unset
BASH_BUILTINS(1) BASH_BUILTINS(1)
NAME
bash, :, ., alias, bg, bind, break, builtin, case, cd,
command, continue, declare, dirs, disown, 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, shopt,
source, suspend, test, times, trap, type, typeset, ulimit,
umask, unalias, unset, until, wait, while - bash built-in
commands, see bash(1)
BASH BUILTIN COMMANDS
Unless otherwise noted, each builtin command documented in
this section as accepting options preceded by - accepts --
to signify the end of the options.
: [arguments]
No effect; the command does nothing beyond expand
ing arguments and performing any specified redirec
tions. A zero exit code is returned.
. filename [arguments]
source filename [arguments]
Read and execute commands from filename in the cur
rent shell environment and return the exit status
of the last command executed from filename. If
filename does not contain a slash, file names in
PATH are used to find the directory containing
filename. The file searched for in PATH need not
be executable. The current directory is searched
if no file is found in PATH. If the sourcepath
option to the shopt builtin command is turned off,
the PATH is not searched. If any arguments are
supplied, they become the positional parameters
when filename 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 or cannot be read.
alias [-p] [name[=value] ...]
Alias with no arguments or with the -p option
prints the list of aliases in the form alias
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]
Resume the suspended job jobspec in the background,
as if it had been started with &. If jobspec is
GNU 1996 Mar 20 1
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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 with
out job control.
bind [-m keymap] [-lpsvPSV]
bind [-m keymap] [-q function] [-u function] [-r keyseq]
bind [-m keymap] -f filename
bind [-m keymap] -x keyseq:shell-command
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., '"\C-x\C-r":
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-command, and vi-insert.
vi is equivalent to vi-command; emacs is
equivalent to emacs-standard.
-l List the names of all readline functions.
-p Display readline function names and bindings
in such a way that they can be re-read.
-P List current readline function names and
bindings.
-v Display readline variable names and values
in such a way that they can be re-read.
-V List current readline variable names and
values.
-s Display readline key sequences bound to
macros and the strings they output in such a
way that they can be re-read.
-S Display readline key sequences bound to
macros and the strings they output.
-f filename
Read key bindings from filename.
-q function
Query about which keys invoke the named
function.
-u function
Unbind all keys bound to the named function.
-r keyseq
Remove any current binding for keyseq.
-x keyseq:shell-command
Cause shell-command to be executed whenever
keyseq is entered.
The return value is 0 unless an unrecognized option
is given or an error occurred.
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break [n]
Exit from within a for, while, until, or select
loop. If n is specified, break n levels. n must
be >= 1. If n is greater than the number of
enclosing loops, all enclosing loops are exited.
The return value is 0 unless the shell is not exe
cuting a loop when break is executed.
builtin shell-builtin [arguments]
Execute the specified shell builtin, passing it
arguments, and return its exit status. This is
useful when defining a function whose name is the
same as a shell builtin, retaining the functional
ity of the builtin within the function. The cd
builtin is commonly redefined this way. The return
status is false if shell-builtin is not a shell
builtin command.
cd [-LP] [dir]
Change the current directory to dir. The variable
HOME is the default dir. The variable CDPATH
defines the search path for the directory contain
ing dir. Alternative directory names in CDPATH 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. The -P option says to use the physical
directory structure instead of following symbolic
links (see also the -P option to the set builtin
command); the -L option forces symbolic links to be
followed. An argument of - is equivalent to $OLD
PWD. The return value is true if the directory was
successfully changed; false 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 indi
cating the command or file name used to invoke com
mand to be displayed; the -V option produces a more
verbose description. 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 command builtin is the exit status of com
mand.
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compgen [option] [word]
Generate possible completion matches for word
according to the options, which may be any option
accepted by the complete builtin with the exception
of -p and -r, and write the matches to the standard
output. When using the -F or -C options, the vari
ous shell variables set by the programmable comple
tion facilities, while available, will not have
useful values.
The matches will be generated in the same way as if
the programmable completion code had generated them
directly from a completion specification with the
same flags. If word is specified, only those com
pletions matching word will be displayed.
The return value is true unless an invalid option
is supplied, or no matches were generated.
complete [-abcdefjkvu] [-A action] [-G globpat] [-W
wordlist] [-P prefix] [-S suffix]
[-X filterpat] [-F function] [-C command] name
[name ...]
complete -pr [name ...]
