parameters and
+subscripted arrays:
+
+@verbatim
+$ string=01234567890abcdefgh
+$ echo ${string:7}
+7890abcdefgh
+$ echo ${string:7:0}
+
+$ echo ${string:7:2}
+78
+$ echo ${string:7:-2}
+7890abcdef
+$ echo ${string: -7}
+bcdefgh
+$ echo ${string: -7:0}
+
+$ echo ${string: -7:2}
+bc
+$ echo ${string: -7:-2}
+bcdef
+$ set -- 01234567890abcdefgh
+$ echo ${1:7}
+7890abcdefgh
+$ echo ${1:7:0}
+
+$ echo ${1:7:2}
+78
+$ echo ${1:7:-2}
+7890abcdef
+$ echo ${1: -7}
+bcdefgh
+$ echo ${1: -7:0}
+
+$ echo ${1: -7:2}
+bc
+$ echo ${1: -7:-2}
+bcdef
+$ array[0]=01234567890abcdefgh
+$ echo ${array[0]:7}
+7890abcdefgh
+$ echo ${array[0]:7:0}
+
+$ echo ${array[0]:7:2}
+78
+$ echo ${array[0]:7:-2}
+7890abcdef
+$ echo ${array[0]: -7}
+bcdefgh
+$ echo ${array[0]: -7:0}
+
+$ echo ${array[0]: -7:2}
+bc
+$ echo ${array[0]: -7:-2}
+bcdef
+@end verbatim
+
+If @var{parameter} is @samp{@@}, the result is @var{length} positional
+parameters beginning at @var{offset}.
+A negative @var{offset} is taken relative to one greater than the greatest
+positional parameter, so an offset of -1 evaluates to the last positional
+parameter.
+It is an expansion error if @var{length} evaluates to a number less than zero.
+
+The following examples illustrate substring expansion using positional
+parameters:
+
+@verbatim
+$ set -- 1 2 3 4 5 6 7 8 9 0 a b c d e f g h
+$ echo ${@:7}
+7 8 9 0 a b c d e f g h
+$ echo ${@:7:0}
+
+$ echo ${@:7:2}
+7 8
+$ echo ${@:7:-2}
+bash: -2: substring expression < 0
+$ echo ${@: -7:2}
+b c
+$ echo ${@:0}
+./bash 1 2 3 4 5 6 7 8 9 0 a b c d e f g h
+$ echo ${@:0:2}
+./bash 1
+$ echo ${@: -7:0}
+
+@end verbatim
+
+If @var{parameter} is an indexed array name subscripted
+by @samp{@@} or @samp{*}, the result is the @var{length}
+members of the array beginning with @code{$@{@var{parameter}[@var{offset}]@}}.
+A negative @var{offset} is taken relative to one greater than the maximum
+index of the specified array.
+It is an expansion error if @var{length} evaluates to a number less than zero.
+
+These examples show how you can use substring expansion with indexed
+arrays:
+
+@verbatim
+$ array=(0 1 2 3 4 5 6 7 8 9 0 a b c d e f g h)
+$ echo ${array[@]:7}
+7 8 9 0 a b c d e f g h
+$ echo ${array[@]:7:2}
+7 8
+$ echo ${array[@]: -7:2}
+b c
+$ echo ${array[@]: -7:-2}
+bash: -2: substring expression < 0
+$ echo ${array[@]:0}
+0 1 2 3 4 5 6 7 8 9 0 a b c d e f g h
+$ echo ${array[@]:0:2}
+0 1
+$ echo ${array[@]: -7:0}
+
+@end verbatim
+
+Substring expansion applied to an associative array produces undefined
+results.
+
+Substring indexing is zero-based unless the positional parameters
+are used, in which case the indexing starts at 1 by default.
+If @var{offset} is 0, and the positional parameters are used, @code{$0} is
+prefixed to the list.
+
+@item $@{!@var{prefix}*@}
+@itemx $@{!@var{prefix}@@@}
+Expands to the names of variables whose names begin with @var{prefix},
+separated by the first character of the @env{IFS} special variable.
+When @samp{@@} is used and the expansion appears within double quotes, each
+variable name expands to a separate word.
+
+@item $@{!@var{name}[@@]@}
+@itemx $@{!@var{name}[*]@}
+If @var{name} is an array variable, expands to the list of array indices
+(keys) assigned in @var{name}.
+If @var{name} is not an array, expands to 0 if @var{name} is set and null
+otherwise.
+When @samp{@@} is used and the expansion appears within double quotes, each
+key expands to a separate word.
+
+@item $@{#@var{parameter}@}
+The length in characters of the expanded value of @var{parameter} is
+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.
+If @var{parameter}
+is an indexed array name subscripted by a negative number, that number is
+interpreted as relative to one greater than the maximum index of
+@var{parameter}, so negative indices count back from the end of the
+array, and an index of -1 references the last element.
+
+@item $@{@var{parameter}#@var{word}@}
+@itemx $@{@var{parameter}##@var{word}@}
+The @var{word}
+is expanded to produce a pattern and matched according to the rules
+described below (@pxref{Pattern Matching}).  If the pattern matches
+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{*},
+the pattern removal operation is applied to each positional
+parameter in turn, and the expansion is the resultant list.
+If @var{parameter} is an array variable subscripted with
+@samp{@@} or @samp{*},
+the pattern removal operation is applied to each member of the
+array in turn, and the expansion is the resultant list.
+
+@item $@{@var{parameter}%@var{word}@}
+@itemx $@{@var{parameter}%%@var{word}@}
+The @var{word}
+is expanded to produce a pattern and matched according to the rules
+described below (@pxref{Pattern Matching}).
+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.
+If @var{parameter}
+is an array variable subscripted with @samp{@@} or @samp{*},
+the pattern removal operation is applied to each member of the
+array in turn, and the expansion is the resultant list.
+
+@item $@{@var{parameter}/@var{pattern}/@var{string}@} 
+
+The @var{pattern} is expanded to produce a pattern just as in
+filename expansion.
+@var{Parameter} is expanded and the longest match of @var{pattern}
+against its value is replaced with @var{string}.
+The match is performed according to the rules described below
+(@pxref{Pattern Matching}).
+If @var{pattern} begins with @samp{/}, all matches of @var{pattern} are
+replaced with @var{string}.  Normally only the first match is replaced.
+If @var{pattern} begins with @samp{#}, it must match at the beginning
+of the expanded value of @var{parameter}.
+If @var{pattern} begins with @samp{%}, it must match at the end
+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 the @code{nocasematch} shell option   
+(see the description of @code{shopt} in @ref{The Shopt Builtin})
+is enabled, the match is performed without regard to the case   
+of alphabetic characters.
+If @var{parameter} is @samp{@@} or @samp{*},
+the substitution operation is applied to each positional
+parameter in turn, and the expansion is the resultant list.
+If @var{parameter}
+is an array variable subscripted with @samp{@@} or @samp{*},
+the substitution operation is applied to each member of the
+array in turn, and the expansion is the resultant list.
+
+@item $@{@var{parameter}^@var{pattern}@}
+@itemx $@{@var{parameter}^^@var{pattern}@}
+@itemx $@{@var{parameter},@var{pattern}@}
+@itemx $@{@var{parameter},,@var{pattern}@}
+This expansion modifies the case of alphabetic characters in @var{parameter}.
+The @var{pattern} is expanded to produce a pattern just as in
+filename expansion.
+Each character in the expanded value of @var{parameter} is tested against
+@var{pattern}, and, if it matches the pattern, its case is converted.
+The pattern should not attempt to match more than one character.
+The @samp{^} operator converts lowercase letters matching @var{pattern}
+to uppercase; the @samp{,} operator converts matching uppercase letters
+to lowercase.
+The @samp{^^} and @samp{,,} expansions convert each matched character in the
+expanded value; the @samp{^} and @samp{,} expansions match and convert only
+the first character in the expanded value.
+If @var{pattern} is omitted, it is treated like a @samp{?}, which matches
+every character.
+If @var{parameter} is @samp{@@} or @samp{*},
+the case modification operation is applied to each positional
+parameter in turn, and the expansion is the resultant list.
+If @var{parameter}
+is an array variable subscripted with @samp{@@} or @samp{*},
+the case modification operation is applied to each member of the
+array in turn, and the expansion is the resultant list.
+
+@item $@{@var{parameter}@@@var{operator}@}
+The expansion is either a transformation of the value of @var{parameter}
+or information about @var{parameter} itself, depending on the value of
+@var{operator}.  Each @var{operator} is a single letter:
+
+@table @code
+@item U
+The expansion is a string that is the value of @var{parameter} with lowercase
+alphabetic characters converted to uppercase.
+@item u
+The expansion is a string that is the value of @var{parameter} with the first
+character converted to uppercase, if it is alphabetic.
+@item L
+The expansion is a string that is the value of @var{parameter} with uppercase
+alphabetic characters converted to lowercase.
+@item Q
+The expansion is a string that is the value of @var{parameter} quoted in a
+format that can be reused as input.
+@item E
+The expansion is a string that is the value of @var{parameter} with backslash
+escape sequences expanded as with the @code{$'@dots{}'} quoting mechanism.
+@item P
+The expansion is a string that is the result of expanding the value of
+@var{parameter} as if it were a prompt string (@pxref{Controlling the Prompt}).
+@item A
+The expansion is a string in the form of
+an assignment statement or @code{declare} command that, if
+evaluated, will recreate @var{parameter} with its attributes and value.
+@item K
+Produces a possibly-quoted version of the value of @var{parameter},
+except that it prints the values of
+indexed and associative arrays as a sequence of quoted key-value pairs
+(@pxref{Arrays}).
+@item a
+The expansion is a string consisting of flag values representing
+@var{parameter}'s attributes.
+@end table
+
+If @var{parameter} is @samp{@@} or @samp{*},
+the operation is applied to each positional
+parameter in turn, and the expansion is the resultant list.
+If @var{parameter}
+is an array variable subscripted with @samp{@@} or @samp{*},
+the operation is applied to each member of the
+array in turn, and the expansion is the resultant list.
+
+The result of the expansion is subject to word splitting and filename
+expansion as described below.
+@end table
+
+@node Command Substitution
+@subsection Command Substitution
+@cindex command substitution
+
+Command substitution allows the output of a command to replace
+the command itself.
+Command substitution occurs when a command is enclosed as follows:
+@example
+$(@var{command})
+@end example
+@noindent
+or
+@example
+`@var{command}`
+@end example
+
+@noindent
+Bash performs the expansion by executing @var{command} in a subshell environment
+and replacing the command substitution with the standard output of the
+command, with any trailing newlines deleted.
+Embedded newlines are not deleted, but they may be removed during
+word splitting.
+The command substitution @code{$(cat @var{file})} 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{\}. 
+The first backquote not preceded by a backslash terminates the
+command substitution.
+When using the @code{$(@var{command})} form, all characters between
+the parentheses make up the command; none are treated specially.
+
+Command substitutions may be nested.  To nest when using the backquoted
+form, escape the inner backquotes with backslashes.
+
+If the substitution appears within double quotes, word splitting and
+filename expansion are not performed on the results.
+
+@node Arithmetic Expansion
+@subsection Arithmetic Expansion
+@cindex expansion, arithmetic
+@cindex arithmetic expansion
+
+Arithmetic expansion allows the evaluation of an arithmetic expression
+and the substitution of the result.  The format for arithmetic expansion is:
+
+@example
+$(( @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 and variable expansion,
+command substitution, and quote removal.
+The result is treated as the arithmetic expression to be evaluated.
+Arithmetic expansions may be nested. 
+
+The evaluation is performed according to the rules listed below
+(@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 allows a process's input or output to be
+referred to using a filename.
+It takes the form of 
+@example
+<(@var{list})
+@end example
+@noindent
+or
+@example
+>(@var{list})
+@end example
+@noindent
+The process @var{list} is run asynchronously, and its input or output 
+appears as a filename.
+This filename is
+passed as an argument to the current command as the result of the
+expansion.
+If the @code{>(@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.
+Process substitution is supported on systems that support named
+pipes (@sc{fifo}s) or the @file{/dev/fd} method of naming open files.
+
+When available, process substitution is performed simultaneously with
+parameter and variable expansion, command substitution, and arithmetic
+expansion.
+
+@node Word Splitting
+@subsection Word Splitting
+@cindex word splitting
+
+The shell scans the results of parameter expansion, command substitution,
+and arithmetic expansion that did not occur within double quotes for
+word splitting.
+
+The shell treats each character of @env{$IFS} as a delimiter, and splits
+the results of the other expansions into words using these characters
+as field terminators.
+If @env{IFS} is unset, or its value is exactly @code{<space><tab><newline>},
+the default, then sequences of
+@code{ <space>}, @code{<tab>}, and @code{<newline>}
+at the beginning and end of the results of the previous
+expansions are ignored, and any sequence of @env{IFS}
+characters not at the beginning or end serves to delimit words.
+If @env{IFS} has a value other than the default, then sequences of
+the whitespace characters @code{space}, @code{tab}, and @code{newline}
+are ignored at the beginning and end of the
+word, as long as the whitespace character is in the
+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 @env{IFS} is null, no word splitting occurs.
+
+Explicit null arguments (@code{""} or @code{''}) are retained
+and passed to commands as empty strings.
+Unquoted implicit null arguments, resulting from the expansion of
+parameters that have no values, are removed.
+If a parameter with no value is expanded within double quotes, a
+null argument results and is retained
+and passed to a command as an empty string.
+When a quoted null argument appears as part of a word whose expansion is
+non-null, the null argument is removed.
+That is, the word
+@code{-d''} becomes @code{-d} after word splitting and
+null argument removal.
+
+Note that if no expansion occurs, no splitting
+is performed.
+
+@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 @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, and is not quoted, then the word is
+regarded as a @var{pattern},
+and replaced with an alphabetically sorted list of
+filenames matching the pattern (@pxref{Pattern Matching}).
+If no matching filenames are found,
+and the shell option @code{nullglob} is disabled, the word is left
+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 expansion, 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 filenames @samp{.} and @samp{..} must always be matched explicitly,
+even if @code{dotglob} is set.
+In other cases, the @samp{.} character is not treated specially.
+
+When matching a filename, the slash character must always be
+matched explicitly by a slash in the pattern, but in other matching
+contexts it can be matched by a special pattern character as described
+below (@pxref{Pattern Matching}).
+
+See the description of @code{shopt} in @ref{The Shopt Builtin},
+for a description of the @code{nocaseglob}, @code{nullglob},
+@code{failglob}, and @code{dotglob} options.
+
+The @env{GLOBIGNORE}
+shell variable may be used to restrict the set of file names matching a
+pattern.  If @env{GLOBIGNORE}
+is set, each matching file name that also matches one of the patterns in
+@env{GLOBIGNORE} is removed from the list of matches.
+If the @code{nocaseglob} option is set, the matching against the patterns in
+@env{GLOBIGNORE} is performed without regard to case.
+The filenames
+@file{.} and @file{..}
+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 @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 string, including the null string.
+When the @code{globstar} shell option is enabled, and @samp{*} is used in
+a filename expansion context, two adjacent @samp{*}s used as a single
+pattern will match all files and zero or more directories and
+subdirectories.
+If followed by a @samp{/}, two adjacent @samp{*}s will match only
+directories and subdirectories.
+@item ?
+Matches any single character.
+@item [@dots{}]
+Matches any one of the enclosed characters.  A pair of characters
+separated by a hyphen denotes a @var{range expression};
+any character that falls 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 values of the
+@env{LC_COLLATE} and @env{LC_ALL} shell variables, 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}, or enable the
+@code{globasciiranges} shell option.
+
+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} 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
+
+Complicated extended pattern matching against long strings is slow,
+especially when the patterns contain alternations and the strings
+contain multiple matches.
+Using separate matches against shorter strings, or using arrays of
+strings instead of a single long string, may be faster.
+
+@node Quote Removal
+@subsection Quote Removal
+
+After the preceding expansions, all unquoted occurrences of the
+characters @samp{\}, @samp{'}, and @samp{"} that did not
+result from one of the above expansions are removed.
+
+@node Redirections
+@section Redirections
+@cindex redirection
+
+Before a command is executed, its input and output
+may be @var{redirected}
+using a special notation interpreted by the shell.
+Redirection allows commands' file handles to be
+duplicated, opened, closed,
+made to refer to different files,
+and can change the files the command reads from and writes to.
+Redirection may also be used to modify file handles in the
+current shell execution environment.  The following redirection
+operators may precede or appear anywhere within a
+simple command or may follow a command.
+Redirections are processed in the order they appear, from
+left to right.
+
+Each redirection that may be preceded by a file descriptor number
+may instead be preceded by a word of the form @{@var{varname}@}.
+In this case, for each redirection operator except
+>&- and <&-, the shell will allocate a file descriptor greater
+than 10 and assign it to @{@var{varname}@}.  If >&- or <&- is preceded
+by @{@var{varname}@}, the value of @var{varname} defines the file
+descriptor to close.
+If @{@var{varname}@} is supplied, the redirection persists beyond
+the scope of the command, allowing the shell programmer to manage
+the file descriptor's lifetime manually.
+
+In the following descriptions, if the file descriptor number is
+omitted, and the first character of the redirection operator is
+@samp{<}, the redirection refers to the standard input (file
+descriptor 0).  If the first character of the redirection operator
+is @samp{>}, the redirection refers to the standard output (file
+descriptor 1).
+
+The word following the redirection operator in the following
+descriptions, unless otherwise noted, is subjected to brace expansion,
+tilde expansion, parameter expansion, command substitution, arithmetic
+expansion, quote removal, filename expansion, and word splitting.
+If it expands to more than one word, Bash reports an error.
+
+Note that the order of redirections is significant.  For example,
+the command
+@example
+ls > @var{dirlist} 2>&1
+@end example
+@noindent
+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
+@noindent
+directs only the standard output to file @var{dirlist},
+because the standard error was made a copy of the 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.
+If the operating system on which Bash is running provides these
+special files, bash will use them; otherwise it will emulate them
+internally with the behavior described below.
+
+@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
+the corresponding TCP 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 
+the corresponding UDP 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}
+to be opened for reading on file descriptor @code{n},
+or the standard input (file descriptor 0) if @code{n}
+is not specified.
+
+The general format for redirecting input is:
+@example
+[@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 @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
+[@var{n}]>[|]@var{word}
+@end example
+
+If the redirection operator is @samp{>}, and the @code{noclobber}
+option to the @code{set} builtin has been enabled, the redirection
+will fail if the 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 @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
+[@var{n}]>>@var{word}
+@end example
+
+@subsection Redirecting Standard Output and Standard Error
+This construct allows both the
+standard output (file descriptor 1) and
+the standard error output (file descriptor 2)
+to be redirected to the file whose name is the
+expansion of @var{word}.
+
+There are two formats for redirecting standard output and
+standard error:
+@example
+&>@var{word}
+@end example
+@noindent
+and
+@example
+>&@var{word}
+@end example
+@noindent
+Of the two forms, the first is preferred.
+This is semantically equivalent to
+@example
+>@var{word} 2>&1
+@end example
+When using the second form, @var{word} may not expand to a number or
+@samp{-}.  If it does, other redirection operators apply
+(see Duplicating File Descriptors below) for compatibility reasons.
+
+@subsection Appending Standard Output and Standard Error
+This construct allows both the
+standard output (file descriptor 1) and
+the standard error output (file descriptor 2)
+to be appended to the file whose name is the
+expansion of @var{word}.
+
+The format for appending standard output and standard error is:
+@example
+&>>@var{word}
+@end example
+@noindent
+This is semantically equivalent to
+@example
+>>@var{word} 2>&1
+@end example
+(see Duplicating File Descriptors below).
+
+@subsection Here Documents
+This type of redirection instructs the shell to read input from the
+current source until a line containing only @var{word}
+(with no trailing blanks) is seen.  All of
+the lines read up to that point are then used as the standard
+input (or file descriptor @var{n} if @var{n} is specified) for a command.
+
+The format of here-documents is:
+@example
+[@var{n}]<<[@minus{}]@var{word}
+        @var{here-document}
+@var{delimiter}
+@end example
+
+No parameter and variable expansion, command substitution,
+arithmetic expansion, or filename expansion is performed on
+@var{word}.  If any part of @var{word} is quoted, the
+@var{delimiter} is the result of quote removal on @var{word},
+and the lines in the here-document are not expanded.
+If @var{word} is unquoted,
+all lines of the here-document are subjected to
+parameter expansion, command substitution, and arithmetic expansion,
+the character sequence @code{\newline} is ignored, and @samp{\}
+must be used to quote the characters
+@samp{\}, @samp{$}, and @samp{`}.
+
+If the redirection operator is @samp{<<-},
+then all leading tab characters are stripped from input lines and the
+line containing @var{delimiter}.
+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{n}]<<< @var{word}
+@end example
+
+The @var{word} undergoes
+tilde expansion, parameter and variable expansion,
+command substitution, arithmetic expansion, and quote removal.
+Filename expansion and word splitting are not performed.
+The result is supplied as a single string,
+with a newline appended,
+to the command on its
+standard input (or file descriptor @var{n} if @var{n} is specified).
+
+@subsection Duplicating File Descriptors
+The redirection operator
+@example
+[@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 @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
+[@var{n}]>&@var{word}
+@end example
+@noindent
+is used similarly to duplicate output file descriptors.  If
+@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.
+If @var{word}
+evaluates to @samp{-}, file descriptor @var{n} is closed.
+As a special case, if @var{n} is omitted, and @var{word} does not
+expand to one or more digits or @samp{-}, 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
+[@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
+@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 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, in
+the following order.
+
+@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
+actions are taken.
+
+@enumerate
+@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 in @ref{Shell Functions}.
+
+@item
+If the name does not match a function, the shell searches for
+it in the list of shell builtins.  If a match is found, that
+builtin is invoked.
+
+@item
+If the name is neither a shell function nor a builtin,
+and contains no slashes, Bash searches each element of
+@env{$PATH} for a directory containing an executable file
+by that name.  Bash uses a hash table to remember the full
+pathnames of executable files to avoid multiple @env{PATH} searches
+(see the description of @code{hash} in @ref{Bourne Shell Builtins}).
+A full search of the directories in @env{$PATH}
+is performed only if the command is not found in the hash table.
+If the search is unsuccessful, the shell searches for a defined shell
+function named @code{command_not_found_handle}.
+If that function exists, it is invoked in a separate execution environment
+with the original command and
+the original command's arguments as its arguments, and the function's
+exit status becomes the exit status of that subshell.
