@c %**end of header
@ignore
-Last Change: Wed Jan 20 16:46:26 EST 1999
+Last Change: Tue Mar 14 11:38:10 EST 2000
@end ignore
-@set EDITION 2.3
-@set VERSION 2.03
-@set UPDATED 20 January 1999
-@set UPDATE-MONTH January 1999
+@set EDITION 2.4
+@set VERSION 2.04
+@set UPDATED 14 March 2000
+@set UPDATE-MONTH March 2000
@iftex
@finalout
* Basic Shell Features:: The shell "building blocks".
-* Bourne Shell Features:: Features similar to those found in the
- Bourne shell.
+* Shell Builtin Commands:: Commands that are a part of the shell.
+
+* Shell Variables:: Variables used or set by Bash.
* Bash Features:: Features found only in Bash.
* 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.
+
* Builtin Index:: Index of Bash builtin commands.
* Reserved Word Index:: Index of Bash reserved words.
@section What is Bash?
Bash is the shell, or command language interpreter,
-that will appear in the @sc{GNU} operating system.
+for the @sc{gnu} operating system.
The name is an acronym for the @samp{Bourne-Again SHell},
-a pun on Steve Bourne, the author of the direct ancestor of the current
-Unix shell @code{/bin/sh},
+a pun on Stephen Bourne, the author of the direct ancestor of
+the current Unix shell @code{/bin/sh},
which appeared in the Seventh Edition Bell Labs Research version
of Unix.
-Bash is an @code{sh}-compatible shell that incorporates useful
+Bash is largely compatible with @code{sh} and incorporates useful
features from the Korn shell @code{ksh} and the C shell @code{csh}.
-It is intended to be a conformant implementation of the @sc{IEEE}
-@sc{POSIX} Shell and Tools specification (@sc{IEEE} Working Group 1003.2).
+It is intended to be a conformant implementation of the @sc{ieee}
+@sc{posix} Shell and Tools specification (@sc{ieee} Working Group 1003.2).
It offers functional improvements over @code{sh} for both interactive and
programming use.
-While the @sc{GNU} operating system will include a version
-of @code{csh}, Bash will be the default shell.
-Like other @sc{GNU} software, Bash is quite portable. It currently runs
+While the @sc{gnu} operating system provides other shells, including
+a version of @code{csh}, Bash is the default shell.
+Like other @sc{gnu} software, Bash is quite portable. It currently runs
on nearly every version of Unix and a few other operating systems @minus{}
-independently-supported ports exist for @sc{MS-DOS}, @sc{OS/2},
-Windows @sc{95}, and Windows @sc{NT}.
+independently-supported ports exist for @sc{ms-dos}, @sc{os/2},
+Windows @sc{95/98}, and Windows @sc{nt}.
@node What is a shell?
@section What is a shell?
At its base, a shell is simply a macro processor that executes
commands. A Unix shell is both a command interpreter, which
-provides the user interface to the rich set of Unix utilities,
+provides the user interface to the rich set of @sc{gnu} utilities,
and a programming language, allowing these utilitites to be
combined. Files containing commands can be created, and become
commands themselves. These new commands have the same status as
-system commands in directories like @file{/bin}, allowing users
+system commands in directories such as @file{/bin}, allowing users
or groups to establish custom environments.
-A shell allows execution of Unix commands, both synchronously and
+A shell allows execution of @sc{gnu} commands, both synchronously and
asynchronously.
The shell waits for synchronous commands to complete before accepting
more input; asynchronous commands continue to execute in parallel
with the shell while it reads and executes additional commands.
The @dfn{redirection} constructs permit
-fine-grained control of the input and output of those commands,
-and the shell allows control over the contents of their
-environment. Unix shells also provide a small set of built-in
+fine-grained control of the input and output of those commands.
+Moreover, the shell allows control over the contents of commands'
+environments.
+Shells may be used interactively or non-interactively: they accept
+input typed from the keyboard or from a file.
+
+Shells also provide a small set of built-in
commands (@dfn{builtins}) implementing functionality impossible
-(e.g., @code{cd}, @code{break}, @code{continue}, and
-@code{exec}), or inconvenient (@code{history}, @code{getopts},
-@code{kill}, or @code{pwd}, for example) to obtain via separate
-utilities. Shells may be used interactively or
-non-interactively: they accept input typed from the keyboard or
-from a file. All of the shell builtins are described in
+or inconvenient to obtain via separate utilities.
+For example, @code{cd}, @code{break}, @code{continue}, and
+@code{exec}) cannot be implemented outside of the shell because
+they directly manipulate the shell itself.
+The @code{history}, @code{getopts}, @code{kill}, or @code{pwd}
+builtins, among others, could be implemented in separate utilities,
+but they are more convenient to use as builtin commands.
+All of the shell builtins are described in
subsequent sections.
While executing commands is essential, most of the power (and
languages. Like any high-level language, the shell provides
variables, flow control constructs, quoting, and functions.
-Shells have begun offering features geared specifically for
+Shells offer features geared specifically for
interactive use rather than to augment the programming language.
These interactive features include job control, command line
editing, history and aliases. Each of these features is
@item POSIX
@cindex POSIX
A family of open system standards based on Unix. Bash
-is concerned with @sc{POSIX} 1003.2, the Shell and Tools Standard.
+is concerned with @sc{posix} 1003.2, the Shell and Tools Standard.
@item blank
A space or tab character.
@item process group
@cindex process group
A collection of related processes each having the same process
-group @sc{ID}.
+group @sc{id}.
@item process group ID
@cindex process group ID
@item signal
@cindex signal
-A mechanism by which a process may be notified by the kernal
+A mechanism by which a process may be notified by the kernel
of an event occurring in the system.
@item special builtin
@cindex special builtin
A shell builtin command that has been classified as special by the
-@sc{POSIX.2} standard.
+@sc{posix} 1003.2 standard.
@item token
@cindex token
The Bourne shell is
the traditional Unix shell originally written by Stephen Bourne.
All of the Bourne shell builtin commands are available in Bash,
-and the rules for evaluation and quoting are taken from the @sc{POSIX}
+and the rules for evaluation and quoting are taken from the @sc{posix}
1003.2 specification for the `standard' Unix shell.
This chapter briefly summarizes the shell's `building blocks':
* 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
Each of the shell metacharacters (@pxref{Definitions})
has special meaning to the shell and must be quoted if it is to
-represent itself. There are three quoting mechanisms: the
+represent itself.
+When the command history expansion facilities are being used, the
+@var{history expansion} character, usually @samp{!}, must be quoted
+to prevent history expansion. @xref{Bash History Facilities} for
+more details concerning history expansion.
+There are three quoting mechanisms: the
@var{escape character}, single quotes, and double quotes.
@node Escape Character
@node Single Quotes
@subsubsection Single Quotes
-Enclosing characters in single quotes preserves the literal value
+Enclosing characters in single quotes (@samp{'}) preserves the literal value
of each character within the quotes. A single quote may not occur
between single quotes, even when preceded by a backslash.
@node Double Quotes
@subsubsection Double Quotes
-Enclosing characters in double quotes preserves the literal value
+Enclosing characters in double quotes (@samp{"}) preserves the literal value
of all characters within the quotes, with the exception of
@samp{$}, @samp{`}, and @samp{\}.
The characters @samp{$} and @samp{`}
vertical tab
@item \\
backslash
+@item \'
+single quote
@item \@var{nnn}
the character whose @code{ASCII} code is the octal value @var{nnn}
(one to three digits)
@end table
@noindent
-The result is single-quoted, as if the dollar sign had not been present.
+The expanded result is single-quoted, as if the dollar sign had not
+been present.
@node Locale Translation
@subsubsection Locale-Specific Translation
be ignored. An interactive shell without the @code{interactive_comments}
option enabled does not allow comments. The @code{interactive_comments}
option is on by default in interactive shells.
-@xref{Is This Shell Interactive?}, for a description of what makes
+@xref{Interactive Shells}, for a description of what makes
a shell interactive.
@node Shell Commands
@section Shell Commands
@cindex commands, shell
+
+A simple shell command such as @code{echo a b c} consists of the command
+itself followed by arguments, separated by spaces.
+
+More complex shell commands are composed of simple commands arranged together
+in a variety of ways: in a pipeline in which the output of one command
+becomes the input of a second, in a loop or conditional construct, or in
+some other grouping.
+
@menu
* Simple Commands:: The most common type of command.
* Pipelines:: Connecting the input and output of several
A simple command is the kind of command encountered most often.
It's just a sequence of words separated by @code{blank}s, terminated
by one of the shell's control operators (@pxref{Definitions}). The
-first word generally specifies a command to be executed.
+first word generally specifies a command to be executed, with the
+rest of the words being that command's arguments.
The return status (@pxref{Exit Status}) of a simple command is
its exit status as provided
-by the @sc{POSIX.1} @code{waitpid} function, or 128+@var{n} if the command
-was terminated by signal @var{n}.
+by the @sc{posix} 1003.1 @code{waitpid} function, or 128+@var{n} if
+the command was terminated by signal @var{n}.
@node Pipelines
@subsection Pipelines
The statistics currently consist of elapsed (wall-clock) time and
user and system time consumed by the command's execution.
The @samp{-p} option changes the output format to that specified
-by @sc{POSIX}.
+by @sc{posix}.
The @code{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.
This is known as executing the command in the @var{background}.
The shell does not wait for the command to finish, and the return
status is 0 (true).
-The standard input for asynchronous commands, in the absence of any
+When job control is not active (@pxref{Job Control}),
+the standard input for asynchronous commands, in the absence of any
explicit redirections, is redirected from @code{/dev/null}.
Commands separated by a @samp{;} are executed sequentially; the shell
exit status of the last command executed.
The control operators @samp{&&} and @samp{||}
-denote @sc{AND} lists and @sc{OR} lists, respectively.
-An @sc{AND} list has the form
+denote @sc{and} lists and @sc{or} lists, respectively.
+An @sc{and} list has the form
@example
-@var{command} && @var{command2}
+@var{command1} && @var{command2}
@end example
@noindent
-@var{command2} is executed if, and only if, @var{command}
+@var{command2} is executed if, and only if, @var{command1}
returns an exit status of zero.
-An @sc{OR} list has the form
+An @sc{or} list has the form
@example
-@var{command} || @var{command2}
+@var{command1} || @var{command2}
@end example
@noindent
-@var{command2} is executed if, and only if, @var{command}
+@var{command2} is executed if, and only if, @var{command1}
returns a non-zero exit status.
The return status of
-@sc{AND} and @sc{OR} lists is the exit status of the last command
+@sc{and} and @sc{or} lists is the exit status of the last command
executed in the list.
@node Looping Constructs
Bash supports the following looping constructs.
-Note that wherever you see a @samp{;} in the description of a
+Note that wherever a @samp{;} appears in the description of a
command's syntax, it may be replaced with one or more newlines.
@table @code
@end example
Expand @var{words}, and execute @var{commands} once for each member
in the resultant list, with @var{name} bound to the current member.
-If @samp{in @var{words}} is not present, @samp{in "$@@"} is assumed.
+If @samp{in @var{words}} is not present, the @code{for} command
+executes the @var{commands} once for each positional parameter that is
+set, as if @samp{in "$@@"} had been specified
+(@pxref{Special Parameters}).
The return status is the exit status of the last command that executes.
If there are no items in the expansion of @var{words}, no commands are
executed, and the return status is zero.
+
+An alternate form of the @code{for} command is also supported:
+
+@example
+for (( @var{expr1} ; @var{expr2} ; @var{expr3} )) ; do @var{commands} ; done
+@end example
+First, the arithmetic expression @var{expr1} is evaluated according
+to the rules described below (@pxref{Shell Arithmetic}).
+The arithmetic expression @var{expr2} is then evaluated repeatedly
+until it evaluates to zero.
+Each time @var{expr2} evaluates to a non-zero value, @var{commands} are
+executed and the arithmetic expression @var{expr3} is evaluated.
+If any expression is omitted, it behaves as if it evaluates to 1.
+The return value is the exit status of the last command in @var{list}
+that is executed, or false if any of the expressions is invalid.
+
@end table
The @code{break} and @code{continue} builtins (@pxref{Bourne Shell Builtins})
True if either @var{expression1} or @var{expression2} is true.
@end table
@noindent
-The && and || commands do not execute @var{expression2} if the
+The @code{&&} and @code{||} commands do not execute @var{expression2} if the
value of @var{expression1} is sufficient to determine the return
value of the entire conditional expression.
Shell functions are a way to group commands for later execution
using a single name for the group. They are executed just like
-a "regular" command. Shell functions are executed in the current
+a "regular" command.
+When the name of a shell function is used as a simple command name,
+the list of commands associated with that function name is executed.
+Shell functions are executed in the current
shell context; no new process is created to interpret them.
Functions are declared using this syntax:
name of a command. The exit status of a function is
the exit status of the last command executed in the body.
+Note that for historical reasons, the curly braces that surround
+the body of the function must be separated from the body by
+@code{blank}s or newlines.
+This is because the braces are reserved words and are only recognized
+as such when they are separated by whitespace.
+Also, the @var{command-list} must be terminated with a semicolon
+or a newline.
+
When a function is executed, the arguments to the
function become the positional parameters
during its execution (@pxref{Positional Parameters}).
The special parameter @samp{#} that expands to the number of
positional parameters is updated to reflect the change.
Positional parameter @code{0} is unchanged.
+The @code{FUNCNAME} variable is set to the name of the function
+while the function is executing.
If the builtin command @code{return}
is executed in a function, the function completes and
digits, other than the single digit @code{0}. Positional parameters are
assigned from the shell's arguments when it is invoked,
and may be reassigned using the @code{set} builtin command.
-Positional parameter @code{N} may be referenced as @code{$@{N@}}.
-Positional parameters may not be assigned to
-with assignment statements. The positional parameters are
+Positional parameter @code{N} may be referenced as @code{$@{N@}}, or
+as @code{$N} when @code{N} consists of a single digit.
+Positional parameters may not be assigned to with assignment statements.
+The @code{set} and @code{shift} builtins are used to set and
+unset them (@pxref{Shell Builtin Commands}).
+The positional parameters are
temporarily replaced when a shell function is executed
(@pxref{Shell Functions}).
pipeline.
@item -
-Expands to the current option flags as specified upon invocation,
-by the @code{set}
+(A hyphen.) Expands to the current option flags as specified upon
+invocation, by the @code{set}
builtin command, or those set by the shell itself
(such as the @samp{-i} option).
@item $
-Expands to the process @sc{ID} of the shell. In a @code{()} subshell, it
-expands to the process @sc{ID} of the invoking shell, not the subshell.
+Expands to the process @sc{id} of the shell. In a @code{()} subshell, it
+expands to the process @sc{id} of the invoking shell, not the subshell.
@item !
-Expands to the process @sc{ID} of the most recently executed background
+Expands to the process @sc{id} of the most recently executed background
(asynchronous) command.
@item 0
to the filename used to invoke Bash, as given by argument zero.
@item _
+(An underscore.)
At shell startup, set to the absolute filename of the shell or shell
script being executed as passed in the argument list.
Subsequently, expands to the last argument to the previous command,
@cindex brace expansion
@cindex expansion, brace
-Brace expansion
-is a mechanism by which arbitrary strings
-may be generated. This mechanism is similar to
+Brace expansion is a mechanism by which arbitrary strings may be generated.
+This mechanism is similar to
@var{filename expansion} (@pxref{Filename Expansion}),
-but the file names generated
-need not exist. Patterns to be brace expanded take
-the form of an optional @var{preamble},
-followed by a series of comma-separated strings
-between a pair of braces, followed by an optional @var{postscript}.
-The preamble is prepended to each string contained
-within the braces, and the postscript is then appended
-to each resulting string, expanding left to right.
-
-Brace expansions may be nested. The results of each expanded
-string are not sorted; left to right order is preserved.
+but the file names generated need not exist.
+Patterns to be brace expanded take the form of an optional @var{preamble},
+followed by a series of comma-separated strings 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
in the result. It is strictly textual. Bash
does not apply any syntactic interpretation to the context of the
expansion or the text between the braces.
+To avoid conflicts with parameter expansion, the string @samp{$@{}
+is not considered eligible for brace expansion.
A correctly-formed brace expansion must contain unquoted opening
and closing braces, and at least one unquoted comma.
expanded and that value is used in the rest of the substitution, rather
than the value of @var{parameter} itself.
This is known as @code{indirect expansion}.
+The exception to this is the expansion of $@{!@var{prefix*@}}
+described below.
In each of the cases below, @var{word} is subject to tilde expansion,
parameter expansion, command substitution, and arithmetic expansion.
+
When not performing substring expansion, Bash tests for a parameter
that is unset or null; omitting the colon results in a test only for a
-parameter that is unset.
+parameter that is unset. Put another way, if the colon is included,
+the operator tests for both existence and that the value is not null;
+if the colon is omitted, the operator tests only for existence.
@table @code
@item $@{@var{parameter}:@var{offset}@}
@itemx $@{@var{parameter}:@var{offset}:@var{length}@}
-Expands to up to @var{length} characters of @var{parameter},
+Expands to up to @var{length} characters of @var{parameter}
starting at the character specified by @var{offset}.
If @var{length} is omitted, expands to the substring of
-@var{parameter}, starting at the character specified by @var{offset}.
+@var{parameter} starting at the character specified by @var{offset}.
@var{length} and @var{offset} are arithmetic expressions
(@pxref{Shell Arithmetic}).
This is referred to as Substring Expansion.
Substring indexing is zero-based unless the positional parameters
are used, in which case the indexing starts at 1.
+@item $@{!@var{prefix}*@}
+Expands to the names of variables whose names begin with @var{prefix},
+separated by the first character of the @code{IFS} special variable.
+
@item $@{#@var{parameter}@}
The length in characters of the expanded value of @var{parameter} is
substituted.
@cindex command substitution
Command substitution allows the output of a command to replace
-the command name. There are two forms:
+the command itself.
+Command substitution occurs when a command is enclosed as follows:
@example
$(@var{command})
@end example
@cindex process substitution
Process substitution is supported on systems that support named
-pipes (@sc{FIFO}s) or the @file{/dev/fd} method of naming open files.
+pipes (@sc{fifo}s) or the @file{/dev/fd} method of naming open files.
It takes the form of
@example
<(@var{list})
@end example
@noindent
The process @var{list} is run with its input or output connected to a
-@sc{FIFO} or some file in @file{/dev/fd}. The name of this file is
+@sc{fifo} or some file in @file{/dev/fd}. The name of this file is
passed as an argument to the current command as the result of the
expansion. If the @code{>(@var{list})} form is used, writing to
the file will provide input for @var{list}. If the
@code{<(@var{list})} form is used, the file passed as an
argument should be read to obtain the output of @var{list}.
+Note that no space may appear between the @code{<} or @code{>}
+and the left parenthesis, otherwise the construct would be interpreted
+as a redirection.
When available, process substitution is performed simultaneously with
parameter and variable expansion, command substitution, and arithmetic
Explicit null arguments (@code{""} or @code{''}) are retained.
Unquoted implicit null arguments, resulting from the expansion of
-@var{parameter}s
-that have no values, are removed.
+parameters that have no values, are removed.
If a parameter with no value is expanded within double quotes, a
null argument results and is retained.
After word splitting, unless the @samp{-f} option has been set
(@pxref{The Set Builtin}), Bash scans each word for the characters
-@samp{*}, @samp{?}, @samp{(}, and @samp{[}.
+@samp{*}, @samp{?}, and @samp{[}.
If one of these characters appears, then the word is
regarded as a @var{pattern},
and replaced with an alphabetically sorted list of
@cindex matching, pattern
Any character that appears in a pattern, other than the special pattern
-characters described below, matches itself. The NUL character may not
+characters described below, matches itself. The @sc{nul} character may not
occur in a pattern. The special pattern characters must be quoted if
they are to be matched literally.
Within @samp{[} and @samp{]}, @var{character classes} can be specified
using the syntax
@code{[:}@var{class}@code{:]}, where @var{class} is one of the
-following classes defined in the @sc{POSIX.2} standard:
+following classes defined in the @sc{posix} 1003.2 standard:
@example
alnum alpha ascii blank cntrl digit graph lower
print punct space upper xdigit
The word following the redirection operator in the following
descriptions, unless otherwise noted, is subjected to brace expansion,
tilde expansion, parameter expansion, command substitution, arithmetic
-expansion, quote removal, and filename expansion.
+expansion, quote removal, filename expansion, and word splitting.
If it expands to more than one word, Bash reports an error.
Note that the order of redirections is significant. For example,
ls > @var{dirlist} 2>&1
@end example
@noindent
-directs both standard output and standard error to the file
-@var{dirlist}, while the command
+directs both standard output (file descriptor 1) and standard error
+(file descriptor 2) to the file @var{dirlist}, while the command
@example
ls 2>&1 > @var{dirlist}
@end example
because the standard error was duplicated as standard output
before the standard output was redirected to @var{dirlist}.
+Bash handles several filenames specially when they are used in
+redirections, as described in the following table:
+
+@table @code
+@item /dev/fd/@var{fd}
+If @var{fd} is a valid integer, file descriptor @var{fd} is duplicated.
+
+@item /dev/stdin
+File descriptor 0 is duplicated.
+
+@item /dev/stdout
+File descriptor 1 is duplicated.
+
+@item /dev/stderr
+File descriptor 2 is duplicated.
+
+@item /dev/tcp/@var{host}/@var{port}
+If @var{host} is a valid hostname or Internet address, and @var{port}
+is an integer port number, Bash attempts to open a TCP connection
+to the corresponding socket.
+
+@item /dev/udp/@var{host}/@var{port}
+If @var{host} is a valid hostname or Internet address, and @var{port}
+is an integer port number, Bash attempts to open a UDP connection
+to the corresponding socket.
+
+@end table
+
A failure to open or create a file causes the redirection to fail.
@subsection Redirecting Input
If the redirection operator is @samp{>}, and the @code{noclobber}
option to the @code{set} builtin has been enabled, the redirection
-will fail if the filename whose name results from the expansion of
+will fail if the file whose name results from the expansion of
@var{word} exists and is a regular file.
If the redirection operator is @samp{>|}, or the redirection operator is
@samp{>} and the @code{noclobber} option is not enabled, the redirection
@var{delimiter}
@end example
-No parameter expansion, command substitution, filename
-expansion, or arithmetic expansion is performed on
+No parameter expansion, command substitution, arithmetic expansion,
+or filename expansion is performed on
@var{word}. If any characters in @var{word} are quoted, the
@var{delimiter} is the result of quote removal on @var{word},
and the lines in the here-document are not expanded.
If @var{word} is unquoted,
all lines of the here-document are subjected to parameter expansion,
command substitution, and arithmetic expansion. In the latter
-case, the pair @code{\newline} is ignored, and @samp{\}
+case, the character sequence @code{\newline} is ignored, and @samp{\}
must be used to quote the characters
@samp{\}, @samp{$}, and @samp{`}.
@item
If the command name contains no slashes, the shell attempts to
locate it. If there exists a shell function by that name, that
-function is invoked as described above in @ref{Shell Functions}.
+function is invoked as described in @ref{Shell Functions}.
@item
If the name does not match a function, the shell searches for
shell aliases defined with @code{alias} (@pxref{Aliases})
@item
-various process IDs, including those of background jobs
+various process @sc{id}s, including those of background jobs
(@pxref{Lists}), the value of @code{$$}, and the value of
@code{$PPID}
called the @var{environment}.
This is a list of name-value pairs, of the form @code{name=value}.
-Bash allows you to manipulate the environment in several
-ways. On invocation, the shell scans its own environment and
+Bash provides several ways to manipulate the environment.
+On invocation, the shell scans its own environment and
creates a parameter for each name found, automatically marking
it for @var{export}
to child processes. Executed commands inherit the environment.
This seemingly counter-intuitive scheme is used so there
is one well-defined way to indicate success and a variety of
ways to indicate various failure modes.
-When a command terminates on a fatal signal whose number is @var{n},
-Bash uses the value 128+@var{n} as the exit status.
+When a command terminates on a fatal signal whose number is @var{N},
+Bash uses the value 128+@var{N} as the exit status.
If a command is not found, the child process created to
execute it returns a status of 127. If a command is found
(see the description of @code{hash} in @ref{Bourne Shell Builtins})
are retained by the child.
-Most versions of Unix make this a part of the kernel's command
+Most versions of Unix make this a part of the operating system's command
execution mechanism. If the first line of a script begins with
the two characters @samp{#!}, the remainder of the line specifies
-an interpreter for the program. The arguments to the interpreter
+an interpreter for the program.
+Thus, you can specify Bash, @code{awk}, Perl, or some other
+interpreter and write the rest of the script file in that language.
+
+The arguments to the interpreter
consist of a single optional argument following the interpreter
name on the first line of the script file, followed by the name of
the script file, followed by the rest of the arguments. Bash
themselves. Note that some older versions of Unix limit the interpreter
name and argument to a maximum of 32 characters.
-@node Bourne Shell Features
-@chapter Bourne Shell Style Features
+Bash scripts often begin with @code{#! /bin/bash} (assuming that
+Bash has been installed in @file{/bin}), since this ensures that
+Bash will be used to interpret the script, even if it is executed
+under another shell.
+
+@node Shell Builtin Commands
+@chapter Shell Builtin Commands
@menu
* Bourne Shell Builtins:: Builtin commands inherited from the Bourne
Shell.
-* Bourne Shell Variables:: Variables which Bash uses in the same way
- as the Bourne Shell.
-* Other Bourne Shell Features:: Addtional aspects of Bash which behave in
- the same way as the Bourne Shell.
+* Bash Builtins:: Table of builtins specific to Bash.
+* The Set Builtin:: This builtin is so overloaded it
+ deserves its own section.
+* Special Builtins:: Builtin commands classified specially by
+ POSIX.2.
@end menu
-This section briefly summarizes things which Bash inherits from
-the Bourne Shell: builtins, variables, and other features.
-It also lists the significant differences between Bash and the Bourne Shell.
-Many of the builtins have been extended by @sc{POSIX} or Bash.
+Builtin commands are contained within the shell itself.
+When the name of a builtin command is used as the first word of
+a simple command (@pxref{Simple Commands}), the shell executes
+the command directly, without invoking another program.
+Builtin commands are necessary to implement functionality impossible
+or inconvenient to obtain with separate utilities.
+
+This section briefly 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.
@node Bourne Shell Builtins
@section Bourne Shell Builtins
-The following shell builtin commands are inherited from the Bourne
-Shell. These commands are implemented as specified by the @sc{POSIX}
-1003.2 standard.
+The following shell builtin commands are inherited from the Bourne Shell.