Specify how arguments to each name should be com
pleted. If the -p option is supplied, or if no
options are supplied, existing completion specifi
cations are printed in a way that allows them to be
reused as input. The -r option removes a comple
tion specification for each name, or, if no names
are supplied, all completion specifications.
The process of applying these completion specifica
tions when word completion is attempted is
described above under Programmable Completion.
Other options, if specified, have the following
meanings. The arguments to the -G, -W, and -X
options (and, if necessary, the -P and -S options)
should be quoted to protect them from expansion
before the complete builtin is invoked.
-A action
The action may be one of the following to
generate a list of possible completions:
alias Alias names. May also be specified
as -a.
arrayvar
Array variable names.
binding Readline key binding names.
builtin Names of shell builtin commands.
May also be specified as -b.
command Command names. May also be speci
fied as -c.
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directory
Directory names. May also be spec
ified as -d.
disabled
Names of disabled shell builtins.
enabled Names of enabled shell builtins.
export Names of exported shell variables.
May also be specified as -e.
file File names. May also be specified
as -f.
function
Names of shell functions.
helptopic
Help topics as accepted by the help
builtin.
hostname
Hostnames, as taken from the file
specified by the HOSTFILE shell
variable.
job Job names, if job control is
active. May also be specified as
-j.
keyword Shell reserved words. May also be
specified as -k.
running Names of running jobs, if job con
trol is active.
setopt Valid arguments for the -o option
to the set builtin.
shopt Shell option names as accepted by
the shopt builtin.
signal Signal names.
stopped Names of stopped jobs, if job con
trol is active.
user User names. May also be specified
as -u.
variable
Names of all shell variables. May
also be specified as -v.
-G globpat
The filename expansion pattern globpat is
expanded to generate the possible comple
tions.
-W wordlist
The wordlist is split using the characters
in the IFS special variable as delimiters,
and each resultant word is expanded. The
possible completions are the members of the
resultant list which match the word being
completed.
-C command
command is executed in a subshell environ
ment, and its output is used as the possi
ble completions.
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-F function
The shell function function is executed in
the current shell environment. When it
finishes, the possible completions are
retrieved from the value of the COMPREPLY
array variable.
-X filterpat
filterpat is a pattern as used for filename
expansion. It is applied to the list of
possible completions generated by the pre
ceding options and arguments, and each com
pletion matching filterpat is removed from
the list. A leading ! in filterpat negates
the pattern; in this case, any completion
not matching filterpat is removed.
-P prefix
prefix is added at the beginning of each
possible completion after all other options
have been applied.
-S suffix
suffix is appended to each possible comple
tion after all other options have been
applied.
The return value is true unless an invalid option
is supplied, an option other than -p or -r is sup
plied without a name argument, an attempt is made
to remove a completion specification for a name for
which no specification exists, or an error occurs
adding a completion specification.
continue [n]
Resume the next iteration of the enclosing for,
while, until, or select 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 continue is executed.
declare [-afFirx] [-p] [name[=value]]
typeset [-afFirx] [-p] [name[=value]]
Declare variables and/or give them attributes. If
no names are given then display the values of vari
ables. The -p option will display the attributes
and values of each name. When -p is used, addi
tional options are ignored. The -F option inhibits
the display of function definitions; only the func
tion name and attributes are printed. The -F
option implies -f. The following options can be
used to restrict output to variables with the spec
ified attribute or to give variables attributes:
-a Each name is an array variable (see Arrays
above).
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-f Use function names only.
-i The variable is treated as an integer;
arithmetic evaluation (see ARITHMETIC EVALU
ATION ) is performed when the variable is
assigned a value.
-r Make names readonly. These names cannot
then be assigned values by subsequent
assignment statements or unset.
-x Mark names for export to subsequent commands
via the environment.
Using `+' instead of `-' turns off the attribute
instead, with the exception that +a may not be used
to destroy an array variable. When used in a func
tion, makes each name local, as with the local com
mand. The return value is 0 unless an invalid
option is encountered, an attempt is made to define
a function using ``-f foo=bar'', an attempt is made
to assign a value to a readonly variable, an
attempt is made to assign a value to an array vari
able without using the compound assignment syntax
(see Arrays above), one of the names is not a valid
shell variable name, an attempt is made to turn off
readonly status for a readonly variable, an attempt
is made to turn off array status for an array vari
able, or an attempt is made to display a non-exis
tent function with -f.
dirs [-clpv] [+n] [-n]
Without options, displays the list of currently
remembered directories. The default display is on
a single line with directory names separated by
spaces. Directories are added to the list with the
pushd command; the popd command removes entries
from 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.