+If that function is not defined, the shell prints an error
+message and returns an exit status of 127.
+
+@item
+If the search is successful, or if the command name contains
+one or more slashes, the shell executes the named program in
+a separate execution environment.
+Argument 0 is set to the name given, and the remaining arguments
+to the command are set to the arguments supplied, if any.
+
+@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 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} (@pxref{The Shopt Builtin})
+
+@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.
+
+Subshells spawned to execute command substitutions inherit the value of
+the @option{-e} option from the parent shell.  When not in @sc{posix} mode,
+Bash clears the @option{-e} option in such subshells.
+
+If a command is followed by a @samp{&} and job control is not active, the
+default standard input for the command is the empty file @file{/dev/null}.
+Otherwise, the invoked command inherits the file descriptors of the calling
+shell as modified by redirections.
+
+@node Environment
+@subsection Environment
+@cindex environment
+
+When a program is invoked it is given an array of strings
+called the @var{environment}.
+This is a list of name-value pairs, of the form @code{name=value}.
+
+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.
+The @code{export} and @samp{declare -x}
+commands allow parameters and functions to be added to and
+deleted from the environment.  If the value of a parameter
+in the environment is modified, the new value becomes part
+of the environment, replacing the old.  The environment
+inherited by any executed command consists of the shell's
+initial environment, whose values may be modified in the shell,
+less any pairs removed by the @code{unset} 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
+parameter assignments, as described in @ref{Shell Parameters}.
+These assignment statements affect only the environment seen
+by that command.
+
+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.
+
+When Bash invokes an external command, the variable @samp{$_}
+is set to the full pathname of the command and passed to that
+command in its environment.
+
+@node Exit Status
+@subsection Exit Status
+@cindex exit status
+
+The exit status of an executed command is the value returned by the
+@var{waitpid} system call or equivalent function.  Exit statuses    
+fall between 0 and 255, though, as explained below, the shell may
+use values above 125 specially.  Exit statuses from shell builtins and
+compound commands are also limited to this range.  Under certain
+circumstances, the shell will use special values to indicate specific
+failure modes.
+
+For the shell's purposes, a command which exits with a
+zero exit status has succeeded.
+A non-zero exit status indicates failure.
+This seemingly counter-intuitive scheme is used so there
+is one well-defined way to indicate success and a variety of
+ways to indicate various failure modes.
+When a command terminates on a fatal signal whose number is @var{N},
+Bash uses the value 128+@var{N} as the exit status.
+
+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,
+generally invalid options or missing arguments.
+
+@node Signals
+@subsection Signals
+@cindex signal handling
+
+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).
+When Bash receives a @code{SIGINT}, it breaks out of any executing loops.
+In all cases, Bash ignores @code{SIGQUIT}.
+If job control is in effect (@pxref{Job Control}), Bash
+ignores @code{SIGTTIN}, @code{SIGTTOU}, and @code{SIGTSTP}.
+
+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, 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{The Shopt Builtin}), 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
+@cindex shell script
+
+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 @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.  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.
+If no additional arguments are supplied, the positional parameters
+are unset.
+
+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 @env{$PATH} for a command, it spawns a subshell to
+execute it.  In other words, executing
+@example
+filename @var{arguments}
+@end example
+@noindent
+is equivalent to executing
+@example
+bash filename @var{arguments}
+@end example
+
+@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, 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 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 and, depending on the operating system, one
+or more optional arguments for that interpreter.
+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 one or more optional arguments following the interpreter
+name on the first line of the script file, followed by the name of
+the script file, followed by the rest of the arguments supplied to the
+script.
+The details of how the interpreter line is split into an interpreter name
+and a set of arguments vary across systems.
+Bash will perform this action on operating systems that do not handle it
+themselves.
+Note that some older versions of Unix limit the interpreter
+name and a single argument to a maximum of 32 characters, so it's not
+portable to assume that using more than one argument will work.
+
+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. It's a common idiom to use @code{env} to find
+@code{bash} even if it's been installed in another directory:
+@code{#!/usr/bin/env bash} will find the first occurrence of @code{bash}
+in @env{$PATH}.
+
+@node Shell Builtin Commands
+@chapter Shell Builtin Commands
+
+@menu
+* Bourne Shell Builtins::	Builtin commands inherited from the Bourne
+				Shell.
+* Bash Builtins::		Table of builtins specific to Bash.
+* Modifying Shell Behavior::	Builtins to modify shell attributes and
+				optional behavior.
+* Special Builtins::		Builtin commands classified specially by
+				POSIX.
+@end menu
+
+Builtin commands are contained within the shell itself.
+When the name of a builtin command is used as the first word of
+a simple command (@pxref{Simple Commands}), the shell executes
+the command directly, without invoking another program.
+Builtin commands are necessary to implement functionality impossible
+or inconvenient to obtain with separate utilities.
+
+This section briefly describes the builtins which Bash inherits from
+the Bourne Shell, as well as the builtin commands which are unique
+to or have been extended in Bash.
+
+Several builtin commands are described in other chapters: builtin
+commands which provide the Bash interface to the job control
+facilities (@pxref{Job Control Builtins}), the directory stack
+(@pxref{Directory Stack Builtins}), the command history
+(@pxref{Bash History Builtins}), and the programmable completion
+facilities (@pxref{Programmable Completion Builtins}).
+
+Many of the builtins have been extended by @sc{posix} or Bash.
+
+Unless otherwise noted, each builtin command documented as accepting
+options preceded by @samp{-} accepts @samp{--}
+to signify the end of the options.
+The @code{:}, @code{true}, @code{false}, and @code{test}/@code{[}
+builtins do not accept options and do not treat @samp{--} specially.
+The @code{exit}, @code{logout}, @code{return},
+@code{break}, @code{continue}, @code{let},
+and @code{shift} builtins accept and process arguments beginning
+with @samp{-} without requiring @samp{--}.
+Other builtins that accept arguments but are not specified as accepting
+options interpret arguments beginning with @samp{-} as invalid options and
+require @samp{--} to prevent this interpretation.
+
+@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} standard.
+
+@table @code
+@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 .    @r{(a period)}
+@btindex .
+@example
+. @var{filename} [@var{arguments}]
+@end example
+
+Read and execute commands from the @var{filename} argument in the
+current shell context.  If @var{filename} does not contain a slash,
+the @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.
+If the @option{-T} option is enabled, @code{source} inherits any trap on
+@code{DEBUG}; if it is not, any @code{DEBUG} trap string is saved and
+restored around the call to @code{source}, and @code{source} unsets the
+@code{DEBUG} trap while it executes.
+If @option{-T} is not set, and the sourced file changes
+the @code{DEBUG} trap, the new value is retained when @code{source} completes.
+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
+@example
+break [@var{n}]
+@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 [-L|[-P [-e]] [-@@] [@var{directory}]
+@end example
+
+Change the current working directory to @var{directory}.
+If @var{directory} is not supplied, the value of the @env{HOME}
+shell variable is used.
+Any additional arguments following @var{directory} are ignored.
+If the shell variable
+@env{CDPATH} exists, it is used as a search path:
+each directory name in @env{CDPATH} is searched for
+@var{directory}, with alternative directory names in @env{CDPATH}
+separated by a colon (@samp{:}).
+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 resolved while @code{cd} is traversing @var{directory} and before
+processing an instance of @samp{..} in @var{directory}.
+
+By default, or when the @option{-L} option is supplied, symbolic links
+in @var{directory} are resolved after @code{cd} processes an instance
+of @samp{..} in @var{directory}.
+
+If @samp{..} appears in @var{directory}, it is processed by removing the
+immediately preceding pathname component, back to a slash or the beginning
+of @var{directory}.
+
+If the @option{-e} option is supplied with @option{-P}
+and the current working directory cannot be successfully determined
+after a successful directory change, @code{cd} will return an unsuccessful
+status.
+
+On systems that support it, the @option{-@@} option presents the extended
+attributes associated with a file as a directory.              
+
+If @var{directory} is @samp{-}, it is converted to @env{$OLDPWD}
+before the directory change is attempted.
+
+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
+@example
+continue [@var{n}]
+@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.
+@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, 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}]]
+@end example
+
+If @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 argument passed to @var{command}.
+This is what the @code{login} program does.
+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 @var{command}
+cannot be executed for some reason, a non-interactive shell exits,
+unless the @code{execfail} shell option
+is enabled.  In that case, it returns failure.
+An interactive shell returns failure if the file cannot be executed.
+A subshell exits unconditionally if @code{exec} fails.
+If no @var{command} is specified, redirections may be used to affect
+the current shell environment.  If there are no redirection errors, the
+return status is zero; otherwise the return status is non-zero.
+
+@item exit
+@btindex exit
+@example
+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
+@example
+export [-fn] [-p] [@var{name}[=@var{value}]]
+@end example
+
+Mark each @var{name} to be passed to child processes
+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 names of all exported variables 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
+@example
+getopts @var{optstring} @var{name} [@var{arg} @dots{}]
+@end example
+
+@code{getopts} is used by shell scripts to parse positional parameters.
+@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 whitespace.
+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 @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 @var{name} is set to @samp{?}.
+
+@code{getopts}
+normally parses the positional parameters, but if more arguments are
+supplied as @var{arg} values, @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 invalid options or missing option arguments are
+encountered.
+If the variable @env{OPTERR}
+is set to 0, no error messages will be displayed, even if the first
+character of @code{optstring} is not a colon.
+
+If an invalid option is seen,
+@code{getopts} places @samp{?} into @var{name} and, if not silent,
+prints an error message and unsets @env{OPTARG}.
+If @code{getopts} is silent, the option character found is placed in
+@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 @env{OPTARG} is set to the option character found.
+
+@item hash
+@btindex hash
+@example
+hash [-r] [-p @var{filename}] [-dt] [@var{name}]
+@end example
+
+Each time @code{hash} is invoked, it remembers the full pathnames of the
+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}.
+Any previously-remembered pathname is discarded.
+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 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 [-aAf] [-p] [@var{name}[=@var{value}]] @dots{}
+@end example
+
+Mark each @var{name} as readonly.
+The values of these names may not be changed by subsequent assignment.
+If the @option{-f} option is supplied, each @var{name} refers to a shell
+function.
+The @option{-a} option means each @var{name} refers to an indexed
+array variable; the @option{-A} option means each @var{name} refers
+to an associative array variable.
+If both options are supplied, @option{-A} takes precedence.
+If no @var{name} arguments are given, or if the @option{-p}
+option is supplied, a list of all readonly names is printed.
+The other options may be used to restrict the output to a subset of
+the set of readonly names.
+The @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 stop executing and return the value @var{n}
+to its caller.
+If @var{n} is not supplied, the return value is the exit status of the
+last command executed in the function.
+If @code{return} is executed by a trap handler, the last command used to
+determine the status is the last command executed before the trap handler.
+If @code{return} is executed during a @code{DEBUG} trap, the last command
+used to determine the status is the last command executed by the trap
+handler before @code{return} was invoked.
+@code{return} may also be used to terminate execution of a script
+being executed with the @code{.} (@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.
+If @var{n} is supplied, the return value is its least significant
+8 bits.
+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 supplied a non-numeric
+argument or 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 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}.
+Parameters represented by the numbers @code{$#} down to @code{$#}-@var{n}+1
+are unset.
+@var{n} must be a non-negative number less than or equal to @code{$#}.
+If @var{n} is zero or greater than @code{$#}, the positional parameters
+are not changed.
+If @var{n} is not supplied, it is assumed to be 1.
+The return status is zero unless @var{n} is greater than @code{$#} or
+less than zero, non-zero otherwise.
+
+@item test
+@itemx [
+@btindex test
+@btindex [
+@example
+test @var{expr}
+@end example
+
+Evaluate a conditional expression @var{expr} and return a status of 0
+(true) or 1 (false).
+Each operator and operand must be a separate argument.
+Expressions are composed of the primaries described below in
+@ref{Bash Conditional Expressions}.
+@code{test} does not accept any options, nor does it accept and ignore
+an argument of @option{--} as signifying the end of options.
+
+When the @code{[} form is used, the last argument to the command must
+be a @code{]}.
+
+Expressions may be combined using the following operators, listed in
+decreasing order of precedence.
+The evaluation depends on the number of arguments; see below.
+Operator precedence is used when there are five or more arguments.
+
+@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
+The following conditions are applied in the order listed.
+
+@enumerate
+@item
+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.
+The @samp{-a} and @samp{-o} operators are considered binary operators
+when there are three arguments.
+@item
+If the first argument is @samp{!}, the value is the negation of
+the two-argument test using the second and third arguments.
+@item
+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.
+@item
+Otherwise, the expression is false.
+@end enumerate
+
+@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
+
+When used with @code{test} or @samp{[}, the @samp{<} and @samp{>}
+operators sort lexicographically using ASCII ordering.
+
+@item times
+@btindex times
+@example
+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
+@example
+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 (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 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
+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{extdebug} option to the
+@code{shopt} builtin (@pxref{The Shopt Builtin}) for details of its
+effect on the @code{DEBUG} trap.
+If a @var{sigspec} is @code{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.
+
+If a @var{sigspec} is @code{ERR}, the command @var{arg} 
+is executed whenever
+a pipeline (which may consist of a single simple
+command), a list, or a compound command returns a
+non-zero exit status,
+subject to the following conditions.
+The @code{ERR} 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 following the @code{if} or @code{elif} reserved words,
+part of a command executed in a @code{&&} or @code{||} list
+except the command following the final @code{&&} or @code{||},
+any command in a pipeline but the last,
+or if the command's return
+status is being inverted using @code{!}.
+These are the same conditions obeyed by the @code{errexit} (@option{-e})
+option.
+
+Signals ignored upon entry to the shell cannot be trapped or reset.
+Trapped signals that are not being ignored are reset to their original
+values in a subshell or subshell environment when one is created.
+
+The return status is zero unless a @var{sigspec} does not specify a
+valid signal.
+
+@item umask
+@btindex umask
+@example
+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 @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
+@example
+unset [-fnv] [@var{name}]
+@end example
+
+Remove each variable or function @var{name}.
+If the @option{-v} option is given, each
+@var{name} refers to a shell variable and that variable is removed.
+If the @option{-f} option is given, the @var{name}s refer to shell
+functions, and the function definition is removed.
+If the @option{-n} option is supplied, and @var{name} is a variable with
+the @var{nameref} attribute, @var{name} will be unset rather than the
+variable it references.
+@option{-n} has no effect if the @option{-f} option is supplied.
+If no options are supplied, each @var{name} refers to a variable; if
+there is no variable by that name, a function with that name, if any, is
+unset.
+Readonly variables and functions may not be unset.
+Some shell variables lose their special behavior if they are unset; such
+behavior is noted in the description of the individual variables.
+The return status is zero unless a @var{name} is readonly.
+@end table
+
+@node Bash Builtins
+@section Bash Builtin Commands
+
+This section describes builtin commands which are unique to
+or have been extended in Bash.
+Some of these commands are specified in the @sc{posix} standard.
+
+@table @code
+
+@item alias
+@btindex alias
+@example
+alias [-p] [@var{name}[=@var{value}] @dots{}]
+@end example
+
+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 bind
+@btindex bind
+@example
+bind [-m @var{keymap}] [-lpsvPSVX]
+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 [-m @var{keymap}] @var{keyseq:readline-command}
+@end example
+
+Display current Readline (@pxref{Command Line Editing})
+key and function bindings,
+bind a key sequence to a Readline function or macro,
+or set a Readline variable.
+Each non-option argument is a command as it would appear in a
+Readline initialization file (@pxref{Readline Init File}),
+but each binding or command must be passed as a separate argument;  e.g.,
+@samp{"\C-x\C-r":re-read-init-file}.
+
+Options, if supplied, have the following meanings:
+
+@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{vi-move} is also a
+synonym); @code{emacs} is equivalent to @code{emacs-standard}.
+
+@item -l
+List the names of all Readline functions.
+
+@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 -P
+List current Readline function names and bindings.
+
+@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.
+
+@item -V
+List current Readline variable names and values.
+
+@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.
+
+@item -S
+Display Readline key sequences bound to macros and the strings they output.
+
+@item -f @var{filename}
+Read key bindings from @var{filename}.
+
+@item -q @var{function}
+Query about which keys invoke the named @var{function}.
+
+@item -u @var{function}
+Unbind all keys bound to the named @var{function}.
+
+@item -r @var{keyseq}
+Remove any current binding for @var{keyseq}.
+
+@item -x @var{keyseq:shell-command}
+Cause @var{shell-command} to be executed whenever @var{keyseq} is
+entered.
+When @var{shell-command} is executed, the shell sets the
+@code{READLINE_LINE} variable to the contents of the Readline line
+buffer and the @code{READLINE_POINT} and @code{READLINE_MARK} variables
+to the current location of the insertion point and the saved insertion
+point (the @var{mark}), respectively.
+If the executed command changes the value of any of @code{READLINE_LINE},
+@code{READLINE_POINT}, or @code{READLINE_MARK}, those new values will be
+reflected in the editing state.
+
+@item -X
+List all key sequences bound to shell commands and the associated commands
+in a format that can be reused as input.
+@end table
+
+@noindent
+The return status is zero unless an invalid option is supplied or an
+error occurs.
+
+@item builtin
+@btindex builtin
+@example
+builtin [@var{shell-builtin} [@var{args}]]
+@end example
+
+Run a shell builtin, passing it @var{args}, and return its exit status.
+This is useful when defining a shell function with the same
+name as a shell builtin, retaining the functionality of the builtin within
+the function.
+The return status is non-zero if @var{shell-builtin} is not a shell
+builtin command.
+
+@item 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).
+
+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.
+
+The return value is 0 unless the shell is not executing a subroutine
+call or @var{expr} does not correspond to a valid position in the
+call stack.
+
+@item 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.
+
+If either the @option{-V} or @option{-v} option is supplied, a
+description of @var{command} is printed.  The @option{-v} option
+causes a single word indicating the command or file name used to
+invoke @var{command} to be displayed; the @option{-V} option produces
+a more verbose description.  In this case, the return status is
+zero if @var{command} is found, and non-zero if not.
+
+@item declare
+@btindex declare
+@example
+declare [-aAfFgiIlnrtux] [-p] [@var{name}[=@var{value}] @dots{}]
+@end example
+
+Declare variables and give them attributes.  If no @var{name}s
+are given, then display the values of variables instead. 
+
+The @option{-p} option will display the attributes and values of each
+@var{name}.
+When @option{-p} is used with @var{name} arguments, additional options,
+other than @option{-f} and @option{-F}, are ignored.
+
+When @option{-p} is supplied without @var{name} arguments, @code{declare}
+will display the attributes and values of all variables having the
+attributes specified by the additional options.
+If no other options are supplied with @option{-p}, @code{declare} will
+display the attributes and values of all shell variables.  The @option{-f}
+option will restrict the display to shell functions.
+
+The @option{-F} option inhibits the display of function definitions;
+only the function name and attributes are printed.
+If the @code{extdebug} shell option is enabled using @code{shopt}
+(@pxref{The Shopt Builtin}), the source file name and line number where
+each @var{name} is defined are displayed as well.
+@option{-F} implies @option{-f}.
+
+The @option{-g} option forces variables to be created or modified at
+the global scope, even when @code{declare} is executed in a shell function.
+It is ignored in all other cases.
+
+The @option{-I} option causes local variables to inherit the attributes
+(except the @var{nameref} attribute)
+and value of any existing variable with the same
+@var{name} at a surrounding scope.
+If there is no existing variable, the local variable is initially unset.
+
+The following options can be used to restrict output to variables with
+the specified attributes or to give variables attributes:
+
+@table @code
+@item -a
+Each @var{name} is an indexed array variable (@pxref{Arrays}).
+
+@item -A
+Each @var{name} is an associative array variable (@pxref{Arrays}).
+
+@item -f
+Use function names only.
+
+@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 -l
+When the variable is assigned a value, all upper-case characters are
+converted to lower-case.
+The upper-case attribute is disabled.
+
+@item -n
+Give each @var{name} the @var{nameref} attribute, making
+it a name reference to another variable.
+That other variable is defined by the value of @var{name}.
+All references, assignments, and attribute modifications
+to @var{name}, except for those using or changing the
+@option{-n} attribute itself, are performed on the variable referenced by
+@var{name}'s value.
+The nameref attribute cannot be applied to array variables.
+
+@item -r
+Make @var{name}s readonly.  These names cannot then be assigned values
+by subsequent assignment statements or unset.
+
+@item -t
+Give each @var{name} the @code{trace} attribute.
+Traced functions inherit the @code{DEBUG} and @code{RETURN} traps from
+the calling shell.
+The trace attribute has no special meaning for variables.
+
+@item -u
+When the variable is assigned a value, all lower-case characters are
+converted to upper-case.
+The lower-case attribute is disabled.
+
+@item -x
+Mark each @var{name} for export to subsequent commands via
+the environment.
+@end table
+
+Using @samp{+} instead of @samp{-} turns off the attribute instead,
+with the exceptions that @samp{+a} and @samp{+A}
+may not be used to destroy array variables and @samp{+r} will not
+remove the readonly attribute.
+When used in a function, @code{declare} makes each @var{name} local,
+as with the @code{local} command, unless the @option{-g} option is used.
+If a variable name is followed by =@var{value}, the value of the variable
+is set to @var{value}.
+
+When using @option{-a} or @option{-A} and the compound assignment syntax to 
+create array variables, additional attributes do not take effect until
+subsequent assignments.
+
+The return status is zero unless an invalid option is encountered,
+an attempt is made to define a function using @samp{-f foo=bar},
+an attempt is made to assign a value to a readonly variable,
+an attempt is made to assign a value to an array variable without
+using the compound assignment syntax (@pxref{Arrays}),
+one of the @var{names} is not a valid shell variable name,
+an attempt is made to turn off readonly status for a readonly variable,
+an attempt is made to turn off array status for an array variable,
+or an attempt is made to display a non-existent function with @option{-f}.
+
+@item 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 0 unless a write error occurs.
+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.
+
+@code{echo} interprets the following escape sequences:
+@table @code
+@item \a
+alert (bell)
+@item \b
+backspace
+@item \c
+suppress further output
+@item \e
+@itemx \E
+escape
+@item \f
+form feed
+@item \n
+new line
+@item \r
+carriage return
+@item \t 
+horizontal tab
+@item \v
+vertical tab
+@item \\
+backslash
+@item \0@var{nnn}
+the eight-bit character whose value is the octal value @var{nnn}
+(zero to three octal digits)
+@item \x@var{HH}
+the eight-bit character whose value is the hexadecimal value @var{HH}
+(one or two hex digits)
+@item \u@var{HHHH}
+the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value
+@var{HHHH} (one to four hex digits)
+@item \U@var{HHHHHHHH}
+the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value
+@var{HHHHHHHH} (one to eight hex digits)
+@end table
+
+@item enable
+@btindex enable
+@example
+enable [-a] [-dnps] [-f @var{filename}] [@var{name} @dots{}]
+@end example
+
+Enable and disable builtin shell commands.
