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
: [arguments]
No effect; the command does nothing beyond expanding
arguments and performing any specified redirections. A
zero exit code is returned.

. filename [arguments]
source filename [arguments]
Read and execute commands from filename in the current
shell environment and return the exit status of the
last command executed from filename. If filename does
not contain a slash, pathnames in PATH are used to find
the directory containing filename. 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
arguments are supplied, they become the positional
parameters when file 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 filename
is not found.

alias [name[=value] ...]
Alias with no arguments prints the list of aliases in
the form name=value on standard output. When arguments
are supplied, an alias is defined for each name whose
value is given. A trailing space in value causes the
next word to be checked for alias substitution when the
alias is expanded. For each name in the argument list
for which no value is supplied, the name and value of
the alias is printed. Alias returns true unless a name
is given for which no alias has been defined.

bg [jobspec]
Place jobspec in the background, as if it had been
started with &. If jobspec is not present, the shell’s
notion of the current job is used. bg jobspec returns
0 unless run when job control is disabled or, when run
with job control enabled, if jobspec was not found or
started without job control.

bind [-m keymap] [-lvd] [-q name]
bind [-m keymap] -f filename

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bind [-m keymap] keyseq:function-name
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
.inputrc, but each binding must be passed as a separate
argument; e.g., ’" re-read-init-file’.
Options, if supplied, have the following meanings:
-m keymap
Use keymap as the keymap to be affected by the
subsequent bindings. Acceptable keymap names are
emacs, emacs-standard, emacs-meta, emacs-ctlx, vi,
vi-move, vi-command, and vi-insert. vi is
equivalent to vi-command; emacs is equivalent to
emacs-standard.
-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 filename
Read key bindings from filename
-q function
Query about which keys invoke the named function

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 shell-builtin [arguments]
Execute the specified shell builtin, passing it argu-
ments, 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 shell-builtin is not a shell builtin command.

cd [dir]
Change the current directory to dir. The variable HOME
is the default dir. The variable CDPATH defines the
search path for the directory containing dir. 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 dir 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

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otherwise.

command [-pVv] command [arg ...]
Run command with args 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 command 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 command is
printed. The -v option causes a single word indicating
the command or pathname used to invoke command 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 command was found,
and 1 if not. If neither option is supplied and an
error occurred or command cannot be found, the exit
status is 127. Otherwise, the exit status of the com-
mand builtin is the exit status of command.

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] [name[=value]]
typeset [-frxi] [name[=value]]
Declare variables and/or give them attributes. If no
names 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 names readonly. These names cannot then be
assigned values by subsequent assignment state-
ments.
-x Mark names 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 names 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 names is not a legal shell variable name, an

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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] [arg ...]
Output the args, 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.
alert (bell)
backspace
form feed
new line
carriage return
horizontal tab
vertical tab
\ backslash
0n the character whose ASCII code is nnn (octal)

enable [-n] [-all] [name ...]
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 name is disabled; otherwise, names
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

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not each is enabled. enable accepts -a as a synonym
for -all. The return value is 0 unless a name is not a
shell builtin.

eval [arg ...]
The args 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 args, or only
null arguments, eval returns true.

exec [[-] command [arguments]]
If command is specified, it replaces the shell. No new
process is created. The arguments become the arguments
to command. If the first argument is -, the shell
places a dash in the zeroth arg passed to command.
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 command 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] [name[=word]] ...
export -p
The supplied names are marked for automatic export to
the environment of subsequently executed commands. If
the -f option is given, the names refer to functions.
If no names 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 names is not a legal
shell variable name, or -f is supplied with a name that
is not a function.

fc [-e ename] [-nlr] [first] [last]
fc -s [pat=rep] [cmd]
Fix Command. In the first form, a range of commands
from first to last is selected from the history list.
First and last may be specified as a string (to locate
the last command beginning with that string) or as a

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number (an index into the history list, where a nega-
tive number is used as an offset from the current com-
mand number). If last is not specified it is set to
the current command for listing (so that fc -l -10
prints the last 10 commands) and to first otherwise.
If first 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 ename
is invoked on a file containing those commands. If
ename 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, command is re-executed after each
instance of pat is replaced by rep. 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 first or last
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 cmd does not specify a valid history
line, in which case fc returns failure.

fg [jobspec]
Place jobspec in the foreground, and make it the
current job. If jobspec is not present, the shell’s
notion of the current job 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 jobspec does not
specify a valid job or jobspec specifies a job that was
started without job control.

getopts optstring name [args]
getopts is used by shell procedures to parse positional
parameters. optstring 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 name, initializing name if it does not exist,

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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 optstring is a colon, silent 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 optstring is not a colon.

If an illegal option is seen, getopts places ? into
name 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 name, OPTARG
is unset, and a diagnostic message is printed. If
getopts is silent, then a colon (:) is placed in name
and OPTARG is set to the option character found.

getopts normally parses the positional parameters, but
if more arguments are given in args, 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] [name]
For each name, 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 name is not found or an illegal option is
supplied.

help [pattern]
Display helpful information about builtin commands. If
pattern is specified, help gives detailed help on all
commands matching pattern; otherwise a list of the
builtins is printed. The return status is 0 unless no
command matches pattern.

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history [n]
history -rwan [filename]
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] [ jobspec ... ]
jobs -x command [ args ... ]
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 jobspec 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 jobspec is
supplied.