+These commands are implemented as specified by the @sc{posix} 1003.2 standard.
@table @code
-@item :
+@item : @r{(a colon)}
@btindex :
@example
: [@var{arguments}]
Do nothing beyond expanding @var{arguments} and performing redirections.
The return status is zero.
-@item .
+@item . @r{(a period)}
@btindex .
@example
. @var{filename} [@var{arguments}]
@end example
Read and execute commands from the @var{filename} argument in the
current shell context. If @var{filename} does not contain a slash,
-the @code{$PATH} variable is used to find
+the @code{PATH} variable is used to find
@var{filename}. The current directory is searched if @var{filename}
is not found in @code{$PATH}.
If any @var{arguments} are supplied, they become the positional
The return status is the exit status of the last command executed, or
zero if no commands are executed. If @var{filename} is not found, or
cannot be read, the return status is non-zero.
+This builtin is equivalent to @code{source}.
@item break
@btindex break
@end example
If @var{command}
is supplied, it replaces the shell without creating a new process.
-If the @samp{-l} option is supplied, the shell places a dash in the
-zeroth arg passed to @var{command}.
+If the @samp{-l} option is supplied, the shell places a dash at the
+beginning of the zeroth arg passed to @var{command}.
This is what the @code{login} program does.
The @samp{-c} option causes @var{command} to be executed with an empty
environment.
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
getopts @var{optstring} @var{name} [@var{args}]
@end example
@code{getopts} is used by shell scripts to parse positional parameters.
-@var{optstring} contains the option letters to be recognized; if a letter
-is followed by a colon, the option is expected to have an
+@var{optstring} contains the option characters to be recognized; if a
+character is followed by a colon, the option is expected to have an
argument, which should be separated from it by white space.
+The colon (@samp{:}) and question mark (@samp{?}) may not be
+used as option characters.
Each time it is invoked, @code{getopts}
places the next option in the shell variable @var{name}, initializing
@var{name} if it does not exist,
@example
pwd [-LP]
@end example
-Print the current working directory.
-If the @samp{-P} option is supplied, the path printed will not
+Print the absolute pathname of the current working directory.
+If the @samp{-P} option is supplied, the pathname printed will not
contain symbolic links.
-If the @samp{-L} option is supplied, the path printed may contain
+If the @samp{-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
return [@var{n}]
@end example
Cause a shell function to exit with the return value @var{n}.
+If @var{n} is not supplied, the return value is the exit status of the
+last command executed in the function.
This may also be used to terminate execution of a script being executed
-with the @code{.} builtin, returning either @var{n} or the exit status
-of the last command executed within the script as the exit status of the
-script.
+with the @code{.} (or @code{source}) builtin, returning either @var{n} or
+the exit status of the last command executed within the script as the exit
+status of the script.
The return status is false if @code{return} is used outside a function
-and not during the execution of a script by @samp{.}.
+and not during the execution of a script by @code{.} or @code{source}.
@item shift
@btindex shift
@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.
Expressions are composed of the primaries described below in
@ref{Bash Conditional Expressions}.
+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.
they had when the shell was started.
If @var{arg} is the null string, then the signal specified by
each @var{sigspec} is ignored by the shell and commands it invokes.
-If @var{arg} is @samp{-p}, the shell displays the trap commands
-associated with each @var{sigspec}. If no arguments are supplied, or
+If @var{arg} is not present and @samp{-p} has been supplied,
+the shell displays the trap commands associated with each @var{sigspec}.
+If no arguments are supplied, or
only @samp{-p} is given, @code{trap} prints the list of commands
associated with each signal number in a form that may be reused as
shell 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
readonly.
@end table
-@node Bourne Shell Variables
-@section Bourne Shell Variables
-
-Bash uses certain shell variables in the same way as the Bourne shell.
-In some cases, Bash assigns a default value to the variable.
+@node Bash Builtins
+@section Bash Builtin Commands
-@vtable @code
+This section describes builtin commands which are unique to
+or have been extended in Bash.
+Some of these commands are specified in the @sc{posix} 1003.2 standard.
-@item CDPATH
-A colon-separated list of directories used as a search path for
-the @code{cd} builtin command.
+@table @code
-@item HOME
-The current user's home directory; the default for the @code{cd} builtin
-command.
-The value of this variable is also used by tilde expansion
-(@pxref{Tilde Expansion}).
+@item alias
+@btindex alias
+@example
+alias [@code{-p}] [@var{name}[=@var{value}] @dots{}]
+@end example
-@item IFS
-A list of characters that separate fields; used when the shell splits
-words as part of expansion.
+Without arguments or with the @samp{-p} option, @code{alias} prints
+the list of aliases on the standard output in a form that allows
+them to be reused as input.
+If arguments are supplied, an alias is defined for each @var{name}
+whose @var{value} is given. If no @var{value} is given, the name
+and value of the alias is printed.
+Aliases are described in @ref{Aliases}.
-@item MAIL
-If this parameter is set to a filename and the @code{MAILPATH} variable
-is not set, Bash informs the user of the arrival of mail in
-the specified file.
+@item bind
+@btindex bind
+@example
+bind [-m @var{keymap}] [-lpsvPSV]
+bind [-m @var{keymap}] [-q @var{function}] [-u @var{function}] [-r @var{keyseq}]
+bind [-m @var{keymap}] -f @var{filename}
+bind [-m @var{keymap}] -x @var{keyseq:shell-command}
+bind [-m @var{keymap}] @var{keyseq:function-name}
+@end example
-@item MAILPATH
-A colon-separated list of filenames which the shell periodically checks
-for new mail.
-Each list entry can specify the message that is printed when new mail
-arrives in the mail file by separating the file name from the message with
-a @samp{?}.
-When used in the text of the message, @code{$_} expands to the name of
-the current mail file.
+Display current Readline (@pxref{Command Line Editing})
+key and function bindings, or
+bind a key sequence to a Readline function or macro. The
+binding syntax accepted is identical to that of
+a Readline initialization file (@pxref{Readline Init File}),
+but each binding must be passed as a separate argument: e.g.,
+@samp{"\C-x\C-r":re-read-init-file}.
+Options, if supplied, have the following meanings:
-@item OPTARG
-The value of the last option argument processed by the @code{getopts} builtin.
+@table @code
+@item -m @var{keymap}
+Use @var{keymap} as the keymap to be affected by
+the subsequent bindings. Acceptable @var{keymap}
+names are
+@code{emacs},
+@code{emacs-standard},
+@code{emacs-meta},
+@code{emacs-ctlx},
+@code{vi},
+@code{vi-command}, and
+@code{vi-insert}.
+@code{vi} is equivalent to @code{vi-command};
+@code{emacs} is equivalent to @code{emacs-standard}.
-@item OPTIND
-The index of the last option argument processed by the @code{getopts} builtin.
+@item -l
+List the names of all Readline functions.
-@item PATH
-A colon-separated list of directories in which the shell looks for
-commands.
+@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 PS1
-The primary prompt string. The default value is @samp{\s-\v\$ }.
+@item -P
+List current Readline function names and bindings.
-@item PS2
-The secondary prompt string. The default value is @samp{> }.
+@item -v
+Display Readline variable names and values in such a way that they
+can be used as input or in a Readline initialization file.
-@end vtable
+@item -V
+List current Readline variable names and values.
-@node Other Bourne Shell Features
-@section Other Bourne Shell Features
+@item -s
+Display Readline key sequences bound to macros and the strings they output
+in such a way that they can be used as input or in a Readline
+initialization file.
-@menu
-* Major Differences From The Bourne Shell:: Major differences between
- Bash and the Bourne shell.
-@end menu
+@item -S
+Display Readline key sequences bound to macros and the strings they output.
-Bash implements essentially the same grammar, parameter and
-variable expansion, redirection, and quoting as the Bourne Shell.
-Bash uses the @sc{POSIX} 1003.2 standard as the specification of
-how these features are to be implemented. There are some
-differences between the traditional Bourne shell and Bash; this
-section quickly details the differences of significance. A
-number of these differences are explained in greater depth in
-subsequent sections.
+@item -f @var{filename}
+Read key bindings from @var{filename}.
-@node Major Differences From The Bourne Shell
-@subsection Major Differences From The SVR4.2 Bourne Shell
+@item -q @var{function}
+Query about which keys invoke the named @var{function}.
-@itemize @bullet
+@item -u @var{function}
+Unbind all keys bound to the named @var{function}.
-@item
-Bash is @sc{POSIX}-conformant, even where the @sc{POSIX} specification
-differs from traditional @code{sh} behavior.
+@item -r @var{keyseq}
+Remove any current binding for @var{keyseq}.
-@item
-Bash has multi-character invocation options (@pxref{Invoking Bash}).
+@item -x @var{keyseq:shell-command}
+Cause @var{shell-command} to be executed whenever @var{keyseq} is
+entered.
-@item
-Bash has command-line editing (@pxref{Command Line Editing}) and
-the @code{bind} builtin.
+@end table
-@item
-Bash has command history (@pxref{Bash History Facilities}) and the
-@code{history} and @code{fc} builtins to manipulate it.
+@noindent
+The return status is zero unless an invalid option is supplied or an
+error occurs.
-@item
-Bash implements @code{csh}-like history expansion
-(@pxref{History Interaction}).
+@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
-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 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
+@code{PATH} are executed.
+If there is a shell function named @code{ls}, running @samp{command ls}
+within the function will execute the external command @code{ls}
+instead of calling the function recursively.
+The @samp{-p} option means to use a default value for @code{$PATH}
+that is guaranteed to find all of the standard utilities.
+The return status in this case is 127 if @var{command} cannot be
+found or an error occurred, and the exit status of @var{command}
+otherwise.
-@item
-The @code{$'@dots{}'} quoting syntax, which expands ANSI-C
-backslash-escaped characters in the text between the single quotes,
-is supported (@pxref{ANSI-C Quoting}).
+If either the @samp{-V} or @samp{-v} option is supplied, a
+description of @var{command} is printed. The @samp{-v} option
+causes a single word indicating the command or file name used to
+invoke @var{command} to be displayed; the @samp{-V} option produces
+a more verbose description. In this case, the return status is
+zero if @var{command} is found, and non-zero if not.
-@item
-Bash supports the @code{$"@dots{}"} quoting syntax to do
-locale-specific translation of the characters between the double
-quotes. The @samp{-D}, @samp{--dump-strings}, and @samp{--dump-po-strings}
-invocation options list the translatable strings found in a script
-(@pxref{Locale Translation}).
+@item declare
+@btindex declare
+@example
+declare [-afFrxi] [-p] [@var{name}[=@var{value}]]
+@end example
-@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.
+Declare variables and give them attributes. If no @var{name}s
+are given, then display the values of variables instead.
-@item
-Bash has the @code{time} reserved word and command timing (@pxref{Pipelines}).
-The display of the timing statistics may be controlled with the
-@code{TIMEFORMAT} variable.
+The @samp{-p} option will display the attributes and values of each
+@var{name}. When @samp{-p} is used, additional options are ignored.
+The @samp{-F} option inhibits the display of function definitions;
+only the function name and attributes are printed. @samp{-F} implies
+@samp{-f}. The following options can be used to restrict output
+to variables with the specified attributes or to give variables
+attributes:
-@item
-Bash includes the @code{select} compound command, which allows the
-generation of simple menus (@pxref{Conditional Constructs}).
+@table @code
+@item -a
+Each @var{name} is an array variable (@pxref{Arrays}).
-@item
-Bash includes the @code{[[} compound command, which makes conditional
-testing part of the shell grammar (@pxref{Conditional Constructs}).
+@item -f
+Use function names only.
-@item
-Bash includes brace expansion (@pxref{Brace Expansion}) and tilde
-expansion (@pxref{Tilde Expansion}).
+@item -i
+The variable is to be treated as
+an integer; arithmetic evaluation (@pxref{Shell Arithmetic}) is
+performed when the variable is assigned a value.
-@item
-Bash implements command aliases and the @code{alias} and @code{unalias}
-builtins (@pxref{Aliases}).
+@item -r
+Make @var{name}s readonly. These names cannot then be assigned values
+by subsequent assignment statements or unset.
-@item
-Bash provides shell arithmetic, the @code{((} compound command
-(@pxref{Conditional Constructs}),
-and arithmetic expansion (@pxref{Shell Arithmetic}).
+@item -x
+Mark each @var{name} for export to subsequent commands via
+the environment.
+@end table
-@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.
+Using @samp{+} instead of @samp{-} turns off the attribute instead.
+When used in a function, @code{declare} makes each @var{name} local,
+as with the @code{local} command.
-@item
-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}).
+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 @samp{-f}.
-@item
-The expansion @code{$@{#xx@}}, which returns the length of @code{$@{xx@}},
-is supported (@pxref{Shell Parameter Expansion}).
+@item echo
+@btindex echo
+@example
+echo [-neE] [@var{arg} @dots{}]
+@end example
+Output the @var{arg}s, separated by spaces, terminated with a
+newline.
+The return status is always 0.
+If @samp{-n} is specified, the trailing newline is suppressed.
+If the @samp{-e} option is given, interpretation of the following
+backslash-escaped characters is enabled.
+The @samp{-E} option disables the interpretation of these escape characters,
+even on systems where they are interpreted by default.
+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} interprets the following escape sequences:
+@table @code
+@item \a
+alert (bell)
+@item \b
+backspace
+@item \c
+suppress trailing newline
+@item \e
+escape
+@item \f
+form feed
+@item \n
+new line
+@item \r
+carriage return
+@item \t
+horizontal tab
+@item \v
+vertical tab
+@item \\
+backslash
+@item \@var{nnn}
+the character whose @code{ASCII} code is the octal value @var{nnn}
+(one to three digits)
+@item \x@var{nnn}
+the character whose @code{ASCII} code is the hexadecimal value @var{nnn}
+(one to three digits)
+@end table
-@item
-The expansion @code{$@{var:}@var{offset}@code{[:}@var{length}@code{]@}},
-which expands to the substring of @code{var}'s value of length
-@var{length}, beginning at @var{offset}, is present
-(@pxref{Shell Parameter Expansion}).
+@item enable
+@btindex enable
+@example
+enable [-n] [-p] [-f @var{filename}] [-ads] [@var{name} @dots{}]
+@end example
+Enable and disable builtin shell commands.
+Disabling a builtin allows a disk command which has the same name
+as a shell builtin to be executed without specifying a full pathname,
+even though the shell normally searches for builtins before disk commands.
+If @samp{-n} is used, the @var{name}s become disabled. Otherwise
+@var{name}s are enabled. For example, to use the @code{test} binary
+found via @code{$PATH} instead of the shell builtin version, type
+@samp{enable -n test}.
-@item
-The expansion
-@code{$@{var/[/]}@var{pattern}@code{[/}@var{replacement}@code{]@}},
-which matches @var{pattern} and replaces it with @var{replacement} in
-the value of @code{var}, is available (@pxref{Shell Parameter Expansion}).
+If the @samp{-p} option is supplied, or no @var{name} arguments appear,
+a list of shell builtins is printed. With no other arguments, the list
+consists of all enabled shell builtins.
+The @samp{-a} option means to list
+each builtin with an indication of whether or not it is enabled.
-@item
-Bash has @var{indirect} variable expansion using @code{$@{!word@}}
-(@pxref{Shell Parameter Expansion}).
+The @samp{-f} option means to load the new builtin command @var{name}
+from shared object @var{filename}, on systems that support dynamic loading.
+The @samp{-d} option will delete a builtin loaded with @samp{-f}.
-@item
-Bash can expand positional parameters beyond @code{$9} using
-@code{$@{@var{num}@}}.
+If there are no options, a list of the shell builtins is displayed.
+The @samp{-s} option restricts @code{enable} to the @sc{posix} special
+builtins. If @samp{-s} is used with @samp{-f}, the new builtin becomes
+a special builtin (@pxref{Special Builtins}).
-@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).
+The return status is zero unless a @var{name} is not a shell builtin
+or there is an error loading a new builtin from a shared object.
-@item
-Bash has process substitution (@pxref{Process Substitution}).
+@item help
+@btindex help
+@example
+help [-s] [@var{pattern}]
+@end example
+Display helpful information about builtin commands.
+If @var{pattern} is specified, @code{help} gives detailed help
+on all commands matching @var{pattern}, otherwise a list of
+the builtins is printed.
+The @samp{-s} option restricts the information displayed to a short
+usage synopsis.
+The return status is zero unless no command matches @var{pattern}.
-@item
-Bash automatically assigns variables that provide information about the
-current user (@code{UID}, @code{EUID}, and @code{GROUPS}), the current host
-(@code{HOSTTYPE}, @code{OSTYPE}, @code{MACHTYPE}, and @code{HOSTNAME}),
-and the instance of Bash that is running (@code{BASH},
-@code{BASH_VERSION}, and @code{BASH_VERSINFO}). @xref{Bash Variables},
-for details.
+@item let
+@btindex let
+@example
+let @var{expression} [@var{expression}]
+@end example
+The @code{let} builtin allows arithmetic to be performed on shell
+variables. Each @var{expression} is evaluated according to the
+rules given below in @ref{Shell Arithmetic}. If the
+last @var{expression} evaluates to 0, @code{let} returns 1;
+otherwise 0 is returned.
-@item
-The @code{IFS} variable is used to split only the results of expansion,
-not all words (@pxref{Word Splitting}).
-This closes a longstanding shell security hole.
+@item local
+@btindex local
+@example
+local [@var{option}] @var{name}[=@var{value}]
+@end example
+For each argument, a local variable named @var{name} is created,
+and assigned @var{value}.
+The @var{option} can be any of the options accepted by @code{declare}.
+@code{local} can only be used within a function; it makes the variable
+@var{name} have a visible scope restricted to that function and its
+children. The return status is zero unless @code{local} is used outside
+a function, an invalid @var{name} is supplied, or @var{name} is a
+readonly variable.
-@item
-Bash implements the full set of @sc{POSIX.2} filename expansion operators,
-including @var{character classes}, @var{equivalence classes}, and
-@var{collating symbols} (@pxref{Filename Expansion}).
+@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
-Bash implements extended pattern matching features when the @code{extglob}
-shell option is enabled (@pxref{Pattern Matching}).
+@item printf
+@btindex printf
+@example
+@code{printf} @var{format} [@var{arguments}]
+@end example
+Write the formatted @var{arguments} to the standard output under the
+control of the @var{format}.
+The @var{format} is a character string which contains three types of objects:
+plain characters, which are simply copied to standard output, character
+escape sequences, which are converted and copied to the standard output, and
+format specifications, each of which causes printing of the next successive
+@var{argument}.
+In addition to the standard @code{printf(1)} formats, @samp{%b} causes
+@code{printf} to expand backslash escape sequences in the corresponding
+@var{argument}, and @samp{%q} causes @code{printf} to output the
+corresponding @var{argument} in a format that can be reused as shell input.
-@item
-It is possible to have a variable and a function with the same name;
-@code{sh} does not separate the two name spaces.
+The @var{format} is reused as necessary to consume all of the @var{arguments}.
+If the @var{format} requires more @var{arguments} than are supplied, the
+extra format specifications behave as if a zero value or null string, as
+appropriate, had been supplied. The return value is zero on success,
+non-zero on failure.
-@item
-Bash functions are permitted to have local variables using the
-@code{local} builtin, and thus useful recursive functions may be written.
+@item read
+@btindex read
+@example
+read [-ers] [-a @var{aname}] [-p @var{prompt}] [-t @var{timeout}] [-n @var{nchars}] [-d @var{delim}] [@var{name} @dots{}]
+@end example
+One line is read from the standard input, and the first word
+is assigned to the first @var{name}, the second word to the second @var{name},
+and so on, with leftover words and their intervening separators assigned
+to the last @var{name}.
+If there are fewer words read from the standard input than names,
+the remaining names are assigned empty values.
+The characters in the value of the @code{IFS} variable
+are used to split the line into words.
+The backslash character @samp{\} may be used to remove any special
+meaning for the next character read and for line continuation.
+If no names are supplied, the line read is assigned to the
+variable @code{REPLY}.
+The return code is zero, unless end-of-file is encountered or @code{read}
+times out.
+Options, if supplied, have the following meanings:
-@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.
+@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
-Bash performs filename expansion on filenames specified as operands
-to input and output redirection operators.
+@item -d @var{delim}
+The first character of @var{delim} is used to terminate the input line,
+rather than newline.
-@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 -e
+Readline (@pxref{Command Line Editing}) is used to obtain the line.
-@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 -n @var{nchars}
+@code{read} returns after reading @var{nchars} characters rather than
+waiting for a complete line of input.
-@item
-The Bash @code{cd} and @code{pwd} builtins (@pxref{Bourne Shell Builtins})
-each take @samp{-L} and @samp{-P} builtins to switch between logical and
-physical modes.
+@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
-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 -r
+If this option is given, backslash does not act as an escape character.
+The backslash is considered to be part of the line.
+In particular, a backslash-newline pair may not be used as a line
+continuation.
-@item
-The @code{command} builtin allows selective disabling of functions
-when command lookup is performed (@pxref{Bash Builtins}).
+@item -s
+Silent mode. If input is coming from a terminal, characters are
+not echoed.
-@item
-Individual builtins may be enabled or disabled using the @code{enable}
-builtin (@pxref{Bash Builtins}).
+@item -t @var{timeout}
+Cause @code{read} to time out and return failure if a complete line of
+input is not read within @var{timeout} seconds.
+This option has no effect if @code{read} is not reading input from the
+terminal or a pipe.
-@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}).
+@end table
-@item
-Shell functions may be exported to children via the environment
-using @code{export -f} (@pxref{Shell Functions}).
+@item shopt
+@btindex shopt
+@example
+shopt [-pqsu] [-o] [@var{optname} @dots{}]
+@end example
+Toggle the values of variables controlling optional shell behavior.
+With no options, or with the @samp{-p} option, a list of all settable
+options is displayed, with an indication of whether or not each is set.
+The @samp{-p} option causes output to be displayed in a form that
+may be reused as input.
+Other options have the following meanings:
-@item
-The Bash @code{export}, @code{readonly}, and @code{declare} builtins can
-take a @samp{-f} option to act on shell functions, a @samp{-p} option to
-display variables with various attributes set in a format that can be
-used as shell input, a @samp{-n} option to remove various variable
-attributes, and @samp{name=value} arguments to set variable attributes
-and values simultaneously.
+@table @code
+@item -s
+Enable (set) each @var{optname}.
-@item
-The Bash @code{hash} builtin allows a name to be associated with
-an arbitrary filename, even when that filename cannot be found by
-searching the @code{$PATH}, using @samp{hash -p}
-(@pxref{Bourne Shell Builtins}).
+@item -u
+Disable (unset) each @var{optname}.
-@item
-Bash includes a @code{help} builtin for quick reference to shell
-facilities (@pxref{Bash Builtins}).
+@item -q
+Suppresses normal output; the return status
+indicates whether the @var{optname} is set or unset.
+If multiple @var{optname} arguments are given with @samp{-q},
+the return status is zero if all @var{optnames} are enabled;
+non-zero otherwise.
-@item
-The @code{printf} builtin is available to display formatted output
-(@pxref{Bash Builtins}).
+@item -o
+Restricts the values of
+@var{optname} to be those defined for the @samp{-o} option to the
+@code{set} builtin (@pxref{The Set Builtin}).
+@end table
-@item
-The Bash @code{read} builtin (@pxref{Bash Builtins})
-will read a line ending in @samp{\} with
-the @samp{-r} option, and will use the @code{REPLY} variable as a
-default if no arguments are supplied. The Bash @code{read} builtin
-also accepts a prompt string with the @samp{-p} option and will use
-Readline to obtain the line when given the @samp{-e} option.
+If either @samp{-s} or @samp{-u}
+is used with no @var{optname} arguments, the display is limited to
+those options which are set or unset, respectively.
-@item
-The @code{return} builtin may be used to abort execution of scripts
-executed with the @code{.} or @code{source} builtins
-(@pxref{Bourne Shell Builtins}).
+Unless otherwise noted, the @code{shopt} options are disabled (off)
+by default.
-@item
-Bash includes the @code{shopt} builtin, for finer control of shell
-optional capabilities (@pxref{Bash Builtins}).
+The return status when listing options is zero if all @var{optnames}
+are enabled, non-zero otherwise. When setting or unsetting options,
+the return status is zero unless an @var{optname} is not a valid shell
+option.
-@item
-Bash has much more optional behavior controllable with the @code{set}
-builtin (@pxref{The Set Builtin}).
+The list of @code{shopt} options is:
+@table @code
+@item cdable_vars
+If this is set, an argument to the @code{cd}
+builtin command that
+is not a directory is assumed to be the name of a variable whose
+value is the directory to change to.
-@item
-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 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
-The @code{trap} builtin (@pxref{Bourne Shell Builtins})
-allows a @code{DEBUG} pseudo-signal specification,
-similar to @code{EXIT}. Commands specified with a @code{DEBUG} trap are
-executed after every simple command. The @code{DEBUG} trap is not
-inherited by shell functions.
+@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
-The Bash @code{type} builtin is more extensive and gives more information
-about the names it finds (@pxref{Bash Builtins}).
+@item checkwinsize
+If set, Bash checks the window size after each command
+and, if necessary, updates the values of
+@code{LINES} and @code{COLUMNS}.
-@item
-The Bash @code{umask} builtin permits a @samp{-p} option to cause
-the output to be displayed in the form of a @code{umask} command
-that may be reused as input (@pxref{Bourne Shell Builtins}).
+@item cmdhist
+If set, Bash
+attempts to save all lines of a multiple-line
+command in the same history entry. This allows
+easy re-editing of multi-line commands.
-@item
-Bash implements a @code{csh}-like directory stack, and provides the
-@code{pushd}, @code{popd}, and @code{dirs} builtins to manipulate it
-(@pxref{The Directory Stack}).
-Bash also makes the directory stack visible as the value of the
-@code{DIRSTACK} shell variable.
+@item dotglob
+If set, Bash includes filenames beginning with a `.' in
+the results of filename expansion.
-@item
-Bash interprets special backslash-escaped characters in the prompt
-strings when interactive (@pxref{Printing a Prompt}).
+@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
-The Bash restricted mode is more useful (@pxref{The Restricted Shell});
-the @sc{SVR4.2} shell restricted mode is too limited.
+@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
-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 extglob
+If set, the extended pattern matching features described above
+(@pxref{Pattern Matching}) are enabled.
-@item
-The @sc{SVR4.2} shell has two privilege-related builtins
-(@code{mldmode} and @code{priv}) not present in Bash.
+@item histappend
+If set, the history list is appended to the file named by the value
+of the @code{HISTFILE}
+variable when the shell exits, rather than overwriting the file.