+Disabling a builtin allows a disk command which has the same name
+as a shell builtin to be executed without specifying a full pathname,
+even though the shell normally searches for builtins before disk commands.
+If @option{-n} is used, the @var{name}s become disabled.  Otherwise
+@var{name}s are enabled.  For example, to use the @code{test} binary
+found via @env{$PATH} instead of the shell builtin version, type
+@samp{enable -n test}.
+
+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. 
+
+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}.
+
+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}).
+
+The return status is zero unless a @var{name} is not a shell builtin
+or there is an error loading a new builtin from a shared object.
+
+@item help
+@btindex help
+@example
+help [-dms] [@var{pattern}]
+@end example
+
+Display helpful information about builtin commands.
+If @var{pattern} is specified, @code{help} gives detailed help
+on all commands matching @var{pattern}, otherwise a list of
+the builtins is printed.
+
+Options, if supplied, have the following meanings:
+
+@table @code
+@item -d
+Display a short description of each @var{pattern}
+@item -m
+Display the description of each @var{pattern} in a manpage-like format
+@item -s
+Display only a short usage synopsis for each @var{pattern}
+@end table
+
+The return status is zero unless no command matches @var{pattern}.
+
+@item let
+@btindex let
+@example
+let @var{expression} [@var{expression} @dots{}]
+@end example
+
+The @code{let} builtin allows arithmetic to be performed on shell
+variables.  Each @var{expression} is evaluated according to the
+rules given below in @ref{Shell Arithmetic}.  If the
+last @var{expression} evaluates to 0, @code{let} returns 1;
+otherwise 0 is returned.
+
+@item local
+@btindex local
+@example
+local [@var{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.
+If @var{name} is @samp{-}, the set of shell options is made local to the
+function in which @code{local} is invoked: shell options changed using
+the @code{set} builtin inside the function are restored to their original
+values when the function returns.
+The restore is effected as if a series of @code{set} commands were executed
+to restore the values that were in place before the function.
+The return status is zero unless @code{local} is used outside
+a function, an invalid @var{name} is supplied, or @var{name} is a
+readonly variable.
+
+@item 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 mapfile
+@btindex mapfile
+@example
+mapfile [-d @var{delim}] [-n @var{count}] [-O @var{origin}] [-s @var{count}]
+    [-t] [-u @var{fd}] [-C @var{callback}] [-c @var{quantum}] [@var{array}]
+@end example
+
+Read lines from the standard input into the indexed array variable @var{array},
+or from file descriptor @var{fd}
+if the @option{-u} option is supplied.
+The variable @code{MAPFILE} is the default @var{array}.
+Options, if supplied, have the following meanings:
+
+@table @code
+
+@item -d
+The first character of @var{delim} is used to terminate each input line,
+rather than newline.
+If @var{delim} is the empty string, @code{mapfile} will terminate a line
+when it reads a NUL character.
+@item -n
+Copy at most @var{count} lines.  If @var{count} is 0, all lines are copied.
+@item -O
+Begin assigning to @var{array} at index @var{origin}.
+The default index is 0.
+@item -s
+Discard the first @var{count} lines read.
+@item -t
+Remove a trailing @var{delim} (default newline) from each line read.
+@item -u
+Read lines from file descriptor @var{fd} instead of the standard input.
+@item -C
+Evaluate @var{callback} each time @var{quantum} lines are read.
+The @option{-c} option specifies @var{quantum}.
+@item -c
+Specify the number of lines read between each call to @var{callback}.
+@end table
+
+If @option{-C} is specified without @option{-c},
+the default quantum is 5000.
+When @var{callback}  is evaluated, it is supplied the index of the next
+array element to be assigned and the line to be assigned to that element
+as additional arguments.
+@var{callback} is evaluated after the line is read but before the
+array element is assigned.
+
+If not supplied with an explicit origin, @code{mapfile} will clear @var{array}
+before assigning to it.
+
+@code{mapfile} returns successfully unless an invalid option or option
+argument is supplied, @var{array} is invalid or unassignable, or @var{array}
+is not an indexed array.
+
+@item printf
+@btindex printf
+@example
+printf [-v @var{var}] @var{format} [@var{arguments}]
+@end example
+
+Write the formatted @var{arguments} to the standard output under the
+control of the @var{format}.
+The @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 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, @code{printf}
+interprets the following extensions:
+
+@table @code
+@item %b
+Causes @code{printf} to expand backslash escape sequences in the
+corresponding @var{argument} in the same way as @code{echo -e}
+(@pxref{Bash Builtins}).
+@item %q
+Causes @code{printf} to output the
+corresponding @var{argument} in a format that can be reused as shell input.
+@item %(@var{datefmt})T
+Causes @code{printf} to output the date-time string resulting from using
+@var{datefmt} as a format string for @code{strftime}(3).
+The corresponding @var{argument} is an integer representing the number of
+seconds since the epoch.
+Two special argument values may be used: -1 represents the current
+time, and -2 represents the time the shell was invoked.
+If no argument is specified, conversion behaves as if -1 had been given.
+This is an exception to the usual @code{printf} behavior.
+@end table
+
+@noindent
+The %b, %q, and %T directives all use the field width and precision
+arguments from the format specification and write that many bytes from    
+(or use that wide a field for) the expanded argument, which usually
+contains more characters than the original.
+
+Arguments to non-string format specifiers are treated as C language constants,
+except that a leading plus or minus sign is allowed, and if the leading
+character is a single or double quote, the value is the ASCII value of
+the following character.
+
+The @var{format} is reused as necessary to consume all of the @var{arguments}.
+If the @var{format} requires more @var{arguments} than are supplied, the
+extra format specifications behave as if a zero value or null string, as
+appropriate, had been supplied.  The return value is zero on success,
+non-zero on failure.
+
+@item read
+@btindex read
+@example
+read [-ers] [-a @var{aname}] [-d @var{delim}] [-i @var{text}] [-n @var{nchars}]
+    [-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,
+split into words as described above in @ref{Word Splitting},
+and the first word
+is assigned to the first @var{name}, the second word to the second @var{name},
+and so on.
+If there are more words than names,
+the remaining words and their intervening delimiters are 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 using the same rules the shell
+uses for expansion (described above in @ref{Word Splitting}).
+The backslash character @samp{\} may be used to remove any special
+meaning for the next character read and for line continuation.
+
+Options, if supplied, have the following meanings:
+
+@table @code
+@item -a @var{aname}
+The words are assigned to sequential indices of the array variable
+@var{aname}, starting at 0.
+All elements are removed from @var{aname} before the assignment.
+Other @var{name} arguments are ignored.
+
+@item -d @var{delim}
+The first character of @var{delim} is used to terminate the input line,
+rather than newline.
+If @var{delim} is the empty string, @code{read} will terminate a line
+when it reads a NUL character.
+
+@item -e
+Readline (@pxref{Command Line Editing}) is used to obtain the line.
+Readline uses the current (or default, if line editing was not previously
+active) editing settings, but uses Readline's default filename completion.
+
+@item -i @var{text}
+If Readline is being used to read the line, @var{text} is placed into
+the editing buffer before editing begins.
+
+@item -n @var{nchars}
+@code{read} returns after reading @var{nchars} characters rather than
+waiting for a complete line of input, but honors a delimiter if fewer
+than @var{nchars} characters are read before the delimiter.
+
+@item -N @var{nchars}
+@code{read} returns after reading exactly @var{nchars} characters rather
+than waiting for a complete line of input, unless EOF is encountered or
+@code{read} times out.
+Delimiter characters encountered in the input are
+not treated specially and do not cause @code{read} to return until
+@var{nchars} characters are read.
+The result is not split on the characters in @code{IFS}; the intent is
+that the variable is assigned exactly the characters read
+(with the exception of backslash; see the @option{-r} option below).
+
+@item -p @var{prompt}
+Display @var{prompt}, without a trailing newline, before attempting
+to read any input.
+The prompt is displayed only if input is coming from a terminal.
+
+@item -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 then be used as a line
+continuation.
+
+@item -s
+Silent mode.  If input is coming from a terminal, characters are
+not echoed.
+
+@item -t @var{timeout}
+Cause @code{read} to time out and return failure if a complete line of
+input (or a specified number of characters)
+is not read within @var{timeout} seconds.
+@var{timeout}  may be a decimal number with a fractional portion following
+the decimal point.
+This option is only effective if @code{read} is reading input from a
+terminal, pipe, or other special file; it has no effect when reading
+from regular files.
+If @code{read} times out, @code{read} saves any partial input read into
+the specified variable @var{name}.
+If @var{timeout} is 0, @code{read} returns immediately, without trying to
+read any data.  The exit status is 0 if input is available on
+the specified file descriptor, non-zero otherwise.
+The exit status is greater than 128 if the timeout is exceeded.
+
+@item -u @var{fd}
+Read input from file descriptor @var{fd}.
+@end table
+
+If no @var{name}s are supplied, the line read,
+without the ending delimiter but otherwise unmodified,
+is assigned to the
+variable @env{REPLY}.
+The exit status is zero, unless end-of-file is encountered, @code{read}
+times out (in which case the status is greater than 128),
+a variable assignment error (such as assigning to a readonly variable) occurs,
+or an invalid file descriptor is supplied as the argument to @option{-u}.
+
+@item readarray
+@btindex readarray
+@example
+readarray [-d @var{delim}] [-n @var{count}] [-O @var{origin}] [-s @var{count}]
+    [-t] [-u @var{fd}] [-C @var{callback}] [-c @var{quantum}] [@var{array}]
+@end example
+
+Read lines from the standard input into the indexed array variable @var{array},
+or from file descriptor @var{fd}
+if the @option{-u} option is supplied.
+
+A synonym for @code{mapfile}.
+
+@item source
+@btindex source
+@example
+source @var{filename}
+@end example
+
+A synonym for @code{.} (@pxref{Bourne Shell Builtins}).
+
+@item type
+@btindex type
+@example
+type [-afptP] [@var{name} @dots{}]
+@end example
+
+For each @var{name}, indicate how it would be interpreted if used as a
+command name.
+
+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,
+which is 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 all of the @var{names} are found, non-zero
+if any are not found.
+
+@item typeset
+@btindex typeset
+@example
+typeset [-afFgrxilnrtux] [-p] [@var{name}[=@var{value}] @dots{}]
+@end example
+
+The @code{typeset} command is supplied for compatibility with the Korn
+shell.
+It is a synonym for the @code{declare} builtin command.
+
+@item ulimit
+@btindex ulimit
+@example
+ulimit [-HS] -a
+ulimit [-HS] [-bcdefiklmnpqrstuvxPRT] [@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; no limits are set.
+
+@item -b
+The maximum socket buffer size.
+
+@item -c
+The maximum size of core files created.
+
+@item -d
+The maximum size of a process's data segment.
+
+@item -e
+The maximum scheduling priority ("nice").
+
+@item -f
+The maximum size of files written by the shell and its children.
+
+@item -i
+The maximum number of pending signals.
+
+@item -k
+The maximum number of kqueues that may be allocated.
+
+@item -l
+The maximum size that may be locked into memory.
+
+@item -m
+The maximum resident set size (many systems do not honor this limit).
+
+@item -n
+The maximum number of open file descriptors (most systems do not
+allow this value to be set).
+
+@item -p
+The pipe buffer size.
+
+@item -q
+The maximum number of bytes in @sc{posix} message queues.
+
+@item -r
+The maximum real-time scheduling priority.
+
+@item -s
+The maximum stack size.
+
+@item -t
+The maximum amount of cpu time in seconds.
+
+@item -u
+The maximum number of processes available to a single user.
+
+@item -v
+The maximum amount of virtual memory available to the shell, and, on
+some systems, to its children.
+
+@item -x
+The maximum number of file locks.
+
+@item -P
+The maximum number of pseudoterminals.
+
+@item -R
+The maximum time a real-time process can run before blocking, in microseconds.
+
+@item -T
+The maximum number of threads.
+@end table
+
+If @var{limit} is given, and the @option{-a} option is not used,
+@var{limit} is the new value of the specified resource.
+The special @var{limit} values @code{hard}, @code{soft}, and
+@code{unlimited} stand for the current hard limit, the current soft limit,
+and no limit, respectively.
+A hard limit cannot be increased by a non-root user once it is set;
+a soft limit may be increased up to the value of the hard limit.
+Otherwise, the current value of the soft limit for the specified resource
+is printed, unless the @option{-H} option is supplied.
+When more than one
+resource is specified, the limit name and unit, if appropriate,
+are printed before the value.
+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{-R}, which is in microseconds;
+@option{-p}, which is in units of 512-byte blocks;
+@option{-P},
+@option{-T},
+@option{-b},
+@option{-k},
+@option{-n} and @option{-u}, which are unscaled values;
+and, when in @sc{posix} Mode (@pxref{Bash POSIX Mode}),
+@option{-c} and @option{-f}, which are in 512-byte increments.
+
+The return status is zero unless an invalid option or argument is supplied,
+or an error occurs while setting a new limit.
+
+@item unalias
+@btindex unalias
+@example
+unalias [-a] [@var{name} @dots{} ]
+@end example
+
+Remove each @var{name} from the list of aliases.  If @option{-a} is
+supplied, all aliases are removed.
+Aliases are described in @ref{Aliases}.
+@end table
+
+@node Modifying Shell Behavior
+@section Modifying Shell Behavior
+ 
+@menu
+* The Set Builtin::		Change the values of shell attributes and
+				positional parameters.
+* The Shopt Builtin::		Modify shell optional behavior.
+@end menu
+
+@node The Set Builtin
+@subsection The Set Builtin
+
+This builtin is so complicated that it deserves its own section.  @code{set}
+allows you to change the values of shell options and set the positional
+parameters, or to display the names and values of shell variables.
+
+@table @code
+@item set
+@btindex set
+@example
+set [--abefhkmnptuvxBCEHPT] [-o @var{option-name}] [@var{argument} @dots{}]
+set [+abefhkmnptuvxBCEHPT] [+o @var{option-name}] [@var{argument} @dots{}]
+@end example
+
+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.
+
+When options are supplied, they set or unset shell attributes.
+Options, if specified, have the following meanings:
+
+@table @code
+@item -a
+Each variable or function that is created or modified is given the
+export attribute and marked for export to the environment of
+subsequent commands.
+
+@item -b
+Cause the status of terminated background jobs to be reported
+immediately, rather than before printing the next primary prompt.
+
+@item -e
+Exit immediately if
+a pipeline (@pxref{Pipelines}), which may consist of a single simple command
+(@pxref{Simple Commands}),
+a list (@pxref{Lists}),
+or a compound command (@pxref{Compound Commands})
+returns a non-zero status.
+The shell does not exit if the command that fails is part of the
+command list immediately following a @code{while} or @code{until} keyword,
+part of the test in an @code{if} statement,
+part of any command executed in a @code{&&} or @code{||} list except
+the command following the final @code{&&} or @code{||},
+any command in a pipeline but the last,
+or if the command's return status is being inverted with @code{!}.
+If a compound command other than a subshell
+returns a non-zero status because a command failed
+while @option{-e} was being ignored, the shell does not exit.
+A trap on @code{ERR}, if set, is executed before the shell exits.
+
+This option applies to the shell environment and each subshell environment
+separately (@pxref{Command Execution Environment}), and may cause
+subshells to exit before executing all the commands in the subshell.
+
+If a compound command or shell function executes in a context where
+@option{-e} is being ignored,
+none of the commands executed within the compound command or function body
+will be affected by the @option{-e} setting, even if @option{-e} is set
+and a command returns a failure status.
+If a compound command or shell function sets @option{-e} while executing in
+a context where @option{-e} is ignored, that setting will not have any
+effect until the compound command or the command containing the function
+call completes.
+
+@item -f
+Disable filename expansion (globbing).
+
+@item -h
+Locate and remember (hash) commands as they are looked up for execution.
+This option is enabled by default.
+
+@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 -m
+Job control is enabled (@pxref{Job Control}).
+All processes run in a separate process group.
+When a background job completes, the shell prints a line
+containing its exit status.
+
+@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 -o @var{option-name}
+
+Set the option corresponding to @var{option-name}:
+
+@table @code
+@item allexport
+Same as @code{-a}.
+
+@item braceexpand
+Same as @code{-B}.
+
+@item emacs
+Use an @code{emacs}-style line editing interface (@pxref{Command Line Editing}).
+This also affects the editing interface used for @code{read -e}.
+
+@item errexit
+Same as @code{-e}.
+
+@item errtrace
+Same as @code{-E}.
+
+@item functrace
+Same as @code{-T}.
+
+@item hashall
+Same as @code{-h}.
+
+@item histexpand
+Same as @code{-H}.
+
+@item history
+Enable command history, as described in @ref{Bash History Facilities}.
+This option is on by default in interactive shells.
+
+@item ignoreeof
+An interactive shell will not exit upon reading EOF.
+
+@item keyword
+Same as @code{-k}.
+
+@item monitor
+Same as @code{-m}.
+
+@item noclobber
+Same as @code{-C}.
+
+@item noexec
+Same as @code{-n}.
+
+@item noglob
+Same as @code{-f}.
+
+@item nolog
+Currently ignored.
+
+@item notify
+Same as @code{-b}.
+
+@item nounset
+Same as @code{-u}.
+
+@item onecmd
+Same as @code{-t}.
+
+@item physical
+Same as @code{-P}.
+
+@item pipefail
+If set, the return value of a pipeline is the value of the last
+(rightmost) command to exit with a non-zero status, or zero if all
+commands in the pipeline exit successfully.
+This option is disabled by default.
+
+@item posix
+Change the behavior of Bash where the default operation differs
+from the @sc{posix} standard to match the standard
+(@pxref{Bash POSIX Mode}).
+This is intended to make Bash behave as a strict superset of that
+standard.
+
+@item privileged
+Same as @code{-p}.
+
+@item verbose
+Same as @code{-v}.
+
+@item vi
+Use a @code{vi}-style line editing interface.
+This also affects the editing interface used for @code{read -e}.
+
+@item xtrace
+Same as @code{-x}.
+@end table
+
+@item -p
+Turn on privileged mode.
+In this mode, the @env{$BASH_ENV} and @env{$ENV} files are not
+processed, shell functions are not inherited from the environment,
+and the @env{SHELLOPTS}, @env{BASHOPTS}, @env{CDPATH} and @env{GLOBIGNORE}
+variables, if they appear in the environment, are ignored.
+If the shell is started with the effective user (group) id not equal to the
+real user (group) id, and the @option{-p} option is not supplied, these actions
+are taken and the effective user id is set to the real user id.
+If the @option{-p} option is supplied at startup, the effective user id is
+not reset.
+Turning this option off causes the effective user
+and group ids to be set to the real user and group ids.
+
+@item -t
+Exit after reading and executing one command.
+
+@item -u
+Treat unset variables and parameters other than the special parameters
+@samp{@@} or @samp{*} as an error when performing parameter expansion.
+An error message will be written to the standard error, and a non-interactive
+shell will exit.
+
+@item -v
+Print shell input lines as they are read.
+
+@item -x
+Print a trace of simple commands, @code{for} commands, @code{case}
+commands, @code{select} commands, and arithmetic @code{for} commands
+and their arguments or associated word lists after they are
+expanded and before they are executed.  The value of the @env{PS4}
+variable is expanded and the resultant value is printed before
+the command and its expanded arguments.
+
+@item -B
+The shell will perform brace expansion (@pxref{Brace Expansion}).
+This option is on by default.
+
+@item -C
+Prevent output redirection using @samp{>}, @samp{>&}, and @samp{<>}
+from overwriting existing files.
+
+@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 -H
+Enable @samp{!} style history substitution (@pxref{History Interaction}).
+This option is on by default for interactive shells.
+
+@item -P
+If set, do not resolve symbolic links when performing commands such as
+@code{cd} which change the current directory.  The physical directory
+is used instead.  By default, Bash follows
+the logical chain of directories when performing commands
+which change the current directory.
+
+For example, if @file{/usr/sys} is a symbolic link to @file{/usr/local/sys}
+then:
+@example
+$ cd /usr/sys; echo $PWD
+/usr/sys
+$ cd ..; pwd
+/usr
+@end example
+
+@noindent
+If @code{set -P} is on, then:
+@example
+$ cd /usr/sys; echo $PWD
+/usr/local/sys
+$ cd ..; pwd
+/usr/local
+@end example
+
+@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 --
+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 -
+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
+
+Using @samp{+} rather than @samp{-} causes these options to be
+turned off.  The options can also be used upon invocation of the
+shell.  The current set of options may be found in @code{$-}.
+
+The remaining N @var{arguments} are positional parameters and are
+assigned, in order, to @code{$1}, @code{$2}, @dots{}  @code{$N}.
+The special parameter @code{#} is set to N.
+
+The return status is always zero unless an invalid option is supplied.
+@end table
+
+@node The Shopt Builtin
+@subsection The Shopt Builtin
+
+This builtin allows you to change additional shell optional behavior.
+
+@table @code
+
+@item shopt
+@btindex shopt
+@example
+shopt [-pqsu] [-o] [@var{optname} @dots{}]
+@end example
+
+Toggle the values of settings controlling optional shell behavior.
+The settings can be either those listed below, or, if the
+@option{-o} option is used, those available with the @option{-o}
+option to the @code{set} builtin command (@pxref{The Set Builtin}).
+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;
+if @var{optnames} are supplied, the output is restricted to those options.
+The @option{-p} option causes output to be displayed in a form that
+may be reused as input.
+Other options have the following meanings:
+
+@table @code
+@item -s
+Enable (set) each @var{optname}.
+
+@item -u
+Disable (unset) each @var{optname}.
+
+@item -q
+Suppresses normal output; the return status
+indicates whether the @var{optname} is set or unset.
+If multiple @var{optname} arguments are given with @option{-q},
+the return status is zero if all @var{optnames} are enabled;
+non-zero otherwise.
+
+@item -o
+Restricts the values of
+@var{optname} to be those defined for the @option{-o} option to the
+@code{set} builtin (@pxref{The Set Builtin}).
+@end table
+
+If either @option{-s} or @option{-u}
+is used with no @var{optname} arguments, @code{shopt} shows only
+those options which are set or unset, respectively.
