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BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)
NAME
bash, :, ., alias, bg, bind, break, builtin, bye, case, cd,
command, continue, declare, dirs, echo, enable, eval, exec,
exit, export, fc, fg, for, getopts, hash, help, history, if,
jobs, kill, let, local, logout, popd, pushd, pwd, read,
readonly, return, set, shift, source, suspend, test, times,
trap, type, typeset, ulimit, umask, unalias, unset, until,
wait, while - bash built-in commands, see bash(1)
BASH BUILTIN COMMANDS
: [_a_r_g_u_m_e_n_t_s]
No effect; the command does nothing beyond expanding
_a_r_g_u_m_e_n_t_s and performing any specified redirections. A
zero exit code is returned.
. _f_i_l_e_n_a_m_e [_a_r_g_u_m_e_n_t_s]
source _f_i_l_e_n_a_m_e [_a_r_g_u_m_e_n_t_s]
Read and execute commands from _f_i_l_e_n_a_m_e in the current
shell environment and return the exit status of the
last command executed from _f_i_l_e_n_a_m_e. If _f_i_l_e_n_a_m_e does
not contain a slash, pathnames in PATH are used to find
the directory containing _f_i_l_e_n_a_m_e. The file searched
for in PATH need not be executable. The current direc-
tory is searched if no file is found in PATH. If any
_a_r_g_u_m_e_n_t_s are supplied, they become the positional
parameters when _f_i_l_e is executed. Otherwise the posi-
tional parameters are unchanged. The return status is
the status of the last command exited within the script
(0 if no commands are executed), and false if _f_i_l_e_n_a_m_e
is not found.
alias [_n_a_m_e[=_v_a_l_u_e] ...]
Alias with no arguments prints the list of aliases in
the form _n_a_m_e=_v_a_l_u_e on standard output. When arguments
are supplied, an alias is defined for each _n_a_m_e whose
_v_a_l_u_e is given. A trailing space in _v_a_l_u_e causes the
next word to be checked for alias substitution when the
alias is expanded. For each _n_a_m_e in the argument list
for which no _v_a_l_u_e is supplied, the name and value of
the alias is printed. Alias returns true unless a _n_a_m_e
is given for which no alias has been defined.
bg [_j_o_b_s_p_e_c]
Place _j_o_b_s_p_e_c in the background, as if it had been
started with &. If _j_o_b_s_p_e_c is not present, the shell's
notion of the _c_u_r_r_e_n_t _j_o_b is used. bg _j_o_b_s_p_e_c returns
0 unless run when job control is disabled or, when run
with job control enabled, if _j_o_b_s_p_e_c was not found or
started without job control.
bind [-m _k_e_y_m_a_p] [-lvd] [-q _n_a_m_e]
bind [-m _k_e_y_m_a_p] -f _f_i_l_e_n_a_m_e
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BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)
bind [-m _k_e_y_m_a_p] _k_e_y_s_e_q:_f_u_n_c_t_i_o_n-_n_a_m_e
Display current readline key and function bindings, or
bind a key sequence to a readline function or macro.
The binding syntax accepted is identical to that of
._i_n_p_u_t_r_c, but each binding must be passed as a separate
argument; e.g., '"\C-x\C-r": re-read-init-file'.
Options, if supplied, have the following meanings:
-m _k_e_y_m_a_p
Use _k_e_y_m_a_p as the keymap to be affected by the
subsequent bindings. Acceptable _k_e_y_m_a_p names are
_e_m_a_c_s, _e_m_a_c_s-_s_t_a_n_d_a_r_d, _e_m_a_c_s-_m_e_t_a, _e_m_a_c_s-_c_t_l_x, _v_i,
_v_i-_m_o_v_e, _v_i-_c_o_m_m_a_n_d, and _v_i-_i_n_s_e_r_t. _v_i is
equivalent to _v_i-_c_o_m_m_a_n_d; _e_m_a_c_s is equivalent to
_e_m_a_c_s-_s_t_a_n_d_a_r_d.
-l List the names of all readline functions
-v List current function names and bindings
-d Dump function names and bindings in such a way
that they can be re-read
-f _f_i_l_e_n_a_m_e
Read key bindings from _f_i_l_e_n_a_m_e
-q _f_u_n_c_t_i_o_n
Query about which keys invoke the named _f_u_n_c_t_i_o_n
The return value is 0 unless an unrecognized option is
given or an error occurred.
break [_n]
Exit from within a for, while, or until loop. If _n is
specified, break _n levels. _n must be >_ 1. If _n is
greater than the number of enclosing loops, all enclos-
ing loops are exited. The return value is 0 unless the
shell is not executing a loop when break is executed.
