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doc/bashref.texi
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@ -5,13 +5,13 @@
@c %**end of header
@ignore
Last Change: Tue Nov 13 12:48:51 EST 2001
Last Change: Mon Jul 15 15:21:16 EDT 2002
@end ignore
@set EDITION 2.5a
@set VERSION 2.05a
@set UPDATED 13 November 2001
@set UPDATE-MONTH November 2001
@set EDITION 2.5b
@set VERSION 2.05b
@set UPDATED 15 July 2002
@set UPDATE-MONTH July 2002
@iftex
@finalout
@ -36,7 +36,7 @@ This is Edition @value{EDITION}, last updated @value{UPDATED},
of @cite{The GNU Bash Reference Manual},
for @code{Bash}, Version @value{VERSION}.
Copyright (C) 1991-2001 Free Software Foundation, Inc.
Copyright (C) 1991-2002 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
@ -70,7 +70,7 @@ by the Free Software Foundation.
@author Brian Fox, Free Software Foundation
@page
@vskip 0pt plus 1filll
Copyright @copyright{} 1991-1999 Free Software Foundation, Inc.
Copyright @copyright{} 1991-2002 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
@ -100,7 +100,7 @@ This is Edition @value{EDITION}, last updated @value{UPDATED},
of @cite{The GNU Bash Reference Manual},
for @code{Bash}, Version @value{VERSION}.
Copyright (C) 1991, 1993, 1996 Free Software Foundation, Inc.
Copyright (C) 1991-2002 Free Software Foundation, Inc.
Bash contains features that appear in other popular shells, and some
features that only appear in Bash. Some of the shells that Bash has
@ -548,6 +548,8 @@ the eight-bit character whose value is the octal value @var{nnn}
@item \x@var{HH}
the eight-bit character whose value is the hexadecimal value @var{HH}
(one or two hex digits)
@item \c@var{x}
a control-@var{x} character
@end table
@noindent
@ -688,6 +690,9 @@ Of these list operators, @samp{&&} and @samp{||}
have equal precedence, followed by @samp{;} and @samp{&},
which have equal precedence.
A sequence of one or more newlines may appear in a @code{list}
to delimit commands, equivalent to a semicolon.
If a command is terminated by the control operator @samp{&},
the shell executes the command asynchronously in a subshell.
This is known as executing the command in the @var{background}.
@ -972,7 +977,7 @@ True if both @var{expression1} and @var{expression2} are true.
True if either @var{expression1} or @var{expression2} is true.
@end table
@noindent
The @code{&&} and @code{||} commands do not execute @var{expression2} if the
The @code{&&} and @code{||} operators do not evaluate @var{expression2} if the
value of @var{expression1} is sufficient to determine the return
value of the entire conditional expression.
@ -1778,10 +1783,12 @@ using the syntax
following classes defined in the @sc{posix} 1003.2 standard:
@example
alnum alpha ascii blank cntrl digit graph lower
print punct space upper xdigit
print punct space upper word xdigit
@end example
@noindent
A character class matches any character belonging to that class.
The @code{word} character class matches letters, digits, and the character
@samp{_}.
Within @samp{[} and @samp{]}, an @var{equivalence class} can be
specified using the syntax @code{[=}@var{c}@code{=]}, which
@ -1905,20 +1912,20 @@ is not specified.
The general format for redirecting input is:
@example
[n]<@var{word}
[@var{n}]<@var{word}
@end example
@subsection Redirecting Output
Redirection of output causes the file whose name results from
the expansion of @var{word}
to be opened for writing on file descriptor @code{n},
or the standard output (file descriptor 1) if @code{n}
to be opened for writing on file descriptor @var{n},
or the standard output (file descriptor 1) if @var{n}
is not specified. If the file does not exist it is created;
if it does exist it is truncated to zero size.
The general format for redirecting output is:
@example
[n]>[|]@var{word}
[@var{n}]>[|]@var{word}
@end example
If the redirection operator is @samp{>}, and the @code{noclobber}
@ -1933,13 +1940,13 @@ is attempted even if the file named by @var{word} exists.