+
+Unless otherwise noted, the @code{shopt} options are disabled (off)
+by default.
+
+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 assoc_expand_once
+If set, the shell suppresses multiple evaluation of associative array
+subscripts during arithmetic expression evaluation, while executing
+builtins that can perform variable assignments,
+and while executing builtins that perform array dereferencing.
+
+@item autocd
+If set, a command name that is the name of a directory is executed as if
+it were the argument to the @code{cd} command.
+This option is only used by interactive shells.
+
+@item cdable_vars
+If this is set, an argument to the @code{cd} builtin command that
+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.
+
+@item checkjobs
+If set, Bash lists the status of any stopped and running jobs before
+exiting an interactive shell.  If any jobs are running, this causes
+the exit to be deferred until a second exit is attempted without an
+intervening command (@pxref{Job Control}).
+The shell always postpones exiting if any jobs are stopped.
+
+@item checkwinsize
+If set, Bash checks the window size after each external (non-builtin)
+command and, if necessary, updates the values of    
+@env{LINES} and @env{COLUMNS}.
+This option is enabled by default.
+
+@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.
+This option is enabled by default, but only has an effect if command
+history is enabled (@pxref{Bash History Facilities}).
+
+@item compat31
+@itemx compat32
+@itemx compat40
+@itemx compat41
+@itemx compat42
+@itemx compat43
+@itemx compat44
+These control aspects of the shell's compatibility mode
+(@pxref{Shell Compatibility Mode}).
+
+@item complete_fullquote
+If set, Bash
+quotes all shell metacharacters in filenames and directory names when
+performing completion.
+If not set, Bash
+removes metacharacters such as the dollar sign from the set of
+characters that will be quoted in completed filenames
+when these metacharacters appear in shell variable references in words to be
+completed.
+This means that dollar signs in variable names that expand to directories
+will not be quoted;
+however, any dollar signs appearing in filenames will not be quoted, either.
+This is active only when bash is using backslashes to quote completed
+filenames.
+This variable is set by default, which is the default Bash behavior in
+versions through 4.2.
+
+@item direxpand
+If set, Bash
+replaces directory names with the results of word expansion when performing
+filename completion.  This changes the contents of the readline editing
+buffer.
+If not set, Bash attempts to preserve what the user typed.
+
+@item dirspell
+If set, Bash
+attempts spelling correction on directory names during word completion 
+if the directory name initially supplied does not exist.
+
+@item dotglob
+If set, Bash includes filenames beginning with a `.' in
+the results of filename expansion.
+The filenames @samp{.} and @samp{..} must always be matched explicitly,
+even if @code{dotglob} is set.
+
+@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 expand_aliases
+If set, aliases are expanded as described below under Aliases,
+@ref{Aliases}.
+This option is enabled by default for interactive shells.
+
+@item extdebug
+If set at shell invocation,
+or in a shell startup file,
+arrange to execute the debugger profile
+before the shell starts, identical to the @option{--debugger} option.
+If set after invocation, behavior intended for use by debuggers is enabled:
+
+@enumerate
+@item
+The @option{-F} option to the @code{declare} builtin (@pxref{Bash Builtins})
+displays the source file name and line number corresponding to each function
+name supplied as an argument.
+
+@item
+If the command run by the @code{DEBUG} trap returns a non-zero value, the
+next command is skipped and not executed.
+
+@item
+If the command run by the @code{DEBUG} trap returns a value of 2, and the
+shell is executing in a subroutine (a shell function or a shell script
+executed by the @code{.} or @code{source} builtins), the shell simulates
+a call to @code{return}.
+
+@item
+@code{BASH_ARGC} and @code{BASH_ARGV} are updated as described in their
+descriptions (@pxref{Bash Variables}).
+
+@item
+Function tracing is enabled: command substitution, shell functions, and
+subshells invoked with @code{( @var{command} )} inherit the
+@code{DEBUG} and @code{RETURN} traps.
+
+@item
+Error tracing is enabled: command substitution, shell functions, and
+subshells invoked with @code{( @var{command} )} inherit the
+@code{ERR} trap.
+@end enumerate
+
+@item extglob
+If set, the extended pattern matching features described above
+(@pxref{Pattern Matching}) are enabled.
+
+@item extquote
+If set, @code{$'@var{string}'} and @code{$"@var{string}"} quoting is  
+performed within @code{$@{@var{parameter}@}} expansions                     
+enclosed in double quotes.  This option is enabled by default. 
+
+@item failglob
+If set, patterns which fail to match filenames during filename expansion
+result in an expansion error.
+
+@item force_fignore
+If set, the suffixes specified by the @env{FIGNORE} shell variable
+cause words to be ignored when performing word completion even if
+the ignored words are the only possible completions.
+@xref{Bash Variables}, for a description of @env{FIGNORE}.
+This option is enabled by default.
+
+@item globasciiranges
+If set, range expressions used in pattern matching bracket expressions
+(@pxref{Pattern Matching})
+behave as if in the traditional C locale when performing
+comparisons.  That is, the current locale's collating sequence
+is not taken into account, so
+@samp{b} will not collate between @samp{A} and @samp{B},
+and upper-case and lower-case ASCII characters will collate together.   
+
+@item globstar
+If set, the pattern @samp{**} used in a filename expansion context will
+match all files and zero or more directories and subdirectories.
+If the pattern is followed by a @samp{/}, only directories and
+subdirectories match.
+
+@item gnu_errfmt
+If set, shell error messages are written in the standard @sc{gnu} error
+message format.
+
+@item histappend
+If set, the history list is appended to the file named by the value
+of the @env{HISTFILE}
+variable when the shell exits, rather than overwriting the file.
+
+@item histreedit
+If set, and Readline
+is being used, a user is given the opportunity to re-edit a
+failed history substitution.
+
+@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 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.
+
+@item huponexit
+If set, Bash will send @code{SIGHUP} to all jobs when an interactive
+login shell exits (@pxref{Signals}).
+
+@item inherit_errexit
+If set, command substitution inherits the value of the @code{errexit} option,
+instead of unsetting it in the subshell environment.
+This option is enabled when @sc{posix} mode is enabled.
+
+@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 lastpipe
+If set, and job control is not active, the shell runs the last command of
+a pipeline not executed in the background in the current shell environment.
+
+@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 localvar_inherit
+If set, local variables inherit the value and attributes of a variable of
+the same name that exists at a previous scope before any new value is
+assigned.  The @var{nameref} attribute is not inherited.
+
+@item localvar_unset
+If set, calling @code{unset} on local variables in previous function scopes
+marks them so subsequent lookups find them unset until that function
+returns. This is identical to the behavior of unsetting local variables
+at the current function scope.
+
+@item login_shell
+The shell sets this option if it is started as a login shell
+(@pxref{Invoking Bash}).
+The value may not be changed.
+
+@item mailwarn
+If set, and a file that Bash is checking for mail has been
+accessed since the last time it was checked, the message
+@code{"The mail in @var{mailfile} has been read"} is displayed.
+
+@item no_empty_cmd_completion
+If set, and Readline is being used, Bash will not attempt to search
+the @env{PATH} for possible completions when completion is attempted
+on an empty line.
+
+@item nocaseglob
+If set, Bash matches filenames in a case-insensitive fashion when
+performing filename expansion.
+
+@item nocasematch
+If set, Bash matches patterns in a case-insensitive fashion when
+performing matching while executing @code{case} or @code{[[}
+conditional commands,
+when performing pattern substitution word expansions,
+or when filtering possible completions as part of programmable completion.
+
+@item nullglob
+If set, Bash allows filename patterns which match no
+files to expand to a null string, rather than themselves.
+
+@item progcomp
+If set, the programmable completion facilities
+(@pxref{Programmable Completion}) are enabled.
+This option is enabled by default.
+
+@item progcomp_alias
+If set, and programmable completion is enabled, Bash treats a command
+name that doesn't have any completions as a possible alias and attempts
+alias expansion. If it has an alias, Bash attempts programmable
+completion using the command word resulting from the expanded alias.
+
+@item promptvars
+If set, prompt strings undergo
+parameter expansion, command substitution, arithmetic
+expansion, and quote removal after being expanded
+as described below (@pxref{Controlling the Prompt}).
+This option is enabled by default.
+
+@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.
+
+@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 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.
+
+@item xpg_echo
+If set, the @code{echo} builtin expands backslash-escape sequences
+by default.
+
+@end table
+@end table
+
+@node Special Builtins
+@section Special Builtins
+@cindex special builtin
+
+For historical reasons, the @sc{posix} standard has classified
+several builtin commands as @emph{special}.
+When Bash is executing in @sc{posix} mode, the special builtins
+differ from other builtin commands in three respects:
+
+@enumerate
+@item
+Special builtins are found before shell functions during command lookup.
+
+@item
+If a special builtin returns an error status, a non-interactive shell exits.
+
+@item
+Assignment statements preceding the command stay in effect in the shell
+environment after the command completes.
+@end enumerate
+
+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}. 
+
+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 Shell Variables
+@chapter Shell Variables
+
+@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
+
+This chapter describes the shell variables that Bash uses.
+Bash automatically assigns default values to a number of variables.
+
+@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.
+
+@vtable @code
+
+@item CDPATH
+A colon-separated list of directories used as a search path for
+the @code{cd} builtin command.
+
+@item HOME
+The current user's home directory; the default for the @code{cd} builtin
+command.
+The value of this variable is also used by tilde expansion
+(@pxref{Tilde Expansion}).
+
+@item IFS
+A list of characters that separate fields; used when the shell splits
+words as part of expansion.
+
+@item MAIL
+If this parameter is set to a filename or directory name
+and the @env{MAILPATH} variable
+is not set, Bash informs the user of the arrival of mail in
+the specified file or Maildir-format directory.
+
+@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 filename from the message with
+a @samp{?}.
+When used in the text of the message, @code{$_} expands to the name of
+the current mail file.
+
+@item OPTARG
+The value of the last option argument processed by the @code{getopts} builtin.
+
+@item OPTIND
+The index of the last option argument processed by the @code{getopts} builtin.
+
+@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.
+
+@item PS1
+The primary prompt string.  The default value is @samp{\s-\v\$ }.
+@xref{Controlling the Prompt}, for the complete list of escape
+sequences that are expanded before @env{PS1} is displayed.
+
+@item PS2
+The secondary prompt string.  The default value is @samp{> }.
+@env{PS2} is expanded in the same way as @env{PS1} before being
+displayed.
+
+@end vtable
+
+@node Bash Variables
+@section Bash Variables
+
+These variables are set or used by Bash, but other shells
+do not normally treat them specially.
+
+A few variables used by Bash are described in different chapters:
+variables for controlling the job control facilities
+(@pxref{Job Control Variables}).
+
+@vtable @code
+
+@item _
+@vindex $_
+($_, an underscore.)
+At shell startup, set to the pathname used to invoke the
+shell or shell script being executed as passed in the environment
+or argument list.
+Subsequently, expands to the last argument to the previous simple
+command executed in the foreground, after expansion. 
+Also set to the full pathname used to invoke each command executed
+and placed in the environment exported to that command.
+When checking mail, this parameter holds the name of the mail file.
+
+@item BASH
+The full pathname used to execute the current instance of Bash.
+
+@item BASHOPTS
+A colon-separated list of enabled shell options.  Each word in
+the list is a valid argument for the @option{-s} option to the
+@code{shopt} builtin command (@pxref{The Shopt Builtin}).
+The options appearing in @env{BASHOPTS} are those reported
+as @samp{on} by @samp{shopt}.
+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 BASHPID
+Expands to the process ID of the current Bash process.
+This differs from @code{$$} under certain circumstances, such as subshells
+that do not require Bash to be re-initialized.
+Assignments to @env{BASHPID} have no effect.
+If @env{BASHPID}
+is unset, it loses its special properties, even if it is
+subsequently reset.
+
+@item BASH_ALIASES
+An associative array variable whose members correspond to the internal
+list of aliases as maintained by the @code{alias} builtin.
+(@pxref{Bourne Shell Builtins}).
+Elements added to this array appear in the alias list; however,
+unsetting array elements currently does not cause aliases to be removed
+from the alias list.
+If @env{BASH_ALIASES}
+is unset, it loses its special properties, even if it is
+subsequently reset.
+
+@item BASH_ARGC
+An array variable whose values are the number of parameters in each
+frame of the current bash execution call stack.  The number of
+parameters to the current subroutine (shell function or script executed
+with @code{.} or @code{source}) is at the top of the stack.  When a
+subroutine is executed, the number of parameters passed is pushed onto
+@code{BASH_ARGC}.
+The shell sets @code{BASH_ARGC} only when in extended debugging mode
+(see @ref{The Shopt Builtin}
+for a description of the @code{extdebug} option to the @code{shopt}
+builtin).
+Setting @code{extdebug} after the shell has started to execute a script,
+or referencing this variable when @code{extdebug} is not set,
+may result in inconsistent values.
+
+@item BASH_ARGV
+An array variable containing all of the parameters in the current bash
+execution call stack.  The final parameter of the last subroutine call
+is at the top of the stack; the first parameter of the initial call is
+at the bottom.  When a subroutine is executed, the parameters supplied
+are pushed onto @code{BASH_ARGV}.
+The shell sets @code{BASH_ARGV} only when in extended debugging mode
+(see @ref{The Shopt Builtin}
+for a description of the @code{extdebug} option to the @code{shopt}
+builtin).
+Setting @code{extdebug} after the shell has started to execute a script,
+or referencing this variable when @code{extdebug} is not set,
+may result in inconsistent values.
+
+@item BASH_ARGV0
+When referenced, this variable expands to the name of the shell or shell
+script (identical to @code{$0}; @xref{Special Parameters},
+for the description of special parameter 0).
+Assignment to @code{BASH_ARGV0}
+causes the value assigned to also be assigned to @code{$0}.
+If @env{BASH_ARGV0}
+is unset, it loses its special properties, even if it is
+subsequently reset.
+
+@item BASH_CMDS
+An associative array variable whose members correspond to the internal
+hash table of commands as maintained by the @code{hash} builtin
+(@pxref{Bourne Shell Builtins}).
+Elements added to this array appear in the hash table; however,
+unsetting array elements currently does not cause command names to be removed
+from the hash table.
+If @env{BASH_CMDS}
+is unset, it loses its special properties, even if it is
+subsequently reset.
+
+@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.
+If @env{BASH_COMMAND}
+is unset, it loses its special properties, even if it is
+subsequently reset.
+
+@item BASH_COMPAT
+The value is used to set the shell's compatibility level.
+@xref{Shell Compatibility Mode}, for a description of the various
+compatibility levels and their effects.
+The value may be a decimal number (e.g., 4.2) or an integer (e.g., 42)
+corresponding to the desired compatibility level.
+If @env{BASH_COMPAT} is unset or set to the empty string, the compatibility
+level is set to the default for the current version.
+If @env{BASH_COMPAT} is set to a value that is not one of the valid
+compatibility levels, the shell prints an error message and sets the
+compatibility level to the default for the current version.
+The valid values correspond to the compatibility levels
+described below (@pxref{Shell Compatibility Mode}).
+For example, 4.2 and 42 are valid values that correspond
+to the @code{compat42} @code{shopt} option
+and set the compatibility level to 42.
+The current version is also a valid value.
+
+@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 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
+where each corresponding member of @var{FUNCNAME} was invoked.
+@code{$@{BASH_LINENO[$i]@}} is the line number in the source file
+(@code{$@{BASH_SOURCE[$i+1]@}}) where
+@code{$@{FUNCNAME[$i]@}} was called (or @code{$@{BASH_LINENO[$i-1]@}} if
+referenced within another shell function). 
+Use @code{LINENO} to obtain the current line number.
+
+@item BASH_LOADABLES_PATH
+A colon-separated list of directories in which the shell looks for
+dynamically loadable builtins specified by the
+@code{enable} command.
+
+@item BASH_REMATCH
+An array variable whose members are assigned by the @samp{=~} binary
+operator to the @code{[[} conditional command
+(@pxref{Conditional Constructs}).
+The element with index 0 is the portion of the string
+matching the entire regular expression.
+The element with index @var{n} is the portion of the
+string matching the @var{n}th parenthesized subexpression.
+
+@item BASH_SOURCE
+An array variable whose members are the source filenames where the
+corresponding shell function names in the @code{FUNCNAME} array
+variable are defined.
+The shell function @code{$@{FUNCNAME[$i]@}} is defined in the file
+@code{$@{BASH_SOURCE[$i]@}} and called from @code{$@{BASH_SOURCE[$i+1]@}}
+
+@item BASH_SUBSHELL
+Incremented by one within each subshell or subshell environment when
+the shell begins executing in that environment.
+The initial value is 0.
+If @env{BASH_SUBSHELL}
+is unset, it loses its special properties, even if it is
+subsequently reset.
+
+@item BASH_VERSINFO
+A readonly array variable (@pxref{Arrays})
+whose members hold version information for this instance of Bash.
+The values assigned to the array members are as follows:
+
+@table @code
+
+@item BASH_VERSINFO[0]
+The major version number (the @var{release}).
+
+@item BASH_VERSINFO[1]
+The minor version number (the @var{version}).
+
+@item BASH_VERSINFO[2]
+The patch level.
+
+@item BASH_VERSINFO[3]
+The build version.
+
+@item BASH_VERSINFO[4]
+The release status (e.g., @var{beta1}).
+
+@item BASH_VERSINFO[5]
+The value of @env{MACHTYPE}.
+@end table
+
+@item BASH_VERSION
+The version number of the current instance of Bash.
+
+@item BASH_XTRACEFD
+If set to an integer corresponding to a valid file descriptor, Bash
+will write the trace output generated when @samp{set -x}
+is enabled to that file descriptor.
+This allows tracing output to be separated from diagnostic and error
+messages.
+The file descriptor is closed when @code{BASH_XTRACEFD} is unset or assigned
+a new value.
+Unsetting @code{BASH_XTRACEFD} or assigning it the empty string causes the
+trace output to be sent to the standard error.
+Note that setting @code{BASH_XTRACEFD} to 2 (the standard error file
+descriptor) and then unsetting it will result in the standard error
+being closed.
+
+@item CHILD_MAX
+Set the number of exited child status values for the shell to remember.
+Bash will not allow this value to be decreased below a @sc{posix}-mandated
+minimum, and there is a maximum value (currently 8192) that this may
+not exceed.
+The minimum value is system-dependent.
+
+@item COLUMNS
+Used by the @code{select} command to determine the terminal width
+when printing selection lists.
+Automatically set if the @code{checkwinsize} option is enabled
+(@pxref{The Shopt Builtin}), or in an interactive shell upon receipt of a
+@code{SIGWINCH}.
+
+@item COMP_CWORD
+An index into @env{$@{COMP_WORDS@}} of the word containing the current
+cursor position.
+This variable is available only in shell functions invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
+
+@item COMP_LINE
+The current command line.
+This variable is available only in shell functions and external
+commands invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
+
+@item COMP_POINT
+The index of the current cursor position relative to the beginning of
+the current command.
+If the current cursor position is at the end of the current command,
+the value of this variable is equal to @code{$@{#COMP_LINE@}}.
+This variable is available only in shell functions and external
+commands invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
+
+@item COMP_TYPE
+Set to an integer value corresponding to the type of completion attempted
+that caused a completion function to be called:
+@var{TAB}, for normal completion,
+@samp{?}, for listing completions after successive tabs,
+@samp{!}, for listing alternatives on partial word completion,
+@samp{@@}, to list completions if the word is not unmodified,
+or
+@samp{%}, for menu completion.
+This variable is available only in shell functions and external
+commands invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
+
+@item COMP_KEY
+The key (or final key of a key sequence) used to invoke the current
+completion function.
+
+@item COMP_WORDBREAKS
+The set of characters that the Readline library treats as word
+separators when performing word completion.
+If @env{COMP_WORDBREAKS}
+is unset, it loses its special properties,
+even if it is subsequently reset.
+
+@item COMP_WORDS
+An array variable consisting of the individual
+words in the current command line.
+The line is split into words as Readline would split it, using
+@code{COMP_WORDBREAKS} as described above.
+This variable is available only in shell functions invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
+
+@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}).
+Each array element contains one possible completion.
+
+@item COPROC
+An array variable created to hold the file descriptors
+for output from and input to an unnamed coprocess (@pxref{Coprocesses}).
+
+@item DIRSTACK
+An array variable containing the current contents of the directory stack.
+Directories appear in the stack in the order they are displayed by the
+@code{dirs} builtin.
+Assigning to members of this array variable may be used to modify
+directories already in the stack, but the @code{pushd} and @code{popd}
+builtins must be used to add and remove directories.
+Assignment to this variable will not change the current directory.
+If @env{DIRSTACK}
+is unset, it loses its special properties, even if
+it is subsequently reset.
+
+@item EMACS
+If Bash finds this variable in the environment when the shell
+starts with value @samp{t}, it assumes that the shell is running in an
+Emacs shell buffer and disables line editing.
+
+@item ENV
+Expanded and executed similarlty to @code{BASH_ENV}
+(@pxref{Bash Startup Files})
+when an interactive shell is invoked in
+@sc{posix} Mode (@pxref{Bash POSIX Mode}).
+
+@item EPOCHREALTIME
+Each time this parameter is referenced, it expands to the number of seconds
+since the Unix Epoch as a floating point value with micro-second granularity
+(see the documentation for the C library function @var{time} for the
+definition of Epoch).
+Assignments to @env{EPOCHREALTIME} are ignored.
+If @env{EPOCHREALTIME}
+is unset, it loses its special properties, even if
+it is subsequently reset.
+
+@item EPOCHSECONDS
+Each time this parameter is referenced, it expands to the number of seconds
+since the Unix Epoch (see the documentation for the C library function
+@var{time} for the definition of Epoch).
+Assignments to @env{EPOCHSECONDS} are ignored.
+If @env{EPOCHSECONDS}
+is unset, it loses its special properties, even if
+it is subsequently reset.
+
+@item EUID
+The numeric effective user id of the current user.  This variable
+is readonly.
+
+@item EXECIGNORE
+A colon-separated list of shell patterns (@pxref{Pattern Matching})
+defining the list of filenames to be ignored by command search using
+@code{PATH}.
+Files whose full pathnames match one of these patterns are not considered
+executable files for the purposes of completion and command execution
+via @code{PATH} lookup.
+This does not affect the behavior of the @code{[}, @code{test}, and @code{[[}
+commands.
+Full pathnames in the command hash table are not subject to @code{EXECIGNORE}.