builtin _s_h_e_l_l-_b_u_i_l_t_i_n [_a_r_g_u_m_e_n_t_s]
Execute the specified shell builtin, passing it _a_r_g_u_-
_m_e_n_t_s, and return its exit status. This is useful when
you wish to define a function whose name is the same as
a shell builtin, but need the functionality of the
builtin within the function itself. The cd builtin is
commonly redefined this way. The return status is
false if _s_h_e_l_l-_b_u_i_l_t_i_n is not a shell builtin command.
cd [_d_i_r]
Change the current directory to _d_i_r. The variable HOME
is the default _d_i_r. The variable CDPATH defines the
search path for the directory containing _d_i_r. Alterna-
tive directory names are separated by a colon (:). A
null directory name in CDPATH is the same as the
current directory, i.e., ``.''. If _d_i_r begins with a
slash (/), then CDPATH is not used. An argument of -
is equivalent to $OLDPWD. The return value is true if
the directory was successfully changed; false
GNU Last change: 1993 September 16 2
BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)
otherwise.
command [-pVv] _c_o_m_m_a_n_d [_a_r_g ...]
Run _c_o_m_m_a_n_d with _a_r_g_s suppressing the normal shell
function lookup. Only builtin commands or commands
found in the PATH are executed. If the -p option is
given, the search for _c_o_m_m_a_n_d is performed using a
default value for PATH that is guaranteed to find all
of the standard utilities. If either the -V or -v
option is supplied, a description of _c_o_m_m_a_n_d is
printed. The -v option causes a single word indicating
the command or pathname used to invoke _c_o_m_m_a_n_d to be
printed; the -V option produces a more verbose descrip-
tion. An argument of -- disables option checking for
the rest of the arguments. If the -V or -v option is
supplied, the exit status is 0 if _c_o_m_m_a_n_d was found,
and 1 if not. If neither option is supplied and an
error occurred or _c_o_m_m_a_n_d cannot be found, the exit
status is 127. Otherwise, the exit status of the com-
mand builtin is the exit status of _c_o_m_m_a_n_d.
continue [_n]
Resume the next iteration of the enclosing for, while,
or until loop. If _n is specified, resume at the _nth
enclosing loop. _n must be >_ 1. If _n is greater than
the number of enclosing loops, the last enclosing loop
(the `top-level' loop) is resumed. The return value is
0 unless the shell is not executing a loop when con-
tinue is executed.
declare [-frxi] [_n_a_m_e[=_v_a_l_u_e]]
typeset [-frxi] [_n_a_m_e[=_v_a_l_u_e]]
Declare variables and/or give them attributes. If no
_n_a_m_es are given, then display the values of variables
instead. The options can be used to restrict output to
variables with the specified attribute.
-f Use function names only
-r Make _n_a_m_es readonly. These names cannot then be
assigned values by subsequent assignment state-
ments.
-x Mark _n_a_m_es for export to subsequent commands via
the environment.
-i The variable is treated as an integer; arithmetic
evaluation (see ARITHMETIC EVALUATION ) is per-
formed when the variable is assigned a value.
Using `+' instead of `-' turns off the attribute
instead. When used in a function, makes _n_a_m_es local,
as with the local command. The return value is 0
unless an illegal option is encountered, an attempt is
made to define a function using "-f foo=bar", one of
the _n_a_m_e_s is not a legal shell variable name, an
GNU Last change: 1993 September 16 3
BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)
attempt is made to turn off readonly status for a
readonly variable, or an attempt is made to display a
non-existant function with -f.
dirs [-l] [+/-n]
Display the list of currently remembered directories.
Directories are added to the list with the pushd com-
mand; the popd command moves back up through the list.
+n displays the _nth entry counting from the left of
the list shown by dirs when invoked without
options, starting with zero.
-n displays the _nth entry counting from the right of
the list shown by dirs when invoked without
options, starting with zero.
-l produces a longer listing; the default listing
format uses a tilde to denote the home directory.
The return value is 0 unless an illegal option is sup-
plied or _n indexes beyond the end of the directory
stack.
echo [-neE] [_a_r_g ...]
Output the _a_r_gs, separated by spaces. The return
status is always 0. If -n is specified, the trailing
newline is suppressed. If the -e option is given,
interpretation of the following backslash-escaped char-
acters is enabled. The -E option disables the
interpretation of these escape characters, even on sys-
tems where they are interpreted by default.
\a alert (bell)
\b backspace
\c suppress trailing newline
\f form feed
\n new line
\r carriage return
\t horizontal tab
\v vertical tab
\\ backslash
\nnn the character whose ASCII code is _n_n_n (octal)
enable [-n] [-all] [_n_a_m_e ...]
Enable and disable builtin shell commands. This allows
the execution of a disk command which has the same name
as a shell builtin without specifying a full pathname.