Redirection of output in this fashion
causes the file whose name results from
the expansion of @var{word}
to be opened for appending on file descriptor @code{n},
or the standard output (file descriptor 1) if @code{n}
to be opened for appending on file descriptor @var{n},
or the standard output (file descriptor 1) if @var{n}
is not specified. If the file does not exist it is created.
The general format for appending output is:
@example
[n]>>@var{word}
[@var{n}]>>@var{word}
@end example
@subsection Redirecting Standard Output and Standard Error
@ -1973,7 +1980,7 @@ current source until a line containing only @var{word}
the lines read up to that point are then used as the standard
input for a command.
The format of here-documents is as follows:
The format of here-documents is:
@example
<<[@minus{}]@var{word}
@var{here-document}
@ -1998,45 +2005,71 @@ line containing @var{delimiter}.
This allows here-documents within shell scripts to be indented in a
natural fashion.
@subsection Here Strings
A variant of here documents, the format is:
@example
<<< @var{word}
@end example
The @var{word} is expanded and supplied to the command on its standard
input.
@subsection Duplicating File Descriptors
The redirection operator
@example
[n]<&@var{word}
[@var{n}]<&@var{word}
@end example
@noindent
is used to duplicate input file descriptors.
If @var{word}
expands to one or more digits, the file descriptor denoted by @code{n}
expands to one or more digits, the file descriptor denoted by @var{n}
is made to be a copy of that file descriptor.
If the digits in @var{word} do not specify a file descriptor open for
input, a redirection error occurs.
If @var{word}
evaluates to @samp{-}, file descriptor @code{n} is closed. If
@code{n} is not specified, the standard input (file descriptor 0) is used.
evaluates to @samp{-}, file descriptor @var{n} is closed. If
@var{n} is not specified, the standard input (file descriptor 0) is used.
The operator
@example
[n]>&@var{word}
[@var{n}]>&@var{word}
@end example
@noindent
is used similarly to duplicate output file descriptors. If
@code{n}
is not specified, the standard output (file descriptor 1) is used.
@var{n} is not specified, the standard output (file descriptor 1) is used.
If the digits in @var{word} do not specify a file descriptor open for
output, a redirection error occurs.
As a special case, if @code{n} is omitted, and @var{word} does not
As a special case, if @var{n} is omitted, and @var{word} does not
expand to one or more digits, the standard output and standard
error are redirected as described previously.
@subsection Moving File Descriptors
The redirection operator
@example
[@var{n}]<&@var{digit}-
@end example
@noindent
moves the file descriptor @var{digit} to file descriptor @var{n},
or the standard input (file descriptor 0) if @var{n} is not specified.
@var{digit} is closed after being duplicated to @var{n}.
Similarly, the redirection operator
@example
[@var{n}]>&@var{digit}-
@end example
@noindent
moves the file descriptor @var{digit} to file descriptor @var{n},
or the standard output (file descriptor 1) if @var{n} is not specified.
@subsection Opening File Descriptors for Reading and Writing
The redirection operator
@example
[n]<>@var{word}
[@var{n}]<>@var{word}
@end example
@noindent
causes the file whose name is the expansion of @var{word}
to be opened for both reading and writing on file descriptor
@code{n}, or on file descriptor 0 if @code{n}
@var{n}, or on file descriptor 0 if @var{n}
is not specified. If the file does not exist, it is created.
@node Executing Commands
@ -2501,7 +2534,7 @@ The return status is zero unless @var{n} is not greater than or equal to 1.
@item cd
@btindex cd
@example
cd [-LP] [@var{directory}]
cd [-L|-P] [@var{directory}]
@end example
Change the current working directory to @var{directory}. If @var{directory}
is not given, the value of the @env{HOME} shell variable is used. If the
@ -2637,7 +2670,7 @@ If @code{getopts} is silent, then a colon (@samp{:}) is placed in
@item hash
@btindex hash
@example
hash [-r] [-p @var{filename}] [-t] [@var{name}]
hash [-'r] [-p @var{filename}] [-dt] [@var{name}]
@end example
Remember the full pathnames of commands specified as @var{name} arguments,
so they need not be searched for on subsequent invocations.
@ -2646,11 +2679,16 @@ The commands are found by searching through the directories listed in
The @option{-p} option inhibits the path search, and @var{filename} is
used as the location of @var{name}.