+Use this variable to ignore shared library files that have the executable
+bit set, but are not executable files.
+The pattern matching honors the setting of the @code{extglob} shell 
+option.
+
+@item FCEDIT
+The editor used as a default by the @option{-e} option to the @code{fc}
+builtin command.
+
+@item FIGNORE
+A colon-separated list of suffixes to ignore when performing
+filename completion.
+A filename whose suffix matches one of the entries in 
+@env{FIGNORE}
+is excluded from the list of matched filenames.  A sample
+value is @samp{.o:~}
+
+@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 (the one with the highest index)
+is @code{"main"}.
+This variable exists only when a shell function is executing.
+Assignments to @env{FUNCNAME} have no effect.
+If @env{FUNCNAME}
+is unset, it loses its special properties, even if
+it is subsequently reset.
+
+This variable can be used with @code{BASH_LINENO} and @code{BASH_SOURCE}.
+Each element of @code{FUNCNAME} has corresponding elements in
+@code{BASH_LINENO} and @code{BASH_SOURCE} to describe the call stack.
+For instance, @code{$@{FUNCNAME[$i]@}} was called from the file
+@code{$@{BASH_SOURCE[$i+1]@}} at line number @code{$@{BASH_LINENO[$i]@}}.
+The @code{caller} builtin displays the current call stack using this
+information.
+
+@item FUNCNEST
+If set to a numeric value greater than 0, defines a maximum function
+nesting level.  Function invocations that exceed this nesting level
+will cause the current command to abort.
+
+@item GLOBIGNORE
+A colon-separated list of patterns defining the set of file names to
+be ignored by filename expansion.
+If a file name matched by a filename expansion pattern also matches one
+of the patterns in @env{GLOBIGNORE}, it is removed from the list
+of matches.
+The pattern matching honors the setting of the @code{extglob} shell
+option.
+
+@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.
+If @env{GROUPS}
+is unset, it loses its special properties, even if it is
+subsequently reset.
+
+@item histchars
+Up to three characters which control history expansion, quick
+substitution, and tokenization (@pxref{History Interaction}).
+The first character is the
+@var{history expansion} character, that is, the character which signifies the
+start of a history expansion, normally @samp{!}.  The second character is the
+character which signifies `quick substitution' when seen as the first
+character on a line, normally @samp{^}.  The optional third character is the
+character which indicates that the remainder of the line is a comment when
+found as the first character of a word, usually @samp{#}.  The history
+comment character causes history substitution to be skipped for the
+remaining words on the line.  It does not necessarily cause the shell
+parser to treat the rest of the line as a comment.
+
+@item HISTCMD
+The history number, or index in the history list, of the current
+command.
+Assignments to @env{HISTCMD} are ignored.
+If @env{HISTCMD}
+is unset, it loses its special properties,
+even if it is subsequently reset.
+
+@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 HISTFILE
+The name of the file to which the command history is saved.  The
+default value is @file{~/.bash_history}.
+
+@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
+by removing the oldest entries.
+The history file is also truncated to this size after
+writing it when a shell exits.
+If the value is 0, the history file is truncated to zero size.
+Non-numeric values and numeric values less than zero inhibit truncation.
+The shell sets the default value to the value of @env{HISTSIZE}
+after reading any startup files.
+
+@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}.
+The pattern matching honors the setting of the @code{extglob} shell
+option.
+
+@env{HISTIGNORE} subsumes the function of @env{HISTCONTROL}.  A
+pattern of @samp{&} is identical to @code{ignoredups}, and a
+pattern of @samp{[ ]*} is identical to @code{ignorespace}. 
+Combining these two patterns, separating them with a colon,
+provides the functionality of @code{ignoreboth}. 
+
+@item HISTSIZE
+The maximum number of commands to remember on the history list.
+If the value is 0, commands are not saved in the history list.
+Numeric values less than zero result in every command being saved
+on the history list (there is no limit).
+The shell sets the default value to 500 after reading any startup files.
+
+@item HISTTIMEFORMAT
+If this variable is set and not null, its value is used as a format string
+for @var{strftime} to print the time stamp associated with each history
+entry displayed by the @code{history} builtin.
+If this variable is set, time stamps are written to the history file so
+they may be preserved across shell sessions.
+This uses the history comment character to distinguish timestamps from
+other history lines.
+
+@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, or does not name a readable file,
+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 HOSTNAME
+The name of the current host.
+
+@item HOSTTYPE
+A string describing the machine Bash is running on.
+
+@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 INPUTRC
+The name of the Readline initialization file, overriding the default
+of @file{~/.inputrc}.
+
+@item INSIDE_EMACS
+If Bash finds this variable in the environment when the shell
+starts, it assumes that the shell is running in an Emacs shell buffer
+and may disable line editing depending on the value of @env{TERM}.
+
+@item LANG  
+Used to determine the locale category for any category not specifically
+selected with a variable starting with @code{LC_}.
+
+@item LC_ALL
+This variable overrides the value of @env{LANG} and any other
+@code{LC_} variable specifying a locale category.
+
+@item LC_COLLATE
+This variable determines the collation order used when sorting the
+results of filename expansion, and
+determines the behavior of range expressions, equivalence classes,
+and collating sequences within filename expansion and pattern matching
+(@pxref{Filename Expansion}).
+
+@item LC_CTYPE
+This variable determines the interpretation of characters and the
+behavior of character classes within filename expansion and pattern
+matching (@pxref{Filename Expansion}).
+
+@item LC_MESSAGES
+This variable determines the locale used to translate double-quoted
+strings preceded by a @samp{$} (@pxref{Locale Translation}).
+
+@item LC_NUMERIC
+This variable determines the locale category used for number formatting.
+
+@item LC_TIME
+This variable determines the locale category used for data and time
+formatting.
+
+@item LINENO
+The line number in the script or shell function currently executing.
+If @env{LINENO}
+is unset, it loses its special properties, even if it is
+subsequently reset.
+
+@item LINES
+Used by the @code{select} command to determine the column length
+for printing selection lists.
+Automatically set if the @code{checkwinsize} option is enabled
+(@pxref{The Shopt Builtin}), or in an interactive shell upon receipt of a
+@code{SIGWINCH}.
+
+@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 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 MAPFILE
+An array variable created to hold the text read by the
+@code{mapfile} builtin when no variable name is supplied.
+
+@item OLDPWD
+The previous working directory as set by the @code{cd} builtin.
+
+@item OPTERR
+If set to the value 1, Bash displays error messages
+generated by the @code{getopts} builtin command.
+
+@item OSTYPE
+A string describing the operating system Bash is running on.
+
+@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 POSIXLY_CORRECT
+If this variable is in the environment when 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, Bash enables @sc{posix} mode,
+as if the command
+@example
+@code{set -o posix}
+@end example
+@noindent
+had been executed.
+When the shell enters @sc{posix} mode, it sets this variable if it was
+not already set.
+
+@item PPID
+The process @sc{id} of the shell's parent process.  This variable
+is readonly.
+
+@item PROMPT_COMMAND
+If this variable is set, and is an array,
+the value of each set element is interpreted as a command to execute
+before printing the primary prompt (@env{$PS1}).
+If this is set but not an array variable,
+its value is used as a command to execute instead.
+
+@item PROMPT_DIRTRIM
+If set to a number greater than zero, the value is used as the number of
+trailing directory components to retain when expanding the @code{\w} and
+@code{\W} prompt string escapes (@pxref{Controlling the Prompt}).
+Characters removed are replaced with an ellipsis.
+
+@item PS0
+The value of this parameter is expanded like @env{PS1}
+and displayed by interactive shells after reading a command
+and before the command is executed.
+
+@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 PS4
+The value of this parameter is expanded like @var{PS1}
+and the expanded 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 the expanded value is replicated multiple times,
+as necessary, to indicate multiple levels of indirection.
+The default is @samp{+ }.
+
+@item PWD
+The current working directory as set by the @code{cd} builtin.
+
+@item RANDOM
+Each time this parameter is referenced, it expands to a random integer
+between 0 and 32767. Assigning a value to this
+variable seeds the random number generator.
+If @env{RANDOM}
+is unset, it loses its special properties, even if it is
+subsequently reset.
+
+@item READLINE_LINE
+The contents of the Readline line buffer, for use
+with @samp{bind -x} (@pxref{Bash Builtins}).
+
+@item READLINE_MARK
+The position of the @var{mark} (saved insertion point) in the
+Readline line buffer, for use
+with @samp{bind -x} (@pxref{Bash Builtins}).
+The characters between the insertion point and the mark are often
+called the @var{region}.
+
+@item READLINE_POINT
+The position of the insertion point in the Readline line buffer, for use
+with @samp{bind -x} (@pxref{Bash Builtins}).
+
+@item REPLY
+The default variable for the @code{read} builtin.
+
+@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.
+The number of seconds at shell invocation and the current time is always
+determined by querying the system clock.
+If @env{SECONDS}
+is unset, it loses its special properties,
+even if it is subsequently reset.
+
+@item SHELL
+This environment variable expands to the full pathname to the shell.
+If it is not set when the shell starts,
+Bash assigns to it the full pathname of the current user's login shell.
+
+@item SHELLOPTS
+A colon-separated list of enabled shell options.  Each word in
+the list is a valid argument for the @option{-o} option to the
+@code{set} builtin command (@pxref{The Set Builtin}).
+The options appearing in @env{SHELLOPTS} are those reported
+as @samp{on} by @samp{set -o}.
+If this variable is in the environment when Bash
+starts up, each shell option in the list will be enabled before
+reading any startup files.  This variable is readonly.
+
+@item 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 SRANDOM
+This variable expands to a 32-bit pseudo-random number each time it is
+referenced. The random number generator is not linear on systems that
+support @file{/dev/urandom} or @code{arc4random}, so each returned number
+has no relationship to the numbers preceding it.
+The random number generator cannot be seeded, so assignments to this
+variable have no effect.
+If @env{SRANDOM}
+is unset, it loses its special properties,
+even if it is subsequently reset.
+
+@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. 
+
+@table @code
+
+@item %%
+A literal @samp{%}.
+
+@item %[@var{p}][l]R
+The elapsed time in seconds. 
+
+@item %[@var{p}][l]U
+The number of CPU seconds spent in user mode. 
+
+@item %[@var{p}][l]S
+The number of CPU seconds spent in system mode. 
+
+@item %P
+The CPU percentage, computed as (%U + %S) / %R. 
+@end table
+
+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. 
+
+The optional @code{l} specifies a longer format, including minutes, of
+the form @var{MM}m@var{SS}.@var{FF}s.
+The value of @var{p} determines whether or not the fraction is included. 
+
+If 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 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.
+
+In an interactive shell, the value is interpreted as
+the number of seconds to wait for a line of input after issuing
+the primary prompt.
+Bash
+terminates after waiting for that number of seconds if a complete
+line of input does not arrive.
+
+@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 UID
+The numeric real user id of the current user.  This variable is readonly.
+
+@end vtable
+
+@node Bash Features
+@chapter Bash Features
+
+This chapter describes features unique to Bash.
+
+@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.
+* Controlling the Prompt::	Customizing the various prompt strings.
+* The Restricted Shell::	A more controlled mode of shell execution.
+* Bash POSIX Mode::		Making Bash behave more closely to what
+				the POSIX standard specifies.
+* Shell Compatibility Mode::	How Bash supports behavior that was present
+				in earlier versions and has changed.
+@end menu
+
+@node Invoking Bash
+@section Invoking Bash
+
+@example
+bash [long-opt] [-ir] [-abefhkmnptuvxdBCDHP] [-o @var{option}]
+    [-O @var{shopt_option}] [@var{argument} @dots{}]
+bash [long-opt] [-abefhkmnptuvxdBCDHP] [-o @var{option}]
+    [-O @var{shopt_option}] -c @var{string} [@var{argument} @dots{}]
+bash [long-opt] -s [-abefhkmnptuvxdBCDHP] [-o @var{option}]
+    [-O @var{shopt_option}] [@var{argument} @dots{}]
+@end example
+
+All of the single-character options used with the @code{set} builtin
+(@pxref{The Set Builtin}) can be used as options when the shell is invoked.
+In addition, there are several multi-character
+options that you can use.  These options must appear on the command
+line before the single-character options to be recognized. 
+
+@table @code
+@item --debugger
+Arrange for the debugger profile to be executed before the shell
+starts.  Turns on extended debugging mode (see @ref{The Shopt Builtin}
+for a description of the @code{extdebug} option to the @code{shopt}
+builtin).
+
+@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 --dump-strings
+Equivalent to @option{-D}.
+
+@item --help
+Display a usage message on standard output and exit successfully.
+
+@item --init-file @var{filename}
+@itemx --rcfile @var{filename}
+Execute commands from @var{filename} (instead of @file{~/.bashrc})
+in an interactive shell.
+
+@item --login
+Equivalent to @option{-l}.
+
+@item --noediting
+Do not use the @sc{gnu} Readline library (@pxref{Command Line Editing})
+to read  command lines when the shell is interactive.
+
+@item --noprofile
+Don't load the system-wide startup file @file{/etc/profile}
+or any of the personal initialization files
+@file{~/.bash_profile}, @file{~/.bash_login}, or @file{~/.profile}
+when Bash is invoked as a login shell.
+
+@item --norc
+Don't read the @file{~/.bashrc} initialization file in an
+interactive shell.  This is on by default if the shell is
+invoked as @code{sh}.
+
+@item --posix
+Change the behavior of Bash where the default operation differs
+from the @sc{posix} standard to match the standard.  This
+is intended to make Bash behave as a strict superset of that
+standard.  @xref{Bash POSIX Mode}, for a description of the Bash
+@sc{posix} mode.
+
+@item --restricted
+Make the shell a restricted shell (@pxref{The Restricted Shell}).
+
+@item --verbose
+Equivalent to @option{-v}.  Print shell input lines as they're read.
+
+@item --version
+Show version information for this instance of
+Bash on the standard output and exit successfully.
+@end table
+
+There are several single-character options that may be supplied at
+invocation which are not available with the @code{set} builtin.
+
+@table @code
+@item -c
+Read and execute commands from the first non-option argument
+@var{command_string}, then exit. 
+If there are arguments after the @var{command_string},
+the first argument is assigned to @code{$0}
+and any remaining arguments are assigned to the positional parameters.
+The assignment to @code{$0} sets the name of the shell, which is used
+in warning and error messages.
+
+@item -i
+Force the shell to run interactively.  Interactive shells are
+described in @ref{Interactive Shells}.
+
+@item -l
+Make this shell act as if it had been directly invoked by login.
+When the shell is interactive, this is equivalent to starting a
+login shell with @samp{exec -l bash}.
+When the shell is not interactive, the login shell startup files will
+be executed.
+@samp{exec bash -l} or @samp{exec bash --login}
+will replace the current shell with a Bash login shell.
+@xref{Bash Startup Files}, for a description of the special behavior
+of a login shell.
+
+@item -r
+Make the shell a restricted shell (@pxref{The Restricted Shell}).
+
+@item -s
+If this option is present, or if no arguments remain after option
+processing, then commands are read from the standard input.
+This option allows the positional parameters to be set
+when invoking an interactive shell or when reading input
+through a pipe.
+
+@item -D
+A list of all double-quoted strings preceded by @samp{$}
+is printed on the standard output.
+These are the strings that
+are subject to language translation when the current locale
+is not @code{C} or @code{POSIX} (@pxref{Locale Translation}).
+This implies the @option{-n} option; no commands will be executed.
+
+@item [-+]O [@var{shopt_option}]
+@var{shopt_option} is one of the shell options accepted by the
+@code{shopt} builtin (@pxref{The Shopt Builtin}).
+If @var{shopt_option} is present, @option{-O} sets the value of that option;
+@option{+O} unsets it.  
+If @var{shopt_option} is not supplied, the names and values of the shell
+options accepted by @code{shopt} are printed on the standard output.
+If the invocation option is @option{+O}, the output is displayed in a format
+that may be reused as input.
+
+@item --
+A @code{--} signals the end of options and disables further option
+processing.
+Any arguments after the @code{--} are treated as filenames and arguments.
+@end table
+
+@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.
+
+@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.
+
+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.
+
+@node Bash Startup Files
+@section Bash Startup Files
+@cindex startup files
+
+This section describes how Bash executes its startup files.
+If any of the files exist but cannot be read, Bash reports an error.
+Tildes are expanded in filenames as described above under
+Tilde Expansion (@pxref{Tilde Expansion}).
+
+Interactive shells are described in @ref{Interactive Shells}.
+
+@subsubheading Invoked as an interactive login shell, or with @option{--login}
+
+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.
+
+When an interactive login shell exits,
+or a non-interactive login shell executes the @code{exit} builtin command,
+Bash reads and executes commands from
+the file @file{~/.bash_logout}, if it exists.
+
+@subsubheading Invoked as an interactive non-login shell
+
+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}.
+
+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.
+
+@subsubheading Invoked non-interactively
+
+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
+filename.
+
+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. 
+
+@subsubheading Invoked with name @code{sh}
+
+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 with its standard input
+connected to a network connection, as when executed by the remote shell
+daemon, usually @code{rshd}, or the secure shell daemon @code{sshd}.
+If Bash determines it is being run in
+this fashion, it reads and executes commands from @file{~/.bashrc}, if that
+file exists and is readable.
+It will not do this if invoked as @code{sh}.
+The @option{--norc} option may be used to inhibit this behavior, and the
+@option{--rcfile} option may be used to force another file to be read, but
+neither @code{rshd} nor @code{sshd} 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 @option{-p} option is not supplied, no startup
+files are read, shell functions are not inherited from the environment,
+the @env{SHELLOPTS}, @env{BASHOPTS}, @env{CDPATH}, and @env{GLOBIGNORE}
+variables, if they appear in the environment, are ignored, and the effective
+user id is set to the real user id.
+If the @option{-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 specifying the @option{-c} option, and
+whose input and error output are both
+connected to terminals (as determined by @code{isatty(3)}),
+or one started with the @option{-i} option.
+
+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:
+
+@example
+case "$-" in
+*i*)	echo This shell is interactive ;;
+*)	echo This shell is not interactive ;;
+esac
+@end example
+
+Alternatively, startup scripts may examine the variable
+@env{PS1}; it is unset in non-interactive shells, and set in
+interactive shells.  Thus:
+
+@example
+if [ -z "$PS1" ]; then
+        echo This shell is not interactive
+else
+        echo This shell is interactive
+fi
+@end example
+
+@node Interactive Shell Behavior
+@subsection Interactive Shell Behavior
+
+When the shell is running interactively, it changes its behavior in
+several ways.
+
+@enumerate
+@item
+Startup files are read and executed as described in @ref{Bash Startup Files}.
+
+@item
+Job Control (@pxref{Job Control}) is enabled by default.  When job
+control is in effect, Bash ignores the keyboard-generated job control
+signals @code{SIGTTIN}, @code{SIGTTOU}, and @code{SIGTSTP}.
+
+@item
+Bash expands and displays @env{PS1} before reading the first line
+of a command, and expands and displays @env{PS2} before reading the
+second and subsequent lines of a multi-line command.
+Bash expands and displays @env{PS0} after it reads a command but before
+executing it.
+See @ref{Controlling the Prompt}, for a complete list of prompt
+string escape sequences.
+
+@item
+Bash executes the values of the set elements of the @env{PROMPT_COMMANDS}
+array variable as commands before printing the primary prompt, @env{$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{$HISTFILE}
+when a shell with history enabled exits.
+
+@item
+Alias expansion (@pxref{Aliases}) is performed by default.
+
+@item
+In the absence of any traps, Bash ignores @code{SIGTERM}
+(@pxref{Signals}).
+
+@item
+In the absence of any traps, @code{SIGINT} is caught and handled
+(@pxref{Signals}).
+@code{SIGINT} will interrupt some shell builtins.
+
+@item
+An interactive login shell sends a @code{SIGHUP} to all jobs on exit
+if the @code{huponexit} shell option has been enabled (@pxref{Signals}).
+
+@item
+The @option{-n} invocation option is ignored, and @samp{set -n} has
+no effect (@pxref{The Set Builtin}).
+
+@item
+Bash will check for mail periodically, depending on the values of the
+@env{MAIL}, @env{MAILPATH}, and @env{MAILCHECK} shell variables
+(@pxref{Bash Variables}).
+
+@item
+Expansion errors due to references to unbound shell variables after
+@samp{set -u} has been enabled will not cause the shell to exit
+(@pxref{The Set Builtin}).
+
+@item
+The shell will not exit on expansion errors caused by @var{var} being unset
+or null in @code{$@{@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{The Shopt Builtin}).
+
+@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{[[} compound command
+and the @code{test} and @code{[} builtin commands. The @code{test}
+and @code{[} commands determine their behavior based on the number
+of arguments; see the descriptions of those commands for any other
+command-specific actions.
+
+Expressions may be unary or binary,
+and are formed from the following primaries.
+Unary expressions are often used to examine the status of a file.
+There are string operators and numeric comparison operators as well.
+Bash handles several filenames specially when they are used in
+expressions.
+If the operating system on which Bash is running provides these
+special files, Bash will use them; otherwise it will emulate them
+internally with this behavior:
+If the @var{file} 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.
+
+When used with @code{[[}, the @samp{<} and @samp{>} operators sort
+lexicographically using the current locale.
+The @code{test} command uses ASCII ordering.
+
+Unless otherwise specified, primaries that operate on files follow symbolic
+links and operate on the target of the link, rather than the link itself.
+
+@table @code
+@item -a @var{file}
+True if @var{file} exists.
+
+@item -b @var{file}
+True if @var{file} exists and is a block special file.
+
+@item -c @var{file}
+True if @var{file} exists and is a character special file.
+
+@item -d @var{file}
+True if @var{file} exists and is a directory.
+
+@item -e @var{file}
+True if @var{file} exists.
+
+@item -f @var{file}
+True if @var{file} exists and is a regular file.
+
+@item -g @var{file}
+True if @var{file} exists and its set-group-id bit is set.
+
+@item -h @var{file}
+True if @var{file} exists and is a symbolic link.
+
+@item -k @var{file}
+True if @var{file} exists and its "sticky" bit is set.
+
+@item -p @var{file}
+True if @var{file} exists and is a named pipe (FIFO).
+
+@item -r @var{file}
+True if @var{file} exists and is readable.
+
+@item -s @var{file}
+True if @var{file} exists and has a size greater than zero.
+
+@item -t @var{fd}
+True if file descriptor @var{fd} is open and refers to a terminal.
+
+@item -u @var{file}
+True if @var{file} exists and its set-user-id bit is set.