-c Clears the directory stack by deleting all
of the entries.
-l Produces a longer listing; the default list
ing format uses a tilde to denote the home
directory.
-p Print the directory stack with one entry per
line.
-v Print the directory stack with one entry per
line, prefixing each entry with its index in
the stack.
The return value is 0 unless an invalid option is
supplied or n indexes beyond the end of the
GNU 1996 Mar 20 7
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directory stack.
disown [-ar] [-h] [jobspec ...]
Without options, each jobspec is removed from the
table of active jobs. If the -h option is given,
each jobspec is not removed from the table, but is
marked so that SIGHUP is not sent to the job if the
shell receives a SIGHUP. If no jobspec is present,
and neither the -a nor the -r option is supplied,
the current job is used. If no jobspec is sup
plied, the -a option means to remove or mark all
jobs; the -r option without a jobspec argument
restricts operation to running jobs. The return
value is 0 unless a jobspec does not specify a
valid job.
echo [-neE] [arg ...]
Output the args, separated by spaces, followed by a
newline. The return status is always 0. If -n is
specified, the trailing newline is suppressed. If
the -e option is given, interpretation of the fol
lowing backslash-escaped characters is enabled.
The -E option disables the interpretation of these
escape characters, even on systems where they are
interpreted by default. The xpg_echo shell option
to the may be used to dynamically determine whether
or not echo expands these escape characters by
default. echo does not interpret -- to mean the
end of options. echo interprets the following
escape sequences:
\a alert (bell)
\b backspace
\c suppress trailing newline
\e an escape character
\f form feed
\n new line
\r carriage return
\t horizontal tab
\v vertical tab
\\ backslash
\nnn the character whose ASCII code is the octal
value nnn (one to three digits)
\xnnn the character whose ASCII code is the hex
adecimal value nnn (one to three digits)
enable [-adnps] [-f filename] [name ...]
Enable and disable builtin shell commands. Dis
abling a builtin allows a disk command which has
the same name as a shell builtin to be executed
without specifying a full pathname, even though the
shell normally searches for builtins before disk
commands. If -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
GNU 1996 Mar 20 8
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shell builtin version, run enable -n test. The -f
option means to load the new builtin command name
from shared object filename, on systems that sup
port dynamic loading. The -d option will delete a
builtin previously loaded with -f. If no name
arguments are given, or if the -p option is sup
plied, a list of shell builtins is printed. With
no other option arguments, the list consists of all
enabled shell builtins. If -n is supplied, only
disabled builtins are printed. If -a is supplied,
the list printed includes all builtins, with an
indication of whether or not each is enabled. If
-s is supplied, the output is restricted to the
POSIX special builtins. The return value is 0
unless a name is not a shell builtin or there is an
error loading a new builtin from a shared object.
eval [arg ...]
The args are read and concatenated together into a
single command. This command is then read and exe
cuted by the shell, and its exit status is returned
as the value of eval. If there are no args, or
only null arguments, eval returns 0.
exec [-cl] [-a name] [command [arguments]]
If command is specified, it replaces the shell. No
new process is created. The arguments become the
arguments to command. If the -l option is sup
plied, the shell places a dash at the beginning of
the zeroth arg passed to command. This is what
login(1) does. The -c option causes command to be
executed with an empty environment. If -a is sup
plied, the shell passes name as the zeroth argument
to the executed command. If command cannot be exe
cuted for some reason, a non-interactive shell
exits, unless the shell option execfail is enabled,
in which case it returns failure. An interactive
shell returns failure if the file cannot be exe
cuted. If command is not specified, any redirec
tions take effect in the current shell, and the
return status is 0. If there is a redirection
error, the return status is 1.
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 [-fn] [name[=word]] ...
export -p
The supplied names are marked for automatic export
to the environment of subsequently executed com
mands. If the -f option is given, the names refer
GNU 1996 Mar 20 9
BASH_BUILTINS(1) BASH_BUILTINS(1)
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. export returns an exit status of
0 unless an invalid option is encountered, one of
the names is not a valid 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 com
mands from first to last is selected from the his
tory list. First and last may be specified as a
string (to locate the last command beginning with
that string) or as a number (an index into the his
tory list, where a negative number is used as an
offset from the current command 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 option suppresses the command numbers when
listing. The -r option reverses the order of the
commands. If the -l option is given, the commands
are listed on standard output. Otherwise, the edi
tor 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 complete, 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 typ
ing ``r cc'' runs the last command beginning with
``cc'' and typing ``r'' re-executes the last com
mand.