If -n is used, each _n_a_m_e is disabled; otherwise, _n_a_m_e_s
are enabled. For example, to use the test binary found
via the PATH instead of the shell builtin version, type
``enable -n test''. If no arguments are given, a list
of all enabled shell builtins is printed. If only -n
is supplied, a list of all disabled builtins is
printed. If only -all is supplied, the list printed
includes all builtins, with an indication of whether or
GNU Last change: 1993 September 16 4
BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)
not each is enabled. enable accepts -a as a synonym
for -all. The return value is 0 unless a _n_a_m_e is not a
shell builtin.
eval [_a_r_g ...]
The _a_r_gs are read and concatenated together into a sin-
gle command. This command is then read and executed by
the shell, and its exit status is returned as the value
of the eval command. If there are no _a_r_g_s, or only
null arguments, eval returns true.
exec [[-] _c_o_m_m_a_n_d [_a_r_g_u_m_e_n_t_s]]
If _c_o_m_m_a_n_d is specified, it replaces the shell. No new
process is created. The _a_r_g_u_m_e_n_t_s become the arguments
to _c_o_m_m_a_n_d. If the first argument is -, the shell
places a dash in the zeroth arg passed to _c_o_m_m_a_n_d.
This is what login does. If the file cannot be exe-
cuted for some reason, a non-interactive shell exits,
unless the shell variable no_exit_on_failed_exec
exists, in which case it returns failure. An interac-
tive shell returns failure if the file cannot be exe-
cuted. If _c_o_m_m_a_n_d is not specified, any redirections
take effect in the current shell, and the return status
is 0.
exit [_n]
Cause the shell to exit with a status of _n. If _n is
omitted, the exit status is that of the last command
executed. A trap on EXIT is executed before the shell
terminates.
export [-nf] [_n_a_m_e[=_w_o_r_d]] ...
export -p
The supplied _n_a_m_e_s are marked for automatic export to
the environment of subsequently executed commands. If
the -f option is given, the _n_a_m_e_s refer to functions.
If no _n_a_m_e_s are given, or if the -p option is supplied,
a list of all names that are exported in this shell is
printed. The -n option causes the export property to
be removed from the named variables. An argument of --
disables option checking for the rest of the arguments.
export returns an exit status of 0 unless an illegal
option is encountered, one of the _n_a_m_e_s is not a legal
shell variable name, or -f is supplied with a _n_a_m_e that
is not a function.
fc [-e _e_n_a_m_e] [-nlr] [_f_i_r_s_t] [_l_a_s_t]
fc -s [_p_a_t=_r_e_p] [_c_m_d]
Fix Command. In the first form, a range of commands
from _f_i_r_s_t to _l_a_s_t is selected from the history list.
_F_i_r_s_t and _l_a_s_t may be specified as a string (to locate
the last command beginning with that string) or as a
GNU Last change: 1993 September 16 5
BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)
number (an index into the history list, where a nega-
tive number is used as an offset from the current com-
mand number). If _l_a_s_t is not specified it is set to
the current command for listing (so that fc -l -10
prints the last 10 commands) and to _f_i_r_s_t otherwise.
If _f_i_r_s_t is not specified it is set to the previous
command for editing and -16 for listing.
The -n flag suppresses the command numbers when list-
ing. The -r flag reverses the order of the commands.
If the -l flag is given, the commands are listed on
standard output. Otherwise, the editor given by _e_n_a_m_e
is invoked on a file containing those commands. If
_e_n_a_m_e is not given, the value of the FCEDIT variable is
used, and the value of EDITOR if FCEDIT is not set. If
neither variable is set, is used. When editing is com-
plete, the edited commands are echoed and executed.
In the second form, _c_o_m_m_a_n_d is re-executed after each
instance of _p_a_t is replaced by _r_e_p. A useful alias to
use with this is ``r=fc -s'', so that typing ``r cc''
runs the last command beginning with ``cc'' and typing
``r'' re-executes the last command.
If the first form is used, the return value is 0 unless
an illegal option is encountered or _f_i_r_s_t or _l_a_s_t
specify history lines out of range. If the -e option
is supplied, the return value is the value of the last
command executed or failure if an error occurs with the
temporary file of commands. If the second form is
used, the return status is that of the command re-
executed, unless _c_m_d does not specify a valid history
line, in which case fc returns failure.
fg [_j_o_b_s_p_e_c]
Place _j_o_b_s_p_e_c in the foreground, and make it the
current job. If _j_o_b_s_p_e_c is not present, the shell's
notion of the _c_u_r_r_e_n_t _j_o_b is used. The return value is
that of the command placed into the foreground, or
failure if run when job control is disabled or, when
run with job control enabled, if _j_o_b_s_p_e_c does not
specify a valid job or _j_o_b_s_p_e_c specifies a job that was
started without job control.