-@item
-Bash does not have the @code{stop} or @code{newgrp} builtins.
+@item histreedit
+If set, and Readline
+is being used, a user is given the opportunity to re-edit a
+failed history substitution.
-@item
-Bash does not use the @code{SHACCT} variable or perform shell accounting.
+@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
-The @sc{SVR4.2} @code{sh} uses a @code{TIMEOUT} variable like Bash uses
-@code{TMOUT}.
+@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.
-@end itemize
+@item huponexit
+If set, Bash will send @code{SIGHUP} to all jobs when an interactive
+login shell exits (@pxref{Signals}).
-@noindent
-More features unique to Bash may be found in @ref{Bash Features}.
+@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.
-@subsection Implementation Differences From The SVR4.2 Shell
+@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.
-Since Bash is a completely new implementation, it does not suffer from
-many of the limitations of the @sc{SVR4.2} shell. For instance:
+@item 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.
-@itemize @bullet
+@item no_empty_cmd_completion
+If set, and Readline is being used, Bash will not attempt to search
+the @code{PATH} for possible completions when completion is attempted
+on an empty line.
-@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 nocaseglob
+If set, Bash matches filenames in a case-insensitive fashion when
+performing filename expansion.
-@item
-Bash does not allow unbalanced quotes. The @sc{SVR4.2} shell will silently
-insert a needed closing quote at @code{EOF} under certain circumstances.
-This can be the cause of some hard-to-find errors.
+@item nullglob
+If set, Bash allows filename patterns which match no
+files to expand to a null string, rather than themselves.
-@item
-The @sc{SVR4.2} shell uses a baroque memory management scheme based on
-trapping @code{SIGSEGV}. If the shell is started from a process with
-@code{SIGSEGV} blocked (e.g., by using the @code{system()} C library
-function call), it misbehaves badly.
+@item progcomp
+If set, the programmable completion facilities
+(@pxref{Programmable Completion}) are enabled.
+This option is enabled by default.
-@item
-In a questionable attempt at security, the @sc{SVR4.2} shell,
-when invoked without the @samp{-p} option, will alter its real
-and effective @sc{UID} and @sc{GID} if they are less than some
-magic threshold value, commonly 100.
-This can lead to unexpected results.
+@item promptvars
+If set, prompt strings undergo variable and parameter expansion after
+being expanded (@pxref{Printing a Prompt}).
+This option is enabled by default.
-@item
-The @sc{SVR4.2} shell does not allow users to trap @code{SIGSEGV},
-@code{SIGALRM}, or @code{SIGCHLD}.
+@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
-The @sc{SVR4.2} shell does not allow the @code{IFS}, @code{MAILCHECK},
-@code{PATH}, @code{PS1}, or @code{PS2} variables to be unset.
+@item 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
-The @sc{SVR4.2} shell treats @samp{^} as the undocumented equivalent of
-@samp{|}.
+@item sourcepath
+If set, the @code{source} builtin uses the value of @code{PATH}
+to find the directory containing the file supplied as an argument.
+This option is enabled by default.
-@item
-Bash allows multiple option arguments when it is invoked (@code{-x -v});
-the @sc{SVR4.2} shell allows only one option argument (@code{-xv}). In
-fact, some versions of the shell dump core if the second argument begins
-with a @samp{-}.
+@item xpg_echo
+If set, the @code{echo} builtin expands backslash-escape sequences
+by default.
-@item
-The @sc{SVR4.2} shell exits a script if any builtin fails; Bash exits
-a script only if one of the @sc{POSIX.2} special builtins fails, and
-only for certain failures, as enumerated in the @sc{POSIX.2} standard.
+@end table
-@item
-The @sc{SVR4.2} shell behaves differently when invoked as @code{jsh}
-(it turns on job control).
-@end itemize
+@noindent
+The return status when listing options is zero if all @var{optnames}
+are enabled, non-zero otherwise.
+When setting or unsetting options, the return status is zero unless an
+@var{optname} is not a valid shell option.
-@node Bash Features
-@chapter Bash Features
+@item source
+@btindex source
+@example
+source @var{filename}
+@end example
+A synonym for @code{.} (@pxref{Bourne Shell Builtins}).
-This section describes features unique to Bash.
+@item type
+@btindex type
+@example
+type [-atp] [@var{name} @dots{}]
+@end example
+For each @var{name}, indicate how it would be interpreted if used as a
+command name.
-@menu
-* Invoking Bash:: Command line options that you can give
- to Bash.
-* Bash Startup Files:: When and how Bash executes scripts.
-* Is This Shell Interactive?:: Determining the state of a running Bash.
-* Bash Builtins:: Table of builtins specific to Bash.
-* The Set Builtin:: This builtin is so overloaded it
- deserves its own section.
-* Bash Conditional Expressions:: Primitives used in composing expressions for
- the @code{test} builtin.
-* Bash Variables:: List of variables that exist in Bash.
-* Shell Arithmetic:: Arithmetic on shell variables.
-* Aliases:: Substituting one command for another.
-* Arrays:: Array Variables.
-* The Directory Stack:: History of visited directories.
-* Printing a Prompt:: Controlling the PS1 string.
-* The Restricted Shell:: A more controlled mode of shell execution.
-* Bash POSIX Mode:: Making Bash behave more closely to what
- the POSIX standard specifies.
-@end menu
+If the @samp{-t} option is used, @code{type} prints a single word
+which is one of @samp{alias}, @samp{function}, @samp{builtin},
+@samp{file} or @samp{keyword},
+if @var{name} is an alias, shell function, shell builtin,
+disk file, or shell reserved word, respectively.
+If the @var{name} is not found, then nothing is printed, and
+@code{type} returns a failure status.
-@node Invoking Bash
-@section Invoking Bash
+If the @samp{-p} option is used, @code{type} either returns the name
+of the disk file that would be executed, or nothing if @samp{-t}
+would not return @samp{file}.
+
+If the @samp{-a} option is used, @code{type} returns all of the places
+that contain an executable named @var{file}.
+This includes aliases and functions, if and only if the @samp{-p} option
+is not also used.
+
+The return status is zero if any of the @var{names} are found, non-zero
+if none are found.
+@item typeset
+@btindex typeset
@example
-bash [long-opt] [-ir] [-abefhkmnptuvxdBCDHP] [-o @var{option}] [@var{argument} @dots{}]
-bash [long-opt] [-abefhkmnptuvxdBCDHP] [-o @var{option}] -c @var{string} [@var{argument} @dots{}]
-bash [long-opt] -s [-abefhkmnptuvxdBCDHP] [-o @var{option}] [@var{argument} @dots{}]
+typeset [-afFrxi] [-p] [@var{name}[=@var{value}]]
@end example
+The @code{typeset} command is supplied for compatibility with the Korn
+shell; however, it has been deprecated in favor of the @code{declare}
+builtin command.
-In addition to the single-character shell command-line options
-(@pxref{The Set Builtin}), there are several multi-character
-options that you can use. These options must appear on the command
-line before the single-character options in order for them
-to be recognized.
-
+@item ulimit
+@btindex ulimit
+@example
+ulimit [-acdflmnpstuvSH] [@var{limit}]
+@end example
+@code{ulimit} provides control over the resources available to processes
+started by the shell, on systems that allow such control. If an
+option is given, it is interpreted as follows:
@table @code
-@item --dump-po-strings
-Equivalent to @samp{-D}, but the output is in the GNU @code{gettext}
-PO (portable object) file format.
-
-@item --dump-strings
-Equivalent to @samp{-D}.
+@item -S
+Change and report the soft limit associated with a resource.
-@item --help
-Display a usage message on standard output and exit sucessfully.
+@item -H
+Change and report the hard limit associated with a resource.
-@item --login
-Make this shell act as if it were directly invoked by login.
-This is equivalent to @samp{exec -l bash} but can be issued from
-another shell, such as @code{csh}. @samp{exec bash --login}
-will replace the current shell with a Bash login shell.
+@item -a
+All current limits are reported.
-@item --noediting
-Do not use the @sc{GNU} Readline library (@pxref{Command Line Editing})
-to read interactive command lines.
+@item -c
+The maximum size of core files created.
-@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 -d
+The maximum size of a process's data segment.
-@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 -f
+The maximum size of files created by the shell.
-@item --posix
-Change the behavior of Bash where the default operation differs
-from the @sc{POSIX} 1003.2 standard to match the standard. This
-is intended to make Bash behave as a strict superset of that
-standard. @xref{Bash POSIX Mode}, for a description of the Bash
-@sc{POSIX} mode.
+@item -l
+The maximum size that may be locked into memory.
-@item --rcfile @var{filename}
-Execute commands from @var{filename} (instead of @file{~/.bashrc})
-in an interactive shell.
+@item -m
+The maximum resident set size.
-@item --restricted
-Make the shell a restricted shell (@pxref{The Restricted Shell}).
+@item -n
+The maximum number of open file descriptors.
-@item --verbose
-Equivalent to @samp{-v}.
+@item -p
+The pipe buffer size.
-@item --version
-Show version information for this instance of
-Bash on the standard output and exit successfully.
+@item -s
+The maximum stack size.
-@end table
+@item -t
+The maximum amount of cpu time in seconds.
-There are several single-character options that may be supplied at
-invocation which are not available with the @code{set} builtin.
+@item -u
+The maximum number of processes available to a single user.
-@table @code
-@item -c @var{string}
-Read and execute commands from @var{string} after processing the
-options, then exit. Any remaining arguments are assigned to the
-positional parameters, starting with @code{$0}.
+@item -v
+The maximum amount of virtual memory available to the process.
-@item -i
-Force the shell to run interactively.
+@end table
-@item -r
-Make the shell a restricted shell (@pxref{The Restricted Shell}).
+If @var{limit} is given, it is the new value of the specified resource.
+Otherwise, the current value of the soft limit for the specified resource
+is printed, unless the @samp{-H} option is supplied.
+When setting new limits, if neither @samp{-H} nor @samp{-S} is supplied,
+both the hard and soft limits are set.
+If no option is given, then @samp{-f} is assumed. Values are in 1024-byte
+increments, except for @samp{-t}, which is in seconds, @samp{-p},
+which is in units of 512-byte blocks, and @samp{-n} and @samp{-u}, which
+are unscaled values.
-@item -s
-If this option is present, or if no arguments remain after option
-processing, then commands are read from the standard input.
-This option allows the positional parameters to be set
-when invoking an interactive shell.
+The return status is zero unless an invalid option is supplied, a
+non-numeric argument other than @code{unlimited} is supplied as a
+@var{limit}, or an error occurs while setting a new limit.
-@item -D
-A list of all double-quoted strings preceded by @samp{$}
-is printed on the standard ouput.
-These are the strings that
-are subject to language translation when the current locale
-is not @code{C} or @code{POSIX} (@pxref{Locale Translation}).
-This implies the @samp{-n} option; no commands will be executed.
+@item unalias
+@btindex unalias
+@example
+unalias [-a] [@var{name} @dots{} ]
+@end example
-@item --
-A @code{--} signals the end of options and disables further option
-processing.
-Any arguments after the @code{--} are treated as filenames and arguments.
+Remove each @var{name} from the list of aliases. If @samp{-a} is
+supplied, all aliases are removed.
+Aliases are described in @ref{Aliases}.
@end table
-@cindex interactive shell
-An @emph{interactive} shell is one whose input and output are both
-connected to terminals (as determined by @code{isatty(3)}), or one
-started with the @samp{-i} option.
+@node The Set Builtin
+@section The Set Builtin
-If arguments remain after option processing, and neither the
-@samp{-c} nor the @samp{-s}
-option has been supplied, the first argument is assumed to
-be the name of a file containing shell commands (@pxref{Shell Scripts}).
-When Bash is invoked in this fashion, @code{$0}
-is set to the name of the file, and the positional parameters
-are set to the remaining arguments.
-Bash reads and executes commands from this file, then exits.
-Bash's exit status is the exit status of the last command executed
-in the script. If no commands are executed, the exit status is 0.
+This builtin is so complicated that it deserves its own section.
-@node Bash Startup Files
-@section Bash Startup Files
-@cindex startup files
+@table @code
+@item set
+@btindex set
+@example
+set [--abefhkmnptuvxBCHP] [-o @var{option}] [@var{argument} @dots{}]
+@end example
-This section describs how Bash executes its startup files.
-If any of the files exist but cannot be read, Bash reports an error.
-Tildes are expanded in file names as described above under
-Tilde Expansion (@pxref{Tilde Expansion}).
+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.
-When Bash is invoked as an interactive login shell, or as a
-non-interactive shell with the @samp{--login} option, it first reads and
-executes commands from the file @file{/etc/profile}, if that file exists.
-After reading that file, it looks for @file{~/.bash_profile},
-@file{~/.bash_login}, and @file{~/.profile}, in that order, and reads
-and executes commands from the first one that exists and is readable.
-The @samp{--noprofile} option may be used when the shell is started to
-inhibit this behavior.
+When options are supplied, they set or unset shell attributes.
+Options, if specified, have the following meanings:
-When a login shell exits, Bash reads and executes commands from
-the file @file{~/.bash_logout}, if it exists.
+@table @code
+@item -a
+Mark variables which are modified or created for export.
-When an interactive shell that is not a login shell is started, Bash
-reads and executes commands from @file{~/.bashrc}, if that file exists.
-This may be inhibited by using the @samp{--norc} option.
-The @samp{--rcfile @var{file}} option will force Bash to read and
-execute commands from @var{file} instead of @file{~/.bashrc}.
+@item -b
+Cause the status of terminated background jobs to be reported
+immediately, rather than before printing the next primary prompt.
-So, typically, your @file{~/.bash_profile} contains the line
-@example
-@code{if [ -f @file{~/.bashrc} ]; then . @file{~/.bashrc}; fi}
-@end example
-@noindent
-after (or before) any login-specific initializations.
-
-When Bash is started non-interactively, to run a shell script,
-for example, it looks for the variable @code{BASH_ENV} in the environment,
-expands its value if it appears there, and uses the expanded value as
-the name of a file to read and execute. Bash behaves as if the
-following command were executed:
-@example
-@code{if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi}
-@end example
-@noindent
-but the value of the @code{PATH} variable is not used to search for the
-file name.
-
-If Bash is invoked with the name @code{sh}, it tries to mimic the
-startup behavior of historical versions of @code{sh} as closely as
-possible, while conforming to the @sc{POSIX} standard as well.
+@item -e
+Exit immediately if a simple command (@pxref{Simple Commands}) exits
+with a non-zero status, unless the command that fails is part of an
+@code{until} or @code{while} loop, part of an @code{if} statement,
+part of a @code{&&} or @code{||} list, or if the command's return
+status is being inverted using @code{!}.
-When invoked as an interactive login shell, or as a non-interactive
-shell with the @samp{--login} option, it first attempts to read
-and execute commands from @file{/etc/profile} and @file{~/.profile}, in
-that order.
-The @samp{--noprofile} option may be used to inhibit this behavior.
-When invoked as an interactive shell with the name @code{sh}, Bash
-looks for the variable @code{ENV}, expands its value if it is defined,
-and uses the expanded value as the name of a file to read and execute.
-Since a shell invoked as @code{sh} does not attempt to read and execute
-commands from any other startup files, the @samp{--rcfile} option has
-no effect.
-A non-interactive shell invoked with the name @code{sh} does not attempt
-to read any other startup files.
+@item -f
+Disable file name generation (globbing).
-When invoked as @code{sh}, Bash enters @sc{POSIX} mode after
-the startup files are read.
+@item -h
+Locate and remember (hash) commands as they are looked up for execution.
+This option is enabled by default.
-When Bash is started in @sc{POSIX} mode, as with the
-@samp{--posix} command line option, it follows the @sc{POSIX} standard
-for startup files.
-In this mode, interactive shells expand the @code{ENV} variable
-and commands are read and executed from the file whose name is the
-expanded value.
-No other startup files are read.
+@item -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.
-Bash attempts to determine when it is being run by the remote shell
-daemon, usually @code{rshd}. If Bash determines it is being run by
-rshd, it reads and executes commands from @file{~/.bashrc}, if that
-file exists and is readable.
-It will not do this if invoked as @code{sh}.
-The @samp{--norc} option may be used to inhibit this behavior, and the
-@samp{--rcfile} option may be used to force another file to be read, but
-@code{rshd} does not generally invoke the shell with those options or
-allow them to be specified.
+@item -m
+Job control is enabled (@pxref{Job Control}).
-If Bash is started with the effective user (group) id not equal to the
-real user (group) id, and the @code{-p} option is not supplied, no startup
-files are read, shell functions are not inherited from the environment,
-the @code{SHELLOPTS} variable, if it appears in the environment, is ignored,
-and the effective user id is set to the real user id.
-If the @code{-p} option is supplied at invocation, the startup behavior is
-the same, but the effective user id is not reset.
+@item -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.
-@node Is This Shell Interactive?
-@section Is This Shell Interactive?
-@cindex interactive shell
+@item -o @var{option-name}
-As defined in @ref{Invoking Bash}, an interactive shell
-is one whose input and output are both
-connected to terminals (as determined by @code{isatty(3)}),
-or one started with the @samp{-i} option.
+Set the option corresponding to @var{option-name}:
-To determine within a startup script whether Bash is
-running interactively or not, examine the variable
-@code{$PS1}; it is unset in non-interactive shells, and set in
-interactive shells. Thus:
+@table @code
+@item allexport
+Same as @code{-a}.
-@example
-if [ -z "$PS1" ]; then
- echo This shell is not interactive
-else
- echo This shell is interactive
-fi
-@end example
+@item braceexpand
+Same as @code{-B}.
-Alternatively, startup scripts may test the value of the @samp{-}
-special parameter.
-It contains @code{i} when the shell is interactive. For example:
+@item emacs
+Use an @code{emacs}-style line editing interface (@pxref{Command Line Editing}).
-@example
-case "$-" in
-*i*) echo This shell is interactive ;;
-*) echo This shell is not interactive ;;
-esac
-@end example
+@item errexit
+Same as @code{-e}.
-@node Bash Builtins
-@section Bash Builtin Commands
+@item hashall
+Same as @code{-h}.
-This section describes builtin commands which are unique to
-or have been extended in Bash.
+@item histexpand
+Same as @code{-H}.
-@table @code
+@item history
+Enable command history, as described in @ref{Bash History Facilities}.
+This option is on by default in interactive shells.
-@item bind
-@btindex bind
-@example
-bind [-m @var{keymap}] [-lpsvPSV]
-bind [-m @var{keymap}] [-q @var{function}] [-u @var{function}] [-r @var{keyseq}]
-bind [-m @var{keymap}] -f @var{filename}
-bind [-m @var{keymap}] @var{keyseq:function-name}
-@end example
+@item ignoreeof
+An interactive shell will not exit upon reading EOF.
-Display current Readline (@pxref{Command Line Editing})
-key and function bindings, or
-bind a key sequence to a Readline function or macro. The
-binding syntax accepted is identical to that of
-@file{.inputrc} (@pxref{Readline Init File}),
-but each binding must be passed as a separate argument: e.g.,
-@samp{"\C-x\C-r":re-read-init-file}.
-Options, if supplied, have the following meanings:
+@item keyword
+Same as @code{-k}.
-@table @code
-@item -m @var{keymap}
-Use @var{keymap} as the keymap to be affected by
-the subsequent bindings. Acceptable @var{keymap}
-names are
-@code{emacs},
-@code{emacs-standard},
-@code{emacs-meta},
-@code{emacs-ctlx},
-@code{vi},
-@code{vi-command}, and
-@code{vi-insert}.
-@code{vi} is equivalent to @code{vi-command};
-@code{emacs} is equivalent to @code{emacs-standard}.
+@item monitor
+Same as @code{-m}.
-@item -l
-List the names of all Readline functions.
+@item noclobber
+Same as @code{-C}.
-@item -p
-Display Readline function names and bindings in such a way that they
-can be re-read.
+@item noexec
+Same as @code{-n}.
-@item -P
-List current Readline function names and bindings.
+@item noglob
+Same as @code{-f}.
-@item -v
-Display Readline variable names and values in such a way that they
-can be re-read.
+@item notify
+Same as @code{-b}.
-@item -V
-List current Readline variable names and values.
+@item nounset
+Same as @code{-u}.
-@item -s
-Display Readline key sequences bound to macros and the strings they output
-in such a way that they can be re-read.
+@item onecmd
+Same as @code{-t}.
-@item -S
-Display Readline key sequences bound to macros and the strings they output.
+@item physical
+Same as @code{-P}.
-@item -f @var{filename}
-Read key bindings from @var{filename}.
+@item posix
+Change the behavior of Bash where the default operation differs
+from the @sc{posix} 1003.2 standard to match the standard
+(@pxref{Bash POSIX Mode}).
+This is intended to make Bash behave as a strict superset of that
+standard.
-@item -q @var{function}
-Query about which keys invoke the named @var{function}.
+@item privileged
+Same as @code{-p}.
-@item -u @var{function}
-Unbind all keys bound to the named @var{function}.
+@item verbose
+Same as @code{-v}.
-@item -r @var{keyseq}
-Remove any current binding for @var{keyseq}.
+@item vi
+Use a @code{vi}-style line editing interface.
+@item xtrace
+Same as @code{-x}.
@end table
-@noindent
-The return status is zero unless an invalid option is supplied or an
-error occurs.
+@item -p
+Turn on privileged mode.
+In this mode, the @code{$BASH_ENV} and @code{$ENV} files are not
+processed, shell functions are not inherited from the environment,
+and the @code{SHELLOPTS} variable, if it appears in the environment,
+is ignored.
+If the shell is started with the effective user (group) id not equal to the
+real user (group) id, and the @code{-p} option is not supplied, these actions
+are taken and the effective user id is set to the real user id.
+If the @code{-p} option is supplied at startup, the effective user id is
+not reset.
+Turning this option off causes the effective user
+and group ids to be set to the real user and group ids.
-@item 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 -t
+Exit after reading and executing one command.
-@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
-@code{PATH} are executed.
-If there is a shell function named @code{ls}, running @samp{command ls}
-within the function will execute the external command @code{ls}
-instead of calling the function recursively.
-The @samp{-p} option means to use a default value for @code{$PATH}
-that is guaranteed to find all of the standard utilities.
-The return status in this case is 127 if @var{command} cannot be
-found or an error occurred, and the exit status of @var{command}
-otherwise.
+@item -u
+Treat unset variables as an error when performing parameter expansion.
+An error message will be written to the standard error, and a non-interactive
+shell will exit.
-If either the @samp{-V} or @samp{-v} option is supplied, a
-description of @var{command} is printed. The @samp{-v} option
-causes a single word indicating the command or file name used to
-invoke @var{command} to be displayed; the @samp{-V} option produces
-a more verbose description. In this case, the return status is
-zero if @var{command} is found, and non-zero if not.
+@item -v
+Print shell input lines as they are read.
-@item declare
-@btindex declare
-@example
-declare [-afFrxi] [-p] [@var{name}[=@var{value}]]
-@end example
+@item -x
+Print a trace of simple commands and their arguments after they are
+expanded and before they are executed.
-Declare variables and give them attributes. If no @var{name}s
-are given, then display the values of variables instead.
+@item -B
+The shell will perform brace expansion (@pxref{Brace Expansion}).
+This option is on by default.
-The @samp{-p} option will display the attributes and values of each
-@var{name}. When @samp{-p} is used, additional options are ignored.
-The @samp{-F} option inhibits the display of function definitions;
-only the function name and attributes are printed. @samp{-F} implies
-@samp{-f}. The following options can be used to restrict output
-to variables with the specified attributes or to give variables
-attributes:
+@item -C
+Prevent output redirection using @samp{>}, @samp{>&}, and @samp{<>}
+from overwriting existing files.
-@table @code
-@item -a
-Each @var{name} is an array variable (@pxref{Arrays}).
+@item -H
+Enable @samp{!} style history substitution (@pxref{History Interaction}).
+This option is on by default for interactive shells.
-@item -f
-Use function names only.
+@item -P
+If set, do not follow symbolic links when performing commands such as
+@code{cd} which change the current directory. The physical directory
+is used instead. By default, Bash follows
+the logical chain of directories when performing commands
+which change the current directory.
-@item -i
-The variable is to be treated as
-an integer; arithmetic evaluation (@pxref{Shell Arithmetic}) is
-performed when the variable is assigned a value.
+For example, if @file{/usr/sys} is a symbolic link to @file{/usr/local/sys}
+then:
+@example
+$ cd /usr/sys; echo $PWD
+/usr/sys
+$ cd ..; pwd
+/usr
+@end example
-@item -r
-Make @var{name}s readonly. These names cannot then be assigned values
-by subsequent assignment statements or unset.
+@noindent
+If @code{set -P} is on, then:
+@example
+$ cd /usr/sys; echo $PWD
+/usr/local/sys
+$ cd ..; pwd
+/usr/local
+@end example
-@item -x
-Mark each @var{name} for export to subsequent commands via
-the environment.
+@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 @samp{-x}
+and @samp{-v} options are turned off.
+If there are no arguments, the positional parameters remain unchanged.
@end table
-Using @samp{+} instead of @samp{-} turns off the attribute instead.
-When used in a function, @code{declare} makes each @var{name} local,
-as with the @code{local} command.
+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 return status is zero unless an invalid option is encountered,
-an attempt is made to define a function using @code{-f foo=bar},
-an attempt is made to assign a value to a readonly variable,
-an attempt is made to assign a value to an array variable without
-using the compound assignment syntax (@pxref{Arrays}),
-one of the @var{names} is not a valid shell variable name,
-an attempt is made to turn off readonly status for a readonly variable,
-an attempt is made to turn off array status for an array variable,
-or an attempt is made to display a non-existent function with @samp{-f}.
+The remaining N @var{arguments} are positional parameters and are
+assigned, in order, to @code{$1}, @code{$2}, @dots{} @code{$N}.
+The special parameter @code{#} is set to N.
-@item echo
-@btindex echo
-@example
-echo [-neE] [@var{arg} @dots{}]
-@end example
-Output the @var{arg}s, separated by spaces, terminated with a
-newline.
-The return status is always 0.
-If @samp{-n} is specified, the trailing newline is suppressed.
-If the @samp{-e} option is given, interpretation of the following
-backslash-escaped characters is enabled.
-The @samp{-E} option disables the interpretation of these escape characters,
-even on systems where they are interpreted by default.