If the first form is used, the return value is 0
unless an invalid 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 spec
ify a valid history line, in which case fc returns
failure.
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fg [jobspec]
Resume 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 con
trol.
getopts optstring name [args]
getopts is used by shell procedures to parse posi
tional parameters. optstring contains the option
characters to be recognized; if a character is fol
lowed by a colon, the option is expected to have an
argument, which should be separated from it by
white space. The colon and question mark charac
ters may not be used as option characters. Each
time it is invoked, getopts places the next option
in the shell variable name, initializing name if it
does not exist, 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 argument 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.
When the end of options is encountered, getopts
exits with a return value greater than zero.
OPTIND is set to the index of the first non-option
argument, and name is set to ?.
getopts normally parses the positional parameters,
but if more arguments are given in args, getopts
parses those instead.
getopts can report errors in two ways. If the
first character of optstring is a colon, silent
error reporting is used. In normal operation diag
nostic messages are printed when invalid options or
missing option arguments are encountered. If the
variable OPTERR is set to 0, no error messages will
be displayed, even if the first character of opt
string is not a colon.
If an invalid option is seen, getopts places ? into
name and, if not silent, prints an error message
and unsets OPTARG. If getopts is silent, the
option character found is placed in OPTARG and no
GNU 1996 Mar 20 11
BASH_BUILTINS(1) BASH_BUILTINS(1)
diagnostic message 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 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] [-p filename] [name]
For each name, the full file name of the command is
determined by searching the directories in $PATH
and remembered. If the -p option is supplied, no
path search is performed, and filename is used as
the full file name of the command. The -r option
causes the shell to forget all remembered loca
tions. If no arguments are given, information
about remembered commands is printed. The return
status is true unless a name is not found or an
invalid option is supplied.
help [-s] [pattern]
Display helpful information about builtin commands.
If pattern is specified, help gives detailed help
on all commands matching pattern; otherwise help
for all the builtins and shell control structures
is printed. The -s option restricts the informa
tion displayed to a short usage synopsis. The
return status is 0 unless no command matches pat
tern.
history [n]
history -c
history -d offset
history -anrw [filename]
history -p arg [arg ...]
history -s arg [arg ...]
With no options, display the command history list
with line numbers. Lines listed with a * have been
modified. An argument of n lists only the last n
lines. If filename 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:
-c Clear the history list by deleting all the
entries.
-d offset
Delete the history entry at position offset.
-a Append the ``new'' history lines (history
lines entered since the beginning of the
GNU 1996 Mar 20 12
BASH_BUILTINS(1) BASH_BUILTINS(1)
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 his
tory 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 con
tents.
-p Perform history substitution on the follow
ing args and display the result on the stan
dard output. Does not store the results in
the history list. Each arg must be quoted
to disable normal history expansion.
-s Store the args in the history list as a sin
gle entry. The last command in the history
list is removed before the args are added.
The return value is 0 unless an invalid option is
encountered, an error occurs while reading or writ
ing the history file, an invalid offset is supplied
as an argument to -d, or the history expansion sup
plied as an argument to -p fails.
jobs [-lnprs] [ jobspec ... ]
jobs -x command [ args ... ]
The first form lists the active jobs. The options
have the following meanings:
-l List process IDs in addition to the normal
information.
-p List only the process ID of the job's pro
cess group leader.
-n Display information only about jobs that
have changed status since the user was last
notified of their status.
-r Restrict output to running jobs.
-s Restrict output to stopped jobs.
If jobspec is given, output is restricted to infor
mation about that job. The return status is 0
unless an invalid option is encountered or an
invalid jobspec is supplied.