getopts _o_p_t_s_t_r_i_n_g _n_a_m_e [_a_r_g_s]
getopts is used by shell procedures to parse positional
parameters. _o_p_t_s_t_r_i_n_g contains the option letters to
be recognized; if a letter is followed by a colon, the
option is expected to have an argument, which should be
separated from it by white space. Each time it is
invoked, getopts places the next option in the shell
variable _n_a_m_e, initializing _n_a_m_e if it does not exist,
GNU Last change: 1993 September 16 6
BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)
and the index of the next argument to be processed into
the variable OPTIND. OPTIND is initialized to 1 each
time the shell or a shell script is invoked. When an
option requires an argument, getopts places that argu-
ment into the variable OPTARG. The shell does not
reset OPTIND automatically; it must be manually reset
between multiple calls to getopts within the same shell
invocation if a new set of parameters is to be used.
getopts can report errors in two ways. If the first
character of _o_p_t_s_t_r_i_n_g is a colon, _s_i_l_e_n_t error report-
ing is used. In normal operation diagnostic messages
are printed when illegal options or missing option
arguments are encountered. If the variable OPTERR is
set to 0, no error message will be displayed, even if
the first character of _o_p_t_s_t_r_i_n_g is not a colon.
If an illegal option is seen, getopts places ? into
_n_a_m_e and, if not silent, prints an error message and
unsets OPTARG. If getopts is silent, the option char-
acter found is placed in OPTARG and no diagnostic mes-
sage is printed.
If a required argument is not found, and getopts is not
silent, a question mark (?) is placed in _n_a_m_e, OPTARG
is unset, and a diagnostic message is printed. If
getopts is silent, then a colon (:) is placed in _n_a_m_e
and OPTARG is set to the option character found.
getopts normally parses the positional parameters, but
if more arguments are given in _a_r_g_s, getopts parses
those instead. getopts returns true if an option,
specified or unspecified, is found. It returns false
if the end of options is encountered or an error
occurs.
hash [-r] [_n_a_m_e]
For each _n_a_m_e, the full pathname of the command is
determined and remembered. The -r option causes the
shell to forget all remembered locations. If no argu-
ments are given, information about remembered commands
is printed. An argument of -- disables option checking
for the rest of the arguments. The return status is
true unless a _n_a_m_e is not found or an illegal option is
supplied.
help [_p_a_t_t_e_r_n]
Display helpful information about builtin commands. If
_p_a_t_t_e_r_n is specified, help gives detailed help on all
commands matching _p_a_t_t_e_r_n; otherwise a list of the
builtins is printed. The return status is 0 unless no
command matches _p_a_t_t_e_r_n.
GNU Last change: 1993 September 16 7
BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)
history [_n]
history -rwan [_f_i_l_e_n_a_m_e]
With no options, display the command history list with
line numbers. Lines listed with a * have been modi-
fied. An argument of _n lists only the last _n lines.
If a non-option argument is supplied, it is used as the
name of the history file; if not, the value of HISTFILE
is used. Options, if supplied, have the following
meanings:
-a Append the ``new'' history lines (history lines
entered since the beginning of the current bash
session) to the history file
-n Read the history lines not already read from the
history file into the current history list. These
are lines appended to the history file since the
beginning of the current bash session.
-r Read the contents of the history file and use them
as the current history
-w Write the current history to the history file,
overwriting the history file's contents.
The return value is 0 unless an illegal option is
encountered or an error occurs while reading or writing
the history file.
jobs [-lnp] [ _j_o_b_s_p_e_c ... ]
jobs -x _c_o_m_m_a_n_d [ _a_r_g_s ... ]
The first form lists the active jobs. The -l option
lists process IDs in addition to the normal informa-
tion; the -p option lists only the process ID of the
job's process group leader. The -n option displays
only jobs that have changed status since last notified.
If _j_o_b_s_p_e_c is given, output is restricted to informa-
tion about that job. The return status is 0 unless an
illegal option is encountered or an illegal _j_o_b_s_p_e_c is
supplied.
If the -x option is supplied, jobs replaces any _j_o_b_s_p_e_c
found in _c_o_m_m_a_n_d or _a_r_g_s with the corresponding process
group ID, and executes _c_o_m_m_a_n_d passing it _a_r_g_s, return-
ing its exit status.
kill [-s sigspec | -sigspec] [_p_i_d | _j_o_b_s_p_e_c] ...
kill -l [_s_i_g_n_u_m]
Send the signal named by _s_i_g_s_p_e_c to the processes named
by _p_i_d or _j_o_b_s_p_e_c. _s_i_g_s_p_e_c is either a signal name
such as SIGKILL or a signal number. If _s_i_g_s_p_e_c is a
signal name, the name is case insensitive and may be
given with or without the SIG prefix. If _s_i_g_s_p_e_c is
not present, then SIGTERM is assumed. An argument of
-l lists the signal names. If any arguments are sup-
plied when -l is given, the names of the specified
GNU Last change: 1993 September 16 8
BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)
signals are listed, and the return status is 0. An
argument of -- disables option checking for the rest of
the arguments. kill returns true if at least one sig-
nal was successfully sent, or false if an error occurs
or an illegal option is encountered.
let _a_r_g [_a_r_g ...]