-@code{echo} interprets the following escape sequences:
-@table @code
-@item \a
-alert (bell)
-@item \b
-backspace
-@item \c
-suppress trailing newline
-@item \e
-escape
-@item \f
-form feed
-@item \n
-new line
-@item \r
-carriage return
-@item \t
-horizontal tab
-@item \v
-vertical tab
-@item \\
-backslash
-@item \@var{nnn}
-the character whose @code{ASCII} code is the octal value @var{nnn}
-(one to three digits)
-@item \x@var{nnn}
-the character whose @code{ASCII} code is the hexadecimal value @var{nnn}
-(one to three digits)
+The return status is always zero unless an invalid option is supplied.
@end table
-@item enable
-@btindex enable
-@example
-enable [-n] [-p] [-f @var{filename}] [-ads] [@var{name} @dots{}]
-@end example
-Enable and disable builtin shell commands.
-Disabling a builtin allows a disk command which has the same name
-as a shell builtin to be executed with specifying a full pathname,
-even though the shell normally searches for builtins before disk commands.
-If @samp{-n} is used, the @var{name}s become disabled. Otherwise
-@var{name}s are enabled. For example, to use the @code{test} binary
-found via @code{$PATH} instead of the shell builtin version, type
-@samp{enable -n test}.
-
-If the @samp{-p} option is supplied, or no @var{name} arguments appear,
-a list of shell builtins is printed. With no other arguments, the list
-consists of all enabled shell builtins.
-The @samp{-a} option means to list
-each builtin with an indication of whether or not it is enabled.
-
-The @samp{-f} option means to load the new builtin command @var{name}
-from shared object @var{filename}, on systems that support dynamic loading.
-The @samp{-d} option will delete a builtin loaded with @samp{-f}.
+@node Special Builtins
+@section Special Builtins
+@cindex special builtin
-If there are no options, a list of the shell builtins is displayed.
-The @samp{-s} option restricts @code{enable} to the @sc{POSIX} special
-builtins. If @samp{-s} is used with @samp{-f}, the new builtin becomes
-a special builtin.
+For historical reasons, the @sc{posix} 1003.2 standard has classified
+several builtin commands as @emph{special}.
+When Bash is executing in @sc{posix} mode, the special builtins
+differ from other builtin commands in three respects:
-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.
+@enumerate
+@item
+Special builtins are found before shell functions during command lookup.
-@item help
-@btindex help
-@example
-help [@var{pattern}]
-@end example
-Display helpful information about builtin commands.
-If @var{pattern} is specified, @code{help} gives detailed help
-on all commands matching @var{pattern}, otherwise a list of
-the builtins is printed. The return status is zero unless no
-command matches @var{pattern}.
+@item
+If a special builtin returns an error status, a non-interactive shell exits.
-@item let
-@btindex let
-@example
-let @var{expression} [@var{expression}]
-@end example
-The @code{let} builtin allows arithmetic to be performed on shell
-variables. Each @var{expression} is evaluated according to the
-rules given below in @ref{Shell Arithmetic}. If the
-last @var{expression} evaluates to 0, @code{let} returns 1;
-otherwise 0 is returned.
+@item
+Assignment statements preceding the command stay in effect in the shell
+environment after the command completes.
+@end enumerate
-@item local
-@btindex local
-@example
-local @var{name}[=@var{value}]
-@end example
-For each argument, a local variable named @var{name} is created,
-and assigned @var{value}.
-@code{local} can only be used within a function; it makes the variable
-@var{name} have a visible scope restricted to that function and its
-children. The return status is zero unless @code{local} is used outside
-a function or an invalid @var{name} is supplied.
+When Bash is not executing in @sc{posix} mode, these builtins behave no
+differently than the rest of the Bash builtin commands.
+The Bash @sc{posix} mode is described in @ref{Bash POSIX Mode}.
-@item logout
-@btindex logout
+These are the @sc{posix} special builtins:
@example
-logout [@var{n}]
+@w{break : . continue eval exec exit export readonly return set}
+@w{shift trap unset}
@end example
-Exit a login shell, returning a status of @var{n} to the shell's
-parent.
-@item printf
-@btindex printf
-@example
-@code{printf} @var{format} [@var{arguments}]
-@end example
-Write the formatted @var{arguments} to the standard output under the
-control of the @var{format}.
-The @var{format} is a character string which contains three types of objects:
-plain characters, which are simply copied to standard output, character
-escape sequences, which are converted and copied to the standard output, and
-format specifications, each of which causes printing of the next successive
-@var{argument}.
-In addition to the standard @code{printf(1)} formats, @samp{%b} causes
-@code{printf} to expand backslash escape sequences in the corresponding
-@var{argument}, and @samp{%q} causes @code{printf} to output the
-corresponding @var{argument} in a format that can be reused as shell input.
+@node Shell Variables
+@chapter Shell Variables
-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.
+@menu
+* Bourne Shell Variables:: Variables which Bash uses in the same way
+ as the Bourne Shell.
+* Bash Variables:: List of variables that exist in Bash.
+@end menu
-@item read
-@btindex read
-@example
-read [-a @var{aname}] [-p @var{prompt}] [-er] [@var{name} @dots{}]
-@end example
-One line is read from the standard input, and the first word
-is assigned to the first @var{name}, the second word to the second @var{name},
-and so on, with leftover words and their intervening separators assigned
-to the last @var{name}.
-If there are fewer words read from the standard input than names,
-the remaining names are assigned empty values.
-The characters in the value of the @code{IFS} variable
-are used to split the line into words.
-The backslash character @samp{\} may be used to remove any special
-meaning for the next character read and for line continuation.
-If no names are supplied, the line read is assigned to the
-variable @code{REPLY}.
-The return code is zero, unless end-of-file is encountered.
-Options, if supplied, have the following meanings:
+This chapter describes the shell variables that Bash uses.
+Bash automatically assigns default values to a number of variables.
-@table @code
-@item -r
-If this option is given, backslash does not act as an escape
-character. The backslash is considered to be part of the line.
-In particular, a backslash-newline pair may not be used as a line
-continuation.
+@node Bourne Shell Variables
+@section Bourne Shell Variables
-@item -p @var{prompt}
-Display @var{prompt}, without a
-trailing newline, before attempting to read any input. The prompt
-is displayed only if input is coming from a terminal.
+Bash uses certain shell variables in the same way as the Bourne shell.
+In some cases, Bash assigns a default value to the variable.
-@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.
+@vtable @code
-@item -e
-Readline (@pxref{Command Line Editing})
-is used to obtain the line.
-@end table
+@item CDPATH
+A colon-separated list of directories used as a search path for
+the @code{cd} builtin command.
-@item shopt
-@btindex shopt
-@example
-shopt [-pqsu] [-o] [@var{optname} @dots{}]
-@end example
-Toggle the values of variables controlling optional shell behavior.
-With no options, or with the @samp{-p} option, a list of all settable
-options is displayed, with an indication of whether or not each is set.
-The @samp{-p} option causes output to be displayed in a form that
-may be reused as input.
-Other options have the following meanings:
-
-@table @code
-@item -s
-Enable (set) each @var{optname}.
-
-@item -u
-Disable (unset) each @var{optname}.
+@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 -q
-Suppresses normal output; the return status
-indicates whether the @var{optname} is set or unset.
-If multiple @var{optname} arguments are given with @samp{-q},
-the return status is zero if all @var{optnames} are enabled;
-non-zero otherwise.
+@item IFS
+A list of characters that separate fields; used when the shell splits
+words as part of expansion.
-@item -o
-Restricts the values of
-@var{optname} to be those defined for the @samp{-o} option to the
-@code{set} builtin (@pxref{The Set Builtin}).
-@end table
+@item MAIL
+If this parameter is set to a filename and the @code{MAILPATH} variable
+is not set, Bash informs the user of the arrival of mail in
+the specified file.
-If either @samp{-s} or @samp{-u}
-is used with no @var{optname} arguments, the display is limited to
-those options which are set or unset, respectively.
+@item MAILPATH
+A colon-separated list of filenames which the shell periodically checks
+for new mail.
+Each list entry can specify the message that is printed when new mail
+arrives in the mail file by separating the file name from the message with
+a @samp{?}.
+When used in the text of the message, @code{$_} expands to the name of
+the current mail file.
-Unless otherwise noted, the @code{shopt} options are disabled (off)
-by default.
+@item OPTARG
+The value of the last option argument processed by the @code{getopts} builtin.
-The return status when listing options is zero if all @var{optnames}
-are enabled, non-zero otherwise. When setting or unsetting options,
-the return status is zero unless an @var{optname} is not a valid shell
-option.
+@item OPTIND
+The index of the last option argument processed by the @code{getopts} builtin.
-The list of @code{shopt} options is:
-@table @code
-@item cdable_vars
-If this is set, an argument to the @code{cd}
-builtin command that
-is not a directory is assumed to be the name of a variable whose
-value is the directory to change to.
+@item PATH
+A colon-separated list of directories in which the shell looks for
+commands.
-@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 PS1
+The primary prompt string. The default value is @samp{\s-\v\$ }.
+@xref{Printing a Prompt}, for the complete list of escape
+sequences that are expanded before @code{PS1} is displayed.
-@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 PS2
+The secondary prompt string. The default value is @samp{> }.
-@item checkwinsize
-If set, Bash checks the window size after each command
-and, if necessary, updates the values of
-@code{LINES} and @code{COLUMNS}.
+@end vtable
-@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.
+@node Bash Variables
+@section Bash Variables
-@item dotglob
-If set, Bash includes filenames beginning with a `.' in
-the results of filename expansion.
+These variables are set or used by Bash, but other shells
+do not normally treat them specially.
-@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.
+A few variables used by Bash are described in different chapters:
+variables for controlling the job control facilities
+(@pxref{Job Control Variables}).
-@item expand_aliases
-If set, aliases are expanded as described below< under Aliases
-(@pxref{Aliases}).
-This option is enabled by default for interactive shells.
+@vtable @code
-@item extglob
-If set, the extended pattern matching features described above
-(@pxref{Pattern Matching}) are enabled.
+@item BASH
+The full pathname used to execute the current instance of Bash.
-@item histappend
-If set, the history list is appended to the file named by the value
-of the @code{HISTFILE}
-variable when the shell exits, rather than overwriting the file.
+@item 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 histreedit
-If set, and Readline
-is being used, a user is given the opportunity to re-edit a
-failed history substitution.
+@item BASH_VERSION
+The version number of the current instance of Bash.
-@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 BASH_VERSINFO
+A readonly array variable (@pxref{Arrays})
+whose members hold version information for this instance of Bash.
+The values assigned to the array members are as follows:
-@item 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.
+@table @code
-@item huponexit
-If set, Bash will send @code{SIGHUP} to all jobs when an interactive
-login shell exits (@pxref{Signals}).
+@item BASH_VERSINFO[0]
+The major version number (the @var{release}).
-@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 BASH_VERSINFO[1]
+The minor version number (the @var{version}).
-@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 BASH_VERSINFO[2]
+The patch level.
-@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 BASH_VERSINFO[3]
+The build version.
-@item nocaseglob
-If set, Bash matches filenames in a case-insensitive fashion when
-performing filename expansion.
+@item BASH_VERSINFO[4]
+The release status (e.g., @var{beta1}).
-@item nullglob
-If set, Bash allows filename patterns which match no
-files to expand to a null string, rather than themselves.
+@item BASH_VERSINFO[5]
+The value of @code{MACHTYPE}.
-@item promptvars
-If set, prompt strings undergo variable and parameter expansion after
-being expanded (@pxref{Printing a Prompt}).
-This option is enabled by default.
+@end table
-@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 COMP_WORDS
+An array variable consisting of the individual
+words in the current command line.
+This variable is available only in shell functions invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
+
+@item COMP_CWORD
+An index into @code{$@{COMP_WORDS@}} of the word containing the current
+cursor position.
+This variable is available only in shell functions invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
+
+@item COMP_LINE
+The current command line.
+This variable is available only in shell functions and external
+commands invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
+
+@item COMP_POINT
+The index of the current cursor position relative to the beginning of
+the current command.
+If the current cursor position is at the end of the current command,
+the value of this variable is equal to @code{$@{#COMP_LINE@}}.
+This variable is available only in shell functions and external
+commands invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
+
+@item COMPREPLY
+An array variable from which Bash reads the possible completions
+generated by a shell function invoked by the programmable completion
+facility (@pxref{Programmable Completion}).
-@item 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 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 @code{DIRSTACK} is unset, it loses its special properties, even if
+it is subsequently reset.
-@item sourcepath
-If set, the @code{source} builtin uses the value of @code{PATH}
-to find the directory containing the file supplied as an argument.
-This option is enabled by default.
-@end table
+@item EUID
+The numeric effective user id of the current user. This variable
+is readonly.
-@noindent
-The return status when listing options is zero if all @var{optnames}
-are enabled, non-zero otherwise.
-When setting or unsetting options, the return status is zero unless an
-@var{optname} is not a valid shell option.
+@item FCEDIT
+The editor used as a default by the @samp{-e} option to the @code{fc}
+builtin command.
-@item source
-@btindex source
-@example
-source @var{filename}
-@end example
-A synonym for @code{.} (@pxref{Bourne Shell Builtins}).
+@item FIGNORE
+A colon-separated list of suffixes to ignore when performing
+filename completion.
+A file name whose suffix matches one of the entries in
+@code{FIGNORE}
+is excluded from the list of matched file names. A sample
+value is @samp{.o:~}
-@item type
-@btindex type
-@example
-type [-atp] [@var{name} @dots{}]
-@end example
-For each @var{name}, indicate how it would be interpreted if used as a
-command name.
+@item GLOBIGNORE
+A colon-separated list of patterns defining the set of filenames to
+be ignored by filename expansion.
+If a filename matched by a filename expansion pattern also matches one
+of the patterns in @code{GLOBIGNORE}, it is removed from the list
+of matches.
-If the @samp{-t} option is used, @code{type} prints a single word
-which is one of @samp{alias}, @samp{function}, @samp{builtin},
-@samp{file} or @samp{keyword},
-if @var{name} is an alias, shell function, shell builtin,
-disk file, or shell reserved word, respectively.
-If the @var{name} is not found, then nothing is printed, and
-@code{type} returns a failure status.
+@item GROUPS
+An array variable containing the list of groups of which the current
+user is a member.
+Assignments to @code{GROUPS} have no effect and are silently discarded.
+If @code{GROUPS} is unset, it loses its special properties, even if it is
+subsequently reset.
-If the @samp{-p} option is used, @code{type} either returns the name
-of the disk file that would be executed, or nothing if @samp{-t}
-would not return @samp{file}.
+@item histchars
+Up to three characters which control history expansion, quick
+substitution, and tokenization (@pxref{History Interaction}).
+The first character is the
+@var{history expansion} character, that is, the character which signifies the
+start of a history expansion, normally @samp{!}. The second character is the
+character which signifies `quick substitution' when seen as the first
+character on a line, normally @samp{^}. The optional third character is the
+character which indicates that the remainder of the line is a comment when
+found as the first character of a word, usually @samp{#}. The history
+comment character causes history substitution to be skipped for the
+remaining words on the line. It does not necessarily cause the shell
+parser to treat the rest of the line as a comment.
-If the @samp{-a} option is used, @code{type} returns all of the places
-that contain an executable named @var{file}.
-This includes aliases and functions, if and only if the @samp{-p} option
-is not also used.
+@item HISTCMD
+The history number, or index in the history list, of the current
+command. If @code{HISTCMD} is unset, it loses its special properties,
+even if it is subsequently reset.
-The return status is zero if any of the @var{names} are found, non-zero
-if none are found.
+@item FUNCNAME
+The name of any currently-executing shell function.
+This variable exists only when a shell function is executing.
+Assignments to @code{FUNCNAME} have no effect and are silently discarded.
+If @code{FUNCNAME} is unset, it loses its special properties, even if
+it is subsequently reset.
-@item typeset
-@btindex typeset
-@example
-typeset [-afFrxi] [-p] [@var{name}[=@var{value}]]
-@end example
-The @code{typeset} command is supplied for compatibility with the Korn
-shell; however, it has been deprecated in favor of the @code{declare}
-builtin command.
+@item HISTCONTROL
+A value of @samp{ignorespace} means to not enter lines which
+begin with a space or tab into the history list.
+A value of @samp{ignoredups} means to not enter lines which match the last
+entered line.
+A value of @samp{ignoreboth} combines the two options.
+Unset, or set to any other value than those above, means to save
+all lines on the history list.
+The second and subsequent lines of a multi-line compound command are
+not tested, and are added to the history regardless of the value of
+@code{HISTCONTROL}.
-@item ulimit
-@btindex ulimit
-@example
-ulimit [-acdflmnpstuvSH] [@var{limit}]
-@end example
-@code{ulimit} provides control over the resources available to processes
-started by the shell, on systems that allow such control. If an
-option is given, it is interpreted as follows:
-@table @code
-@item -S
-Change and report the soft limit associated with a resource.
+@item 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 @code{HISTCONTROL}
+are applied. In addition to the normal shell pattern matching
+characters, @samp{&} matches the previous history line. @samp{&}
+may be escaped using a backslash; the backslash is removed
+before attempting a match.
+The second and subsequent lines of a multi-line compound command are
+not tested, and are added to the history regardless of the value of
+@code{HISTIGNORE}.
-@item -H
-Change and report the hard limit associated with a resource.
+@code{HISTIGNORE} subsumes the function of @code{HISTCONTROL}. A
+pattern of @samp{&} is identical to @code{ignoredups}, and a
+pattern of @samp{[ ]*} is identical to @code{ignorespace}.
+Combining these two patterns, separating them with a colon,
+provides the functionality of @code{ignoreboth}.
-@item -a
-All current limits are reported.
+@item HISTFILE
+The name of the file to which the command history is saved. The
+default value is @file{~/.bash_history}.
-@item -c
-The maximum size of core files created.
+@item HISTSIZE
+The maximum number of commands to remember on the history list.
+The default value is 500.
-@item -d
-The maximum size of a process's data segment.
+@item HISTFILESIZE
+The maximum number of lines contained in the history file. When this
+variable is assigned a value, the history file is truncated, if
+necessary, to contain no more than that number of lines.
+The history file is also truncated to this size after
+writing it when an interactive shell exits.
+The default value is 500.
-@item -f
-The maximum size of files created by the shell.
+@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 @code{HOSTFILE} is set, but has no value, Bash attempts to read
+@file{/etc/hosts} to obtain the list of possible hostname completions.
+When @code{HOSTFILE} is unset, the hostname list is cleared.
-@item -l
-The maximum size that may be locked into memory.
+@item HOSTNAME
+The name of the current host.
-@item -m
-The maximum resident set size.
+@item HOSTTYPE
+A string describing the machine Bash is running on.
-@item -n
-The maximum number of open file descriptors.
+@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 -p
-The pipe buffer size.
+@item INPUTRC
+The name of the Readline initialization file, overriding the default
+of @file{~/.inputrc}.
-@item -s
-The maximum stack size.
+@item LANG
+Used to determine the locale category for any category not specifically
+selected with a variable starting with @code{LC_}.
-@item -t
-The maximum amount of cpu time in seconds.
+@item LC_ALL
+This variable overrides the value of @code{LANG} and any other
+@code{LC_} variable specifying a locale category.
-@item -u
-The maximum number of processes available to a single user.
+@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 -v
-The maximum amount of virtual memory available to the process.
+@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}).
-@end table
+@item LC_MESSAGES
+This variable determines the locale used to translate double-quoted
+strings preceded by a @samp{$} (@pxref{Locale Translation}).
-If @var{limit} is given, it is the new value of the specified resource.
-Otherwise, the current value of the soft limit for the specified resource
-is printed, unless the @samp{-H} option is supplied.
-When setting new limits, if neither @samp{-H} nor @samp{-S} is supplied,
-both the hard and soft limits are set.
-If no option is given, then @samp{-f} is assumed. Values are in 1024-byte
-increments, except for @samp{-t}, which is in seconds, @samp{-p},
-which is in units of 512-byte blocks, and @samp{-n} and @samp{-u}, which
-are unscaled values.
+@item LC_NUMERIC
+This variable determines the locale category used for number formatting.
-The return status is zero unless an invalid option is supplied, a
-non-numeric argument other than @code{unlimited} is supplied as a
-@var{limit}, or an error occurs while setting a new limit.
+@item LINENO
+The line number in the script or shell function currently executing.
-@end table
+@item MACHTYPE
+A string that fully describes the system type on which Bash
+is executing, in the standard @sc{gnu} @var{cpu-company-system} format.
-@node The Set Builtin
-@section The Set Builtin
+@item MAILCHECK
+How often (in seconds) that the shell should check for mail in the
+files specified in the @code{MAILPATH} or @code{MAIL} variables.
-This builtin is so complicated that it deserves its own section.
+@item OLDPWD
+The previous working directory as set by the @code{cd} builtin.
-@table @code
-@item set
-@btindex set
-@example
-set [--abefhkmnptuvxBCHP] [-o @var{option}] [@var{argument} @dots{}]
-@end example
+@item OPTERR
+If set to the value 1, Bash displays error messages
+generated by the @code{getopts} builtin command.
-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.
+@item OSTYPE
+A string describing the operating system Bash is running on.
-When options are supplied, they set or unset shell attributes.
-Options, if specified, have the following meanings:
+@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).
-@table @code
-@item -a
-Mark variables which are modified or created for export.
+@item PPID
+The process @sc{id} of the shell's parent process. This variable
+is readonly.
-@item -b
-Cause the status of terminated background jobs to be reported
-immediately, rather than before printing the next primary prompt.
+@item PROMPT_COMMAND
+If set, the value is interpreted as a command to execute
+before the printing of each primary prompt (@code{$PS1}).
-@item -e
-Exit immediately if a simple command (@pxref{Simple Commands}) exits
-with a non-zero status, unless the command that fails is part of an
-@code{until} or @code{while} loop, part of an @code{if} statement,
-part of a @code{&&} or @code{||} list, or if the command's return
-status is being inverted using @code{!}.
+@item 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 -f
-Disable file name generation (globbing).
+@item PS4
+The value is the prompt printed before the command line is echoed
+when the @samp{-x} option is set (@pxref{The Set Builtin}).
+The first character of @code{PS4} is replicated multiple times, as
+necessary, to indicate multiple levels of indirection.
+The default is @samp{+ }.
-@item -h
-Locate and remember (hash) commands as they are looked up for execution.
-This option is enabled by default.
+@item PWD
+The current working directory as set by the @code{cd} builtin.
-@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 RANDOM
+Each time this parameter is referenced, a random integer
+between 0 and 32767 is generated. Assigning a value to this
+variable seeds the random number generator.
-@item -m
-Job control is enabled (@pxref{Job Control}).
+@item REPLY
+The default variable for the @code{read} builtin.
-@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 SECONDS
+This variable expands to the number of seconds since the
+shell was started. Assignment to this variable resets
+the count to the value assigned, and the expanded value
+becomes the value assigned plus the number of seconds
+since the assignment.
-@item -o @var{option-name}
+@item SHELLOPTS
+A colon-separated list of enabled shell options. Each word in
+the list is a valid argument for the @samp{-o} option to the
+@code{set} builtin command (@pxref{The Set Builtin}).
+The options appearing in @code{SHELLOPTS} are those reported
+as @samp{on} by @samp{set -o}.
+If this variable is in the environment when Bash
+starts up, each shell option in the list will be enabled before
+reading any startup files. This variable is readonly.
-Set the option corresponding to @var{option-name}:
+@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.
-@table @code
-@item allexport
-Same as @code{-a}.
-
-@item braceexpand
-Same as @code{-B}.
-
-@item emacs
-Use an @code{emacs}-style line editing interface (@pxref{Command Line Editing}).
-
-@item errexit
-Same as @code{-e}.
+@item TIMEFORMAT
+The value of this parameter is used as a format string specifying
+how the timing information for pipelines prefixed with the @code{time}
+reserved word should be displayed.
+The @samp{%} character introduces an
+escape sequence that is expanded to a time value or other
+information.
+The escape sequences and their meanings are as
+follows; the braces denote optional portions.
-@item hashall
-Same as @code{-h}.
+@table @code
-@item histexpand
-Same as @code{-H}.
+@item %%
+A literal @samp{%}.
-@item history
-Enable command history, as described in @ref{Bash History Facilities}.
-This option is on by default in interactive shells.
+@item %[@var{p}][l]R
+The elapsed time in seconds.
-@item ignoreeof
-An interactive shell will not exit upon reading EOF.
+@item %[@var{p}][l]U
+The number of CPU seconds spent in user mode.
-@item keyword
-Same as @code{-k}.
+@item %[@var{p}][l]S
+The number of CPU seconds spent in system mode.
-@item monitor
-Same as @code{-m}.
+@item %P
+The CPU percentage, computed as (%U + %S) / %R.
+@end table
-@item noclobber
-Same as @code{-C}.
+The optional @var{p} is a digit specifying the precision, the number of
+fractional digits after a decimal point.
+A value of 0 causes no decimal point or fraction to be output.
+At most three places after the decimal point may be specified; values
+of @var{p} greater than 3 are changed to 3.
+If @var{p} is not specified, the value 3 is used.
-@item noexec
-Same as @code{-n}.
+The optional @code{l} specifies a longer format, including minutes, of
+the form @var{MM}m@var{SS}.@var{FF}s.
+The value of @var{p} determines whether or not the fraction is included.
-@item noglob
-Same as @code{-f}.
+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 notify
-Same as @code{-b}.
+@item TMOUT
+If set to a value greater than zero, the value is interpreted as
+the number of seconds to wait for input after issuing the primary
+prompt when the shell is interactive.
+Bash terminates after that number of seconds if input does
+not arrive.
-@item nounset
-Same as @code{-u}.
+@item UID
+The numeric real user id of the current user. This variable is readonly.
-@item onecmd
-Same as @code{-t}.
+@end vtable
-@item physical
-Same as @code{-P}.
+@node Bash Features
+@chapter Bash Features
-@item posix
-Change the behavior of Bash where the default operation differs
-from the @sc{POSIX} 1003.2 standard to match the standard
-(@pxref{Bash POSIX Mode}).
-This is intended to make Bash behave as a strict superset of that
-standard.
+This section describes features unique to Bash.
-@item privileged
-Same as @code{-p}.
+@menu
+* Invoking Bash:: Command line options that you can give
+ to Bash.
+* Bash Startup Files:: When and how Bash executes scripts.
+* Interactive Shells:: What an interactive shell is.
+* Bash Conditional Expressions:: Primitives used in composing expressions for
+ the @code{test} builtin.
+* Shell Arithmetic:: Arithmetic on shell variables.
+* Aliases:: Substituting one command for another.
+* Arrays:: Array Variables.
+* The Directory Stack:: History of visited directories.
+* Printing a Prompt:: Controlling the PS1 string.
+* The Restricted Shell:: A more controlled mode of shell execution.
+* Bash POSIX Mode:: Making Bash behave more closely to what
+ the POSIX standard specifies.