If the -x option is supplied, jobs replaces any
jobspec found in command or args with the corre
sponding process group ID, and executes command
passing it args, returning its exit status.
kill [-s sigspec | -n signum | -sigspec] [pid | jobspec]
...
kill -l [sigspec | exit_status]
Send the signal named by sigspec or signum to the
GNU 1996 Mar 20 13
BASH_BUILTINS(1) BASH_BUILTINS(1)
processes named by pid or jobspec. sigspec is
either a signal name such as SIGKILL or a signal
number; signum is a signal number. If sigspec is a
signal name, the name 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 supplied when
-l is given, the names of the signals corresponding
to the arguments are listed, and the return status
is 0. The exit_status argument to -l is a number
specifying either a signal number or the exit sta
tus of a process terminated by a signal. kill
returns true if at least one signal was success
fully sent, or false if an error occurs or an
invalid option is encountered.
let arg [arg ...]
Each arg is an arithmetic expression to be evalu
ated (see ARITHMETIC EVALUATION). If the last arg
evaluates to 0, let returns 1; 0 is returned other
wise.
local [option] [name[=value] ...]
For each argument, a local variable named name is
created, and assigned value. The option can be any
of the options accepted by declare. When local is
used within a function, 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 variables to the standard output. It
is an error to use local when not within a func
tion. The return status is 0 unless local is used
outside a function, an invalid name is supplied, or
name is a readonly variable.
logout Exit a login shell.
popd [-n] [+n] [-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.
Arguments, if supplied, have the following mean
ings:
+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.
-n Suppresses the normal change of directory
when removing directories from the stack, so
GNU 1996 Mar 20 14
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that only the stack is manipulated.
If the popd command is successful, a dirs is per
formed as well, and the return status is 0. popd
returns false if an invalid option is encountered,
the directory stack is empty, a non-existent direc
tory stack entry is specified, or the directory
change fails.
printf format [arguments]
Write the formatted arguments to the standard out
put under the control of the format. The format is
a character string which contains three types of
objects: plain characters, which are simply copied
to standard output, character escape sequences,
which are converted and copied to the standard out
put, and format specifications, each of which
causes printing of the next successive argument.
In addition to the standard printf(1) formats, %b
causes printf to expand backslash escape sequences
in the corresponding argument, and %q causes printf
to output the corresponding argument in a format
that can be reused as shell input.
The format is reused as necessary to consume all of
the arguments. If the format requires more argu
ments than are supplied, the extra format specifi
cations behave as if a zero value or null string,
as appropriate, had been supplied. The return
value is zero on success, non-zero on failure.
pushd [-n] [dir]
pushd [-n] [+n] [-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 argu
ments, exchanges the top two directories and
returns 0, unless the directory stack is empty.
Arguments, if supplied, have the following mean
ings:
+n Rotates the stack so that the nth directory
(counting from the left of the list shown by
dirs, starting with zero) is at the top.
-n Rotates the stack so that the nth directory
(counting from the right of the list shown
by dirs, starting with zero) is at the top.
-n Suppresses the normal change of directory
when adding directories to the stack, so
that only the stack is manipulated.
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 per
formed as well. If the first form is used, pushd
GNU 1996 Mar 20 15
BASH_BUILTINS(1) BASH_BUILTINS(1)
returns 0 unless the cd to dir fails. With the
second form, pushd returns 0 unless the directory
stack is empty, a non-existent directory stack ele
ment is specified, or the directory change to the
specified new current directory fails.
pwd [-LP]
Print the absolute pathname of the current working
directory. The pathname printed contains no sym
bolic links if the -P option is supplied or the -o
physical option to the set builtin command is
enabled. If the -L option is used, the pathname
printed may contain symbolic links. The return
status is 0 unless an error occurs while reading
the name of the current directory or an invalid
option is supplied.
read [-ers] [-t timeout] [-a aname] [-p prompt] [-n
nchars] [-d delim] [name ...]
One line is read from the standard input, and the
first word is assigned to the first name, the sec
ond word to the second name, and so on, with left
over words and their intervening separators
assigned to the last name. If there are fewer
words read from the standard input than names, the
remaining names are assigned empty values. The
characters in IFS are used to split the line into
words. The backslash character (\) may be used to
remove any special meaning for the next character
read and for line continuation. Options, if sup
plied, have the following meanings:
-a aname
The words are assigned to sequential indices
of the array variable aname, starting at 0.
aname is unset before any new values are
assigned. Other name arguments are ignored.
-d delim
The first character of delim is used to ter
minate the input line, rather than newline.
-e If the standard input is coming from a ter
minal, readline (see READLINE above) is used
to obtain the line.
-n nchars
read returns after reading nchars characters
rather than waiting for a complete line of
input.