The @option{-r} option causes the shell to forget all remembered locations.
The @option{-d} option causes the shell to forget the remembered location
of each @var{name}.
If the @option{-t} option is supplied, the full pathname to which each
@var{name} corresponds is printed. If multiple @var{name} arguments are
supplied with @option{-t} the @var{name} is printed before the hashed
full pathname.
If no arguments are given, information about remembered commands is printed.
The @option{-l} option causes output to be displayed in a format
that may be reused as input.
If no arguments are given, or if only @option{-l} is supplied,
information about remembered commands is printed.
The return status is zero unless a @var{name} is not found or an invalid
option is supplied.
@ -2905,14 +2943,16 @@ bind [-m @var{keymap}] [-q @var{function}] [-u @var{function}] [-r @var{keyseq}]
bind [-m @var{keymap}] -f @var{filename}
bind [-m @var{keymap}] -x @var{keyseq:shell-command}
bind [-m @var{keymap}] @var{keyseq:function-name}
bind @var{readline-command}
@end example
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
key and function bindings,
bind a key sequence to a Readline function or macro,
or set a Readline variable.
Each non-option argument is a command as it would appear in a
a Readline initialization file (@pxref{Readline Init File}),
but each binding must be passed as a separate argument: e.g.,
but each binding or command must be passed as a separate argument; e.g.,
@samp{"\C-x\C-r":re-read-init-file}.
Options, if supplied, have the following meanings:
@ -3019,7 +3059,7 @@ zero if @var{command} is found, and non-zero if not.
@item declare
@btindex declare
@example
declare [-afFrxi] [-p] [@var{name}[=@var{value}]]
declare [-afFirtx] [-p] [@var{name}[=@var{value}]]
@end example
Declare variables and give them attributes. If no @var{name}s
@ -3049,6 +3089,11 @@ performed when the variable is assigned a value.
Make @var{name}s readonly. These names cannot then be assigned values
by subsequent assignment statements or unset.
@item -t
Give each @var{name} the @code{trace} attribute.
Traced functions inherit the @code{DEBUG} trap from the calling shell.
The trace attribute has no special meaning for variables.
@item -x
Mark each @var{name} for export to subsequent commands via
the environment.
@ -3106,9 +3151,12 @@ horizontal tab
vertical tab
@item \\
backslash
@item \0@var{nnn}
the eight-bit character whose value is the octal value @var{nnn}
(zero to three octal digits)
@item \@var{nnn}
the eight-bit character whose value is the octal value @var{nnn}
(one to three digits)
(one to three octal digits)
@item \x@var{HH}
the eight-bit character whose value is the hexadecimal value @var{HH}
(one or two hex digits)
@ -3218,13 +3266,14 @@ non-zero on failure.
@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{}]
read [-ers] [-a @var{aname}] [-d @var{delim}] [-n @var{nchars}] [-p @var{prompt}] [-t @var{timeout}] [-u @var{fd}] [@var{name} @dots{}]
@end example
One line is read from the standard input, and the first word
One line is read from the standard input, or from the file descriptor
@var{fd} supplied as an argument to the @option{-u} option, and the first word
is assigned to the first @var{name}, the second word to the second @var{name},
and so on, with leftover words and their intervening separators assigned
to the last @var{name}.
If there are fewer words read from the standard input than names,
If there are fewer words read from the input stream than names,
the remaining names are assigned empty values.
The characters in the value of the @env{IFS} variable
are used to split the line into words.
@ -3232,8 +3281,9 @@ The backslash character @samp{\} may be used to remove any special
meaning for the next character read and for line continuation.
If no names are supplied, the line read is assigned to the
variable @env{REPLY}.
The return code is zero, unless end-of-file is encountered or @code{read}
times out.
The return code is zero, unless end-of-file is encountered, @code{read}
times out, or an invalid file descriptor is supplied as the argument to
@option{-u}.
Options, if supplied, have the following meanings:
@table @code
@ -3275,6 +3325,9 @@ 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 -u @var{fd}
Read input from file descriptor @var{fd}.
@end table
@item shopt
@ -3482,7 +3535,7 @@ A synonym for @code{.} (@pxref{Bourne Shell Builtins}).