+@end menu
-@item verbose
-Same as @code{-v}.
+@node Invoking Bash
+@section Invoking Bash
-@item vi
-Use a @code{vi}-style line editing interface.
+@example
+bash [long-opt] [-ir] [-abefhkmnptuvxdBCDHP] [-o @var{option}] [@var{argument} @dots{}]
+bash [long-opt] [-abefhkmnptuvxdBCDHP] [-o @var{option}] -c @var{string} [@var{argument} @dots{}]
+bash [long-opt] -s [-abefhkmnptuvxdBCDHP] [-o @var{option}] [@var{argument} @dots{}]
+@end example
-@item xtrace
-Same as @code{-x}.
-@end table
+In addition to the single-character shell command-line options
+(@pxref{The Set Builtin}), there are several multi-character
+options that you can use. These options must appear on the command
+line before the single-character options in order for them
+to be recognized.
-@item -p
-Turn on privileged mode.
-In this mode, the @code{$BASH_ENV} and @code{$ENV} files are not
-processed, shell functions are not inherited from the environment,
-and the @code{SHELLOPTS} variable, if it appears in the environment,
-is ignored.
-If the shell is started with the effective user (group) id not equal to the
-real user (group) id, and the @code{-p} option is not supplied, these actions
-are taken and the effective user id is set to the real user id.
-If the @code{-p} option is supplied at startup, the effective user id is
-not reset.
-Turning this option off causes the effective user
-and group ids to be set to the real user and group ids.
+@table @code
+@item --dump-po-strings
+A list of all double-quoted strings preceded by @samp{$}
+is printed on the standard ouput
+in the @sc{gnu} @code{gettext} PO (portable object) file format.
+Equivalent to @samp{-D} except for the output format.
-@item -t
-Exit after reading and executing one command.
+@item --dump-strings
+Equivalent to @samp{-D}.
-@item -u
-Treat unset variables as an error when performing parameter expansion.
-An error message will be written to the standard error, and a non-interactive
-shell will exit.
+@item --help
+Display a usage message on standard output and exit sucessfully.
-@item -v
-Print shell input lines as they are read.
+@item --login
+Make this shell act as if it were directly invoked by login.
+This is equivalent to @samp{exec -l bash} but can be issued from
+another shell, such as @code{csh}. @samp{exec bash --login}
+will replace the current shell with a Bash login shell.
+@xref{Bash Startup Files}, for a description of the special behavior
+of a login shell.
-@item -x
-Print a trace of simple commands and their arguments after they are
-expanded and before they are executed.
+@item --noediting
+Do not use the @sc{gnu} Readline library (@pxref{Command Line Editing})
+to read command lines when the shell is interactive.
-@item -B
-The shell will perform brace expansion (@pxref{Brace Expansion}).
-This option is on by default.
+@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 -C
-Prevent output redirection using @samp{>}, @samp{>&}, and @samp{<>}
-from overwriting existing files.
+@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 -H
-Enable @samp{!} style history substitution (@pxref{History Interaction}).
-This option is on by default for interactive shells.
+@item --posix
+Change the behavior of Bash where the default operation differs
+from the @sc{posix} 1003.2 standard to match the standard. This
+is intended to make Bash behave as a strict superset of that
+standard. @xref{Bash POSIX Mode}, for a description of the Bash
+@sc{posix} mode.
-@item -P
-If set, do not follow symbolic links when performing commands such as
-@code{cd} which change the current directory. The physical directory
-is used instead. By default, Bash follows
-the logical chain of directories when performing commands
-which change the current directory.
+@item --rcfile @var{filename}
+Execute commands from @var{filename} (instead of @file{~/.bashrc})
+in an interactive shell.
-For example, if @file{/usr/sys} is a symbolic link to @file{/usr/local/sys}
-then:
-@example
-$ cd /usr/sys; echo $PWD
-/usr/sys
-$ cd ..; pwd
-/usr
-@end example
+@item --restricted
+Make the shell a restricted shell (@pxref{The Restricted Shell}).
-@noindent
-If @code{set -P} is on, then:
-@example
-$ cd /usr/sys; echo $PWD
-/usr/local/sys
-$ cd ..; pwd
-/usr/local
-@end example
+@item --verbose
+Equivalent to @samp{-v}. Print shell input lines as they're read.
-@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 --version
+Show version information for this instance of
+Bash on the standard output and exit successfully.
-@item -
-Signal the end of options, cause all remaining @var{arguments}
-to be assigned to the positional parameters. The @samp{-x}
-and @samp{-v} options are turned off.
-If there are no arguments, the positional parameters remain unchanged.
@end table
-Using @samp{+} rather than @samp{-} causes these options to be
-turned off. The options can also be used upon invocation of the
-shell. The current set of options may be found in @code{$-}.
-
-The remaining N @var{arguments} are positional parameters and are
-assigned, in order, to @code{$1}, @code{$2}, @dots{} @code{$N}.
-The special parameter @code{#} is set to N.
+There are several single-character options that may be supplied at
+invocation which are not available with the @code{set} builtin.
-The return status is always zero unless an invalid option is supplied.
-@end table
+@table @code
+@item -c @var{string}
+Read and execute commands from @var{string} after processing the
+options, then exit. Any remaining arguments are assigned to the
+positional parameters, starting with @code{$0}.
-@node Bash Conditional Expressions
-@section Bash Conditional Expressions
-@cindex expressions, conditional
+@item -i
+Force the shell to run interactively. Interactive shells are
+described in @ref{Interactive Shells}.
-Conditional expressions are used by the @code{[[} compound command
-and the @code{test} and @code{[} builtin commands.
+@item -r
+Make the shell a restricted shell (@pxref{The Restricted Shell}).
-Expressions may be unary or binary.
-Unary expressions are often used to examine the status of a file.
-There are string operators and numeric comparison operators as well.
-If any @var{file} argument to one of the primaries is of the form
-@file{/dev/fd/@var{N}}, then file descriptor @var{N} is checked.
+@item -s
+If this option is present, or if no arguments remain after option
+processing, then commands are read from the standard input.
+This option allows the positional parameters to be set
+when invoking an interactive shell.
+
+@item -D
+A list of all double-quoted strings preceded by @samp{$}
+is printed on the standard ouput.
+These are the strings that
+are subject to language translation when the current locale
+is not @code{C} or @code{POSIX} (@pxref{Locale Translation}).
+This implies the @samp{-n} option; no commands will be executed.
+
+@item --
+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 interactive shell
+An @emph{interactive} shell is one started without non-option arguments,
+unless @samp{-s} is specified,
+without specifying the @samp{-c} option, and whose input and output are both
+connected to terminals (as determined by @code{isatty(3)}), or one
+started with the @samp{-i} option. @xref{Interactive Shells} for more
+information.
+
+If arguments remain after option processing, and neither the
+@samp{-c} nor the @samp{-s}
+option has been supplied, the first argument is assumed to
+be the name of a file containing shell commands (@pxref{Shell Scripts}).
+When Bash is invoked in this fashion, @code{$0}
+is set to the name of the file, and the positional parameters
+are set to the remaining arguments.
+Bash reads and executes commands from this file, then exits.
+Bash's exit status is the exit status of the last command executed
+in the script. If no commands are executed, the exit status is 0.
+
+@node Bash Startup Files
+@section Bash Startup Files
+@cindex startup files
+
+This section describs how Bash executes its startup files.
+If any of the files exist but cannot be read, Bash reports an error.
+Tildes are expanded in file names as described above under
+Tilde Expansion (@pxref{Tilde Expansion}).
+
+Interactive shells are described in @ref{Interactive Shells}.
+
+@subsubheading Invoked as an interactive login shell, or with @samp{--login}
+
+When Bash is invoked as an interactive login shell, or as a
+non-interactive shell with the @samp{--login} option, it first reads and
+executes commands from the file @file{/etc/profile}, if that file exists.
+After reading that file, it looks for @file{~/.bash_profile},
+@file{~/.bash_login}, and @file{~/.profile}, in that order, and reads
+and executes commands from the first one that exists and is readable.
+The @samp{--noprofile} option may be used when the shell is started to
+inhibit this behavior.
+
+When a login shell exits, 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 @samp{--norc} option.
+The @samp{--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 @code{BASH_ENV} in the environment,
+expands its value if it appears there, and uses the expanded value as
+the name of a file to read and execute. Bash behaves as if the
+following command were executed:
+@example
+@code{if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi}
+@end example
+@noindent
+but the value of the @code{PATH} variable is not used to search for the
+file name.
+
+@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 @samp{--login} option, it first attempts to read
+and execute commands from @file{/etc/profile} and @file{~/.profile}, in
+that order.
+The @samp{--noprofile} option may be used to inhibit this behavior.
+When invoked as an interactive shell with the name @code{sh}, Bash
+looks for the variable @code{ENV}, expands its value if it is defined,
+and uses the expanded value as the name of a file to read and execute.
+Since a shell invoked as @code{sh} does not attempt to read and execute
+commands from any other startup files, the @samp{--rcfile} option has
+no effect.
+A non-interactive shell invoked with the name @code{sh} does not attempt
+to read any other startup files.
+
+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
+@samp{--posix} command line option, it follows the @sc{posix} standard
+for startup files.
+In this mode, interactive shells expand the @code{ENV} variable
+and commands are read and executed from the file whose name is the
+expanded value.
+No other startup files are read.
+
+@subsubheading Invoked by remote shell daemon
+
+Bash attempts to determine when it is being run by the remote shell
+daemon, usually @code{rshd}. If Bash determines it is being run by
+rshd, it reads and executes commands from @file{~/.bashrc}, if that
+file exists and is readable.
+It will not do this if invoked as @code{sh}.
+The @samp{--norc} option may be used to inhibit this behavior, and the
+@samp{--rcfile} option may be used to force another file to be read, but
+@code{rshd} does not generally invoke the shell with those options or
+allow them to be specified.
+
+@subsubheading Invoked with unequal effective and real @sc{uid/gid}s
+
+If Bash is started with the effective user (group) id not equal to the
+real user (group) id, and the @code{-p} option is not supplied, no startup
+files are read, shell functions are not inherited from the environment,
+the @code{SHELLOPTS} variable, if it appears in the environment, is ignored,
+and the effective user id is set to the real user id.
+If the @code{-p} option is supplied at invocation, the startup behavior is
+the same, but the effective user id is not reset.
+
+@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 @samp{-s} is
+specified, without specifiying the @samp{-c} option, and
+whose input and output are both
+connected to terminals (as determined by @code{isatty(3)}),
+or one started with the @samp{-i} option.
+
+An interactive shell generally reads from and writes to a user's
+terminal.
+
+The @samp{-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
+@code{$PS1}; it is unset in non-interactive shells, and set in
+interactive shells. Thus:
+
+@example
+if [ -z "$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 @code{$PS1} before reading the first line
+of a command, and expands and displays @code{$PS2} before reading the
+second and subsequent lines of a multi-line command.
+
+@item
+Bash executes the value of the @code{PROMPT_COMMAND} variable as a command
+before printing the primary prompt, @code{$PS1}
+(@pxref{Bash Variables}).
+
+@item
+Readline (@pxref{Command Line Editing}) is used to read commands from
+the user's terminal.
+
+@item
+Bash inspects the value of the @code{ignoreeof} option to @code{set -o}
+instead of exiting immediately when it receives an @code{EOF} on its
+standard input when reading a command (@pxref{The Set Builtin}).
+
+@item
+Command history (@pxref{Bash History Facilities})
+and history expansion (@pxref{History Interaction})
+are enabled by default.
+Bash will save the command history to the file named by @code{$HISTFILE}
+when an interactive shell exits.
+
+@item
+Alias expansion (@pxref{Aliases}) is performed by default.
+
+@item
+In the absence of any traps, Bash ignores @code{SIGTERM}
+(@pxref{Signals}).
+
+@item
+In the absence of any traps, @code{SIGINT} is caught and handled
+((@pxref{Signals}).
+@code{SIGINT} will interrupt some shell builtins.
+
+@item
+An interactive login shell sends a @code{SIGHUP} to all jobs on exit
+if the @code{hupoxexit} shell option has been enabled (@pxref{Signals}).
+
+@item
+The @samp{-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
+@code{MAIL}, @code{MAILPATH}, and @code{MAILCHECK} shell variables
+(@pxref{Bash Variables}).
+
+@item
+Expansion errors due to references to unbound shell variables after
+@samp{set -u} has been enabled will not cause the shell to exit
+(@pxref{The Set Builtin}).
+
+@item
+The shell will not exit on expansion errors caused by @var{var} being unset
+or null in @code{$@{@var{var}:?@var{word}@}} expansions
+(@pxref{Shell Parameter Expansion}).
+
+@item
+Redirection errors encountered by shell builtins will not cause the
+shell to exit.
+
+@item
+When running in @sc{posix} mode, a special builtin returning an error
+status will not cause the shell to exit (@pxref{Bash POSIX Mode}).
+@item
+A failed @code{exec} will not cause the shell to exit
+(@pxref{Bourne Shell Builtins}).
+
+@item
+Parser syntax errors will not cause the shell to exit.
+
+@item
+Simple spelling correction for directory arguments to the @code{cd}
+builtin is enabled by default (see the description of the @code{cdspell}
+option to the @code{shopt} builtin in @ref{Bash Builtins}).
+
+@item
+The shell will check the value of the @code{TMOUT} variable and exit
+if a command is not read within the specified number of seconds after
+printing @code{$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.
+
+Expressions may be unary or binary.
+Unary expressions are often used to examine the status of a file.
+There are string operators and numeric comparison operators as well.
+If the @var{file} argument to one of the primaries is of the form
+@file{/dev/fd/@var{N}}, then file descriptor @var{N} is checked.
+If the @var{file} argument to one of the primaries is one of
+@file{/dev/stdin}, @file{/dev/stdout}, or @file{/dev/stderr}, file
+descriptor 0, 1, or 2, respectively, is checked.
@table @code
@item -a @var{file}
@end table
-@node Bash Variables
-@section Bash Variables
-
-These variables are set or used by Bash, but other shells
-do not normally treat them specially.
+@node Shell Arithmetic
+@section Shell Arithmetic
+@cindex arithmetic, shell
+@cindex shell arithmetic
+@cindex expressions, arithmetic
+@cindex evaluation, arithmetic
+@cindex arithmetic evaluation
-@vtable @code
+The shell allows arithmetic expressions to be evaluated, as one of
+the shell expansions or by the @code{let} builtin.
-@item BASH
-The full pathname used to execute the current instance of Bash.
+Evaluation is done in long integers with no check for overflow,
+though division by 0 is trapped and flagged as an error.
+The operators and their precedence and associativity 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.
-@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}.
+@table @code
-@item BASH_VERSION
-The version number of the current instance of Bash.
+@item @var{id}++ @var{id}--
+variable post-increment and post-decrement
-@item BASH_VERSINFO
-A readonly array variable whose members hold version information for
-this instance of Bash.
-The values assigned to the array members are as follows:
+@item ++@var{id} --@var{id}
+variable pre-increment and pre-decrement
-@table @code
+@item - +
+unary minus and plus
-@item BASH_VERSINFO[0]
-The major version number (the @var{release}).
+@item ! ~
+logical and bitwise negation
-@item BASH_VERSINFO[1]
-The minor version number (the @var{version}).
+@item **
+exponentiation
-@item BASH_VERSINFO[2]
-The patch level.
+@item * / %
+multiplication, division, remainder
-@item BASH_VERSINFO[3]
-The build version.
+@item + -
+addition, subtraction
-@item BASH_VERSINFO[4]
-The release status (e.g., @var{beta1}).
+@item << >>
+left and right bitwise shifts
-@item BASH_VERSINFO[5]
-The value of @code{MACHTYPE}.
+@item <= >= < >
+comparison
-@end table
+@item == !=
+equality and inequality
-@item DIRSTACK
-An array variable (@pxref{Arrays})
-containing the current contents of the directory stack.
-Directories appear in the stack in the order they are displayed by the
-@code{dirs} builtin.
-Assigning to members of this array variable may be used to modify
-directories already in the stack, but the @code{pushd} and @code{popd}
-builtins must be used to add and remove directories.
-Assignment to this variable will not change the current directory.
-If @code{DIRSTACK} is unset, it loses its special properties, even if
-it is subsequently reset.
+@item &
+bitwise AND
-@item EUID
-The numeric effective user id of the current user. This variable
-is readonly.
+@item ^
+bitwise exclusive OR
-@item FCEDIT
-The editor used as a default by the @samp{-e} option to the @code{fc}
-builtin command.
+@item |
+bitwise OR
-@item FIGNORE
-A colon-separated list of suffixes to ignore when performing
-filename completion.
-A file name whose suffix matches one of the entries in
-@code{FIGNORE}
-is excluded from the list of matched file names. A sample
-value is @samp{.o:~}
+@item &&
+logical AND
-@item GLOBIGNORE
-A colon-separated list of patterns defining the set of filenames to
-be ignored by filename expansion.
-If a filename matched by a filename expansion pattern also matches one
-of the patterns in @code{GLOBIGNORE}, it is removed from the list
-of matches.
+@item ||
+logical OR
-@item GROUPS
-An array variable containing the list of groups of which the current
-user is a member. This variable is readonly.
+@item expr ? expr : expr
+conditional evaluation
-@item histchars
-Up to three characters which control history expansion, quick
-substitution, and tokenization (@pxref{History Interaction}).
-The first character is the
-@dfn{history-expansion-char}, that is, the character which signifies the
-start of a history expansion, normally @samp{!}. The second character is the
-character which signifies `quick substitution' when seen as the first
-character on a line, normally @samp{^}. The optional third character is the
-character which indicates that the remainder of the line is a comment when
-found as the first character of a word, usually @samp{#}. The history
-comment character causes history substitution to be skipped for the
-remaining words on the line. It does not necessarily cause the shell
-parser to treat the rest of the line as a comment.
+@item = *= /= %= += -= <<= >>= &= ^= |=
+assignment
-@item HISTCMD
-The history number, or index in the history list, of the current
-command. If @code{HISTCMD} is unset, it loses its special properties,
-even if it is subsequently reset.
+@item expr1 , expr2
+comma
+@end table
-@item HISTCONTROL
-Set to a value of @samp{ignorespace}, it means don't enter lines which
-begin with a space or tab into the history list. Set to a value
-of @samp{ignoredups}, it means don't enter lines which match the last
-entered line. A value of @samp{ignoreboth} combines the two options.
-Unset, or set to any other value than those above, means to save
-all lines on the history list.
-The second and subsequent lines of a multi-line compound command are
-not tested, and are added to the history regardless of the value of
-@code{HISTCONTROL}.
+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.
+The value of a variable is evaluated as an arithmetic expression
+when it is referenced.
+A shell variable need not have its integer attribute turned on
+to be used in an expression.
-@item HISTIGNORE
-A colon-separated list of patterns used to decide which command
-lines should be saved on the history list. Each pattern is
-anchored at the beginning of the line and must fully specify the
-line (no implicit @samp{*} is appended). Each pattern is tested
-against the line after the checks specified by @code{HISTCONTROL}
-are applied. In addition to the normal shell pattern matching
-characters, @samp{&} matches the previous history line. @samp{&}
-may be escaped using a backslash. The backslash is removed
-before attempting a match.
-The second and subsequent lines of a multi-line compound command are
-not tested, and are added to the history regardless of the value of
-@code{HISTIGNORE}.
+Constants with a leading 0 are interpreted as octal numbers.
+A leading @samp{0x} or @samp{0X} denotes hexadecimal. Otherwise,
+numbers take the form [@var{base}@code{#}]@var{n}, where @var{base}
+is a decimal number between 2 and 64 representing the arithmetic
+base, and @var{n} is a number in that base. If @var{base}@code{#} is
+omitted, then base 10 is used.
+The digits greater than 9 are represented by the lowercase letters,
+the uppercase letters, @samp{_}, and @samp{@@}, in that order.
+If @var{base} is less than or equal to 36, lowercase and uppercase
+letters may be used interchangably to represent numbers between 10
+and 35.
-@code{HISTIGNORE} subsumes the function of @code{HISTCONTROL}. A
-pattern of @samp{&} is identical to @code{ignoredups}, and a
-pattern of @samp{[ ]*} is identical to @code{ignorespace}.
-Combining these two patterns, separating them with a colon,
-provides the functionality of @code{ignoreboth}.
+Operators are evaluated in order of precedence. Sub-expressions in
+parentheses are evaluated first and may override the precedence
+rules above.
-@item HISTFILE
-The name of the file to which the command history is saved. The
-default is @file{~/.bash_history}.
+@node Aliases
+@section Aliases
+@cindex alias expansion
-@item HISTSIZE
-The maximum number of commands to remember on the history list.
-The default value is 500.
+@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.
-@item HISTFILESIZE
-The maximum number of lines contained in the history file. When this
-variable is assigned a value, the history file is truncated, if
-necessary, to contain no more than that number of lines. The default
-value is 500. The history file is also truncated to this size after
-writing it when an interactive shell exits.
+The first word of each simple command, if unquoted, is checked to see
+if it has an alias.
+If so, that word is replaced by the text of the alias.
+The alias name and the replacement text may contain any valid
+shell input, including shell metacharacters, with the exception
+that the alias name may not contain @samp{=}.
+The first word of the replacement text is tested for
+aliases, but a word that is identical to an alias being expanded
+is not expanded a second time. This means that one may alias
+@code{ls} to @code{"ls -F"},
+for instance, and Bash does not try to recursively expand the
+replacement text. If the last character of the alias value is a
+space or tab character, then the next command word following the
+alias is also checked for alias expansion.
-@item HOSTFILE
-Contains the name of a file in the same format as @file{/etc/hosts} that
-should be read when the shell needs to complete a hostname. You can
-change the file interactively; the next time you attempt to complete a
-hostname, Bash will add the contents of the new file to the already
-existing database.
+Aliases are created and listed with the @code{alias}
+command, and removed with the @code{unalias} command.
-@item HOSTNAME
-The name of the current host.
+There is no mechanism for using arguments in the replacement text,
+as in @code{csh}.
+If arguments are needed, a shell function should be used
+(@pxref{Shell Functions}).
-@item HOSTTYPE
-A string describing the machine Bash is running on.
+Aliases are not expanded when the shell is not interactive,
+unless the @code{expand_aliases} shell option is set using
+@code{shopt} (@pxref{Bash Builtins}).
-@item 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.
+The rules concerning the definition and use of aliases are
+somewhat confusing. Bash
+always reads at least one complete line
+of input before executing any
+of the commands on that line. Aliases are expanded when a
+command is read, not when it is executed. Therefore, an
+alias definition appearing on the same line as another
+command does not take effect until the next line of input is read.
+The commands following the alias definition
+on that line are not affected by the new alias.
+This behavior is also an issue when functions are executed.
+Aliases are expanded when a function definition is read,
+not when the function is executed, because a function definition
+is itself a compound command. As a consequence, aliases
+defined in a function are not available until after that
+function is executed. To be safe, always put
+alias definitions on a separate line, and do not use @code{alias}
+in compound commands.
-@item INPUTRC
-The name of the Readline startup file, overriding the default
-of @file{~/.inputrc}.
+For almost every purpose, shell functions are preferred over aliases.
-@item LANG
-Used to determine the locale category for any category not specifically
-selected with a variable starting with @code{LC_}.
+@node Arrays
+@section Arrays
+@cindex arrays
-@item LC_ALL
-This variable overrides the value of @code{LANG} and any other
-@code{LC_} variable specifying a locale category.
+Bash provides one-dimensional array variables. Any variable may be used as
+an array; the @code{declare} builtin will explicitly declare an array.
+There is no maximum
+limit on the size of an array, nor any requirement that members
+be indexed or assigned contiguously. Arrays are zero-based.
-@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}).
+An array is created automatically if any variable is assigned to using
+the syntax
+@example
+name[@var{subscript}]=@var{value}
+@end example
-@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}).
+@noindent
+The @var{subscript}
+is treated as an arithmetic expression that must evaluate to a number
+greater than or equal to zero. To explicitly declare an array, use
+@example
+declare -a @var{name}
+@end example
+@noindent
+The syntax
+@example
+declare -a @var{name}[@var{subscript}]
+@end example
+@noindent
+is also accepted; the @var{subscript} is ignored. Attributes may be
+specified for an array variable using the @code{declare} and
+@code{readonly} builtins. Each attribute applies to all members of
+an array.
-@item LC_MESSAGES
-This variable determines the locale used to translate double-quoted
-strings preceded by a @samp{$} (@pxref{Locale Translation}).
+Arrays are assigned to using compound assignments of the form
+@example
+name=(value@var{1} @dots{} value@var{n})
+@end example
+@noindent
+where each
+@var{value} is of the form @code{[[@var{subscript}]=]}@var{string}. If
+the optional subscript is supplied, that index is assigned to;
+otherwise the index of the element assigned is the last index assigned
+to by the statement plus one. Indexing starts at zero.
+This syntax is also accepted by the @code{declare}
+builtin. Individual array elements may be assigned to using the
+@code{name[}@var{subscript}@code{]=}@var{value} syntax introduced above.
-@item LINENO
-The line number in the script or shell function currently executing.
+Any element of an array may be referenced using
+@code{$@{name[}@var{subscript}@code{]@}}.
+The braces are required to avoid
+conflicts with the shell's filename expansion operators. If the
+@var{subscript} is @samp{@@} or @samp{*}, the word expands to all members
+of the array @var{name}. These subscripts differ only when the word
+appears within double quotes. If the word is double-quoted,
+@code{$@{name[*]@}} expands to a single word with
+the value of each array member separated by the first character of the
+@code{IFS} variable, and @code{$@{name[@@]@}} expands each element of
+@var{name} to a separate word. When there are no array members,
+@code{$@{name[@@]@}} expands to nothing. This is analogous to the
+expansion of the special parameters @samp{@@} and @samp{*}.
+@code{$@{#name[}@var{subscript}@code{]@}} expands to the length of
+@code{$@{name[}@var{subscript}@code{]@}}.
+If @var{subscript} is @samp{@@} or
+@samp{*}, the expansion is the number of elements in the array.
+Referencing an array variable without a subscript is equivalent to
+referencing element zero.
-@item MACHTYPE
-A string that fully describes the system type on which Bash
-is executing, in the standard GNU @var{cpu-company-system} format.
+The @code{unset} builtin is used to destroy arrays.
+@code{unset} @var{name[subscript]}
+destroys the array element at index @var{subscript}.
+@code{unset} @var{name}, where @var{name} is an array, removes the
+entire array. A subscript of @samp{*} or @samp{@@} also removes the
+entire array.