If the -x option is supplied, jobs replaces any jobspec
found in command or args with the corresponding process
group ID, and executes command passing it args, return-
ing its exit status.

kill [-s sigspec | -sigspec] [pid | jobspec] ...
kill -l [signum]
Send the signal named by sigspec to the processes named
by pid or jobspec. sigspec is either a signal name
such as SIGKILL or a signal number. If sigspec is a
signal name, the name is case insensitive and may be
given with or without the SIG prefix. If sigspec 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

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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 arg [arg ...]
Each arg is an arithmetic expression to be evaluated
(see ARITHMETIC EVALUATION). If the last arg evaluates
to 0, let returns 1; 0 is returned otherwise.

local [name[=value] ...]
For each argument, create a local variable named name,
and assign it value. When local is used within a func-
tion, it causes the variable name 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 name 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 [dir]
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

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(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 dir 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 dir 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] [name ...]
One line is read from the standard input, and the first
word is assigned to the first name, the second word to
the second name, and so on, with leftover words
assigned to the last name. Only the characters in IFS
are recognized as word delimiters. If no names 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] [name ...]
readonly -p
The given names are marked readonly and the values of
these names may not be changed by subsequent assign-
ment. If the -f option is supplied, the functions
corresponding to the names 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 names is not a legal shell
variable name, or -f is supplied with a name 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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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 option] [arg ...]
-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 simple-command (see SHELL
GRAMMAR above) exits with a non-zero status.
The shell does not exit if the command that
fails is part of an until or while loop, part
of an if 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 option-name
The option-name 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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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 option-name is supplied, the values of
the current options are printed.
-p Turn on privileged 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 simple-command, bash

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displays the expanded value of PS4, followed by
the command and its expanded arguments.
-l Save and restore the binding of name in a for
name [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 args,
even if some of them begin with a -.
- Signal the end of options, cause all remaining
args to be assigned to the positional parame-
ters. The -x and -v options are turned off.
If there are no args, 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 args are treated as values for
the positional parameters and are assigned, in order,
to $1, $2, ... $n. If no options or args 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 .... If n is not given, it is assumed to be 1. The
exit status is 1 if n is greater than $#; otherwise 0.

suspend [-f]
Suspend the execution of this shell until it receives a
SIGCONT signal. The -f option says not to complain if
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 expr

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[ expr ]
Return a status of 0 (true) or 1 (false) depending on
the evaluation of the conditional expression expr.
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 file is of the form /dev/fd/n, then file
descriptor n is checked.
-b file
True if file exists and is block special.
-c file
True if file exists and is character special.
-d file
True if file exists and is a directory.
-e file
True if file exists.
-f file
True if file exists and is a regular file.
-g file
True if file exists and is set-group-id.
-k file
True if file has its ‘‘sticky’’ bit set.
-L file
True if file exists and is a symbolic link.
-p file
True if file exists and is a named pipe.
-r file
True if file exists and is readable.
-s file
True if file exists and has a size greater than
zero.
-S file
True if file exists and is a socket.
-t fd
True if fd is opened on a terminal.
-u file
True if file exists and its set-user-id bit is
set.
-w file
True if file exists and is writable.
-x file
True if file exists and is executable.
-O file
True if file exists and is owned by the effective
user id.
-G file
True if file exists and is owned by the effective
group id.
file1 -nt file2
True if file1 is newer (according to modification
date) than file2.

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BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)

file1 -ot file2
True if file1 is older than file2.
file1 -ef file
True if file1 and file2 have the same device and
inode numbers.
-z string
True if the length of string is zero.
-n string
string
True if the length of string is non-zero.
string1 = string2
True if the strings are equal.
string1 != string2
True if the strings are not equal.
! expr
True if expr is false.
expr1 -a expr2
True if both expr1 AND expr2 are true.
expr1 -o expr2
True if either expr1 OR expr2 is true.
arg1 OP arg2
OP is one of -eq, -ne, -lt, -le, -gt, or -ge.
These arithmetic binary operators return true if
arg1 is equal, not-equal, less-than, less-than-
or-equal, greater-than, or greater-than-or-equal
than arg2, respectively. Arg1 and arg2 may be
positive integers, negative integers, or the spe-
cial expression -l string, which evaluates to the
length of string.

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] [arg] [sigspec]
The command arg is to be read and executed when the
shell receives signal(s) sigspec. If arg is absent or
-, all specified signals are reset to their original
values (the values they had upon entrance to the
shell). If arg is the null string this signal is
ignored by the shell and by the commands it invokes.
sigspec is either a signal name defined in <signal.h>,
or a signal number. If sigspec is EXIT (0) the command
arg 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
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

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BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)

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] name [name ...]
With no options, indicate how each name would be inter-
preted if used as a command name. If the -type flag is
used, type prints a phrase which is one of alias, key-
word, function, builtin, or file if name 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 name were
specified as a command name, or nothing if -type would
not return file. 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
name. 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 [limit]]
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 limit 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 limit 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
-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

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BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)

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 limit 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 limit, or an error occurs
while setting a new limit.

umask [-S] [mode]
The user file-creation mask is set to mode. If mode
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 chmod(1). If mode 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 mode argument was supplied, and false otherwise.

unalias [-a] [name ...]
Remove names from the list of defined aliases. If -a
is supplied, all alias definitions are removed. The
return value is true unless a supplied name is not a
defined alias.

unset [-fv] [name ...]
For each name, 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,
even if they are subsequently reset. The exit status
is true unless a name does not exist or is non-
unsettable.

wait [n]

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BASH_BUILTINS(1) USER COMMANDS BASH_BUILTINS(1)

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.