@item type
@btindex type
@example
type [-atp] [@var{name} @dots{}]
type [-afptP] [@var{name} @dots{}]
@end example
For each @var{name}, indicate how it would be interpreted if used as a
command name.
@ -3499,11 +3552,20 @@ If the @option{-p} option is used, @code{type} either returns the name
of the disk file that would be executed, or nothing if @option{-t}
would not return @samp{file}.
The @option{-P} option forces a path search for each @var{name}, even if
@option{-t} would not return @samp{file}.
If a command is hashed, @option{-p} and @option{-P} print the hashed value,
not necessarily the file that appears first in @code{$PATH}.
If the @option{-a} option is used, @code{type} returns all of the places
that contain an executable named @var{file}.
This includes aliases and functions, if and only if the @option{-p} option
is not also used.
If the @option{-f} option is used, @code{type} does not attempt to find
shell functions, as with the @code{command} builtin.
The return status is zero if any of the @var{names} are found, non-zero
if none are found.
@ -4329,7 +4391,13 @@ If the value is null, no timing information is displayed.
A trailing newline is added when the format string is displayed.
@item TMOUT
If set to a value greater than zero, the value is interpreted as
If set to a value greater than zero, @code{TMOUT} is treated as the
default timeout for the @code{read} builtin (@pxref{Bash Builtins}).
The @code{select} command (@pxref{Conditional Constructs}) terminates
if input does not arrive after @code{TMOUT} seconds when input is coming
from a terminal.
In an interative shell, the value is interpreted as
the number of seconds to wait for input after issuing the primary
prompt when the shell is interactive.
Bash terminates after that number of seconds if input does
@ -4374,8 +4442,7 @@ bash [long-opt] -s [-abefhkmnptuvxdBCDHP] [-o @var{option}] [-O @var{shopt_optio
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.
line before the single-character options to be recognized.
@table @code
@item --dump-po-strings
@ -4396,15 +4463,7 @@ Execute commands from @var{filename} (instead of @file{~/.bashrc})
in an interactive shell.
@item --login
Make this shell act as if it had been directly invoked by login.
When the shell is interactive, this is equivalent to starting a
login shell with @samp{exec -l bash}.
When the shell is not interactive, the login shell startup files will
be executed.
@samp{exec bash --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.
Equivalent to @option{-l}.
@item --noediting
Do not use the @sc{gnu} Readline library (@pxref{Command Line Editing})
@ -4453,6 +4512,17 @@ positional parameters, starting with @code{$0}.
Force the shell to run interactively. Interactive shells are
described in @ref{Interactive Shells}.
@item -l
Make this shell act as if it had been directly invoked by login.
When the shell is interactive, this is equivalent to starting a
login shell with @samp{exec -l bash}.
When the shell is not interactive, the login shell startup files will
be executed.
@samp{exec bash -l} or @samp{exec bash --login}
will replace the current shell with a Bash login shell.
@xref{Bash Startup Files}, for a description of the special behavior
of a login shell.
@item -r
Make the shell a restricted shell (@pxref{The Restricted Shell}).
@ -4860,14 +4930,15 @@ True if @var{file} exists and is a socket.
True if @var{file} exists and has been modified since it was last read.
@item @var{file1} -nt @var{file2}
True if @var{file1} is newer (according to
modification date) than @var{file2}.
True if @var{file1} is newer (according to modification date)
than @var{file2}, or if @var{file1} exists and @var{file2} does not.
@item @var{file1} -ot @var{file2}
True if @var{file1} is older than @var{file2}.
True if @var{file1} is older than @var{file2},
or if @var{file2} exists and @var{file1} does not.
@item @var{file1} -ef @var{file2}
True if @var{file1} and @var{file2} have the same device and
True if @var{file1} and @var{file2} refer to the same device and
inode numbers.
@item -o @var{optname}
@ -4884,7 +4955,7 @@ True if the length of @var{string} is non-zero.
@item @var{string1} == @var{string2}
True if the strings are equal.
@samp{=} may be used in place of @samp{==}.
@samp{=} may be used in place of @samp{==} for strict @sc{posix} compliance.
@item @var{string1} != @var{string2}
True if the strings are not equal.
@ -4919,7 +4990,7 @@ may be positive or negative integers.