-@item MAILCHECK
-How often (in seconds) that the shell should check for mail in the
-files specified in the @code{MAILPATH} or @code{MAIL} variables.
+The @code{declare}, @code{local}, and @code{readonly}
+builtins each accept a @samp{-a}
+option to specify an array. The @code{read}
+builtin accepts a @samp{-a}
+option to assign a list of words read from the standard input
+to an array, and can read values from the standard input into
+individual array elements. The @code{set} and @code{declare}
+builtins display array values in a way that allows them to be
+reused as input.
-@item OLDPWD
-The previous working directory as set by the @code{cd} builtin.
+@node The Directory Stack
+@section The Directory Stack
+@cindex directory stack
-@item OPTERR
-If set to the value 1, Bash displays error messages
-generated by the @code{getopts} builtin command.
+@menu
+* Directory Stack Builtins:: Bash builtin commands to manipulate
+ the directory stack.
+@end menu
-@item OSTYPE
-A string describing the operating system Bash is running on.
+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.
-@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).
+The contents of the directory stack are also visible
+as the value of the @code{DIRSTACK} shell variable.
-@item PPID
-The process id of the shell's parent process. This variable
-is readonly.
+@node Directory Stack Builtins
+@subsection Directory Stack Builtins
-@item PROMPT_COMMAND
-If present, this contains a string which is a command to execute
-before the printing of each primary prompt (@code{$PS1}).
+@table @code
-@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 dirs
+@btindex dirs
+@example
+dirs [+@var{N} | -@var{N}] [-clpv]
+@end example
+Display the list of currently remembered directories. Directories
+are added to the list with the @code{pushd} command; the
+@code{popd} command removes directories from the list.
+@table @code
+@item +@var{N}
+Displays the @var{N}th directory (counting from the left of the
+list printed by @code{dirs} when invoked without options), starting
+with zero.
+@item -@var{N}
+Displays the @var{N}th directory (counting from the right of the
+list printed by @code{dirs} when invoked without options), starting
+with zero.
+@item -c
+Clears the directory stack by deleting all of the elements.
+@item -l
+Produces a longer listing; the default listing format uses a
+tilde to denote the home directory.
+@item -p
+Causes @code{dirs} to print the directory stack with one entry per
+line.
+@item -v
+Causes @code{dirs} to print the directory stack with one entry per
+line, prefixing each entry with its index in the stack.
+@end table
+
+@item popd
+@btindex popd
+@example
+popd [+@var{N} | -@var{N}] [-n]
+@end example
+
+Remove the top entry from the directory stack, and @code{cd}
+to the new top directory.
+When no arguments are given, @code{popd}
+removes the top directory from the stack and
+performs a @code{cd} to the new top directory. The
+elements are numbered from 0 starting at the first directory listed with
+@code{dirs}; i.e., @code{popd} is equivalent to @code{popd +0}.
+@table @code
+@item +@var{N}
+Removes the @var{N}th directory (counting from the left of the
+list printed by @code{dirs}), starting with zero.
+@item -@var{N}
+Removes the @var{N}th directory (counting from the right of the
+list printed by @code{dirs}), starting with zero.
+@item -n
+Suppresses the normal change of directory when removing directories
+from the stack, so that only the stack is manipulated.
+@end table
+
+@btindex pushd
+@item pushd
+@example
+pushd [@var{dir} | @var{+N} | @var{-N}] [-n]
+@end example
+
+Save the current directory on the top of the directory stack
+and then @code{cd} to @var{dir}.
+With no arguments, @code{pushd} exchanges the top two directories.
+
+@table @code
+@item +@var{N}
+Brings the @var{N}th directory (counting from the left of the
+list printed by @code{dirs}, starting with zero) to the top of
+the list by rotating the stack.
+@item -@var{N}
+Brings the @var{N}th directory (counting from the right of the
+list printed by @code{dirs}, starting with zero) to the top of
+the list by rotating the stack.
+@item -n
+Suppresses the normal change of directory when adding directories
+to the stack, so that only the stack is manipulated.
+@item @var{dir}
+Makes the current working directory be the top of the stack, and then
+executes the equivalent of `@code{cd} @var{dir}'.
+@code{cd}s to @var{dir}.
+@end table
+
+@end table
+
+@node Printing a Prompt
+@section Controlling the Prompt
+@cindex prompting
-@item PS4
-This is the prompt printed before the command line is echoed
-when the @samp{-x} option is set (@pxref{The Set Builtin}).
-The first character of @code{PS4} is replicated multiple times, as
-necessary, to indicate multiple levels of indirection.
-The default is @samp{+ }.
+The value of the variable @code{PROMPT_COMMAND} is examined just before
+Bash prints each primary prompt. If @code{PROMPT_COMMAND} is set and
+has a non-null value, then the
+value is executed just as if it had been typed on the command line.
-@item PWD
-The current working directory as set by the @code{cd} builtin.
+In addition, the following table describes the special characters which
+can appear in the prompt variables:
-@item RANDOM
-Each time this parameter is referenced, a random integer
-between 0 and 32767 is generated. Assigning a value to this
-variable seeds the random number generator.
+@table @code
+@item \a
+A bell character.
+@item \d
+The date, in "Weekday Month Date" format (e.g., "Tue May 26").
+@item \e
+An escape character.
+@item \h
+The hostname, up to the first `.'.
+@item \H
+The hostname.
+@item \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{$0} (the portion
+following the final slash).
+@item \t
+The time, in 24-hour HH:MM:SS format.
+@item \T
+The time, in 12-hour HH:MM:SS format.
+@item \@@
+The time, in 12-hour am/pm format.
+@item \u
+The username of the current user.
+@item \v
+The version of Bash (e.g., 2.00)
+@item \V
+The release of Bash, version + patchlevel (e.g., 2.00.0)
+@item \w
+The current working directory.
+@item \W
+The basename of @code{$PWD}.
+@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
-@item REPLY
-The default variable for the @code{read} builtin.
+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.
-@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.
+After the string is decoded, it is expanded via
+parameter expansion, command substitution, arithmetic
+expansion, and quote removal, subject to the value of the
+@code{promptvars} shell option (@pxref{Bash Builtins}).
-@item SHELLOPTS
-A colon-separated list of enabled shell options. Each word in
-the list is a valid argument for the @samp{-o} option to the
-@code{set} builtin command (@pxref{The Set Builtin}).
-The options appearing in @code{SHELLOPTS} are those reported
-as @samp{on} by @samp{set -o}.
-If this variable is in the environment when Bash
-starts up, each shell option in the list will be enabled before
-reading any startup files. This variable is readonly.
+@node The Restricted Shell
+@section The Restricted Shell
+@cindex restricted shell
-@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.
+If Bash is started with the name @code{rbash}, or the
+@samp{--restricted}
+option is supplied at invocation, the shell becomes restricted.
+A restricted shell is used to
+set up an environment more controlled than the standard shell.
+A restricted shell behaves identically to @code{bash}
+with the exception that the following are disallowed:
+@itemize @bullet
+@item
+Changing directories with the @code{cd} builtin.
+@item
+Setting or unsetting the values of the @code{SHELL}, @code{PATH},
+@code{ENV}, or @code{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 @samp{-p}
+option to the @code{hash} builtin command.
+@item
+Importing function definitions from the shell environment at startup.
+@item
+Parsing the value of @code{SHELLOPTS} from the shell environment at startup.
+@item
+Redirecting output using the @samp{>}, @samp{>|}, @samp{<>}, @samp{>&},
+@samp{&>}, and @samp{>>} redirection operators.
+@item
+Using the @code{exec} builtin to replace the shell with another command.
+@item
+Adding or deleting builtin commands with the
+@samp{-f} and @samp{-d} options to the @code{enable} builtin.
+@item
+Specifying the @samp{-p} option to the @code{command} builtin.
+@item
+Turning off restricted mode with @samp{set +r} or @samp{set +o restricted}.
+@end itemize
-@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.
+@node Bash POSIX Mode
+@section Bash POSIX Mode
+@cindex POSIX Mode
-@table @code
+Starting Bash with the @samp{--posix} command-line option or executing
+@samp{set -o posix} while Bash is running will cause Bash to conform more
+closely to the @sc{posix} 1003.2 standard by changing the behavior to
+match that specified by @sc{posix} in areas where the Bash default differs.
-@item %%
-A literal @samp{%}.
+The following list is what's changed when `@sc{posix} mode' is in effect:
-@item %[@var{p}][l]R
-The elapsed time in seconds.
+@enumerate
+@item
+When a command in the hash table no longer exists, Bash will re-search
+@code{$PATH} to find the new location. This is also available with
+@samp{shopt -s checkhash}.
-@item %[@var{p}][l]U
-The number of CPU seconds spent in user mode.
+@item
+The @samp{>&} redirection does not redirect stdout and stderr.
-@item %[@var{p}][l]S
-The number of CPU seconds spent in system mode.
+@item
+The message printed by the job control code and builtins when a job
+exits with a non-zero status is `Done(status)'.
-@item %P
-The CPU percentage, computed as (%U + %S) / %R.
-@end table
+@item
+Reserved words may not be aliased.
-The optional @var{p} is a digit specifying the precision, the number of
-fractional digits after a decimal point.
-A value of 0 causes no decimal point or fraction to be output.
-At most three places after the decimal point may be specified; values
-of @var{p} greater than 3 are changed to 3.
-If @var{p} is not specified, the value 3 is used.
+@item
+The @sc{posix} 1003.2 @code{PS1} and @code{PS2} expansions of @samp{!} to
+the history number and @samp{!!} to @samp{!} are enabled,
+and parameter expansion is performed on the values of @code{PS1} and
+@code{PS2} regardless of the setting of the @code{promptvars} option.
-The optional @code{l} specifies a longer format, including minutes, of
-the form @var{MM}m@var{SS}.@var{FF}s.
-The value of @var{p} determines whether or not the fraction is included.
+@item
+Interactive comments are enabled by default. (Bash has them on by
+default anyway.)
-If this variable is not set, Bash acts as if it had the value
-@example
-@code{$'\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
+The @sc{posix} 1003.2 startup files are executed (@code{$ENV}) rather than
+the normal Bash files.
-@item TMOUT
-If set to a value greater than zero, the value is interpreted as
-the number of seconds to wait for input after issuing the primary
-prompt.
-Bash terminates after that number of seconds if input does
-not arrive.
+@item
+Tilde expansion is only performed on assignments preceding a command
+name, rather than on all assignment statements on the line.
-@item UID
-The numeric real user id of the current user. This variable is readonly.
+@item
+The default history file is @file{~/.sh_history} (this is the
+default value of @code{$HISTFILE}).
-@end vtable
+@item
+The output of @samp{kill -l} prints all the signal names on a single line,
+separated by spaces.
-@node Shell Arithmetic
-@section Shell Arithmetic
-@cindex arithmetic, shell
-@cindex shell arithmetic
-@cindex expressions, arithmetic
-@cindex evaluation, arithmetic
-@cindex arithmetic evaluation
+@item
+Non-interactive shells exit if @var{filename} in @code{.} @var{filename}
+is not found.
-The shell allows arithmetic expressions to be evaluated, as one of
-the shell expansions or by the @code{let} builtin.
+@item
+Non-interactive shells exit if a syntax error in an arithmetic expansion
+results in an invalid expression.
-Evaluation is done in long integers with no check for overflow,
-though division by 0 is trapped and flagged as an error. The
-following list of operators is grouped into levels of
-equal-precedence operators. The levels are listed in order of
-decreasing precedence.
+@item
+Redirection operators do not perform filename expansion on the word
+in the redirection unless the shell is interactive.
-@table @code
-@item - +
-unary minus and plus
+@item
+Redirection operators do not perform word splitting on the word in the
+redirection.
-@item ! ~
-logical and bitwise negation
+@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 **
-exponentiation
+@item
+@sc{posix} 1003.2 `special' builtins are found before shell functions
+during command lookup.
-@item * / %
-multiplication, division, remainder
+@item
+If a @sc{posix} 1003.2 special builtin returns an error status, a
+non-interactive shell exits. The fatal errors are those listed in
+the POSIX.2 standard, and include things like passing incorrect options,
+redirection errors, variable assignment errors for assignments preceding
+the command name, and so on.
-@item + -
-addition, subtraction
+@item
+If the @code{cd} builtin finds a directory to change to
+using @code{$CDPATH}, the
+value it assigns to the @code{PWD} variable does not contain any
+symbolic links, as if @samp{cd -P} had been executed.
+
+@item
+If @code{$CDPATH} is set, the @code{cd} builtin will not implicitly
+append the current directory to it. This means that @code{cd} will
+fail if no valid directory name can be constructed from
+any of the entries in @code{$CDPATH}, even if the a directory with
+the same name as the name given as an argument to @code{cd} exists
+in the current directory.
-@item << >>
-left and right bitwise shifts
+@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 <= >= < >
-comparison
+@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 == !=
-equality and inequality
+@item
+Process substitution is not available.
-@item &
-bitwise AND
+@item
+Assignment statements preceding @sc{posix} 1003.2 special builtins
+persist in the shell environment after the builtin completes.
-@item ^
-bitwise exclusive OR
+@item
+The @code{export} and @code{readonly} builtin commands display their
+output in the format required by @sc{posix} 1003.2.
-@item |
-bitwise OR
+@end enumerate
-@item &&
-logical AND
+There is other @sc{posix} 1003.2 behavior that Bash does not implement.
+Specifically:
-@item ||
-logical OR
+@enumerate
+@item
+Assignment statements affect the execution environment of all
+builtins, not just special ones.
+@end enumerate
-@item expr ? expr : expr
-conditional evaluation
+@node Job Control
+@chapter Job Control
-@item = *= /= %= += -= <<= >>= &= ^= |=
-assignment
-@end table
+This chapter discusses what job control is, how it works, and how
+Bash allows you to access its facilities.
-Shell variables are allowed as operands; parameter expansion is
-performed before the expression is evaluated.
-The value of a parameter is coerced to a long integer within
-an expression. A shell variable need not have its integer attribute
-turned on to be used in an expression.
+@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
-Constants with a leading 0 are interpreted as octal numbers.
-A leading @samp{0x} or @samp{0X} denotes hexadecimal. Otherwise,
-numbers take the form [@var{base}@code{#}]@var{n}, where @var{base}
-is a decimal number between 2 and 64 representing the arithmetic
-base, and @var{n} is a number in that base. If @var{base} is
-omitted, then base 10 is used.
-The digits greater than 9 are represented by the lowercase letters,
-the uppercase letters, @samp{_}, and @samp{@@}, in that order.
-If @var{base} is less than or equal to 36, lowercase and uppercase
-letters may be used interchangably to represent numbers between 10
-and 35.
+@node Job Control Basics
+@section Job Control Basics
+@cindex job control
+@cindex foreground
+@cindex background
+@cindex suspending jobs
-Operators are evaluated in order of precedence. Sub-expressions in
-parentheses are evaluated first and may override the precedence
-rules above.
+Job control
+refers to the ability to selectively stop (suspend)
+the execution of processes and continue (resume)
+their execution at a later point. A user typically employs
+this facility via an interactive interface supplied jointly
+by the system's terminal driver and Bash.
-@node Aliases
-@section Aliases
-@cindex alias expansion
+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.
-@menu
-* Alias Builtins:: Builtins commands to maniuplate aliases.
-@end menu
+To facilitate the implementation of the user interface to job
+control, the operating system maintains the notion of a current terminal
+process group @sc{id}. Members of this process group (processes whose
+process group @sc{id} is equal to the current terminal process group
+@sc{id}) receive keyboard-generated signals such as @code{SIGINT}.
+These processes are said to be in the foreground. Background
+processes are those whose process group @sc{id} differs from the
+terminal's; such processes are immune to keyboard-generated
+signals. Only foreground processes are allowed to read from or
+write to the terminal. Background processes which attempt to
+read from (write to) the terminal are sent a @code{SIGTTIN}
+(@code{SIGTTOU}) signal by the terminal driver, which, unless
+caught, suspends the process.
-Aliases allow a string to be substituted for a word when it is used
-as the first word of a simple command.
-The shell maintains a list of @var{aliases}
-that may be set and unset with the @code{alias} and
-@code{unalias} builtin commands.
+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.
-The first word of each simple command, if unquoted, is checked to see
-if it has an alias.
-If so, that word is replaced by the text of the alias.
-The alias name and the replacement text may contain any valid
-shell input, including shell metacharacters, with the exception
-that the alias name may not contain @samp{=}.
-The first word of the replacement text is tested for
-aliases, but a word that is identical to an alias being expanded
-is not expanded a second time. This means that one may alias
-@code{ls} to @code{"ls -F"},
-for instance, and Bash does not try to recursively expand the
-replacement text. If the last character of the alias value is a
-space or tab character, then the next command word following the
-alias is also checked for alias expansion.
+There are a number of ways to refer to a job in the shell. The
+character @samp{%} introduces a job name.
-Aliases are created and listed with the @code{alias}
-command, and removed with the @code{unalias} command.
+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. The
+previous job may be referenced using @samp{%-}. In output
+pertaining to jobs (e.g., the output of the @code{jobs} command),
+the current job is always flagged with a @samp{+}, and the
+previous job with a @samp{-}.
-There 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}).
+A job may also be referred to
+using a prefix of the name used to start it, or using a substring
+that appears in its command line. For example, @samp{%ce} refers
+to a stopped @code{ce} job. Using @samp{%?ce}, on the
+other hand, refers to any job containing the string @samp{ce} in
+its command line. If the prefix or substring matches more than one job,
+Bash reports an error.
-Aliases are not expanded when the shell is not interactive,
-unless the @code{expand_aliases} shell option is set using
-@code{shopt} (@pxref{Bash Builtins}).
+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 rules concerning the definition and use of aliases are
-somewhat confusing. Bash
-always reads at least one complete line
-of input before executing any
-of the commands on that line. Aliases are expanded when a
-command is read, not when it is executed. Therefore, an
-alias definition appearing on the same line as another
-command does not take effect until the next line of input is read.
-The commands following the alias definition
-on that line are not affected by the new alias.
-This behavior is also an issue when functions are executed.
-Aliases are expanded when a function definition is read,
-not when the function is executed, because a function definition
-is itself a compound command. As a consequence, aliases
-defined in a function are not available until after that
-function is executed. To be safe, always put
-alias definitions on a separate line, and do not use @code{alias}
-in compound commands.
+The shell learns immediately whenever a job changes state.
+Normally, Bash waits until it is about to print a prompt
+before reporting changes in a job's status so as to not interrupt
+any other output. If the
+the @samp{-b} option to the @code{set} builtin is enabled,
+Bash reports such changes immediately (@pxref{The Set Builtin}).
-For almost every purpose, aliases are superseded by
-shell functions.
+If an attempt to exit Bash is while jobs are stopped, the
+shell prints a message warning that there are stopped jobs.
+The @code{jobs} command may then be used to inspect their status.
+If a second attempt to exit is made without an intervening command,
+Bash does not print another warning, and the stopped jobs are terminated.
-@node Alias Builtins
-@subsection Alias Builtins
+@node Job Control Builtins
+@section Job Control Builtins
@table @code
-@item alias
-@btindex alias
+@item bg
+@btindex bg
@example
-alias [@code{-p}] [@var{name}[=@var{value}] @dots{}]
+bg [@var{jobspec}]
@end example
+Resume the suspended job @var{jobspec} in the background, as if it
+had been started with @samp{&}.
+If @var{jobspec} is not supplied, the current job is used.
+The return status is zero unless it is run when job control is not
+enabled, or, when run with job control enabled, if @var{jobspec} was
+not found or @var{jobspec} specifies a job that was started without
+job control.
-Without arguments or with the @samp{-p} option, @code{alias} prints
-the list of aliases on the standard output in a form that allows
-them to be reused as input.
-If arguments are supplied, an alias is defined for each @var{name}
-whose @var{value} is given. If no @var{value} is given, the name
-and value of the alias is printed.
+@item 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 unalias
-@btindex unalias
+@item jobs
+@btindex jobs
@example
-unalias [-a] [@var{name} @dots{} ]
+jobs [-lnprs] [@var{jobspec}]
+jobs -x @var{command} [@var{arguments}]
@end example
-Remove each @var{name} from the list of aliases. If @samp{-a} is
-supplied, all aliases are removed.
+The first form lists the active jobs. The options have the
+following meanings:
+
+@table @code
+@item -l
+List process @sc{id}s in addition to the normal information.
+
+@item -n
+Display information only about jobs that have changed status since
+the user was last notified of their status.
+
+@item -p
+List only the process @sc{id} of the job's process group leader.
+
+@item -r
+Restrict output to running jobs.
+
+@item -s
+Restrict output to stopped jobs.
@end table
-@node Arrays
-@section Arrays
-@cindex arrays
+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.
-Bash provides one-dimensional array variables. Any variable may be used as
-an array; the @code{declare} builtin will explicitly declare an array.
-There is no maximum
-limit on the size of an array, nor any requirement that members
-be indexed or assigned contiguously. Arrays are zero-based.
+If the @samp{-x} option is supplied, @code{jobs} replaces any
+@var{jobspec} found in @var{command} or @var{arguments} with the
+corresponding process group @sc{id}, and executes @var{command},
+passing it @var{argument}s, returning its exit status.
-An array is created automatically if any variable is assigned to using
-the syntax
+@item kill
+@btindex kill
@example
-name[@var{subscript}]=@var{value}
+kill [-s @var{sigspec}] [-n @var{signum}] [-@var{sigspec}] @var{jobspec} or @var{pid}
+kill -l [@var{exit_status}]
@end example
+Send a signal specified by @var{sigspec} or @var{signum} to the process
+named by job specification @var{jobspec} or process @sc{id} @var{pid}.
+@var{sigspec} is either a signal name such as @code{SIGINT} (with or without
+the @code{SIG} prefix) or a signal number; @var{signum} is a signal number.
+If @var{sigspec} and @var{signum} are not present, @code{SIGTERM} is used.
+The @samp{-l} option lists the signal names.
+If any arguments are supplied when @samp{-l} is given, the names of the
+signals corresponding to the arguments are listed, and the return status
+is zero.
+@var{exit_status} is a number specifying a signal number or the exit
+status of a process terminated by a signal.
+The return status is zero if at least one signal was successfully sent,
+or non-zero if an error occurs or an invalid option is encountered.
-@noindent
-The @var{subscript}
-is treated as an arithmetic expression that must evaluate to a number
-greater than or equal to zero. To explicitly declare an array, use
+@item wait
+@btindex wait
@example
-declare -a @var{name}
+wait [@var{jobspec} or @var{pid}]
@end example
-@noindent
-The syntax
+Wait until the child process specified by process @sc{id} @var{pid} or job
+specification @var{jobspec} exits and return the exit status of the last
+command waited for.
+If a job spec is given, all processes in the job are waited for.
+If no arguments are given, all currently active child processes are
+waited for, and the return status is zero.
+If neither @var{jobspec} nor @var{pid} specifies an active child process
+of the shell, the return status is 127.
+
+@item disown
+@btindex disown
@example
-declare -a @var{name}[@var{subscript}]
+disown [-ar] [-h] [@var{jobspec} @dots{}]
@end example
-@noindent
-is also accepted; the @var{subscript} is ignored. Attributes may be
-specified for an array variable using the @code{declare} and
-@code{readonly} builtins. Each attribute applies to all members of
-an array.
+Without options, each @var{jobspec} is removed from the table of
+active jobs.
+If the @samp{-h} option is given, the job is not removed from the table,
+but is marked so that @code{SIGHUP} is not sent to the job if the shell
+receives a @code{SIGHUP}.
+If @var{jobspec} is not present, and neither the @samp{-a} nor @samp{-r}
+option is supplied, the current job is used.
+If no @var{jobspec} is supplied, the @samp{-a} option means to remove or
+mark all jobs; the @samp{-r} option without a @var{jobspec}
+argument restricts operation to running jobs.
-Arrays are assigned to using compound assignments of the form
+@item suspend
+@btindex suspend
@example
-name=(value@var{1} @dots{} value@var{n})
+suspend [-f]
@end example
-@noindent
-where each
-@var{value} is of the form @code{[[@var{subscript}]=]}@var{string}. If
-the optional subscript is supplied, that index is assigned to;
-otherwise the index of the element assigned is the last index assigned
-to by the statement plus one. Indexing starts at zero.
-This syntax is also accepted by the @code{declare}
-builtin. Individual array elements may be assigned to using the
-@code{name[}@var{subscript}@code{]=}@var{value} syntax introduced above.
+Suspend the execution of this shell until it receives a
+@code{SIGCONT} signal. The @samp{-f} option means to suspend
+even if the shell is a login shell.
-Any element of an array may be referenced using
-@code{$@{name[}@var{subscript}@code{]@}}.
-The braces are required to avoid
-conflicts with the shell's filename expansion operators. If the
-@var{subscript} is @samp{@@} or @samp{*}, the word expands to all members
-of the array @var{name}. These subscripts differ only when the word
-appears within double quotes. If the word is double-quoted,
-@code{$@{name[*]@}} expands to a single word with
-the value of each array member separated by the first character of the
-@code{IFS} variable, and @code{$@{name[@@]@}} expands each element of
-@var{name} to a separate word. When there are no array members,
-@code{$@{name[@@]@}} expands to nothing. This is analogous to the
-expansion of the special parameters @samp{@@} and @samp{*}.
-@code{$@{#name[}@var{subscript}@code{]@}} expands to the length of
-@code{$@{name[}@var{subscript}@code{]@}}.
-If @var{subscript} is @samp{@@} or
-@samp{*}, the expansion is the number of elements in the array.
-Referencing an array variable without a subscript is equivalent to
-referencing element zero.
+@end table
-The @code{unset} builtin is used to destroy arrays.
-@code{unset} @code{name[@var{subscript}]}
-destroys the array element at index @var{subscript}.
-@code{unset} @var{name}, where @var{name} is an array, removes the
-entire array. A subscript of @samp{*} or @samp{@@} also removes the
-entire array.
+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.
-The @code{declare}, @code{local}, and @code{readonly}
-builtins each accept a @samp{-a}
-option to specify an array. The @code{read}
-builtin accepts a @samp{-a}
-option to assign a list of words read from the standard input
-to an array, and can read values from the standard input into
-individual array elements. The @code{set} and @code{declare}
-builtins display array values in a way that allows them to be
-reused as input.
+@node Job Control Variables
+@section Job Control Variables
-@node The Directory Stack
-@section The Directory Stack
-@cindex directory stack
+@vtable @code
-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.
+@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}.
-The contents of the directory stack are also visible
-as the value of the @code{DIRSTACK} shell variable.