Each _a_r_g is an arithmetic expression to be evaluated
(see ARITHMETIC EVALUATION). If the last _a_r_g evaluates
to 0, let returns 1; 0 is returned otherwise.
local [_n_a_m_e[=_v_a_l_u_e] ...]
For each argument, create a local variable named _n_a_m_e,
and assign it _v_a_l_u_e. When local is used within a func-
tion, it causes the variable _n_a_m_e to have a visible
scope restricted to that function and its children.
With no operands, local writes a list of local vari-
ables to the standard output. It is an error to use
local when not within a function. The return status is
0 unless local is used outside a function, or an ille-
gal _n_a_m_e is supplied.
logout
Exit a login shell.
popd [+/-n]
Removes entries from the directory stack. With no
arguments, removes the top directory from the stack,
and performs a cd to the new top directory.
+n removes the _nth entry counting from the left of
the list shown by dirs, starting with zero. For
example: ``popd +0'' removes the first directory,
``popd +1'' the second.
-n removes the _nth entry counting from the right of
the list shown by dirs, starting with zero. For
example: ``popd -0'' removes the last directory,
``popd -1'' the next to last.
If the popd command is successful, a dirs is performed
as well, and the return status is 0. popd returns
false if an illegal option is encountered, the direc-
tory stack is empty, a non-existent directory stack
entry is specified, or the directory change fails.
pushd [_d_i_r]
pushd +/-n
Adds a directory to the top of the directory stack, or
rotates the stack, making the new top of the stack the
current working directory. With no arguments,
exchanges the top two directories and returns 0, unless
the directory stack is empty.
+n Rotates the stack so that the _nth directory
GNU Last change: 1993 September 16 9
BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)
(counting from the left of the list shown by dirs)
is at the top.
-n Rotates the stack so that the _nth directory
(counting from the right) is at the top.
dir adds _d_i_r to the directory stack at the top, making
it the new current working directory.
If the pushd command is successful, a dirs is performed
as well. If the first form is used, pushd returns 0
unless the cd to _d_i_r fails. With the second form,
pushd returns 0 unless the directory stack is empty, a
non-existant directory stack element is specified, or
the directory change to the specified new current
directory fails.
pwd Print the absolute pathname of the current working
directory. The path printed contains no symbolic links
if the -P option to the set builtin command is set.
See also the description of nolinks under Shell Vari-
ables above). The return status is 0 unless an error
occurs while reading the pathname of the current direc-
tory.
read [-r] [_n_a_m_e ...]
One line is read from the standard input, and the first
word is assigned to the first _n_a_m_e, the second word to
the second _n_a_m_e, and so on, with leftover words
assigned to the last _n_a_m_e. Only the characters in IFS
are recognized as word delimiters. If no _n_a_m_e_s are
supplied, the line read is assigned to the variable
REPLY. The return code is zero, unless end-of-file is
encountered. If the -r option is given, a backslash-
newline pair is not ignored, and the backslash is con-
sidered to be part of the line.
readonly [-f] [_n_a_m_e ...]
readonly -p
The given _n_a_m_e_s are marked readonly and the values of
these _n_a_m_e_s may not be changed by subsequent assign-
ment. If the -f option is supplied, the functions
corresponding to the _n_a_m_e_s are so marked. If no argu-
ments are given, or if the -p option is supplied, a
list of all readonly names is printed. An argument of
-- disables option checking for the rest of the argu-
ments. The return status is 0 unless an illegal option
is encountered, one of the _n_a_m_e_s is not a legal shell
variable name, or -f is supplied with a _n_a_m_e that is
not a function.
return [_n]
Causes a function to exit with the return value speci-
fied by _n. If _n is omitted, the return status is that
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BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)
of the last command executed in the function body. If
used outside a function, but during execution of a
script by the . (source) command, it causes the shell
to stop executing that script and return either _n or
the exit status of the last command executed within the
script as the exit status of the script. If used out-
side a function and not during execution of a script by
., the return status is false.
set [--abefhkmnptuvxldCHP] [-o _o_p_t_i_o_n] [_a_r_g ...]
-a Automatically mark variables which are modified
or created for export to the environment of
subsequent commands.
-b Cause the status of terminated background jobs
to be reported immediately, rather than before
the next primary prompt. (Also see notify
under Shell Variables above).
-e Exit immediately if a _s_i_m_p_l_e-_c_o_m_m_a_n_d (see SHELL
GRAMMAR above) exits with a non-zero status.