-p prompt
Display prompt, without a trailing newline,
before attempting to read any input. The
prompt is displayed only if input is coming
from a terminal.
-r Backslash does not act as an escape charac
ter. The backslash is considered to be part
of the line. In particular, a backslash-
GNU 1996 Mar 20 16
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newline pair may not be used as a line con
tinuation.
-s Silent mode. If input is coming from a ter
minal, characters are not echoed.
-t timeout
Cause read to time out and return failure if
a complete line of input is not read within
timeout seconds. This option has no effect
if read is not reading input from the termi
nal or a pipe.
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 or read times
out.
readonly [-apf] [name ...]
The given names are marked readonly; the values of
these names may not be changed by subsequent
assignment. If the -f option is supplied, the
functions corresponding to the names are so marked.
The -a option restricts the variables to arrays.
If no name arguments are given, or if the -p option
is supplied, a list of all readonly names is
printed. The -p option causes output to be dis
played in a format that may be reused as input.
The return status is 0 unless an invalid option is
encountered, one of the names is not a valid 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
specified by n. If n is omitted, the return status
is that of the last command executed in the func
tion 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 sta
tus of the script. If used outside a function and
not during execution of a script by ., the return
status is false.
set [--abefhkmnptuvxBCHP] [-o option] [arg ...]
Without options, the name and value of each shell
variable are displayed in a format that can be
reused as input. The output is sorted according to
the current locale. When options are specified,
they set or unset shell attributes. Any arguments
remaining after the options are processed are
treated as values for the positional parameters and
are assigned, in order, to $1, $2, ... $n.
Options, if specified, have the following meanings:
GNU 1996 Mar 20 17
BASH_BUILTINS(1) BASH_BUILTINS(1)
-a Automatically mark variables which are mod
ified or created for export to the environ
ment of subsequent commands.
-b Report the status of terminated background
jobs immediately, rather than before the
next primary prompt. This is effective
only when job control is enabled.
-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 Remember the location of commands as they
are looked up for execution. This is
enabled by default.
-k All arguments in the form of assignment
statements are placed in the environment
for a command, not just those that precede
the command name.
-m Monitor mode. Job control is enabled.
This option is on by default for interac
tive 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 by
interactive shells.
-o option-name
The option-name can be one of the follow
ing:
allexport
Same as -a.
braceexpand
Same as -B.
emacs Use an emacs-style command line
editing interface. This is enabled
by default when the shell is inter
active, unless the shell is started
with the --noediting option.
errexit Same as -e.
hashall Same as -h.
histexpand
Same as -H.
history Enable command history, as
described above under HISTORY.
This option is on by default in
interactive shells.
GNU 1996 Mar 20 18
BASH_BUILTINS(1) BASH_BUILTINS(1)
ignoreeof
The effect is as if the shell com
mand IGNOREEOF=10 had been executed
(see Shell Variables above).
keyword Same as -k.
monitor Same as -m.
noclobber
Same as -C.
noexec Same as -n.
noglob Same as -f.
notify Same as -b.
nounset Same as -u.
onecmd Same as -t.
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 -o is supplied with no option-name, the
values of the current options are printed.
If +o is supplied with no option-name, a
series of set commands to recreate the cur
rent option settings is displayed on the
standard output.
-p Turn on privileged mode. In this mode, the
$ENV and $BASH_ENV files are not processed,
shell functions are not inherited from the
environment, and the SHELLOPTS variable, if
it appears in the environment, is ignored.
If the shell is started with the effective
user (group) id not equal to the real user
(group) id, and the -p option is not sup
plied, these actions are taken and the
effective user id is set to the real user
id. If the -p option is supplied at
startup, the effective user id is not
reset. Turning this option off causes the
effective user and group ids to be set to
the real user and group ids.
-t Exit after reading and executing one com
mand.
-u Treat unset variables as an error when per
forming parameter expansion. If expansion
is attempted on an unset variable, the
shell prints an error message, and, if not
interactive, exits with a non-zero status.
-v Print shell input lines as they are read.
GNU 1996 Mar 20 19
BASH_BUILTINS(1) BASH_BUILTINS(1)
-x After expanding each simple command, dis
play the expanded value of PS4, followed by
the command and its expanded arguments.
-B The shell performs brace expansion (see
Brace Expansion above). This is on by
default.