The shell allows arithmetic expressions to be evaluated, as one of
the shell expansions or by the @code{let} builtin.
Evaluation is done in long integers with no check for overflow,
Evaluation is done in fixed-width integers with no check for overflow,
though division by 0 is trapped and flagged as an error.
The operators and their precedence and associativity are the same
as in the C language.
@ -5277,6 +5348,10 @@ can appear in the prompt variables:
A bell character.
@item \d
The date, in "Weekday Month Date" format (e.g., "Tue May 26").
@item \D@{@var{format}@}
The @var{format} is passed to @code{strftime}(3) and the result is inserted
into the prompt string; an empty @var{format} results in a locale-specific
time representation. The braces are required.
@item \e
An escape character.
@item \h
@ -5347,11 +5422,14 @@ expansion, and quote removal, subject to the value of the
If Bash is started with the name @code{rbash}, or the
@option{--restricted}
or
@option{-r}
option is supplied at invocation, the shell becomes restricted.
A restricted shell is used to
set up an environment more controlled than the standard shell.
A restricted shell behaves identically to @code{bash}
with the exception that the following are disallowed:
with the exception that the following are disallowed or not performed:
@itemize @bullet
@item
Changing directories with the @code{cd} builtin.
@ -5379,11 +5457,19 @@ Using the @code{exec} builtin to replace the shell with another command.
Adding or deleting builtin commands with the
@option{-f} and @option{-d} options to the @code{enable} builtin.
@item
Using the @code{enable} builtin command to enable disabled shell builtins.
@item
Specifying the @option{-p} option to the @code{command} builtin.
@item
Turning off restricted mode with @samp{set +r} or @samp{set +o restricted}.
@end itemize
These restrictions are enforced after any startup files are read.
When a command that is found to be a shell script is executed
(@pxref{Shell Scripts}), @code{rbash} turns off any restrictions in
the shell spawned to execute the script.
@node Bash POSIX Mode
@section Bash POSIX Mode
@cindex POSIX Mode
@ -5393,6 +5479,9 @@ Starting Bash with the @option{--posix} command-line option or executing
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.
When invoked as @code{sh}, Bash enters @sc{posix} mode after reading the
startup files.
The following list is what's changed when `@sc{posix} mode' is in effect:
@enumerate
@ -5538,6 +5627,12 @@ shell function names and definitions.
When the @code{set} builtin is invoked without options, it displays
variable values without quotes, unless they contain shell metacharacters,
even if the result contains nonprinting characters.
@item
When the @code{cd} builtin is invoked in @var{logical} mode, and the pathname
constructed from @code{$PWD} and the directory name supplied as an argument
does not refer to an existing directory, @code{cd} will fail instead of
falling back to @var{physical} mode.
@end enumerate
There is other @sc{posix} 1003.2 behavior that Bash does not implement.
@ -6129,7 +6224,7 @@ A synonym for @code{--with-bash-malloc}.
@item --with-installed-readline[=@var{PREFIX}]
Define this to make Bash link with a locally-installed version of Readline
rather than the version in @file{lib/readline}. This works only with
Readline 4.2 and later versions. If @var{PREFIX} is @code{yes} or not
Readline 4.3 and later versions. If @var{PREFIX} is @code{yes} or not
supplied, @code{configure} uses the values of the make variables
@code{includedir} and @code{libdir}, which are subdirectories of @code{prefix}
by default, to find the installed version of Readline if it is not in
@ -6158,7 +6253,8 @@ compiled and linked, rather than changing run-time features.
@item --enable-largefile
Enable support for @uref{http://www.sas.com/standards/large_file/x_open.20Mar96.html,
large files} if the operating system requires special compiler options
to build programs which can access large files.
to build programs which can access large files. This is enabled by
default, if the operating system provides large file support.
@item --enable-profiling
This builds a Bash binary that produces profiling information to be
@ -6628,7 +6724,8 @@ 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.
The @code{DEBUG} trap is not inherited by shell functions unless the
function has been given the @code{trace} attribute.
The @code{trap} builtin (@pxref{Bourne Shell Builtins}) allows an
@code{ERR} pseudo-signal specification, similar to @code{EXIT} and @code{DEBUG}.