+
+@item -w @var{file}
+True if @var{file} exists and is writable.
+
+@item -x @var{file}
+True if @var{file} exists and is executable.
+
+@item -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 -N @var{file}
+True if @var{file} exists and has been modified since it was last read.
+
+@item -O @var{file}
+True if @var{file} exists and is owned by the effective user id.
+
+@item -S @var{file}
+True if @var{file} exists and is a socket.
+
+@item @var{file1} -ef @var{file2}
+True if @var{file1} and @var{file2} refer to the same device and
+inode numbers.
+
+@item @var{file1} -nt @var{file2}
+True if @var{file1} is newer (according to modification date)
+than @var{file2}, or if @var{file1} exists and @var{file2} does not.
+
+@item @var{file1} -ot @var{file2}
+True if @var{file1} is older than @var{file2},
+or if @var{file2} exists and @var{file1} does not.
+
+@item -o @var{optname}
+True if the shell option @var{optname} is enabled.
+The list of options appears in the description of the @option{-o}
+option to the @code{set} builtin (@pxref{The Set Builtin}).
+
+@item -v @var{varname}
+True if the shell variable @var{varname} is set (has been assigned a value).
+
+@item -R @var{varname}
+True if the shell variable @var{varname} is set and is a name reference.
+
+@item -z @var{string}
+True if the length of @var{string} is zero.
+
+@item -n @var{string}
+@itemx @var{string}
+True if the length of @var{string} is non-zero.
+
+@item @var{string1} == @var{string2}
+@itemx @var{string1} = @var{string2}
+True if the strings are equal.
+When used with the @code{[[} command, this performs pattern matching as
+described above (@pxref{Conditional Constructs}).
+
+@samp{=} should be used with the @code{test} command for @sc{posix} conformance.
+
+@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.
+
+@item @var{string1} > @var{string2}
+True if @var{string1} sorts after @var{string2} lexicographically.
+
+@item @var{arg1} OP @var{arg2}
+@code{OP} is one of 
+@samp{-eq}, @samp{-ne}, @samp{-lt}, @samp{-le}, @samp{-gt}, or @samp{-ge}.
+These arithmetic binary operators return true if @var{arg1}
+is equal to, not equal to, less than, less than or equal to,
+greater than, or greater than or equal to @var{arg2},
+respectively.  @var{Arg1} and @var{arg2}
+may be positive or negative integers.
+When used with the @code{[[} command, @var{Arg1} and @var{Arg2}
+are evaluated as arithmetic expressions (@pxref{Shell Arithmetic}).
+@end table
+
+@node Shell Arithmetic
+@section Shell Arithmetic
+@cindex arithmetic, shell
+@cindex shell arithmetic
+@cindex expressions, arithmetic
+@cindex evaluation, arithmetic
+@cindex arithmetic evaluation
+
+The shell allows arithmetic expressions to be evaluated, as one of
+the shell expansions or by using the @code{((} compound command, the
+@code{let} builtin, or the @option{-i} option to the @code{declare} builtin.
+
+Evaluation is done in fixed-width integers with no check for overflow,
+though division by 0 is trapped and flagged as an error.
+The operators and their precedence, associativity, and values
+are the same as in the C language.
+The following list of operators is grouped into levels of
+equal-precedence operators.
+The levels are listed in order of decreasing precedence. 
+
+@table @code
+
+@item @var{id}++ @var{id}--
+variable post-increment and post-decrement 
+
+@item ++@var{id} --@var{id}
+variable pre-increment and pre-decrement
+
+@item - +
+unary minus and plus
+
+@item ! ~
+logical and bitwise negation
+
+@item **
+exponentiation
+
+@item * / %
+multiplication, division, remainder
+
+@item + -
+addition, subtraction
+
+@item << >>
+left and right bitwise shifts
+
+@item <= >= < >
+comparison
+
+@item == !=
+equality and inequality
+
+@item &
+bitwise AND
+
+@item ^
+bitwise exclusive OR
+
+@item |
+bitwise OR
+
+@item &&
+logical AND
+
+@item ||
+logical OR
+
+@item expr ? expr : expr
+conditional operator
+
+@item = *= /= %= += -= <<= >>= &= ^= |=
+assignment
+
+@item expr1 , expr2
+comma
+@end table
+
+Shell variables are allowed as operands; parameter expansion is
+performed before the expression is evaluated. 
+Within an expression, shell variables may also be referenced by name
+without using the parameter expansion syntax.
+A shell variable that is null or unset evaluates to 0 when referenced
+by name without using the parameter expansion syntax.
+The value of a variable is evaluated as an arithmetic expression
+when it is referenced, or when a variable which has been given the  
+@var{integer} attribute using @samp{declare -i} is assigned a value.
+A null value evaluates to 0.
+A shell variable need not have its @var{integer} attribute turned on
+to be used in an expression.
+
+Integer constants follow the C language definition, without suffixes or
+character constants.
+Constants with a leading 0 are interpreted as octal numbers.
+A leading @samp{0x} or @samp{0X} denotes hexadecimal.  Otherwise,
+numbers take the form [@var{base}@code{#}]@var{n}, where the optional @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.
+When specifying @var{n},
+if a non-digit is required,
+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
+@var{blank}, then the next command word following the
+alias is also checked for alias expansion.
+
+Aliases are created and listed with the @code{alias}
+command, and removed with the @code{unalias} command.
+
+There is no mechanism for using arguments in the replacement text,
+as in @code{csh}.
+If arguments are needed, a shell function should be used
+(@pxref{Shell Functions}).
+
+Aliases are not expanded when the shell is not interactive,
+unless the @code{expand_aliases} shell option is set using
+@code{shopt} (@pxref{The Shopt Builtin}).
+
+The rules concerning the definition and use of aliases are
+somewhat confusing. Bash
+always reads at least one complete line of input,
+and all lines that make up a compound command,
+before executing any of the commands on that line or the compound command.
+Aliases are expanded when a
+command is read, not when it is executed.  Therefore, an
+alias definition appearing on the same line as another
+command does not take effect until the next line of input is read.
+The commands following the alias definition
+on that line are not affected by the new alias.
+This behavior is also an issue when functions are executed.
+Aliases are expanded when a function definition is read,
+not when the function is executed, because a function definition
+is itself a command.  As a consequence, aliases
+defined in a function are not available until after that
+function is executed.  To be safe, always put
+alias definitions on a separate line, and do not use @code{alias}
+in compound commands.
+
+For almost every purpose, shell functions are preferred over aliases.
+
+@node Arrays
+@section Arrays
+@cindex arrays
+
+Bash provides one-dimensional indexed and associative array variables.
+Any variable may be used as an indexed array;
+the @code{declare} builtin will explicitly declare an array.
+There is no maximum
+limit on the size of an array, nor any requirement that members
+be indexed or assigned contiguously.
+Indexed arrays are referenced using integers (including arithmetic
+expressions (@pxref{Shell Arithmetic})) and are zero-based;
+associative arrays use arbitrary strings.
+Unless otherwise noted, indexed array indices must be non-negative integers.
+
+An indexed array is created automatically if any variable is assigned to
+using the syntax
+@example
+@var{name}[@var{subscript}]=@var{value}
+@end example
+
+@noindent
+The @var{subscript}
+is treated as an arithmetic expression that must evaluate to a number.
+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.
+
+@noindent
+Associative arrays are created using
+@example
+declare -A @var{name}
+@end example
+
+Attributes may be
+specified for an array variable using the @code{declare} and
+@code{readonly} builtins.  Each attribute applies to all members of
+an array.
+
+Arrays are assigned to using compound assignments of the form
+@example
+@var{name}=(@var{value1} @var{value2} @dots{} )
+@end example
+@noindent
+where each
+@var{value} may be of the form @code{[@var{subscript}]=}@var{string}.
+Indexed array assignments do not require anything but @var{string}.
+When assigning to indexed arrays, if
+the optional subscript is supplied, that index is assigned to;
+otherwise the index of the element assigned is the last index assigned
+to by the statement plus one.  Indexing starts at zero.
+
+Each @var{value} in the list undergoes all the shell expansions
+described above (@pxref{Shell Expansions}).
+
+When assigning to an associative array, the words in a compound assignment
+may be either assignment statements, for which the subscript is required,
+or a list of words that is interpreted as a sequence of alternating keys
+and values:
+@var{name}=(@var{key1} @var{value1} @var{key2} @var{value2} @dots{} ).
+These are treated identically to
+@var{name}=( [@var{key1}]=@var{value1} [@var{key2}]=@var{value2} @dots{} ).
+The first word in the list determines how the remaining words
+are interpreted; all assignments in a list must be of the same type.
+When using key/value pairs, the keys may not be missing or empty;
+a final missing value is treated like the empty string.
+
+This syntax is also accepted by the @code{declare}
+builtin.  Individual array elements may be assigned to using the
+@code{@var{name}[@var{subscript}]=@var{value}} syntax introduced above.
+
+When assigning to an indexed array, if @var{name}
+is subscripted by a negative number, that number is
+interpreted as relative to one greater than the maximum index of
+@var{name}, so negative indices count back from the end of the
+array, and an index of -1 references the last element.
+
+Any element of an array may be referenced using
+@code{$@{@var{name}[@var{subscript}]@}}.
+The braces are required to avoid
+conflicts with the shell's filename expansion operators.  If the
+@var{subscript} is @samp{@@} or @samp{*}, the word expands to all members
+of the array @var{name}.  These subscripts differ only when the word
+appears within double quotes.
+If the word is double-quoted,
+@code{$@{@var{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{$@{@var{name}[@@]@}} expands each element of
+@var{name} to a separate word.  When there are no array members,
+@code{$@{@var{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{$@{#@var{name}[@var{subscript}]@}} expands to the length of
+@code{$@{@var{name}[@var{subscript}]@}}.
+If @var{subscript} is @samp{@@} or
+@samp{*}, the expansion is the number of elements in the array. 
+If the @var{subscript}
+used to reference an element of an indexed array
+evaluates to a number less than zero, it is
+interpreted as relative to one greater than the maximum index of the array,
+so negative indices count back from the end of the array,
+and an index of -1 refers to the last element.
+
+Referencing an array variable without a subscript is equivalent to
+referencing with a subscript of 0.
+Any reference to a variable using a valid subscript is legal, and
+@code{bash} will create an array if necessary.
+
+An array variable is considered set if a subscript has been assigned a
+value.  The null string is a valid value.
+
+It is possible to obtain the keys (indices) of an array as well as the values.
+$@{!@var{name}[@@]@} and $@{!@var{name}[*]@} expand to the indices
+assigned in array variable @var{name}.
+The treatment when in double quotes is similar to the expansion of the
+special parameters @samp{@@} and @samp{*} within double quotes.
+
+The @code{unset} builtin is used to destroy arrays.
+@code{unset @var{name}[@var{subscript}]}
+destroys the array element at index @var{subscript}.
+Negative subscripts to indexed arrays are interpreted as described above.
+Unsetting the last element of an array variable does not unset the variable.
+@code{unset @var{name}}, where @var{name} is an array, removes the
+entire array.  A subscript of @samp{*} or @samp{@@} also removes the
+entire array.
+
+When using a variable name with a subscript as an argument to a command,
+such as with @code{unset}, without using the word expansion syntax
+described above, the argument is subject to the shell's filename expansion.
+If filename expansion is not desired, the argument should be quoted.
+
+The @code{declare}, @code{local}, and @code{readonly}
+builtins each accept a @option{-a} option to specify an indexed
+array and a @option{-A} option to specify an associative array.
+If both options are supplied, @option{-A} takes precedence.
+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 current directory is always the "top"
+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 [-clpv] [+@var{N} | -@var{N}]
+@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.
+The current directory is always the first directory in the stack.
+
+@table @code
+@item -c
+Clears the directory stack by deleting all of the elements.
+@item -l
+Produces a listing using full pathnames;
+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.
+@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.
+@end table
+
+@item popd
+@btindex popd
+@example
+popd [-n] [+@var{N} | -@var{N}]
+@end example
+
+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}; that is, @code{popd} is equivalent to @code{popd +0}.
+
+@table @code
+@item -n
+Suppresses the normal change of directory when removing directories
+from the stack, so that only the stack is manipulated.
+@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.
+@end table
+
+@btindex pushd
+@item pushd
+@example
+pushd [-n] [@var{+N} | @var{-N} | @var{dir}]
+@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
+and makes the new top the current directory.
+
+@table @code
+@item -n
+Suppresses the normal change of directory when rotating or
+adding directories to the stack, so that only the stack is manipulated.
+@item +@var{N}
+Brings the @var{N}th directory (counting from the left of the
+list printed by @code{dirs}, starting with zero) to the top of
+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 @var{dir}
+Makes @var{dir} be the top of the stack, making
+it the new current directory as if it had been supplied as an argument
+to the @code{cd} builtin.
+@end table
+@end table
+
+@node Controlling the Prompt
+@section Controlling the Prompt
+@cindex prompting
+
+Bash examines the value of the array variable @env{PROMPT_COMMANDS} just before
+printing each primary prompt.
+If any elements in  @env{PROMPT_COMMANDS} are set and non-null, Bash
+executes each value, in numeric order,
+just as if it had been typed on the command line.
+
+In addition, the following table describes the special characters which
+can appear in the prompt variables @env{PS0}, @env{PS1}, @env{PS2}, and
+@env{PS4}:
+
+@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
+(uses the @env{$PROMPT_DIRTRIM} variable).
+@item \W
+The basename of @env{$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{The Shopt Builtin}).
+This can have unwanted side effects if escaped portions of the string
+appear within command substitution or contain characters special to
+word expansion.
+
+@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{HISTFILE},
+@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 @code{history}
+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
+
+These restrictions are enforced after any startup files are read.
+
+When a command that is found to be a shell script is executed
+(@pxref{Shell Scripts}), @code{rbash} turns off any restrictions in
+the shell spawned to execute the script.
+
+The restricted shell mode is only one component of a useful restricted
+environment. It should be accompanied by setting @env{PATH} to a value
+that allows execution of only a few verified commands (commands that
+allow shell escapes are particularly vulnerable), leaving the user
+in a non-writable directory other than his home directory after login,
+not allowing the restricted shell to execute shell scripts, and cleaning
+the environment of variables that cause some commands to modify their
+behavior (e.g., @env{VISUAL} or @env{PAGER}).
+
+Modern systems provide more secure ways to implement a restricted environment,
+such as @code{jails}, @code{zones}, or @code{containers}.
+
+
+@node Bash POSIX Mode
+@section Bash POSIX Mode
+@cindex POSIX Mode
+
+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} standard by changing the behavior to
+match that specified by @sc{posix} in areas where the Bash default differs.
+
+When invoked as @code{sh}, Bash enters @sc{posix} mode after reading the
+startup files.
+
+The following list is what's changed when `@sc{posix} mode' is in effect:
+
+@enumerate
+@item
+Bash ensures that the @env{POSIXLY_CORRECT} variable is set.
+
+@item
+When a command in the hash table no longer exists, Bash will re-search
+@env{$PATH} to find the new location.  This is also available with
+@samp{shopt -s checkhash}.
+
+@item
+Bash will not insert a command without the execute bit set into the
+command hash table, even if it returns it as a (last-ditch) result
+from a @env{$PATH} search.
+
+@item
+The message printed by the job control code and builtins when a job
+exits with a non-zero status is `Done(status)'.
+
+@item
+The message printed by the job control code and builtins when a job
+is stopped is `Stopped(@var{signame})', where @var{signame} is, for
+example, @code{SIGTSTP}.
+
+@item
+Alias expansion is always enabled, even in non-interactive shells.
+
+@item
+Reserved words appearing in a context where reserved words are recognized
+do not undergo alias expansion.
+
+@item
+The @sc{posix} @env{PS1} and @env{PS2} expansions of @samp{!} to
+the history number and @samp{!!} to @samp{!} are enabled,
+and parameter expansion is performed on the values of @env{PS1} and
+@env{PS2} regardless of the setting of the @code{promptvars} option.
+
+@item
+The @sc{posix} startup files are executed (@env{$ENV}) rather than
+the normal Bash files.
+
+@item
+Tilde expansion is only performed on assignments preceding a command
+name, rather than on all assignment statements on the line.
+
+@item
+The default history file is @file{~/.sh_history} (this is the
+default value of @env{$HISTFILE}).
+
+@item
+Redirection operators do not perform filename expansion on the word
+in the redirection unless the shell is interactive.
+
+@item
+Redirection operators do not perform word splitting on the word in the
+redirection.
+
+@item
+Function names must be valid shell @code{name}s.  That is, they may not
+contain characters other than letters, digits, and underscores, and
+may not start with a digit.  Declaring a function with an invalid name
+causes a fatal syntax error in non-interactive shells.
+
+@item
+Function names may not be the same as one of the @sc{posix} special
+builtins.
+
+@item
+@sc{posix} special builtins are found before shell functions
+during command lookup.
+
+@item
+When printing shell function definitions (e.g., by @code{type}), Bash does
+not print the @code{function} keyword.
+
+@item
+Literal tildes that appear as the first character in elements of
+the @env{PATH} variable are not expanded as described above
+under @ref{Tilde Expansion}.
+
+@item
+The @code{time} reserved word may be used by itself as a command.  When
+used in this way, it displays timing statistics for the shell and its
+completed children.  The @env{TIMEFORMAT} variable controls the format
+of the timing information.
+
+@item
+When parsing and expanding a $@{@dots{}@} expansion that appears within
+double quotes, single quotes are no longer special and cannot be used to
+quote a closing brace or other special character, unless the operator is
+one of those defined to perform pattern removal.  In this case, they do
+not have to appear as matched pairs.
+
+@item
+The parser does not recognize @code{time} as a reserved word if the next
+token begins with a @samp{-}.
+
+@ignore
+@item
+When parsing @code{$()} command substitutions containing here-documents,
+the parser does not allow a here-document to be delimited by the closing
+right parenthesis. The newline after the here-document delimiter is required.
+@end ignore
+
+@item
+The @samp{!} character does not introduce history expansion within a
+double-quoted string, even if the @code{histexpand} option is enabled.
+
+@item
+If a @sc{posix} special builtin returns an error status, a
+non-interactive shell exits.  The fatal errors are those listed in
+the @sc{posix} standard, and include things like passing incorrect options,
+redirection errors, variable assignment errors for assignments preceding
+the command name, and so on.
+
+@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 a variable
+assignment error occurs in an assignment statement preceding a special
+builtin, but not with any other simple command.
+
+@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
+Non-interactive shells exit if @var{filename} in @code{.} @var{filename}
+is not found.
+
+@item
+Non-interactive shells exit if a syntax error in an arithmetic expansion
+results in an invalid expression.
+
+@item
+Non-interactive shells exit if a parameter expansion error occurs.
+
+@item
+Non-interactive shells exit if there is a syntax error in a script read
+with the @code{.} or @code{source} builtins, or in a string processed by
+the @code{eval} builtin.
+
+@item
+While variable indirection is available, it may not be applied to the
+@samp{#} and @samp{?} special parameters.
+
+@item
+When expanding the @samp{*} special parameter in a pattern context where the
+expansion is double-quoted does not treat the @code{$*} as if it were
+double-quoted.
+
+@item
+Assignment statements preceding @sc{posix} special builtins
+persist in the shell environment after the builtin completes.
+
+@item
+The @code{command} builtin does not prevent builtins that take assignment
+statements as arguments from expanding them as assignment statements;
+when not in @sc{posix} mode, assignment builtins lose their assignment
+statement expansion properties when preceded by @code{command}.
+
+@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
+The output of @samp{kill -l} prints all the signal names on a single line,
+separated by spaces, without the @samp{SIG} prefix.
+
+@item
+The @code{kill} builtin does not accept signal names with a @samp{SIG}
+prefix.
+
+@item
+The @code{export} and @code{readonly} builtin commands display their
+output in the format required by @sc{posix}.
+
+@item
+The @code{trap} builtin displays signal names without the leading
+@code{SIG}.
+
+@item
+The @code{trap} builtin doesn't check the first argument for a possible
+signal specification and revert the signal handling to the original
+disposition if it is, unless that argument consists solely of digits and
+is a valid signal number.  If users want to reset the handler for a given
+signal to the original disposition, they should use @samp{-} as the
+first argument.
+
+@item
+@code{trap -p} displays signals whose dispositions are set to SIG_DFL and
+those that were ignored when the shell started.
+
+@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
+Enabling @sc{posix} mode has the effect of setting the
+@code{inherit_errexit} option, so
+subshells spawned to execute command substitutions inherit the value of
+the @option{-e} option from the parent shell.
+When the @code{inherit_errexit} option is not enabled,
+Bash clears the @option{-e} option in such subshells.
+
+@item
+Enabling @sc{posix} mode has the effect of setting the
+@code{shift_verbose} option, so numeric arguments to @code{shift}
+that exceed the number of positional parameters will result in an
+error message.
+
+@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{cd} builtin cannot change a directory because the
+length of the pathname 
+constructed from @code{$PWD} and the directory name supplied as an argument
+exceeds @var{PATH_MAX} when all symbolic links are expanded, @code{cd} will
+fail instead of attempting to use only the supplied directory name.
+
+@item
+The @code{pwd} builtin verifies that the value it prints is the same as the
+current directory, even if it is not asked to check the file system with the
+@option{-P} option.
+
+@item
+When listing the history, the @code{fc} builtin does not include an
+indication of whether or not a history entry has been modified.
+
+@item
+The default editor used by @code{fc} is @code{ed}.
+
+@item
+The @code{type} and @code{command} builtins will not report a non-executable
+file as having been found, though the shell will attempt to execute such a
+file if it is the only so-named file found in @code{$PATH}.
+
+@item
+The @code{vi} editing mode will invoke the @code{vi} editor directly when
+the @samp{v} command is run, instead of checking @code{$VISUAL} and
+@code{$EDITOR}.
+
+@item
+When the @code{xpg_echo} option is enabled, Bash does not attempt to interpret
+any arguments to @code{echo} as options.  Each argument is displayed, after
+escape characters are converted.
+
+@item
+The @code{ulimit} builtin uses a block size of 512 bytes for the @option{-c}
+and @option{-f} options.
+
+@item
+The arrival of @code{SIGCHLD}  when a trap is set on @code{SIGCHLD} does
+not interrupt the @code{wait} builtin and cause it to return immediately.
+The trap command is run once for each child that exits.
+
+@item
+The @code{read} builtin may be interrupted by a signal for which a trap
+has been set.
+If Bash receives a trapped signal while executing @code{read}, the trap
+handler executes and @code{read} returns an exit status greater than 128.