+@end vtable
-@table @code
+@set readline-appendix
+@set history-appendix
+@cindex Readline, how to use
+@include rluser.texinfo
+@cindex History, how to use
+@include hsuser.texinfo
+@clear readline-appendix
+@clear history-appendix
-@item dirs
-@btindex dirs
-@example
-dirs [+@var{N} | -@var{N}] [-clvp]
-@end example
-Display the list of currently remembered directories. Directories
-are added to the list with the @code{pushd} command; the
-@code{popd} command removes directories from the list.
-@table @code
-@item +@var{N}
-Displays the @var{N}th directory (counting from the left of the
-list printed by @code{dirs} when invoked without options), starting
-with zero.
-@item -@var{N}
-Displays the @var{N}th directory (counting from the right of the
-list printed by @code{dirs} when invoked without options), starting
-with zero.
-@item -c
-Clears the directory stack by deleting all of the elements.
-@item -l
-Produces a longer listing; the default listing format uses a
-tilde to denote the home directory.
-@item -p
-Causes @code{dirs} to print the directory stack with one entry per
-line.
-@item -v
-Causes @code{dirs} to print the directory stack with one entry per
-line, prefixing each entry with its index in the stack.
-@end table
+@node Installing Bash
+@chapter Installing Bash
-@item popd
-@btindex popd
-@example
-popd [+@var{N} | -@var{N}] [-n]
-@end example
+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}, Windows @sc{95/98}, and Windows @sc{nt}.
-Remove the top entry from the directory stack, and @code{cd}
-to the new top directory.
-When no arguments are given, @code{popd}
-removes the top directory from the stack and
-performs a @code{cd} to the new top directory. The
-elements are numbered from 0 starting at the first directory listed with
-@code{dirs}; i.e., @code{popd} is equivalent to @code{popd +0}.
-@table @code
-@item +@var{N}
-Removes the @var{N}th directory (counting from the left of the
-list printed by @code{dirs}), starting with zero.
-@item -@var{N}
-Removes the @var{N}th directory (counting from the right of the
-list printed by @code{dirs}), starting with zero.
-@item -n
-Suppresses the normal change of directory when removing directories
-from the stack, so that only the stack is manipulated.
-@end table
+@menu
+* Basic Installation:: Installation instructions.
-@btindex pushd
-@item pushd
-@example
-pushd [@var{dir} | @var{+N} | @var{-N}] [-n]
-@end example
+* Compilers and Options:: How to set special options for various
+ systems.
-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.
+* Compiling For Multiple Architectures:: How to compile Bash for more
+ than one kind of system from
+ the same source tree.
-@table @code
-@item +@var{N}
-Brings the @var{N}th directory (counting from the left of the
-list printed by @code{dirs}, starting with zero) to the top of
-the list by rotating the stack.
-@item -@var{N}
-Brings the @var{N}th directory (counting from the right of the
-list printed by @code{dirs}, starting with zero) to the top of
-the list by rotating the stack.
-@item -n
-Suppresses the normal change of directory when adding directories
-to the stack, so that only the stack is manipulated.
-@item @var{dir}
-Makes the current working directory be the top of the stack, and then
-executes the equivalent of `@code{cd} @var{dir}'.
-@code{cd}s to @var{dir}.
-@end table
+* Installation Names:: How to set the various paths used by the installation.
-@end table
+* Specifying the System Type:: How to configure Bash for a particular system.
-@node Printing a Prompt
-@section Controlling the Prompt
-@cindex prompting
+* Sharing Defaults:: How to share default configuration values among GNU
+ programs.
-The value of the variable @code{PROMPT_COMMAND} is examined just before
-Bash prints each primary prompt. If it is set and non-null, then the
-value is executed just as if it had been typed on the command line.
+* Operation Controls:: Options recognized by the configuration program.
+
+* Optional Features:: How to enable and disable optional features when
+ building Bash.
+@end menu
-In addition, the following table describes the special characters which
-can appear in the prompt variables:
+@node Basic Installation
+@section Basic Installation
+@cindex installation
+@cindex configuration
+@cindex Bash installation
+@cindex Bash configuration
-@table @code
-@item \a
-A bell character.
-@item \d
-The date, in "Weekday Month Date" format (e.g., "Tue May 26").
-@item \e
-An escape character.
-@item \h
-The hostname, up to the first `.'.
-@item \H
-The hostname.
-@item \n
-A newline.
-@item \r
-A carriage return.
-@item \s
-The name of the shell, the basename of @code{$0} (the portion
-following the final slash).
-@item \t
-The time, in 24-hour HH:MM:SS format.
-@item \T
-The time, in 12-hour HH:MM:SS format.
-@item \@@
-The time, in 12-hour am/pm format.
-@item \u
-The username of the current user.
-@item \v
-The version of Bash (e.g., 2.00)
-@item \V
-The release of Bash, version + patchlevel (e.g., 2.00.0)
-@item \w
-The current working directory.
-@item \W
-The basename of @code{$PWD}.
-@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
+These are installation instructions for Bash.
-@node The Restricted Shell
-@section The Restricted Shell
-@cindex restricted shell
+The simplest way to compile Bash is:
-If Bash is started with the name @code{rbash}, or the
-@samp{--restricted}
-option is supplied at invocation, the shell becomes restricted.
-A restricted shell is used to
-set up an environment more controlled than the standard shell.
-A restricted shell behaves identically to @code{bash}
-with the exception that the following are disallowed:
-@itemize @bullet
-@item
-Changing directories with the @code{cd} builtin.
-@item
-Setting or unsetting the values of the @code{SHELL}, @code{PATH},
-@code{ENV}, or @code{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
-Importing function definitions from the shell environment at startup.
-@item
-Parsing the value of @code{SHELLOPTS} from the shell environment at startup.
-@item
-Redirecting output using the @samp{>}, @samp{>|}, @samp{<>}, @samp{>&},
-@samp{&>}, and @samp{>>} redirection operators.
+@enumerate
@item
-Using the @code{exec} builtin to replace the shell with another command.
+@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
-Adding or deleting builtin commands with the
-@samp{-f} and @samp{-d} options to the @code{enable} builtin.
+Type @samp{make} to compile Bash and build the @code{bashbug} bug
+reporting script.
+
@item
-Specifying the @samp{-p} option to the @code{command} builtin.
+Optionally, type @samp{make tests} to run the Bash test suite.
+
@item
-Turning off restricted mode with @samp{set +r} or @samp{set +o restricted}.
-@end itemize
+Type @samp{make install} to install @code{bash} and @code{bashbug}.
+This will also install the manual pages and Info file.
-@node Bash POSIX Mode
-@section Bash POSIX Mode
-@cindex POSIX Mode
+@end enumerate
-Starting Bash with the @samp{--posix} command-line option or executing
-@samp{set -o posix} while Bash is running will cause Bash to conform more
-closely to the @sc{POSIX.2} standard by changing the behavior to match that
-specified by @sc{POSIX.2} in areas where the Bash default differs.
+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.
-The following list is what's changed when `@sc{POSIX} mode' is in effect:
+To find out more about the options and arguments that the
+@code{configure} script understands, type
-@enumerate
-@item
-When a command in the hash table no longer exists, Bash will re-search
-@code{$PATH} to find the new location. This is also available with
-@samp{shopt -s checkhash}.
+@example
+bash-2.04$ ./configure --help
+@end example
-@item
-The @samp{>&} redirection does not redirect stdout and stderr.
+@noindent
+at the Bash prompt in your Bash source directory.
-@item
-The message printed by the job control code and builtins when a job
-exits with a non-zero status is `Done(status)'.
+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.
-@item
-Reserved words may not be aliased.
+The file @file{configure.in} is used to create @code{configure}
+by a program called Autoconf. You only need
+@file{configure.in} if you want to change it or regenerate
+@code{configure} using a newer version of Autoconf. If
+you do this, make sure you are using Autoconf version 2.10 or
+newer.
-@item
-The @sc{POSIX.2} @code{PS1} and @code{PS2} expansions of @samp{!} to
-the history number and @samp{!!} to @samp{!} are enabled,
-and parameter expansion is performed on the values of @code{PS1} and
-@code{PS2} regardless of the setting of the @code{promptvars} option.
+If you need to change @file{configure.in} or regenerate
+@code{configure}, you will need to create two files:
+@file{_distribution} and @file{_patchlevel}. @file{_distribution}
+should contain the major and minor version numbers of the Bash
+distribution, for example @samp{2.01}. @file{_patchlevel} should
+contain the patch level of the Bash distribution, @samp{0} for
+example. The script @file{support/mkconffiles} has been provided
+to automate the creation of these files.
-@item
-Interactive comments are enabled by default. (Bash has them on by
-default anyway.)
+You can remove the program binaries and object files from the
+source code directory by typing @samp{make clean}. To also remove the
+files that @code{configure} created (so you can compile Bash for
+a different kind of computer), type @samp{make distclean}.
-@item
-The @sc{POSIX.2} startup files are executed (@code{$ENV}) rather than
-the normal Bash files.
+@node Compilers and Options
+@section Compilers and Options
-@item
-Tilde expansion is only performed on assignments preceding a command
-name, rather than on all assignment statements on the line.
+Some systems require unusual options for compilation or linking
+that the @code{configure} script does not know about. You can
+give @code{configure} initial values for variables by setting
+them in the environment. Using a Bourne-compatible shell, you
+can do that on the command line like this:
-@item
-The default history file is @file{~/.sh_history} (this is the
-default value of @code{$HISTFILE}).
+@example
+CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure
+@end example
-@item
-The output of @samp{kill -l} prints all the signal names on a single line,
-separated by spaces.
+On systems that have the @code{env} program, you can do it like this:
-@item
-Non-interactive shells exit if @var{filename} in @code{.} @var{filename}
-is not found.
+@example
+env CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure
+@end example
-@item
-Non-interactive shells exit if a syntax error in an arithmetic expansion
-results in an invalid expression.
+The configuration process uses GCC to build Bash if it
+is available.
-@item
-Redirection operators do not perform filename expansion on the word
-in the redirection unless the shell is interactive.
+@node Compiling For Multiple Architectures
+@section Compiling For Multiple Architectures
-@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.
+You can compile Bash for more than one kind of computer at the
+same time, by placing the object files for each architecture in their
+own directory. To do this, you must use a version of @code{make} that
+supports the @code{VPATH} variable, such as GNU @code{make}.
+@code{cd} to the
+directory where you want the object files and executables to go and run
+the @code{configure} script from the source directory. You may need to
+supply the @samp{--srcdir=PATH} argument to tell @code{configure} where the
+source files are. @code{configure} automatically checks for the
+source code in the directory that @code{configure} is in and in `..'.
-@item
-@sc{POSIX.2} `special' builtins are found before shell functions
-during command lookup.
+If you have to use a @code{make} that does not supports the @code{VPATH}
+variable, you can compile Bash for one architecture at a
+time in the source code directory. After you have installed
+Bash for one architecture, use @samp{make distclean} before
+reconfiguring for another architecture.
-@item
-If a @sc{POSIX.2} special builtin returns an error status, a
-non-interactive shell exits. The fatal errors are those listed in
-the POSIX.2 standard, and include things like passing incorrect options,
-redirection errors, variable assignment errors for assignments preceding
-the command name, and so on.
+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
-@item
-If the @code{cd} builtin finds a directory to change to
-using @code{$CDPATH}, the
-value it assigns to the @code{PWD} variable does not contain any
-symbolic links, as if @samp{cd -P} had been executed.
+By default, @samp{make install} will install into
+@file{/usr/local/bin}, @file{/usr/local/man}, etc. You can
+specify an installation prefix other than @file{/usr/local} by
+giving @code{configure} the option @samp{--prefix=@var{PATH}}.
-@item
-If @code{$CDPATH} is set, the @code{cd} builtin will not implicitly
-append the current directory to it. This means that @code{cd} will
-fail if no valid directory name can be constructed from
-any of the entries in @code{$CDPATH}, even if the a directory with
-the same name as the name given as an argument to @code{cd} exists
-in the current directory.
+You can specify separate installation prefixes for
+architecture-specific files and architecture-independent files.
+If you give @code{configure} the option
+@samp{--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.
-@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.
+@node Specifying the System Type
+@section Specifying the System Type
-@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.
+There may be some features @code{configure} can not figure out
+automatically, but needs to determine by the type of host Bash
+will run on. Usually @code{configure} can figure that
+out, but if it prints a message saying it can not guess the host
+type, give it the @samp{--host=TYPE} option. @samp{TYPE} can
+either be a short name for the system type, such as @samp{sun4},
+or a canonical name with three fields: @samp{CPU-COMPANY-SYSTEM}
+(e.g., @samp{sparc-sun-sunos4.1.2}).
-@item
-Process substitution is not available.
+See the file @file{support/config.sub} for the possible
+values of each field.
-@item
-Assignment statements preceding @sc{POSIX.2} special builtins
-persist in the shell environment after the builtin completes.
+@node Sharing Defaults
+@section Sharing Defaults
-@item
-The @code{export} and @code{readonly} builtin commands display their
-output in the format required by @sc{POSIX.2}.
+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.
-@end enumerate
+@node Operation Controls
+@section Operation Controls
-There is other @sc{POSIX.2} behavior that Bash does not implement.
-Specifically:
+@code{configure} recognizes the following options to control how it
+operates.
-@enumerate
-@item
-Assignment statements affect the execution environment of all
-builtins, not just special ones.
-@end enumerate
+@table @code
-@node Job Control
-@chapter Job Control
+@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}.
-This chapter discusses what job control is, how it works, and how
-Bash allows you to access its facilities.
+@item --help
+Print a summary of the options to @code{configure}, and exit.
-@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
+@item --quiet
+@itemx --silent
+@itemx -q
+Do not print messages saying which checks are being made.
-@node Job Control Basics
-@section Job Control Basics
-@cindex job control
-@cindex foreground
-@cindex background
-@cindex suspending jobs
+@item --srcdir=@var{dir}
+Look for the Bash source code in directory @var{dir}. Usually
+@code{configure} can determine that directory automatically.
-Job control
-refers to the ability to selectively stop (suspend)
-the execution of processes and continue (resume)
-their execution at a later point. A user typically employs
-this facility via an interactive interface supplied jointly
-by the system's terminal driver and Bash.
+@item --version
+Print the version of Autoconf used to generate the @code{configure}
+script, and exit.
+@end table
-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.
+@code{configure} also accepts some other, not widely used, boilerplate
+options. @samp{configure --help} prints the complete list.
-To facilitate the implementation of the user interface to job
-control, the system maintains the notion of a current terminal
-process group @sc{ID}. Members of this process group (processes whose
-process group @sc{ID} is equal to the current terminal process group
-@sc{ID}) receive keyboard-generated signals such as @code{SIGINT}.
-These processes are said to be in the foreground. Background
-processes are those whose process group @sc{ID} differs from the
-terminal's; such processes are immune to keyboard-generated
-signals. Only foreground processes are allowed to read from or
-write to the terminal. Background processes which attempt to
-read from (write to) the terminal are sent a @code{SIGTTIN}
-(@code{SIGTTOU}) signal by the terminal driver, which, unless
-caught, suspends the process.
+@node Optional Features
+@section Optional Features
-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.
+The Bash @code{configure} has a number of @samp{--enable-@var{feature}}
+options, where @var{feature} indicates an optional part of Bash.
+There are also several @samp{--with-@var{package}} options,
+where @var{package} is something like @samp{bash-malloc} or @samp{purify}.
+To turn off the default use of a package, use
+@samp{--without-@var{package}}. To configure Bash without a feature
+that is enabled by default, use @samp{--disable-@var{feature}}.
-There are a number of ways to refer to a job in the shell. The
-character @samp{%} introduces a job name. Job number @code{n}
-may be referred to as @samp{%n}. A job may also be referred to
-using a prefix of the name used to start it, or using a substring
-that appears in its command line. For example, @samp{%ce} refers
-to a stopped @code{ce} job. Using @samp{%?ce}, on the
-other hand, refers to any job containing the string @samp{ce} in
-its command line. If the prefix or substring matches more than one job,
-Bash reports an error. The symbols @samp{%%} and
-@samp{%+} refer to the shell's notion of the current job, which
-is the last job stopped while it was in the foreground or started
-in the background. The
-previous job may be referenced using @samp{%-}. In output
-pertaining to jobs (e.g., the output of the @code{jobs} command),
-the current job is always flagged with a @samp{+}, and the
-previous job with a @samp{-}.
+Here is a complete list of the @samp{--enable-} and
+@samp{--with-} options that the Bash @code{configure} recognizes.
-Simply naming a job can be used to bring it into the foreground:
-@samp{%1} is a synonym for @samp{fg %1}, bringing job 1 from the
-background into the foreground. Similarly, @samp{%1 &} resumes
-job 1 in the background, equivalent to @samp{bg %1}
+@table @code
+@item --with-afs
+Define if you are using the Andrew File System from Transarc.
-The shell learns immediately whenever a job changes state.
-Normally, Bash waits until it is about to print a prompt
-before reporting changes in a job's status so as to not interrupt
-any other output. If the
-the @samp{-b} option to the @code{set} builtin is enabled,
-Bash reports such changes immediately (@pxref{The Set Builtin}).
+@item --with-bash-malloc
+Use the Bash version of
+@code{malloc} in @file{lib/malloc/malloc.c}. This is not the same
+@code{malloc} that appears in @sc{gnu} libc, but an older version
+derived from the 4.2 @sc{bsd} @code{malloc}. This @code{malloc} is
+very fast, but wastes some space on each allocation.
+This option is enabled by default.
+The @file{NOTES} file contains a list of systems for
+which this should be turned off, and @code{configure} disables this
+option automatically for a number of systems.
-If an attempt to exit Bash is while jobs are stopped, the
-shell prints a message warning that there are stopped jobs.
-The @code{jobs} command may then be used to inspect their status.
-If a second attempt to exit is made without an intervening command,
-Bash does not print another warning, and the stopped jobs are terminated.
+@item --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.
-@node Job Control Builtins
-@section Job Control Builtins
+@item --with-glibc-malloc
+Use the @sc{gnu} libc version of @code{malloc} in
+@file{lib/malloc/gmalloc.c}. This is not the version of @code{malloc}
+that appears in glibc version 2, but a modified version of the
+@code{malloc} from glibc version 1. This is somewhat slower than the
+default @code{malloc}, but wastes less space on a per-allocation
+basis, and will return memory to the operating system under
+certain circumstances.
-@table @code
+@item --with-gnu-malloc
+A synonym for @code{--with-bash-malloc}.
-@item bg
-@btindex bg
-@example
-bg [@var{jobspec}]
-@end example
-Resume the suspended job @var{jobspec} in the background, as if it
-had been started with @samp{&}.
-If @var{jobspec} is not supplied, the current job is used.
-The return status is zero unless it is run when job control is not
-enabled, or, when run with job control enabled, if @var{jobspec} was
-not found or @var{jobspec} specifies a job that was started without
-job control.
+@item --with-installed-readline
+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 4.1 and later versions.
-@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 --with-purify
+Define this to use the Purify memory allocation checker from Rational
+Software.
-@item jobs
-@btindex jobs
-@example
-jobs [-lpnrs] [@var{jobspec}]
-jobs -x @var{command} [@var{arguments}]
-@end example
+@item --enable-minimal-config
+This produces a shell with minimal features, close to the historical
+Bourne shell.
+@end table
-The first form lists the active jobs. The options have the
-following meanings:
+There are several @samp{--enable-} options that alter how Bash is
+compiled and linked, rather than changing run-time features.
@table @code
-@item -l
-List process @sc{ID}s in addition to the normal information.
+@item --enable-profiling
+This builds a Bash binary that produces profiling information to be
+processed by @code{gprof} each time it is executed.
-@item -n
-Display information only about jobs that have changed status since
-the user was last notified of their status.
+@item --enable-static-link
+This causes Bash to be linked statically, if @code{gcc} is being used.
+This could be used to build a version to use as root's shell.
+@end table
+
+The @samp{minimal-config} option can be used to disable all of
+the following options, but it is processed first, so individual
+options may be enabled using @samp{enable-@var{feature}}.
+
+All of the following options except for @samp{disabled-builtins} and
+@samp{xpg-echo-default} are
+enabled by default, unless the operating system does not provide the
+necessary support.
+
+@table @code
+@item --enable-alias
+Allow alias expansion and include the @code{alias} and @code{unalias}
+builtins (@pxref{Aliases}).
-@item -p
-List only the process @sc{ID} of the job's process group leader.
+@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 -r
-Restrict output to running jobs.
+@item --enable-array-variables
+Include support for one-dimensional array shell variables
+(@pxref{Arrays}).
-@item -s
-Restrict output to stopped jobs.
-@end table
+@item --enable-bang-history
+Include support for @code{csh}-like history substitution
+(@pxref{History Interaction}).
-If @var{jobspec} is given,
-output is restricted to information about that job.
-If @var{jobspec} is not supplied, the status of all jobs is
-listed.
+@item --enable-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.
-If the @samp{-x} option is supplied, @code{jobs} replaces any
-@var{jobspec} found in @var{command} or @var{arguments} with the
-corresponding process group @sc{ID}, and executes @var{command},
-passing it @var{argument}s, returning its exit status.
+@item --enable-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 kill
-@btindex kill
-@example
-kill [-s @var{sigspec}] [-n @var{signum}] [-@var{sigspec}] @var{jobspec} or @var{pid}
-kill -l [@var{exit_status}]
-@end example
-Send a signal specified by @var{sigspec} or @var{signum} to the process
-named by job specification @var{jobspec} or process ID @var{pid}.
-@var{sigspec} is either a signal name such as @code{SIGINT} (with or without
-the @code{SIG} prefix) or a signal number; @var{signum} is a signal number.
-If @var{sigspec} and @var{signum} are not present, @code{SIGTERM} is used.
-The @samp{-l} option lists the signal names.
-If any arguments are supplied when @samp{-l} is given, the names of the
-signals corresponding to the arguments are listed, and the return status
-is zero.
-@var{exit_status} is a number specifying a signal number or the exit
-status of a process terminated by a signal.
-The return status is zero if at least one signal was successfully sent,
-or non-zero if an error occurs or an invalid option is encountered.
+@item --enable-cond-command
+Include support for the @code{[[} conditional command
+(@pxref{Conditional Constructs}).
-@item wait
-@btindex wait
-@example
-wait [@var{jobspec}|@var{pid}]
-@end example
-Wait until the child process specified by process @sc{ID} @var{pid} or job
-specification @var{jobspec} exits and return the exit status of the last
-command waited for.
-If a job spec is given, all processes in the job are waited for.
-If no arguments are given, all currently active child processes are
-waited for, and the return status is zero.
-If neither @var{jobspec} nor @var{pid} specifies an active child process
-of the shell, the return status is 127.
+@item --enable-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 disown
-@btindex disown
-@example
-disown [-ar] [-h] [@var{jobspec} @dots{}]
-@end example
-Without options, each @var{jobspec} is removed from the table of
-active jobs.
-If the @samp{-h} option is given, the job is not removed from the table,
-but is marked so that @code{SIGHUP} is not sent to the job if the shell
-receives a @code{SIGHUP}.
-If @var{jobspec} is not present, and neither the @samp{-a} nor @samp{-r}
-option is supplied, the current job is used.
-If no @var{jobspec} is supplied, the @samp{-a} option means to remove or
-mark all jobs; the @samp{-r} option without a @var{jobspec}
-argument restricts operation to running jobs.
+@item --enable-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 suspend
-@btindex suspend
-@example
-suspend [-f]
-@end example
-Suspend the execution of this shell until it receives a
-@code{SIGCONT} signal. The @samp{-f} option means to suspend
-even if the shell is a login shell.
+@item --enable-dparen-arithmetic
+Include support for the @code{((@dots{}))} command
+(@pxref{Conditional Constructs}).
-@end table
+@item --enable-extended-glob
+Include support for the extended pattern matching features described
+above under @ref{Pattern Matching}.
-When job control is not active, the @code{kill} and @code{wait}
-builtins do not accept @var{jobspec} arguments. They must be
-supplied process @sc{ID}s.
+@item --enable-help-builtin
+Include the @code{help} builtin, which displays help on shell builtins and
+variables (@pxref{Bash Builtins}).
-@node Job Control Variables
-@section Job Control Variables
+@item --enable-history
+Include command history and the @code{fc} and @code{history}
+builtin commands (@pxref{Bash History Facilities}).
-@vtable @code
+@item --enable-job-control
+This enables the job control features (@pxref{Job Control}),
+if the operating system supports them.
-@item auto_resume
-This variable controls how the shell interacts with the user and
-job control. If this variable exists then single word simple
-commands without redirections are treated as candidates for resumption
-of an existing job. There is no ambiguity allowed; if there is
-more than one job beginning with the string typed, then
-the most recently accessed job will be selected.
-The name of a stopped job, in this context, is the command line
-used to start it. If this variable is set to the value @samp{exact},
-the string supplied must match the name of a stopped job exactly;
-if set to @samp{substring},
-the string supplied needs to match a substring of the name of a
-stopped job. The @samp{substring} value provides functionality
-analogous to the @samp{%?} job @sc{ID} (@pxref{Job Control Basics}).
-If set to any other value, the supplied string must
-be a prefix of a stopped job's name; this provides functionality
-analogous to the @samp{%} job @sc{ID}.
+@item --enable-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}).
-@end vtable
+@item --enable-process-substitution
+This enables process substitution (@pxref{Process Substitution}) if
+the operating system provides the necessary support.
-@set readline-appendix
-@set history-appendix
-@cindex History, how to use
-@include hsuser.texinfo
-@cindex Readline, how to use
-@include rluser.texinfo
-@clear readline-appendix
-@clear history-appendix
+@item --enable-prompt-string-decoding
+Turn on the interpretation of a number of backslash-escaped characters
+in the @code{$PS1}, @code{$PS2}, @code{$PS3}, and @code{$PS4} prompt
+strings. See @ref{Printing a Prompt}, for a complete list of prompt
+string escape sequences.
-@node Installing Bash
-@chapter Installing Bash
+@item --enable-progcomp
+Enable the programmable completion facilities
+(@pxref{Programmable Completion}).
+If Readline is not enabled, this option has no effect.
-This chapter provides basic instructions for installing Bash on
-the various supported platforms. The distribution supports nearly every
-version of Unix (and, someday, @sc{GNU}). Other independent ports exist for
-@sc{MS-DOS}, @sc{OS/2}, Windows @sc{95}, and Windows @sc{NT}.
+@item --enable-readline
+Include support for command-line editing and history with the Bash
+version of the Readline library (@pxref{Command Line Editing}).
-@menu
-* Basic Installation:: Installation instructions.
+@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.
-* Compilers and Options:: How to set special options for various
- systems.