The shell does not exit if the command that
fails is part of an _u_n_t_i_l or _w_h_i_l_e loop, part
of an _i_f statement, part of a && or || list, or
if the command's return value is being inverted
via !.
-f Disable pathname expansion.
-h Locate and remember function commands as func-
tions are defined. Function commands are nor-
mally looked up when the function is executed.
-k All keyword arguments are placed in the
environment for a command, not just those that
precede the command name.
-m Monitor mode. Job control is enabled. This
flag is on by default for interactive shells on
systems that support it (see JOB CONTROL
above). Background processes run in a separate
process group and a line containing their exit
status is printed upon their completion.
-n Read commands but do not execute them. This
may be used to check a shell script for syntax
errors. This is ignored for interactive
shells.
-o _o_p_t_i_o_n-_n_a_m_e
The _o_p_t_i_o_n-_n_a_m_e can be one of the following:
allexport
Same as -a.
braceexpand
The shell performs brace expansion (see
Brace Expansion above). This is on by
default.
emacs Use an emacs-style command line editing
interface. This is enabled by default
when the shell is interactive, unless
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BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)
the shell is started with the -nol-
ineediting option.
errexit Same as -e.
histexpand
Same as -H.
ignoreeof
The effect is as if the shell command
`IGNOREEOF=10' had been executed (see
Shell Variables above).
interactive-comments
Allow a word beginning with # to cause
that word and all remaining characters
on that line to be ignored in an
interactive shell (see COMMENTS above).
monitor Same as -m.
noclobber
Same as -C.
noexec Same as -n.
noglob Same as -f.
nohash Same as -d.
notify Same as -b.
nounset Same as -u.
physical
Same as -P.
posix Change the behavior of bash where the
default operation differs from the
Posix 1003.2 standard to match the
standard.
privileged
Same as -p.
verbose Same as -v.
vi Use a vi-style command line editing
interface.
xtrace Same as -x.
If no _o_p_t_i_o_n-_n_a_m_e is supplied, the values of
the current options are printed.
-p Turn on _p_r_i_v_i_l_e_g_e_d mode. In this mode, the
$ENV file is not processed, and shell functions
are not inherited from the environment. This
is enabled automatically on startup if the
effective user (group) id is not equal to the
real user (group) id. Turning this option off
causes the effective user and group ids to be
set to the real user and group ids.
-t Exit after reading and executing one command.
-u Treat unset variables as an error when perform-
ing parameter expansion. If expansion is
attempted on an unset variable, the shell
prints an error message, and, if not interac-
tive, exits with a non-zero status.
-v Print shell input lines as they are read.
-x After expanding each _s_i_m_p_l_e-_c_o_m_m_a_n_d, bash
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BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)
displays the expanded value of PS4, followed by
the command and its expanded arguments.
-l Save and restore the binding of _n_a_m_e in a for
_n_a_m_e [in word] command (see SHELL GRAMMAR
above).
-d Disable the hashing of commands that are looked
up for execution. Normally, commands are
remembered in a hash table, and once found, do
not have to be looked up again.
-C The effect is as if the shell command
`noclobber=' had been executed (see Shell Vari-
ables above).
-H Enable ! style history substitution. This flag
is on by default when the shell is interactive.
-P If set, do not follow symbolic links when per-
forming commands such as cd which change the
current directory. The physical directory is
used instead.
-- If no arguments follow this flag, then the
positional parameters are unset. Otherwise,
the positional parameters are set to the _a_r_gs,
even if some of them begin with a -.
- Signal the end of options, cause all remaining
_a_r_gs to be assigned to the positional parame-
ters. The -x and -v options are turned off.
If there are no _a_r_gs, the positional parameters
remain unchanged.
The flags are off by default unless otherwise noted.
Using + rather than - causes these flags to be turned
off. The flags can also be specified as options to an
invocation of the shell. The current set of flags may
be found in $-. After the option arguments are pro-
cessed, the remaining _n _a_r_gs are treated as values for
the positional parameters and are assigned, in order,
to $1, $2, ... $_n. If no options or _a_r_gs are supplied,
all shell variables are printed. The return status is
always true unless an illegal option is encountered.
shift [_n]
The positional parameters from _n+1 ... are renamed to
$1 .... Parameters represented by the numbers $# down
to $#-_n+1 are unset. If _n is 0, no parameters are
changed. If _n is not given, it is assumed to be 1. _n
must be a non-negative number less than or equal to $#.
If _n is greater than $#, the positional parameters are
not changed. The return status is greater than 0 if _n
is greater than $# or less than 0; otherwise 0.
suspend [-f]
Suspend the execution of this shell until it receives a
SIGCONT signal. The -f option says not to complain if
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BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)
this is a login shell; just suspend anyway. The return
status is 0 unless the shell is a login shell and -f is
not supplied, or if job control is not enabled.
test _e_x_p_r
[ _e_x_p_r ]
Return a status of 0 (true) or 1 (false) depending on
the evaluation of the conditional expression _e_x_p_r.