+
+@item
+Bash removes an exited background process's status from the list of such
+statuses after the @code{wait} builtin is used to obtain it.
+
+@end enumerate
+
+There is other @sc{posix} behavior that Bash does not implement by
+default even when in @sc{posix} mode.
+Specifically:
+
+@enumerate
+
+@item
+The @code{fc} builtin checks @code{$EDITOR} as a program to edit history
+entries if @code{FCEDIT} is unset, rather than defaulting directly to
+@code{ed}.  @code{fc} uses @code{ed} if @code{EDITOR} is unset.
+
+@item
+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 Shell Compatibility Mode
+@section Shell Compatibility Mode
+@cindex Compatibility Level
+@cindex Compatibility Mode
+
+Bash-4.0 introduced the concept of a `shell compatibility level', specified
+as a set of options to the shopt builtin
+(@code{compat31},
+@code{compat32},
+@code{compat40},
+@code{compat41},
+and so on).
+There is only one current
+compatibility level -- each option is mutually exclusive.
+The compatibility level is intended to allow users to select behavior
+from previous versions that is incompatible with newer versions
+while they migrate scripts to use current features and
+behavior. It's intended to be a temporary solution.
+
+This section does not mention behavior that is standard for a particular
+version (e.g., setting @code{compat32} means that quoting the rhs of the regexp
+matching operator quotes special regexp characters in the word, which is
+default behavior in bash-3.2 and above). 
+
+If a user enables, say, @code{compat32}, it may affect the behavior of other
+compatibility levels up to and including the current compatibility level.
+The idea is that each compatibility level controls behavior that changed
+in that version of Bash,
+but that behavior may have been present in earlier versions.
+For instance, the change to use locale-based comparisons with the @code{[[}
+command came in bash-4.1, and earlier versions used ASCII-based comparisons,
+so enabling @code{compat32} will enable ASCII-based comparisons as well.
+That granularity may not be sufficient for
+all uses, and as a result users should employ compatibility levels carefully.
+Read the documentation for a particular feature to find out the
+current behavior.
+
+Bash-4.3 introduced a new shell variable: @env{BASH_COMPAT}.
+The value assigned
+to this variable (a decimal version number like 4.2, or an integer
+corresponding to the @code{compat}@var{NN} option, like 42) determines the
+compatibility level.
+
+Starting with bash-4.4, Bash has begun deprecating older compatibility
+levels.
+Eventually, the options will be removed in favor of @env{BASH_COMPAT}.
+
+Bash-5.0 is the final version for which there will be an individual shopt
+option for the previous version. Users should use @env{BASH_COMPAT}
+on bash-5.0 and later versions.
+
+The following table describes the behavior changes controlled by each
+compatibility level setting.
+The @code{compat}@var{NN} tag is used as shorthand for setting the
+compatibility level
+to @var{NN} using one of the following mechanisms.
+For versions prior to bash-5.0, the compatibility level may be set using
+the corresponding @code{compat}@var{NN} shopt option.
+For bash-4.3 and later versions, the @env{BASH_COMPAT} variable is preferred,
+and it is required for bash-5.1 and later versions.
+
+@table @code
+@item compat31
+@itemize @bullet
+@item
+quoting the rhs of the @code{[[} command's regexp matching operator (=~)
+has no special effect
+@end itemize
+
+@item compat32
+@itemize @bullet
+@item
+interrupting a command list such as "a ; b ; c" causes the execution
+of the next command in the list (in bash-4.0 and later versions,
+the shell acts as if it received the interrupt, so
+interrupting one command in a list aborts the execution of the
+entire list)
+@end itemize
+
+@item compat40
+@itemize @bullet
+@item
+the @samp{<} and @samp{>} operators to the @code{[[} command do not
+consider the current locale when comparing strings; they use ASCII
+ordering.
+Bash versions prior to bash-4.1 use ASCII collation and strcmp(3);
+bash-4.1 and later use the current locale's collation sequence and
+strcoll(3).
+@end itemize
+
+@item compat41
+@itemize @bullet
+@item
+in posix mode, @code{time} may be followed by options and still be
+recognized as a reserved word (this is @sc{posix} interpretation 267)
+@item
+in posix mode, the parser requires that an even number of single
+quotes occur in the @var{word} portion of a double-quoted $@{@dots{}@}
+parameter expansion and treats them specially, so that characters within
+the single quotes are considered quoted
+(this is @sc{posix} interpretation 221)
+@end itemize
+
+@item compat42
+@itemize @bullet
+@item
+the replacement string in double-quoted pattern substitution does not
+undergo quote removal, as it does in versions after bash-4.2
+@item
+in posix mode, single quotes are considered special when expanding
+the @var{word} portion of a double-quoted $@{@dots{}@} parameter expansion
+and can be used to quote a closing brace or other special character
+(this is part of @sc{posix} interpretation 221);
+in later versions, single quotes
+are not special within double-quoted word expansions
+@end itemize
+
+@item compat43
+@itemize @bullet
+@item
+the shell does not print a warning message if an attempt is made to
+use a quoted compound assignment as an argument to declare
+(declare -a foo='(1 2)'). Later versions warn that this usage is
+deprecated
+@item
+word expansion errors are considered non-fatal errors that cause the
+current command to fail, even in posix mode
+(the default behavior is to make them fatal errors that cause the shell
+to exit)
+@item
+when executing a shell function, the loop state (while/until/etc.)
+is not reset, so @code{break} or @code{continue} in that function will break
+or continue loops in the calling context. Bash-4.4 and later reset
+the loop state to prevent this
+@end itemize
+
+@item compat44
+@itemize @bullet
+@item
+the shell sets up the values used by @env{BASH_ARGV} and @env{BASH_ARGC}
+so they can expand to the shell's positional parameters even if extended
+debugging mode is not enabled
+@item
+a subshell inherits loops from its parent context, so @code{break}
+or @code{continue} will cause the subshell to exit.
+Bash-5.0 and later reset the loop state to prevent the exit
+@item
+variable assignments preceding builtins like @code{export} and @code{readonly}
+that set attributes continue to affect variables with the same
+name in the calling environment even if the shell is not in posix
+mode
+@end itemize
+
+@item compat50 (set using BASH_COMPAT)
+@itemize @bullet
+@item
+Bash-5.1 changed the way @code{$RANDOM} is generated to introduce slightly
+more randomness. If the shell compatibility level is set to 50 or
+lower, it reverts to the method from bash-5.0 and previous versions,
+so seeding the random number generator by assigning a value to
+@env{RANDOM} will produce the same sequence as in bash-5.0
+@item
+If the command hash table is empty, Bash versions prior to bash-5.1
+printed an informational message to that effect, even when producing
+output that can be reused as input. Bash-5.1 suppresses that message
+when the @option{-l} option is supplied.
+@end itemize
+@end table
+
+@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 operating system kernel'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, if
+the user so specifies with @code{stty tostop}, write to the terminal.
+Background processes which attempt to
+read from (write to when @code{stty tostop} is in effect) the
+terminal are sent a @code{SIGTTIN} (@code{SIGTTOU})
+signal by the kernel's terminal driver,
+which, unless caught, suspends the process. 
+
+If the operating system on which Bash is running supports
+job control, Bash contains facilities to use it.  Typing the
+@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. 
+
+There are a number of ways to refer to a job in the shell.  The
+character @samp{%} introduces a job specification (@var{jobspec}).
+
+Job number @code{n} may be referred to as @samp{%n}.
+The symbols @samp{%%} and  @samp{%+} refer to the shell's notion of the
+current job, which is the last job stopped while it was in the foreground
+or started in the background.
+A single @samp{%} (with no accompanying job specification) also refers
+to the current job.
+The previous job may be referenced using @samp{%-}.
+If there is only a single job, @samp{%+} and @samp{%-} can both be used
+to refer to that job.
+In output pertaining to jobs (e.g., the output of the @code{jobs}
+command), the current job is always flagged with a @samp{+}, and the
+previous job with a @samp{-}. 
+
+A job may also be referred to
+using a prefix of the name used to start it, or using a substring
+that appears in its command line.  For example, @samp{%ce} refers
+to a stopped job whose command name begins with @samp{ce}.
+Using @samp{%?ce}, on the
+other hand, refers to any job containing the string @samp{ce} in
+its command line.  If the prefix or substring matches more than one job,
+Bash reports an error.
+
+Simply naming a job can be used to bring it into the foreground:
+@samp{%1} is a synonym for @samp{fg %1}, bringing job 1 from the
+background into the foreground.  Similarly, @samp{%1 &} resumes
+job 1 in the background, equivalent to @samp{bg %1}
+
+The shell learns immediately whenever a job changes state. 
+Normally, Bash waits until it is about to print a prompt
+before reporting changes in a job's status so as to not interrupt
+any other output.
+If the @option{-b} option to the @code{set} builtin is enabled,
+Bash reports such changes immediately (@pxref{The Set Builtin}).
+Any trap on @code{SIGCHLD} is executed for each child process
+that exits.
+
+If an attempt to exit Bash is made while jobs are stopped, (or running, if
+the @code{checkjobs} option is enabled -- see @ref{The Shopt Builtin}), the
+shell prints a warning message, and if the @code{checkjobs} option is
+enabled, lists the jobs and their statuses.
+The @code{jobs} command may then be used to inspect their status.
+If a second attempt to exit is made without an intervening command,
+Bash does not print another warning, and any stopped jobs are terminated.
+
+When the shell is waiting for a job or process using the @code{wait}
+builtin, and job control is enabled, @code{wait} will return when the
+job changes state. The @option{-f} option causes @code{wait} to wait
+until the job or process terminates before returning.
+
+@node Job Control Builtins
+@section Job Control Builtins
+
+@table @code
+
+@item bg
+@btindex bg
+@example
+bg [@var{jobspec} @dots{}]
+@end example
+
+Resume each suspended job @var{jobspec} in the background, as if it
+had been started with @samp{&}.
+If @var{jobspec} is not supplied, the current job is used.
+The return status is zero unless it is run when job control is not
+enabled, or, when run with job control enabled, any
+@var{jobspec} was not found or specifies a job
+that was started without job control.
+
+@item fg
+@btindex fg
+@example
+fg [@var{jobspec}]
+@end example
+
+Resume the job @var{jobspec} in the foreground and make it the current job.
+If @var{jobspec} is not supplied, the current job is used.
+The return status is that of the command placed into the foreground,
+or non-zero if run when job control is disabled or, when run with
+job control enabled, @var{jobspec} does not specify a valid job or
+@var{jobspec} specifies a job that was started without job control.
+
+@item jobs
+@btindex jobs
+@example
+jobs [-lnprs] [@var{jobspec}]
+jobs -x @var{command} [@var{arguments}]
+@end example
+
+The first form lists the active jobs.  The options have the
+following meanings:
+
+@table @code
+@item -l
+List process @sc{id}s in addition to the normal information.
+
+@item -n
+Display information only about jobs that have changed status since
+the user was last notified of their status.
+
+@item -p
+List only the process @sc{id} of the job's process group leader.
+
+@item -r
+Display only running jobs.
+
+@item -s
+Display only stopped jobs.
+@end table
+
+If @var{jobspec} is given,
+output is restricted to information about that job. 
+If @var{jobspec} is not supplied, the status of all jobs is
+listed.
+
+If the @option{-x} option is supplied, @code{jobs} replaces any
+@var{jobspec} found in @var{command} or @var{arguments} with the
+corresponding process group @sc{id}, and executes @var{command},
+passing it @var{argument}s, returning its exit status. 
+
+@item kill
+@btindex kill
+@example
+kill [-s @var{sigspec}] [-n @var{signum}] [-@var{sigspec}] @var{jobspec} or @var{pid}
+kill -l|-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 @option{-L} option is equivalent to @option{-l}.
+The return status is zero if at least one signal was successfully sent,
+or non-zero if an error occurs or an invalid option is encountered.
+
+@item wait
+@btindex wait
+@example
+wait [-fn] [-p @var{varname}] [@var{jobspec} or @var{pid} @dots{}]
+@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,
+@code{wait} waits for all running background jobs and
+the last-executed process substitution, if its process id is the same as
+@var{$!},
+and the return status is zero.
+If the @option{-n} option is supplied, @code{wait} waits for a single job
+from the list of @var{pids} or @var{jobspecs} or, if no arguments are
+supplied, any job, 
+to complete and returns its exit status.
+If none of the supplied arguments is a child of the shell, or if no arguments
+are supplied and the shell has no unwaited-for children, the exit status
+is 127.
+If the @option{-p} option is supplied, the process or job identifier of the job
+for which the exit status is returned is assigned to the variable
+@var{varname} named by the option argument.
+The variable will be unset initially, before any assignment.
+This is useful only when the @option{-n} option is supplied.
+Supplying the @option{-f} option, when job control is enabled,
+forces @code{wait} to wait for each @var{pid} or @var{jobspec} to
+terminate before returning its status, intead of returning when it changes
+status.
+If neither @var{jobspec} nor @var{pid} specifies an active child process
+of the shell, the return status is 127.
+
+@item disown
+@btindex disown
+@example
+disown [-ar] [-h] [@var{jobspec} @dots{} | @var{pid} @dots{} ]
+@end example
+
+Without options, remove each @var{jobspec} 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 the
+@option{-r} option is supplied, the current job is used.
+If no @var{jobspec} is supplied, the @option{-a} option means to remove or
+mark all jobs; the @option{-r} option without a @var{jobspec}
+argument restricts operation to running jobs.
+
+@item suspend
+@btindex suspend
+@example
+suspend [-f]
+@end example
+
+Suspend the execution of this shell until it receives a
+@code{SIGCONT} signal.
+A login shell cannot be suspended; the @option{-f}
+option can be used to override this and force the suspension.
+@end table
+
+When job control is not active, the @code{kill} and @code{wait}
+builtins do not accept @var{jobspec} arguments.  They must be
+supplied process @sc{id}s.
+
+@node Job Control Variables
+@section Job Control Variables
+
+@vtable @code
+
+@item auto_resume
+This variable controls how the shell interacts with the user and
+job control.  If this variable exists then single word simple
+commands without redirections are treated as candidates for resumption
+of an existing job.  There is no ambiguity allowed; if there is
+more than one job beginning with the string typed, then
+the most recently accessed job will be selected.
+The name of a stopped job, in this context, is the command line
+used to start it.  If this variable is set to the value @samp{exact},
+the string supplied must match the name of a stopped job exactly;
+if set to @samp{substring},
+the string supplied needs to match a substring of the name of a
+stopped job.  The @samp{substring} value provides functionality
+analogous to the @samp{%?} job @sc{id} (@pxref{Job Control Basics}).
+If set to any other value, the supplied string must
+be a prefix of a stopped job's name; this provides functionality
+analogous to the @samp{%} job @sc{id}.
+
+@end vtable
+
+@set readline-appendix
+@set history-appendix
+@cindex Readline, how to use
+@include rluser.texi
+@cindex History, how to use
+@include hsuser.texi
+@clear readline-appendix
+@clear history-appendix
+
+@node Installing Bash
+@chapter Installing Bash
+
+This chapter provides basic instructions for installing Bash on
+the various supported platforms.  The distribution supports the
+@sc{gnu} operating systems, nearly every version of Unix, and several
+non-Unix systems such as BeOS and Interix.
+Other independent ports exist for
+@sc{ms-dos}, @sc{os/2}, and Windows platforms.
+
+@menu
+* Basic Installation::	Installation instructions.
+* Compilers and Options::	How to set special options for various
+				systems.
+* Compiling For Multiple Architectures::	How to compile Bash for more
+						than one kind of system from
+						the same source tree.
+* Installation Names::	How to set the various paths used by the installation.
+* Specifying the System Type::	How to configure Bash for a particular system.
+* Sharing Defaults::	How to share default configuration values among GNU
+			programs.
+* Operation Controls::	Options recognized by the configuration program.
+* Optional Features::	How to enable and disable optional features when
+			building Bash.
+@end menu
+
+@node Basic Installation
+@section Basic Installation
+@cindex installation
+@cindex configuration
+@cindex Bash installation
+@cindex Bash configuration
+
+These are installation instructions for Bash.
+
+The simplest way to compile Bash is:
+
+@enumerate
+@item
+@code{cd} to the directory containing the source code and type
+@samp{./configure} to configure Bash for your system.  If you're
+using @code{csh} on an old version of System V, you might need to
+type @samp{sh ./configure} instead to prevent @code{csh} from trying
+to execute @code{configure} itself.
+
+Running @code{configure} takes some time.
+While running, it prints messages telling which features it is
+checking for.
+
+@item
+Type @samp{make} to compile Bash and build the @code{bashbug} bug
+reporting script.
+
+@item
+Optionally, type @samp{make tests} to run the Bash test suite.
+
+@item
+Type @samp{make install} to install @code{bash} and @code{bashbug}.
+This will also install the manual pages and Info file.
+
+@end enumerate
+
+The @code{configure} shell script attempts to guess correct
+values for various system-dependent variables used during
+compilation.  It uses those values to create a @file{Makefile} in
+each directory of the package (the top directory, the
+@file{builtins}, @file{doc}, and @file{support} directories,
+each directory under @file{lib}, and several others).  It also creates a
+@file{config.h} file containing system-dependent definitions. 
+Finally, it creates a shell script named @code{config.status} that you
+can run in the future to recreate the current configuration, a
+file @file{config.cache} that saves the results of its tests to
+speed up reconfiguring, and a file @file{config.log} containing
+compiler output (useful mainly for debugging @code{configure}). 
+If at some point
+@file{config.cache} contains results you don't want to keep, you
+may remove or edit it. 
+
+To find out more about the options and arguments that the
+@code{configure} script understands, type 
+
+@example
+bash-4.2$ ./configure --help
+@end example
+
+@noindent
+at the Bash prompt in your Bash source directory.
+
+If you want to build Bash in a directory separate from the source
+directory -- to build for multiple architectures, for example --
+just use the full path to the configure script. The following commands
+will build bash in a directory under @file{/usr/local/build} from
+the source code in @file{/usr/local/src/bash-4.4}:
+
+@example
+mkdir /usr/local/build/bash-4.4
+cd /usr/local/build/bash-4.4
+bash /usr/local/src/bash-4.4/configure
+make
+@end example
+
+See @ref{Compiling For Multiple Architectures} for more information
+about building in a directory separate from the source.
+
+If you need to do unusual things to compile Bash, please
+try to figure out how @code{configure} could check whether or not
+to do them, and mail diffs or instructions to
+@email{bash-maintainers@@gnu.org} so they can be
+considered for the next release.
+
+The file @file{configure.ac} is used to create @code{configure}
+by a program called Autoconf.  You only need
+@file{configure.ac} if you want to change it or regenerate
+@code{configure} using a newer version of Autoconf.  If
+you do this, make sure you are using Autoconf version 2.50 or
+newer.
+
+You can remove the program binaries and object files from the
+source code directory by typing @samp{make clean}.  To also remove the
+files that @code{configure} created (so you can compile Bash for
+a different kind of computer), type @samp{make distclean}.
+
+@node Compilers and Options
+@section Compilers and Options
+
+Some systems require unusual options for compilation or linking
+that the @code{configure} script does not know about.  You can
+give @code{configure} initial values for variables by setting
+them in the environment.  Using a Bourne-compatible shell, you
+can do that on the command line like this:
+
+@example
+CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure
+@end example
+
+On systems that have the @code{env} program, you can do it like this:
+
+@example
+env CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure
+@end example
+
+The configuration process uses GCC to build Bash if it
+is available.
+
+@node Compiling For Multiple Architectures
+@section Compiling For Multiple Architectures
+
+You can compile Bash for more than one kind of computer at the
+same time, by placing the object files for each architecture in their
+own directory.  To do this, you must use a version of @code{make} that
+supports the @code{VPATH} variable, such as GNU @code{make}.
+@code{cd} to the
+directory where you want the object files and executables to go and run
+the @code{configure} script from the source directory
+(@pxref{Basic Installation}).
+You may need to
+supply the @option{--srcdir=PATH} argument to tell @code{configure} where the
+source files are.  @code{configure} automatically checks for the
+source code in the directory that @code{configure} is in and in `..'.
+
+If you have to use a @code{make} that does not supports the @code{VPATH}
+variable, you can compile Bash for one architecture at a
+time in the source code directory.  After you have installed
+Bash for one architecture, use @samp{make distclean} before
+reconfiguring for another architecture.
+
+Alternatively, if your system supports symbolic links, you can use the
+@file{support/mkclone} script to create a build tree which has
+symbolic links back to each file in the source directory.  Here's an
+example that creates a build directory in the current directory from a
+source directory @file{/usr/gnu/src/bash-2.0}:
+
+@example
+bash /usr/gnu/src/bash-2.0/support/mkclone -s /usr/gnu/src/bash-2.0 .
+@end example
+
+@noindent
+The @code{mkclone} script requires Bash, so you must have already built
+Bash for at least one architecture before you can create build
+directories for other architectures.
+
+@node Installation Names
+@section Installation Names
+
+By default, @samp{make install} will install into
+@file{/usr/local/bin}, @file{/usr/local/man}, etc.  You can
+specify an installation prefix other than @file{/usr/local} by
+giving @code{configure} the option @option{--prefix=@var{PATH}},
+or by specifying a value for the @code{DESTDIR} @samp{make}
+variable when running @samp{make install}.
+
+You can specify separate installation prefixes for
+architecture-specific files and architecture-independent files. 
+If you give @code{configure} the option
+@option{--exec-prefix=@var{PATH}}, @samp{make install} will use
+@var{PATH} as the prefix for installing programs and libraries.
+Documentation and other data files will still use the regular prefix. 
+
+@node Specifying the System Type
+@section Specifying the System Type
+
+There may be some features @code{configure} can not figure out
+automatically, but need to determine by the type of host Bash
+will run on.  Usually @code{configure} can figure that
+out, but if it prints a message saying it can not guess the host
+type, give it the @option{--host=TYPE} option.  @samp{TYPE} can
+either be a short name for the system type, such as @samp{sun4},
+or a canonical name with three fields: @samp{CPU-COMPANY-SYSTEM}
+(e.g., @samp{i386-unknown-freebsd4.2}).
+
+See the file @file{support/config.sub} for the possible
+values of each field. 