+@item --enable-select
+Include the @code{select} builtin, which allows the generation of simple
+menus (@pxref{Conditional Constructs}).
-* Compiling For Multiple Architectures:: How to compile Bash for more
- than one kind of system from
- the same source tree.
+@item --enable-usg-echo-default
+A synonym for @code{--enable-xpg-echo-default}.
-* Installation Names:: How to set the various paths used by the installation.
+@item --enable-xpg-echo-default
+Make the @code{echo} builtin expand backslash-escaped characters by default,
+without requiring the @samp{-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 2.
+@xref{Bash Builtins}, for a description of the escape sequences that
+@code{echo} recognizes.
-* Specifying the System Type:: How to configure Bash for a particular system.
+@end table
-* Sharing Defaults:: How to share default configuration values among GNU
- programs.
+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.
-* Operation Controls:: Options recognized by the configuration program.
+@node Reporting Bugs
+@appendix Reporting Bugs
-* Optional Features:: How to enable and disable optional features when
- building Bash.
-@end menu
+Please report all bugs you find in Bash.
+But first, you should
+make sure that it really is a bug, and that it appears in the latest
+version of Bash that you have.
-@node Basic Installation
-@section Basic Installation
-@cindex installation
-@cindex configuration
-@cindex Bash installation
-@cindex Bash configuration
+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}.
-These are installation instructions for Bash.
+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
-The @code{configure} shell script attempts to guess correct
-values for various system-dependent variables used during
-compilation. It uses those values to create a @file{Makefile} in
-each directory of the package (the top directory, the
-@file{builtins} and @file{doc} directories, and the
-each directory under @file{lib}). It also creates a
-@file{config.h} file containing system-dependent definitions.
-Finally, it creates a shell script named @code{config.status} that you
-can run in the future to recreate the current configuration, a
-file @file{config.cache} that saves the results of its tests to
-speed up reconfiguring, and a file @file{config.log} containing
-compiler output (useful mainly for debugging @code{configure}).
-If at some point
-@file{config.cache} contains results you don't want to keep, you
-may remove or edit it.
+@noindent
+@code{bashbug} inserts the first three items automatically into
+the template it provides for filing a bug report.
-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.
+Please send all reports concerning this manual to
+@email{chet@@po.CWRU.Edu}.
-The file @file{configure.in} is used to create @code{configure}
-by a program called Autoconf. You only need
-@file{configure.in} if you want to change it or regenerate
-@code{configure} using a newer version of Autoconf. If
-you do this, make sure you are using Autoconf version 2.10 or
-newer.
+@node Major Differences From The Bourne Shell
+@appendix Major Differences From The Bourne Shell
-If you need to change @file{configure.in} or regenerate
-@code{configure}, you will need to create two files:
-@file{_distribution} and @file{_patchlevel}. @file{_distribution}
-should contain the major and minor version numbers of the Bash
-distribution, for example @samp{2.01}. @file{_patchlevel} should
-contain the patch level of the Bash distribution, @samp{0} for
-example. The script @file{support/mkconffiles} has been provided
-to automate the creation of these files.
+Bash implements essentially the same grammar, parameter and
+variable expansion, redirection, and quoting as the Bourne Shell.
+Bash uses the @sc{posix} 1003.2 standard as the specification of
+how these features are to be implemented. There are some
+differences between the traditional Bourne shell and Bash; this
+section quickly details the differences of significance. A
+number of these differences are explained in greater depth in
+previous sections.
+This section uses the version of @code{sh} included SVR4.2 as
+the baseline reference.
-The simplest way to compile Bash is:
+@itemize @bullet
-@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 awhile. While running, it prints some
-messages telling which features it is checking for.
+Bash is @sc{posix}-conformant, even where the @sc{posix} specification
+differs from traditional @code{sh} behavior.
@item
-Type @samp{make} to compile Bash and build the @code{bashbug} bug
-reporting script.
+Bash has multi-character invocation options (@pxref{Invoking Bash}).
@item
-Optionally, type @samp{make tests} to run the Bash test suite.
+Bash has command-line editing (@pxref{Command Line Editing}) and
+the @code{bind} builtin.
@item
-Type @samp{make install} to install @code{bash} and @code{bashbug}.
-This will also install the manual pages and Info file.
+Bash provides a programmable word completion mechanism
+(@pxref{Programmable Completion}), and two builtin commands,
+@code{complete} and @code{compgen}, to manipulate it.
-@end enumerate
+@item
+Bash has command history (@pxref{Bash History Facilities}) and the
+@code{history} and @code{fc} builtins to manipulate it.
-You can remove the program binaries and object files from the
-source code directory by typing @samp{make clean}. To also remove the
-files that @code{configure} created (so you can compile Bash for
-a different kind of computer), type @samp{make distclean}.
+@item
+Bash implements @code{csh}-like history expansion
+(@pxref{History Interaction}).
-@node Compilers and Options
-@section Compilers and Options
+@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.
-Some systems require unusual options for compilation or linking
-that the @code{configure} script does not know about. You can
-give @code{configure} initial values for variables by setting
-them in the environment. Using a Bourne-compatible shell, you
-can do that on the command line like this:
+@item
+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}).
-@example
-CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure
-@end example
+@item
+Bash supports the @code{$"@dots{}"} quoting syntax to do
+locale-specific translation of the characters between the double
+quotes. The @samp{-D}, @samp{--dump-strings}, and @samp{--dump-po-strings}
+invocation options list the translatable strings found in a script
+(@pxref{Locale Translation}).
-On systems that have the @code{env} program, you can do it like this:
+@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.
-@example
-env CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure
-@end example
+@item
+Bash has the @code{time} reserved word and command timing (@pxref{Pipelines}).
+The display of the timing statistics may be controlled with the
+@code{TIMEFORMAT} variable.
-The configuration process uses GCC to build Bash if it
-is available.
+@item
+Bash implements the @code{for (( @var{expr1} ; @var{expr2} ; @var{expr3} ))}
+arithmetic for command, similar to the C language (@pxref{Looping Constructs}).
-@node Compiling For Multiple Architectures
-@section Compiling For Multiple Architectures
+@item
+Bash includes the @code{select} compound command, which allows the
+generation of simple menus (@pxref{Conditional Constructs}).
-You can compile Bash for more than one kind of computer at the
-same time, by placing the object files for each architecture in their
-own directory. To do this, you must use a version of @code{make} that
-supports the @code{VPATH} variable, such as GNU @code{make}.
-@code{cd} to the
-directory where you want the object files and executables to go and run
-the @code{configure} script from the source directory. You may need to
-supply the @samp{--srcdir=PATH} argument to tell @code{configure} where the
-source files are. @code{configure} automatically checks for the
-source code in the directory that @code{configure} is in and in `..'.
+@item
+Bash includes the @code{[[} compound command, which makes conditional
+testing part of the shell grammar (@pxref{Conditional Constructs}).
-If you have to use a @code{make} that does not supports the @code{VPATH}
-variable, you can compile Bash for one architecture at a
-time in the source code directory. After you have installed
-Bash for one architecture, use @samp{make distclean} before
-reconfiguring for another architecture.
+@item
+Bash includes brace expansion (@pxref{Brace Expansion}) and tilde
+expansion (@pxref{Tilde Expansion}).
-Alternatively, if your system supports symbolic links, you can use the
-@file{support/mkclone} script to create a build tree which has
-symbolic links back to each file in the source directory. Here's an
-example that creates a build directory in the current directory from a
-source directory @file{/usr/gnu/src/bash-2.0}:
+@item
+Bash implements command aliases and the @code{alias} and @code{unalias}
+builtins (@pxref{Aliases}).
-@example
-bash /usr/gnu/src/bash-2.0/support/mkclone -s /usr/gnu/src/bash-2.0 .
-@end example
+@item
+Bash provides shell arithmetic, the @code{((} compound command
+(@pxref{Conditional Constructs}),
+and arithmetic expansion (@pxref{Shell Arithmetic}).
-@noindent
-The @code{mkclone} script requires Bash, so you must have already built
-Bash for at least one architecture before you can create build
-directories for other architectures.
+@item
+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.
-@node Installation Names
-@section Installation Names
+@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}).
-By default, @samp{make install} will install into
-@file{/usr/local/bin}, @file{/usr/local/man}, etc. You can
-specify an installation prefix other than @file{/usr/local} by
-giving @code{configure} the option @samp{--prefix=PATH}.
+@item
+The expansion @code{$@{#xx@}}, which returns the length of @code{$@{xx@}},
+is supported (@pxref{Shell Parameter Expansion}).
-You can specify separate installation prefixes for
-architecture-specific files and architecture-independent files.
-If you give @code{configure} the option
-@samp{--exec-prefix=PATH}, @samp{make install} will use @samp{PATH} as the
-prefix for installing programs and libraries. Documentation and
-other data files will still use the regular prefix.
+@item
+The expansion @code{$@{var:}@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}).
-@node Specifying the System Type
-@section Specifying the System Type
+@item
+The expansion
+@code{$@{var/[/]}@var{pattern}@code{[/}@var{replacement}@code{]@}},
+which matches @var{pattern} and replaces it with @var{replacement} in
+the value of @code{var}, is available (@pxref{Shell Parameter Expansion}).
-There may be some features @code{configure} can not figure out
-automatically, but needs to determine by the type of host Bash
-will run on. Usually @code{configure} can figure that
-out, but if it prints a message saying it can not guess the host
-type, give it the @samp{--host=TYPE} option. @samp{TYPE} can
-either be a short name for the system type, such as @samp{sun4},
-or a canonical name with three fields: @samp{CPU-COMPANY-SYSTEM}
-(e.g., @samp{sparc-sun-sunos4.1.2}).
+@item
+The expansion @code{$@{!@var{prefix@}*}} expansion, which expands to
+the names of all shell variables whose names begin with @var{prefix},
+is available (@pxref{Shell Parameter Expansion}).
-@noindent See the file @file{support/config.sub} for the possible
-values of each field.
+@item
+Bash has @var{indirect} variable expansion using @code{$@{!word@}}
+(@pxref{Shell Parameter Expansion}).
-@node Sharing Defaults
-@section Sharing Defaults
+@item
+Bash can expand positional parameters beyond @code{$9} using
+@code{$@{@var{num}@}}.
-If you want to set default values for @code{configure} scripts to
-share, you can create a site shell script called
-@code{config.site} that gives default values for variables like
-@code{CC}, @code{cache_file}, and @code{prefix}. @code{configure}
-looks for @file{PREFIX/share/config.site} if it exists, then
-@file{PREFIX/etc/config.site} if it exists. Or, you can set the
-@code{CONFIG_SITE} environment variable to the location of the site
-script. A warning: the Bash @code{configure} looks for a site script,
-but not all @code{configure} scripts do.
+@item
+The @sc{posix} @code{$()} form of command substitution
+is implemented (@pxref{Command Substitution}),
+and preferred to the Bourne shell's @code{``} (which
+is also implemented for backwards compatibility).
-@node Operation Controls
-@section Operation Controls
+@item
+Bash has process substitution (@pxref{Process Substitution}).
-@code{configure} recognizes the following options to control how it
-operates.
+@item
+Bash automatically assigns variables that provide information about the
+current user (@code{UID}, @code{EUID}, and @code{GROUPS}), the current host
+(@code{HOSTTYPE}, @code{OSTYPE}, @code{MACHTYPE}, and @code{HOSTNAME}),
+and the instance of Bash that is running (@code{BASH},
+@code{BASH_VERSION}, and @code{BASH_VERSINFO}). @xref{Bash Variables},
+for details.
-@table @code
+@item
+The @code{IFS} variable is used to split only the results of expansion,
+not all words (@pxref{Word Splitting}).
+This closes a longstanding shell security hole.
-@item --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
+Bash implements the full set of @sc{posix} 1003.2 filename expansion operators,
+including @var{character classes}, @var{equivalence classes}, and
+@var{collating symbols} (@pxref{Filename Expansion}).
-@item --help
-Print a summary of the options to @code{configure}, and exit.
+@item
+Bash implements extended pattern matching features when the @code{extglob}
+shell option is enabled (@pxref{Pattern Matching}).
-@item --quiet
-@itemx --silent
-@itemx -q
-Do not print messages saying which checks are being made.
+@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 --srcdir=@var{DIR}
-Look for the Bash source code in directory @var{DIR}. Usually
-@code{configure} can determine that directory automatically.
+@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 --version
-Print the version of Autoconf used to generate the @code{configure}
-script, and exit.
-@end table
+@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.
-@code{configure} also accepts some other, not widely used, boilerplate
-options.
+@item
+Bash performs filename expansion on filenames specified as operands
+to input and output redirection operators (@pxref{Redirections}).
-@node Optional Features
-@section Optional Features
+@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}).
-The Bash @code{configure} has a number of @samp{--enable-@var{FEATURE}}
-options, where @var{FEATURE} indicates an optional part of Bash.
-There are also several @samp{--with-@var{PACKAGE}} options,
-where @var{PACKAGE} is something like @samp{gnu-malloc} or @samp{purify}.
-To turn off the default use of a package, use
-@samp{--without-@var{PACKAGE}}. To configure Bash without a feature
-that is enabled by default, use @samp{--disable-@var{FEATURE}}.
+@item
+Bash treats a number of filenames specially when they are
+used in redirection operators (@pxref{Redirections}).
-Here is a complete list of the @samp{--enable-} and
-@samp{--with-} options that the Bash @code{configure} recognizes.
+@item
+Bash can open network connections to arbitrary machines and services
+with the redirection operators (@pxref{Redirections}).
-@table @code
-@item --with-afs
-Define if you are using the Andrew File System from Transarc.
+@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 --with-curses
-Use the curses library instead of the termcap library. This should
-be supplied if your system has an inadequate or incomplete termcap
-database.
+@item
+The Bash @code{cd} and @code{pwd} builtins (@pxref{Bourne Shell Builtins})
+each take @samp{-L} and @samp{-P} builtins to switch between logical and
+physical modes.
-@item --with-glibc-malloc
-Use the @sc{GNU} libc version of @code{malloc} in
-@file{lib/malloc/gmalloc.c}. This is not the version of @code{malloc}
-that appears in glibc version 2, but a modified version of the
-@code{malloc} from glibc version 1. This is somewhat slower than the
-default @code{malloc}, but wastes less space on a per-allocation
-basis, and will return memory to the operating system under
-some circumstances.
+@item
+Bash allows a function to override a builtin with the same name, and provides
+access to that builtin's functionality within the function via the
+@code{builtin} and @code{command} builtins (@pxref{Bash Builtins}).
-@item --with-gnu-malloc
-Use the @sc{GNU} version of
-@code{malloc} in @file{lib/malloc/malloc.c}. This is not the same
-@code{malloc} that appears in @sc{GNU} libc, but an older version
-derived from the 4.2 @sc{BSD} @code{malloc}. This @code{malloc} is
-very fast, but wastes some space on each allocation.
-This option is enabled by default.
-The @file{NOTES} file contains a list of systems for
-which this should be turned off, and @code{configure} disables this
-option automatically for a number of systems.
+@item
+The @code{command} builtin allows selective disabling of functions
+when command lookup is performed (@pxref{Bash Builtins}).
-@item --with-installed-readline
-Define this to make bash link with a locally-installed version of Readline
-rather than the version in lib/readline. This works only with readline 4.0
-and later versions.
+@item
+Individual builtins may be enabled or disabled using the @code{enable}
+builtin (@pxref{Bash Builtins}).
-@item --with-purify
-Define this to use the Purify memory allocation checker from Pure
-Software.
+@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 --enable-minimal-config
-This produces a shell with minimal features, close to the historical
-Bourne shell.
-@end table
+@item
+Shell functions may be exported to children via the environment
+using @code{export -f} (@pxref{Shell Functions}).
-There are several @samp{--enable-} options that alter how Bash is
-compiled and linked, rather than changing run-time features.
+@item
+The Bash @code{export}, @code{readonly}, and @code{declare} builtins can
+take a @samp{-f} option to act on shell functions, a @samp{-p} option to
+display variables with various attributes set in a format that can be
+used as shell input, a @samp{-n} option to remove various variable
+attributes, and @samp{name=value} arguments to set variable attributes
+and values simultaneously.
-@table @code
-@item --enable-profiling
-This builds a Bash binary that produces profiling information to be
-processed by @code{gprof} each time it is executed.
+@item
+The Bash @code{hash} builtin allows a name to be associated with
+an arbitrary filename, even when that filename cannot be found by
+searching the @code{$PATH}, using @samp{hash -p}
+(@pxref{Bourne Shell Builtins}).
-@item --enable-static-link
-This causes Bash to be linked statically, if @code{gcc} is being used.
-This could be used to build a version to use as root's shell.
-@end table
+@item
+Bash includes a @code{help} builtin for quick reference to shell
+facilities (@pxref{Bash Builtins}).
-The @samp{minimal-config} option can be used to disable all of
-the following options, but it is processed first, so individual
-options may be enabled using @samp{enable-@var{FEATURE}}.
+@item
+The @code{printf} builtin is available to display formatted output
+(@pxref{Bash Builtins}).
-All of the following options except for @samp{disabled-builtins} and
-@samp{usg-echo-default} are
-enabled by default, unless the operating system does not provide the
-necessary support.
+@item
+The Bash @code{read} builtin (@pxref{Bash Builtins})
+will read a line ending in @samp{\} with
+the @samp{-r} option, and will use the @code{REPLY} variable as a
+default if no non-option arguments are supplied.
+The Bash @code{read} builtin
+also accepts a prompt string with the @samp{-p} option and will use
+Readline to obtain the line when given the @samp{-e} option.
+The @code{read} builtin also has additional options to control input:
+the @samp{-s} option will turn off echoing of input characters as
+they are read, the @samp{-t} option will allow @code{read} to time out
+if input does not arrive within a specified number of seconds, the
+@samp{-n} option will allow reading only a specified number of
+characters rather than a full line, and the @samp{-d} option will read
+until a particular character rather than newline.
-@table @code
-@item --enable-alias
-Allow alias expansion and include the @code{alias} and @code{unalias}
-builtins (@pxref{Aliases}).
+@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 --enable-array-variables
-Include support for one-dimensional array shell variables
-(@pxref{Arrays}).
+@item
+Bash includes the @code{shopt} builtin, for finer control of shell
+optional capabilities (@pxref{Bash Builtins}).
-@item --enable-bang-history
-Include support for @code{csh}-like history substitution
-(@pxref{History Interaction}).
+@item
+Bash has much more optional behavior controllable with the @code{set}
+builtin (@pxref{The Set Builtin}).
-@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
+The @code{test} builtin (@pxref{Bourne Shell Builtins})
+is slightly different, as it implements the @sc{posix} algorithm,
+which specifies the behavior based on the number of arguments.
-@item --enable-command-timing
-Include support for recognizing @code{time} as a reserved word and for
-displaying timing statistics for the pipeline following @code{time}. This
-allows pipelines as well as shell builtins and functions to be timed.
+@item
+The @code{trap} builtin (@pxref{Bourne Shell Builtins})
+allows a @code{DEBUG} pseudo-signal specification,
+similar to @code{EXIT}. Commands specified with a @code{DEBUG} trap are
+executed after every simple command. The @code{DEBUG} trap is not
+inherited by shell functions.
-@item --enable-cond-command
-Include support for the @code{[[} conditional command
-(@pxref{Conditional Constructs}).
+@item
+The Bash @code{type} builtin is more extensive and gives more information
+about the names it finds (@pxref{Bash Builtins}).
-@item --enable-directory-stack
-Include support for a @code{csh}-like directory stack and the
-@code{pushd}, @code{popd}, and @code{dirs} builtins
-(@pxref{The Directory Stack}).
+@item
+The Bash @code{umask} builtin permits a @samp{-p} option to cause
+the output to be displayed in the form of a @code{umask} command
+that may be reused as input (@pxref{Bourne Shell Builtins}).
-@item --enable-disabled-builtins
-Allow builtin commands to be invoked via @samp{builtin xxx}
-even after @code{xxx} has been disabled using @samp{enable -n xxx}.
-See @ref{Bash Builtins}, for details of the @code{builtin} and
-@code{enable} builtin commands.
+@item
+Bash implements a @code{csh}-like directory stack, and provides the
+@code{pushd}, @code{popd}, and @code{dirs} builtins to manipulate it
+(@pxref{The Directory Stack}).
+Bash also makes the directory stack visible as the value of the
+@code{DIRSTACK} shell variable.
-@item --enable-dparen-arithmetic
-Include support for the @code{((@dots{}))} command
-(@pxref{Conditional Constructs}).
+@item
+Bash interprets special backslash-escaped characters in the prompt
+strings when interactive (@pxref{Printing a Prompt}).
-@item --enable-extended-glob
-Include support for the extended pattern matching features described
-above under @ref{Pattern Matching}.
+@item
+The Bash restricted mode is more useful (@pxref{The Restricted Shell});
+the SVR4.2 shell restricted mode is too limited.
-@item --enable-help-builtin
-Include the @code{help} builtin, which displays help on shell builtins and
-variables.
+@item
+The @code{disown} builtin can remove a job from the internal shell
+job table (@pxref{Job Control Builtins}) or suppress the sending
+of @code{SIGHUP} to a job when the shell exits as the result of a
+@code{SIGHUP}.
-@item --enable-history
-Include command history and the @code{fc} and @code{history}
-builtin commands.
+@item
+The SVR4.2 shell has two privilege-related builtins
+(@code{mldmode} and @code{priv}) not present in Bash.
-@item --enable-job-control
-This enables the job control features (@pxref{Job Control}),
-if the operating system supports them.
+@item
+Bash does not have the @code{stop} or @code{newgrp} builtins.
-@item --enable-process-substitution
-This enables process substitution (@pxref{Process Substitution}) if
-the operating system provides the necessary support.
+@item
+Bash does not use the @code{SHACCT} variable or perform shell accounting.
-@item --enable-prompt-string-decoding
-Turn on the interpretation of a number of backslash-escaped characters
-in the @code{$PS1}, @code{$PS2}, @code{$PS3}, and @code{$PS4} prompt
-strings. See @ref{Printing a Prompt}, for a complete list of prompt
-string escape sequences.
+@item
+The SVR4.2 @code{sh} uses a @code{TIMEOUT} variable like Bash uses
+@code{TMOUT}.
-@item --enable-readline
-Include support for command-line editing and history with the Bash
-version of the Readline library (@pxref{Command Line Editing}).
+@end itemize
-@item --enable-restricted
-Include support for a @dfn{restricted shell}. If this is enabled, Bash,
-when called as @code{rbash}, enters a restricted mode. See
-@ref{The Restricted Shell}, for a description of restricted mode.
+@noindent
+More features unique to Bash may be found in @ref{Bash Features}.
-@item --enable-select
-Include the @code{select} builtin, which allows the generation of simple
-menus (@pxref{Conditional Constructs}).
-@item --enable-usg-echo-default
-Make the @code{echo} builtin expand backslash-escaped characters by default,
-without requiring the @samp{-e} option. This makes the Bash @code{echo}
-behave more like the System V version.
+@appendixsec Implementation Differences From The SVR4.2 Shell
-@end table
+Since Bash is a completely new implementation, it does not suffer from
+many of the limitations of the SVR4.2 shell. For instance:
-The file @file{config.h.top} contains C Preprocessor
-@samp{#define} statements for options which are not settable from
-@code{configure}.
-Some of these are not meant to be changed; beware of the consequences if
-you do.
-Read the comments associated with each definition for more
-information about its effect.
+@itemize @bullet
-@node Reporting Bugs
-@appendix Reporting Bugs
+@item
+Bash does not fork a subshell when redirecting into or out of
+a shell control structure such as an @code{if} or @code{while}
+statement.
-Please report all bugs you find in Bash.
-But first, you should
-make sure that it really is a bug, and that it appears in the latest
-version of Bash that you have.
+@item
+Bash does not allow unbalanced quotes. The SVR4.2 shell will silently
+insert a needed closing quote at @code{EOF} under certain circumstances.
+This can be the cause of some hard-to-find errors.
-Once you have determined that a bug actually exists, use the
-@code{bashbug} command to submit a bug report.
-If you have a fix, you are encouraged to mail that as well!
-Suggestions and `philosophical' bug reports may be mailed
-to @email{bug-bash@@gnu.org} or posted to the Usenet
-newsgroup @code{gnu.bash.bug}.
+@item
+The SVR4.2 shell uses a baroque memory management scheme based on
+trapping @code{SIGSEGV}. If the shell is started from a process with
+@code{SIGSEGV} blocked (e.g., by using the @code{system()} C library
+function call), it misbehaves badly.
-All bug reports should include:
-@itemize @bullet
@item
-The version number of Bash.
+In a questionable attempt at security, the SVR4.2 shell,
+when invoked without the @samp{-p} option, will alter its real
+and effective @sc{uid} and @sc{gid} if they are less than some
+magic threshold value, commonly 100.
+This can lead to unexpected results.
+
@item
-The hardware and operating system.
+The SVR4.2 shell does not allow users to trap @code{SIGSEGV},
+@code{SIGALRM}, or @code{SIGCHLD}.
+
@item
-The compiler used to compile Bash.
+The SVR4.2 shell does not allow the @code{IFS}, @code{MAILCHECK},
+@code{PATH}, @code{PS1}, or @code{PS2} variables to be unset.
+
@item
-A description of the bug behaviour.
+The SVR4.2 shell treats @samp{^} as the undocumented equivalent of
+@samp{|}.
+
@item
-A short script or `recipe' which exercises the bug and may be used
-to reproduce it.
-@end itemize
+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{-}.
-@noindent
-@code{bashbug} inserts the first three items automatically into
-the template it provides for filing a bug report.
+@item
+The SVR4.2 shell exits a script if any builtin fails; Bash exits
+a script only if one of the @sc{posix} 1003.2 special builtins fails, and
+only for certain failures, as enumerated in the @sc{posix} 1003.2 standard.
-Please send all reports concerning this manual to
-@email{chet@@po.CWRU.Edu}.
+@item
+The SVR4.2 shell behaves differently when invoked as @code{jsh}
+(it turns on job control).
+@end itemize
@node Builtin Index
-@appendix Index of Shell Builtin Commands
+@unnumbered Index of Shell Builtin Commands
@printindex bt
@node Reserved Word Index
-@appendix Shell Reserved Words
+@unnumbered Index of Shell Reserved Words
@printindex rw
@node Variable Index
-@appendix Parameter and Variable Index
+@unnumbered Parameter and Variable Index
@printindex vr
@node Function Index
-@appendix Function Index
+@unnumbered Function Index
@printindex fn
@node Concept Index
-@appendix Concept Index
+@unnumbered Concept Index
@printindex cp
@contents
projects / thirdparty / bash.git / blobdiff