Expressions may be unary or binary. Unary expressions
are often used to examine the status of a file. There
are string operators and numeric comparison operators
as well. Each operator and operand must be a separate
argument. If _f_i_l_e is of the form /dev/fd/_n, then file
descriptor _n is checked.
-b _f_i_l_e
True if _f_i_l_e exists and is block special.
-c _f_i_l_e
True if _f_i_l_e exists and is character special.
-d _f_i_l_e
True if _f_i_l_e exists and is a directory.
-e _f_i_l_e
True if _f_i_l_e exists.
-f _f_i_l_e
True if _f_i_l_e exists and is a regular file.
-g _f_i_l_e
True if _f_i_l_e exists and is set-group-id.
-k _f_i_l_e
True if _f_i_l_e has its ``sticky'' bit set.
-L _f_i_l_e
True if _f_i_l_e exists and is a symbolic link.
-p _f_i_l_e
True if _f_i_l_e exists and is a named pipe.
-r _f_i_l_e
True if _f_i_l_e exists and is readable.
-s _f_i_l_e
True if _f_i_l_e exists and has a size greater than
zero.
-S _f_i_l_e
True if _f_i_l_e exists and is a socket.
-t _f_d
True if _f_d is opened on a terminal.
-u _f_i_l_e
True if _f_i_l_e exists and its set-user-id bit is
set.
-w _f_i_l_e
True if _f_i_l_e exists and is writable.
-x _f_i_l_e
True if _f_i_l_e exists and is executable.
-O _f_i_l_e
True if _f_i_l_e exists and is owned by the effective
user id.
-G _f_i_l_e
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BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)
True if _f_i_l_e exists and is owned by the effective
group id.
_f_i_l_e_1 -nt _f_i_l_e_2
True if _f_i_l_e_1 is newer (according to modification
date) than _f_i_l_e_2.
_f_i_l_e_1 -ot _f_i_l_e_2
True if _f_i_l_e_1 is older than file2.
_f_i_l_e_1 -ef _f_i_l_e
True if _f_i_l_e_1 and _f_i_l_e_2 have the same device and
inode numbers.
-z _s_t_r_i_n_g
True if the length of _s_t_r_i_n_g is zero.
-n _s_t_r_i_n_g
_s_t_r_i_n_g
True if the length of _s_t_r_i_n_g is non-zero.
_s_t_r_i_n_g_1 = _s_t_r_i_n_g_2
True if the strings are equal.
_s_t_r_i_n_g_1 != _s_t_r_i_n_g_2
True if the strings are not equal.
! _e_x_p_r
True if _e_x_p_r is false.
_e_x_p_r_1 -a _e_x_p_r_2
True if both _e_x_p_r_1 AND _e_x_p_r_2 are true.
_e_x_p_r_1 -o _e_x_p_r_2
True if either _e_x_p_r_1 OR _e_x_p_r_2 is true.
_a_r_g_1 OP _a_r_g_2
OP is one of -eq, -ne, -lt, -le, -gt, or -ge.
These arithmetic binary operators return true if
_a_r_g_1 is equal, not-equal, less-than, less-than-
or-equal, greater-than, or greater-than-or-equal
than _a_r_g_2, respectively. _A_r_g_1 and _a_r_g_2 may be
positive integers, negative integers, or the spe-
cial expression -l _s_t_r_i_n_g, which evaluates to the
length of _s_t_r_i_n_g.
times
Print the accumulated user and system times for the
shell and for processes run from the shell. The return
status is 0.
trap [-l] [_a_r_g] [_s_i_g_s_p_e_c]
The command _a_r_g is to be read and executed when the
shell receives signal(s) _s_i_g_s_p_e_c. If _a_r_g is absent or
-, all specified signals are reset to their original
values (the values they had upon entrance to the
shell). If _a_r_g is the null string this signal is
ignored by the shell and by the commands it invokes.
_s_i_g_s_p_e_c is either a signal name defined in <_s_i_g_n_a_l._h>,
or a signal number. If _s_i_g_s_p_e_c is EXIT (0) the command
_a_r_g is executed on exit from the shell. With no argu-
ments, trap prints the list of commands associated with
each signal number. The -l option causes the shell to
GNU Last change: 1993 September 16 15
BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)
print a list of signal names and their corresponding
numbers. An argument of -- disables option checking
for the rest of the arguments. Signals ignored upon
entry to the shell cannot be trapped or reset. Trapped
signals are reset to their original values in a child
process when it is created. The return status is false
if either the trap name or number is invalid; otherwise
trap returns true.
type [-all] [-type | -path] _n_a_m_e [_n_a_m_e ...]