+
+@node Sharing Defaults
+@section Sharing Defaults
+
+If you want to set default values for @code{configure} scripts to
+share, you can create a site shell script called
+@code{config.site} that gives default values for variables like
+@code{CC}, @code{cache_file}, and @code{prefix}.  @code{configure}
+looks for @file{PREFIX/share/config.site} if it exists, then
+@file{PREFIX/etc/config.site} if it exists.  Or, you can set the
+@code{CONFIG_SITE} environment variable to the location of the site
+script.  A warning: the Bash @code{configure} looks for a site script,
+but not all @code{configure} scripts do.
+
+@node Operation Controls
+@section Operation Controls
+
+@code{configure} recognizes the following options to control how it
+operates.
+
+@table @code
+
+@item --cache-file=@var{file}
+Use and save the results of the tests in
+@var{file} instead of @file{./config.cache}.  Set @var{file} to
+@file{/dev/null} to disable caching, for debugging
+@code{configure}. 
+
+@item --help
+Print a summary of the options to @code{configure}, and exit.
+
+@item --quiet
+@itemx --silent
+@itemx -q
+Do not print messages saying which checks are being made.
+
+@item --srcdir=@var{dir}
+Look for the Bash source code in directory @var{dir}.  Usually
+@code{configure} can determine that directory automatically.
+
+@item --version
+Print the version of Autoconf used to generate the @code{configure}
+script, and exit.
+@end table
+
+@code{configure} also accepts some other, not widely used, boilerplate
+options.  @samp{configure --help} prints the complete list.
+
+@node Optional Features
+@section Optional Features
+
+The Bash @code{configure} has a number of @option{--enable-@var{feature}}
+options, where @var{feature} indicates an optional part of Bash.
+There are also several @option{--with-@var{package}} options,
+where @var{package} is something like @samp{bash-malloc} or @samp{purify}.
+To turn off the default use of a package, use
+@option{--without-@var{package}}.  To configure Bash without a feature
+that is enabled by default, use @option{--disable-@var{feature}}.
+
+Here is a complete list of the @option{--enable-} and
+@option{--with-} options that the Bash @code{configure} recognizes. 
+
+@table @code
+@item --with-afs
+Define if you are using the Andrew File System from Transarc.
+
+@item --with-bash-malloc
+Use the Bash version of
+@code{malloc} in the directory @file{lib/malloc}.  This is not the same
+@code{malloc} that appears in @sc{gnu} libc, but an older version
+originally derived from the 4.2 @sc{bsd} @code{malloc}.  This @code{malloc}
+is very fast, but wastes some space on each allocation.
+This option is enabled by default.
+The @file{NOTES} file contains a list of systems for
+which this should be turned off, and @code{configure} disables this
+option automatically for a number of systems.
+
+@item --with-curses
+Use the curses library instead of the termcap library.  This should
+be supplied if your system has an inadequate or incomplete termcap
+database.
+
+@item --with-gnu-malloc
+A synonym for @code{--with-bash-malloc}.
+
+@item --with-installed-readline[=@var{PREFIX}]
+Define this to make Bash link with a locally-installed version of Readline
+rather than the version in @file{lib/readline}.  This works only with
+Readline 5.0 and later versions.  If @var{PREFIX} is @code{yes} or not
+supplied, @code{configure} uses the values of the make variables
+@code{includedir} and @code{libdir}, which are subdirectories of @code{prefix}
+by default, to find the installed version of Readline if it is not in
+the standard system include and library directories.
+If @var{PREFIX} is @code{no}, Bash links with the version in
+@file{lib/readline}.
+If @var{PREFIX} is set to any other value, @code{configure} treats it as
+a directory pathname and looks for
+the installed version of Readline in subdirectories of that directory
+(include files in @var{PREFIX}/@code{include} and the library in
+@var{PREFIX}/@code{lib}).
+
+@item --with-purify
+Define this to use the Purify memory allocation checker from Rational
+Software.
+
+@item --enable-minimal-config
+This produces a shell with minimal features, close to the historical
+Bourne shell.
+@end table
+
+There are several @option{--enable-} options that alter how Bash is
+compiled and linked, rather than changing run-time features.
+
+@table @code
+@item --enable-largefile
+Enable support for @uref{http://www.unix.org/version2/whatsnew/lfs20mar.html,
+large files} if the operating system requires special compiler options
+to build programs which can access large files.  This is enabled by
+default, if the operating system provides large file support.
+
+@item --enable-profiling
+This builds a Bash binary that produces profiling information to be
+processed by @code{gprof} each time it is executed.
+
+@item --enable-static-link
+This causes Bash to be linked statically, if @code{gcc} is being used.
+This could be used to build a version to use as root's shell.
+@end table
+
+The @samp{minimal-config} option can be used to disable all of
+the following options, but it is processed first, so individual
+options may be enabled using @samp{enable-@var{feature}}. 
+
+All of the following options except for @samp{disabled-builtins},
+@samp{direxpand-default}, and
+@samp{xpg-echo-default} are
+enabled by default, unless the operating system does not provide the
+necessary support.
+
+@table @code
+@item --enable-alias
+Allow alias expansion and include the @code{alias} and @code{unalias}
+builtins (@pxref{Aliases}).
+
+@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}).
+
+@item --enable-array-variables
+Include support for one-dimensional array shell variables
+(@pxref{Arrays}).
+
+@item --enable-bang-history
+Include support for @code{csh}-like history substitution
+(@pxref{History Interaction}).
+
+@item --enable-brace-expansion
+Include @code{csh}-like brace expansion
+( @code{b@{a,b@}c} @expansion{} @code{bac bbc} ).
+See @ref{Brace Expansion}, for a complete description.
+
+@item --enable-casemod-attributes
+Include support for case-modifying attributes in the @code{declare} builtin
+and assignment statements.  Variables with the @var{uppercase} attribute,
+for example, will have their values converted to uppercase upon assignment.
+
+@item --enable-casemod-expansion
+Include support for case-modifying word expansions.
+
+@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.
+
+@item --enable-cond-command
+Include support for the @code{[[} conditional command.
+(@pxref{Conditional Constructs}).
+
+@item --enable-cond-regexp
+Include support for matching @sc{posix} regular expressions using the
+@samp{=~} binary operator in the @code{[[} conditional command.
+(@pxref{Conditional Constructs}).
+
+@item --enable-coprocesses
+Include support for coprocesses and the @code{coproc} reserved word
+(@pxref{Pipelines}).
+
+@item --enable-debugger
+Include support for the bash debugger (distributed separately).
+
+@item --enable-dev-fd-stat-broken
+If calling @code{stat} on /dev/fd/@var{N} returns different results than
+calling @code{fstat} on file descriptor @var{N}, supply this option to
+enable a workaround.
+This has implications for conditional commands that test file attributes.
+
+@item --enable-direxpand-default
+Cause the @code{direxpand} shell option (@pxref{The Shopt Builtin})
+to be enabled by default when the shell starts.
+It is normally disabled by default.
+
+@item --enable-directory-stack
+Include support for a @code{csh}-like directory stack and the
+@code{pushd}, @code{popd}, and @code{dirs} builtins
+(@pxref{The Directory Stack}).
+
+@item --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 --enable-dparen-arithmetic
+Include support for the @code{((@dots{}))} command
+(@pxref{Conditional Constructs}).
+
+@item --enable-extended-glob
+Include support for the extended pattern matching features described
+above under @ref{Pattern Matching}.
+
+@item --enable-extended-glob-default
+Set the default value of the @var{extglob} shell option described
+above under @ref{The Shopt Builtin} to be enabled.
+
+@item --enable-function-import
+Include support for importing function definitions exported by another
+instance of the shell from the environment.  This option is enabled by
+default.
+
+@item --enable-glob-asciirange-default
+Set the default value of the @var{globasciiranges} shell option described
+above under @ref{The Shopt Builtin} to be enabled.
+This controls the behavior of character ranges when used in pattern matching
+bracket expressions.
+
+@item --enable-help-builtin
+Include the @code{help} builtin, which displays help on shell builtins and
+variables (@pxref{Bash Builtins}).
+
+@item --enable-history
+Include command history and the @code{fc} and @code{history}
+builtin commands (@pxref{Bash History Facilities}).
+
+@item --enable-job-control
+This enables the job control features (@pxref{Job Control}),
+if the operating system supports them.
+
+@item --enable-multibyte
+This enables support for multibyte characters if the operating
+system provides the necessary support.
+
+@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 --enable-process-substitution
+This enables process substitution (@pxref{Process Substitution}) if
+the operating system provides the necessary support.
+
+@item --enable-progcomp
+Enable the programmable completion facilities
+(@pxref{Programmable Completion}).
+If Readline is not enabled, this option has no effect.
+
+@item --enable-prompt-string-decoding
+Turn on the interpretation of a number of backslash-escaped characters
+in the @env{$PS0}, @env{$PS1}, @env{$PS2}, and @env{$PS4} prompt
+strings.  See @ref{Controlling the Prompt}, for a complete list of prompt
+string escape sequences.
+
+@item --enable-readline
+Include support for command-line editing and history with the Bash
+version of the Readline library (@pxref{Command Line Editing}).
+
+@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{select} compound command, which allows the generation of
+simple menus (@pxref{Conditional Constructs}).
+
+@item --enable-separate-helpfiles
+Use external files for the documentation displayed by the @code{help} builtin
+instead of storing the text internally.
+
+@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.
+
+@item --enable-strict-posix-default
+Make Bash @sc{posix}-conformant by default (@pxref{Bash POSIX Mode}).
+
+@item --enable-usg-echo-default
+A synonym for @code{--enable-xpg-echo-default}.
+
+@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.
+@end table
+
+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.
+
+@node Reporting Bugs
+@appendix Reporting Bugs
+
+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/gnu/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}.
+
+All bug reports should include:
+@itemize @bullet
+@item
+The version number of Bash.
+@item
+The hardware and operating system.
+@item
+The compiler used to compile Bash.
+@item
+A description of the bug behaviour.
+@item
+A short script or `recipe' which exercises the bug and may be used
+to reproduce it.
+@end itemize
+
+@noindent
+@code{bashbug} inserts the first three items automatically into
+the template it provides for filing a bug report.
+
+Please send all reports concerning this manual to
+@email{bug-bash@@gnu.org}.
+
+@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} 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.
+
+@itemize @bullet
+
+@item
+Bash is @sc{posix}-conformant, even where the @sc{posix} specification
+differs from traditional @code{sh} behavior (@pxref{Bash POSIX Mode}).
+
+@item
+Bash has multi-character invocation options (@pxref{Invoking Bash}).
+
+@item
+Bash has command-line editing (@pxref{Command Line Editing}) and
+the @code{bind} builtin.
+
+@item
+Bash provides a programmable word completion mechanism
+(@pxref{Programmable Completion}), and builtin commands
+@code{complete}, @code{compgen}, and @code{compopt}, to
+manipulate it.
+
+@item
+Bash has command history (@pxref{Bash History Facilities}) and the
+@code{history} and @code{fc} builtins to manipulate it.
+The Bash history list maintains timestamp information and uses the
+value of the @code{HISTTIMEFORMAT} variable to display it.
+
+@item
+Bash implements @code{csh}-like history expansion
+(@pxref{History Interaction}).
+
+@item
+Bash has one-dimensional array variables (@pxref{Arrays}), and the
+appropriate variable expansions and assignment syntax to use them.
+Several of the Bash builtins take options to act on arrays.
+Bash provides a number of built-in array variables.
+
+@item
+The @code{$'@dots{}'} quoting syntax, which expands ANSI-C
+backslash-escaped characters in the text between the single quotes,
+is supported (@pxref{ANSI-C Quoting}).
+
+@item
+Bash supports the @code{$"@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}).
+
+@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.
+
+@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.
+
+@item
+Bash implements the @code{for (( @var{expr1} ; @var{expr2} ; @var{expr3} ))}
+arithmetic for command, similar to the C language (@pxref{Looping Constructs}).
+
+@item
+Bash includes the @code{select} compound command, which allows the
+generation of simple menus (@pxref{Conditional Constructs}).
+
+@item
+Bash includes the @code{[[} compound command, which makes conditional
+testing part of the shell grammar (@pxref{Conditional Constructs}), including
+optional regular expression matching.
+
+@item
+Bash provides optional case-insensitive matching for the @code{case} and
+@code{[[} constructs.
+
+@item
+Bash includes brace expansion (@pxref{Brace Expansion}) and tilde
+expansion (@pxref{Tilde Expansion}).
+
+@item
+Bash implements command aliases and the @code{alias} and @code{unalias}
+builtins (@pxref{Aliases}).
+
+@item
+Bash provides shell arithmetic, the @code{((} compound command
+(@pxref{Conditional Constructs}),
+and arithmetic expansion (@pxref{Shell Arithmetic}).
+
+@item
+Variables present in the shell's initial environment are automatically
+exported to child processes.  The Bourne shell does not normally do
+this unless the variables are explicitly marked using the @code{export}
+command.
+
+@item
+Bash supports the @samp{+=} assignment operator, which appends to the value
+of the variable named on the left hand side.
+
+@item
+Bash includes the @sc{posix} pattern removal @samp{%}, @samp{#}, @samp{%%}
+and @samp{##} expansions to remove leading or trailing substrings from
+variable values (@pxref{Shell Parameter Expansion}).
+
+@item
+The expansion @code{$@{#xx@}}, which returns the length of @code{$@{xx@}},
+is supported (@pxref{Shell Parameter Expansion}).
+
+@item
+The expansion @code{$@{var:}@var{offset}@code{[:}@var{length}@code{]@}},
+which expands to the substring of @code{var}'s value of length
+@var{length}, beginning at @var{offset}, is present
+(@pxref{Shell Parameter Expansion}).
+
+@item
+The expansion
+@code{$@{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
+The expansion @code{$@{!@var{prefix}*@}} expansion, which expands to
+the names of all shell variables whose names begin with @var{prefix},
+is available (@pxref{Shell Parameter Expansion}).
+
+@item
+Bash has @var{indirect} variable expansion using @code{$@{!word@}}
+(@pxref{Shell Parameter Expansion}).
+
+@item
+Bash can expand positional parameters beyond @code{$9} using
+@code{$@{@var{num}@}}.
+
+@item
+The @sc{posix} @code{$()} form of command substitution
+is implemented (@pxref{Command Substitution}),
+and preferred to the Bourne shell's @code{``} (which
+is also implemented for backwards compatibility).
+
+@item
+Bash has process substitution (@pxref{Process Substitution}).
+
+@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.
+
+@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.
+
+@item
+The filename expansion bracket expression code uses @samp{!} and @samp{^}
+to negate the set of characters between the brackets.
+The Bourne shell uses only @samp{!}.
+
+@item
+Bash implements the full set of @sc{posix} filename expansion operators,
+including @var{character classes}, @var{equivalence classes}, and
+@var{collating symbols} (@pxref{Filename Expansion}).
+
+@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.
+
+@item
+Bash functions are permitted to have local variables using the
+@code{local} builtin, and thus useful recursive functions may be written
+(@pxref{Bash Builtins}).
+
+@item
+Variable assignments preceding commands affect only that command, even
+builtins and functions (@pxref{Environment}).
+In @code{sh}, all variable assignments 
+preceding commands are global unless the command is executed from the
+file system.
+
+@item
+Bash performs filename expansion on filenames specified as operands
+to input and output redirection operators (@pxref{Redirections}).
+
+@item
+Bash contains the @samp{<>} redirection operator, allowing a file to be
+opened for both reading and writing, and the @samp{&>} redirection
+operator, for directing standard output and standard error to the same
+file (@pxref{Redirections}).
+
+@item
+Bash includes the @samp{<<<} redirection operator, allowing a string to
+be used as the standard input to a command.
+
+@item
+Bash implements the @samp{[n]<&@var{word}} and @samp{[n]>&@var{word}}
+redirection operators, which move one file descriptor to another.
+
+@item
+Bash treats a number of filenames specially when they are
+used in redirection operators (@pxref{Redirections}).
+
+@item
+Bash can open network connections to arbitrary machines and services
+with the redirection operators (@pxref{Redirections}).
+
+@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
+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
+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
+The @code{command} builtin allows selective disabling of functions
+when command lookup is performed (@pxref{Bash Builtins}).
+
+@item
+Individual builtins may be enabled or disabled using the @code{enable}
+builtin (@pxref{Bash Builtins}).
+
+@item
+The Bash @code{exec} builtin takes additional options that allow users
+to control the contents of the environment passed to the executed
+command, and what the zeroth argument to the command is to be
+(@pxref{Bourne Shell Builtins}).
+
+@item
+Shell functions may be exported to children via the environment
+using @code{export -f} (@pxref{Shell Functions}).
+
+@item
+The Bash @code{export}, @code{readonly}, and @code{declare} builtins can
+take a @option{-f} option to act on shell functions, a @option{-p} option to
+display variables with various attributes set in a format that can be
+used as shell input, a @option{-n} option to remove various variable
+attributes, and @samp{name=value} arguments to set variable attributes
+and values simultaneously.
+
+@item
+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}).
+
+@item
+Bash includes a @code{help} builtin for quick reference to shell
+facilities (@pxref{Bash Builtins}).
+
+@item
+The @code{printf} builtin is available to display formatted output
+(@pxref{Bash Builtins}).
+
+@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
+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
+Bash includes the @code{shopt} builtin, for finer control of shell
+optional capabilities (@pxref{The Shopt Builtin}), and allows these options
+to be set and unset at shell invocation (@pxref{Invoking Bash}).
+
+@item
+Bash has much more optional behavior controllable with the @code{set}
+builtin (@pxref{The Set Builtin}).
+
+@item
+The @samp{-x} (@option{xtrace}) option displays commands other than
+simple commands when performing an execution trace
+(@pxref{The Set Builtin}).
+
+@item
+The @code{test} builtin (@pxref{Bourne Shell Builtins})
+is slightly different, as it implements the @sc{posix} algorithm,
+which specifies the behavior based on the number of arguments.
+
+@item
+Bash includes the @code{caller} builtin, which displays the context of
+any active subroutine call (a shell function or a script executed with
+the @code{.} or @code{source} builtins).  This supports the bash
+debugger.
+
+@item
+The @code{trap} builtin (@pxref{Bourne Shell Builtins}) allows a
+@code{DEBUG} pseudo-signal specification, similar to @code{EXIT}.
+Commands specified with a @code{DEBUG} trap are executed before every
+simple command, @code{for} command, @code{case} command,
+@code{select} command, every arithmetic @code{for} command, and before
+the first command executes in a shell function.
+The @code{DEBUG} trap is not inherited by shell functions unless the
+function has been given the @code{trace} attribute or the
+@code{functrace} option has been enabled using the @code{shopt} builtin.
+The @code{extdebug} shell option has additional effects on the
+@code{DEBUG} trap.
+
+The @code{trap} builtin (@pxref{Bourne Shell Builtins}) allows an
+@code{ERR} pseudo-signal specification, similar to @code{EXIT} and @code{DEBUG}.
+Commands specified with an @code{ERR} trap are executed after a simple
+command fails, with a few exceptions.
+The @code{ERR} trap is not inherited by shell functions unless the
+@code{-o errtrace} option to the @code{set} builtin is enabled.
+
+The @code{trap} builtin (@pxref{Bourne Shell Builtins}) allows a
+@code{RETURN} pseudo-signal specification, similar to
+@code{EXIT} and @code{DEBUG}.
+Commands specified with an @code{RETURN} trap are executed before
+execution resumes after a shell function or a shell script executed with
+@code{.} or @code{source} returns.
+The @code{RETURN} trap is not inherited by shell functions unless the
+function has been given the @code{trace} attribute or the
+@code{functrace} option has been enabled using the @code{shopt} builtin.
+
+@item
+The Bash @code{type} builtin is more extensive and gives more information
+about the names it finds (@pxref{Bash Builtins}).
+
+@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
+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
+Bash interprets special backslash-escaped characters in the prompt
+strings when interactive (@pxref{Controlling the Prompt}).
+
+@item
+The Bash restricted mode is more useful (@pxref{The Restricted Shell});
+the SVR4.2 shell restricted mode is too limited.
+
+@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
+Bash includes a number of features to support a separate debugger for
+shell scripts.
+
+@item
+The SVR4.2 shell has two privilege-related builtins
+(@code{mldmode} and @code{priv}) not present in Bash.
+
+@item
+Bash does not have the @code{stop} or @code{newgrp} builtins.
+
+@item
+Bash does not use the @env{SHACCT} variable or perform shell accounting.
+
+@item
+The SVR4.2 @code{sh} uses a @env{TIMEOUT} variable like Bash uses
+@env{TMOUT}.
+
+@end itemize
+
+@noindent
+More features unique to Bash may be found in @ref{Bash Features}.
+
+
+@appendixsec Implementation Differences From The SVR4.2 Shell
+
+Since Bash is a completely new implementation, it does not suffer from
+many of the limitations of the SVR4.2 shell.  For instance:
+
+@itemize @bullet
+
+@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.
+
+@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.
+
+@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.
+
+@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.
+
+@item
+The SVR4.2 shell does not allow users to trap @code{SIGSEGV},
+@code{SIGALRM}, or @code{SIGCHLD}.
+
+@item
+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 SVR4.2 shell treats @samp{^} as the undocumented equivalent of
+@samp{|}.
+
+@item
+Bash allows multiple option arguments when it is invoked (@code{-x -v});
+the SVR4.2 shell allows only one option argument (@code{-xv}).  In
+fact, some versions of the shell dump core if the second argument begins
+with a @samp{-}.
+
+@item
+The SVR4.2 shell exits a script if any builtin fails; Bash exits
+a script only if one of the @sc{posix} special builtins fails, and
+only for certain failures, as enumerated in the @sc{posix} standard.
+
+@item 
+The SVR4.2 shell behaves differently when invoked as @code{jsh}
+(it turns on job control).
+@end itemize
+
+@node GNU Free Documentation License
+@appendix GNU Free Documentation License
+
+@include fdl.texi
+
+@node Indexes
+@appendix Indexes
+
+@menu
+* Builtin Index::		Index of Bash builtin commands.
+* Reserved Word Index::		Index of Bash reserved words.
+* Variable Index::		Quick reference helps you find the
+				variable you want.
+* Function Index::		Index of bindable Readline functions.
+* Concept Index::		General index for concepts described in
+				this manual.
+@end menu
+
+@node Builtin Index
+@appendixsec Index of Shell Builtin Commands
+@printindex bt
+
+@node Reserved Word Index
+@appendixsec Index of Shell Reserved Words
+@printindex rw
+
+@node Variable Index
+@appendixsec Parameter and Variable Index
+@printindex vr
+
+@node Function Index
+@appendixsec Function Index
+@printindex fn
+
+@node Concept Index
+@appendixsec Concept Index
+@printindex cp
+
+@bye