With no options, indicate how each _n_a_m_e would be inter-
preted if used as a command name. If the -type flag is
used, type prints a phrase which is one of _a_l_i_a_s, _k_e_y_-
_w_o_r_d, _f_u_n_c_t_i_o_n, _b_u_i_l_t_i_n, or _f_i_l_e if _n_a_m_e is an alias,
shell reserved word, function, builtin, or disk file,
respectively. If the name is not found, then nothing is
printed, and an exit status of false is returned. If
the -path flag is used, type either returns the name of
the disk file that would be executed if _n_a_m_e were
specified as a command name, or nothing if -type would
not return _f_i_l_e. If a command is hashed, -path prints
the hashed value, not necessarily the file that appears
first in PATH. If the -all flag is used, type prints
all of the places that contain an executable named
_n_a_m_e. This includes aliases and functions, if and only
if the -path flag is not also used. The table of
hashed commands is not consulted when using -all. type
accepts -a, -t, and -p in place of -all, -type, and
-path, respectively. An argument of -- disables option
checking for the rest of the arguments. type returns
true if any of the arguments are found, false if none
are found.
ulimit [-SHacdfmstpnuv [_l_i_m_i_t]]
Ulimit provides control over the resources available to
the shell and to processes started by it, on systems
that allow such control. The value of _l_i_m_i_t can be a
number in the unit specified for the resource, or the
value unlimited. The H and S options specify that the
hard or soft limit is set for the given resource. A
hard limit cannot be increased once it is set; a soft
limit may be increased up to the value of the hard
limit. If neither H nor S is specified, the command
applies to the soft limit. If _l_i_m_i_t is omitted, the
current value of the soft limit of the resource is
printed, unless the H option is given. When more than
one resource is specified, the limit name and unit is
printed before the value. Other options are inter-
preted as follows:
-a all current limits are reported
-c the maximum size of core files created
-d the maximum size of a process's data segment
GNU Last change: 1993 September 16 16
BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)
-f the maximum size of files created by the shell
-m the maximum resident set size
-s the maximum stack size
-t the maximum amount of cpu time in seconds
-p the pipe size in 512-byte blocks (this may not be
set)
-n the maximum number of open file descriptors (most
systems do not allow this value to be set, only
displayed)
-u the maximum number of processes available to a
single user
-v The maximum amount of virtual memory available to
the shell
An argument of -- disables option checking for the rest
of the arguments. If _l_i_m_i_t is given, it is the new
value of the specified resource (the -a option is
display only). If no option is given, then -f is
assumed. Values are in 1024-byte increments, except
for -t, which is in seconds, -p, which is in units of
512-byte blocks, and -n and -u, which are unscaled
values. The return status is 0 unless an illegal
option is encountered, a non-numeric argument other
than unlimited is supplied as _l_i_m_i_t, or an error occurs
while setting a new limit.
umask [-S] [_m_o_d_e]
The user file-creation mask is set to _m_o_d_e. If _m_o_d_e
begins with a digit, it is interpreted as an octal
number; otherwise it is interpreted as a symbolic mode
mask similar to that accepted by _c_h_m_o_d(1). If _m_o_d_e is
omitted, or if the -S option is supplied, the current
value of the mask is printed. The -S option causes the
mask to be printed in symbolic form; the default output
is an octal number. An argument of -- disables option
checking for the rest of the arguments. The return
status is 0 if the mode was successfully changed or if
no _m_o_d_e argument was supplied, and false otherwise.
unalias [-a] [_n_a_m_e ...]
Remove _n_a_m_es from the list of defined aliases. If -a
is supplied, all alias definitions are removed. The
return value is true unless a supplied _n_a_m_e is not a
defined alias.
unset [-fv] [_n_a_m_e ...]
For each _n_a_m_e, remove the corresponding variable or,
given the -f option, function. An argument of -- dis-
ables option checking for the rest of the arguments.
Note that PATH, IFS, PPID, PS1, PS2, UID, and EUID can-
not be unset. If any of RANDOM, SECONDS, LINENO, or
HISTCMD are unset, they lose their special properties,
GNU Last change: 1993 September 16 17
BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)
even if they are subsequently reset. The exit status
is true unless a _n_a_m_e does not exist or is non-
unsettable.
wait [_n]
Wait for the specified process and return its termina-
tion status. _n may be a process ID or a job specifica-
tion; if a job spec is given, all processes in that
job's pipeline are waited for. If _n is not given, all
currently active child processes are waited for, and
the return status is zero. If _n specifies a non-
existant process or job, the return status is 127.
Otherwise, the return status is the exit status of the
last process or job waited for.
SEE ALSO
bash(1), sh(1)
GNU Last change: 1993 September 16 18
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