-C If set, bash does not overwrite an existing
file with the >, >&, and <> redirection
operators. This may be overridden when
creating output files by using the redirec
tion operator >| instead of >.
-H Enable ! style history substitution. This
option is on by default when the shell is
interactive.
-P If set, the shell does not follow symbolic
links when executing commands such as cd
that change the current working directory.
It uses the physical directory structure
instead. By default, bash follows the log
ical chain of directories when performing
commands which change the current direc
tory.
-- If no arguments follow this option, then
the positional parameters are unset. Oth
erwise, 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 posi
tional parameters. The -x and -v options
are turned off. If there are no args, the
positional parameters remain unchanged.
The options are off by default unless otherwise
noted. Using + rather than - causes these options
to be turned off. The options can also be speci
fied as arguments to an invocation of the shell.
The current set of options may be found in $-. The
return status is always true unless an invalid
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. n must be a non-nega
tive number less than or equal to $#. If n is 0,
no parameters are changed. If n is not given, it
is assumed to be 1. If n is greater than $#, the
positional parameters are not changed. The return
status is greater than zero if n is greater than $#
or less than zero; otherwise 0.
shopt [-pqsu] [-o] [optname ...]
Toggle the values of variables controlling optional
GNU 1996 Mar 20 20
BASH_BUILTINS(1) BASH_BUILTINS(1)
shell behavior. With no options, or with the -p
option, a list of all settable options is dis
played, with an indication of whether or not each
is set. The -p option causes output to be dis
played in a form that may be reused as input.
Other options have the following meanings:
-s Enable (set) each optname.
-u Disable (unset) each optname.
-q Suppresses normal output (quiet mode); the
return status indicates whether the optname
is set or unset. If multiple optname argu
ments are given with -q, the return status
is zero if all optnames are enabled; non-
zero otherwise.
-o Restricts the values of optname to be those
defined for the -o option to the set
builtin.
If either -s or -u is used with no optname argu
ments, the display is limited to those options
which are set or unset, respectively. Unless oth
erwise noted, the shopt options are disabled
(unset) by default.
The return status when listing options is zero if
all optnames are enabled, non-zero otherwise. When
setting or unsetting options, the return status is
zero unless an optname is not a valid shell option.
The list of shopt options is:
cdable_vars
If set, an argument to the cd builtin com
mand that is not a directory is assumed to
be the name of a variable whose value is
the directory to change to.
cdspell If set, minor errors in the spelling of a
directory component in a cd command will be
corrected. The errors checked for are
transposed characters, a missing character,
and one character too many. If a correc
tion is found, the corrected file name is
printed, and the command proceeds. This
option is only used by interactive shells.
checkhash
If set, bash checks that a command found in
the hash table exists before trying to exe
cute it. If a hashed command no longer
exists, a normal path search is performed.
checkwinsize
If set, bash checks the window size after
each command and, if necessary, updates the
values of LINES and COLUMNS.
cmdhist If set, bash attempts to save all lines of
GNU 1996 Mar 20 21
BASH_BUILTINS(1) BASH_BUILTINS(1)
a multiple-line command in the same history
entry. This allows easy re-editing of
multi-line commands.
dotglob If set, bash includes filenames beginning
with a `.' in the results of pathname
expansion.
execfail
If set, a non-interactive shell will not
exit if it cannot execute the file speci
fied as an argument to the exec builtin
command. An interactive shell does not
exit if exec fails.
expand_aliases
If set, aliases are expanded as described
above under ALIASES. This option is
enabled by default for interactive shells.
extglob If set, the extended pattern matching fea
tures described above under Pathname Expan
sion are enabled.
histappend
If set, the history list is appended to the
file named by the value of the HISTFILE
variable when the shell exits, rather than
overwriting the file.
histreedit
If set, and readline is being used, a user
is given the opportunity to re-edit a
failed history substitution.
histverify
If set, and readline is being used, the
results of history substitution are not
immediately passed to the shell parser.
Instead, the resulting line is loaded into
the readline editing buffer, allowing fur
ther modification.
hostcomplete
If set, and readline is being used, bash
will attempt to perform hostname completion
when a word containing a @ is being com
pleted (see Completing under READLINE
above). This is enabled by default.
huponexit
If set, bash will send SIGHUP to all jobs
when an interactive login shell exits.
interactive_comments
If set, allow a word beginning with # to
cause that word and all remaining charac
ters on that line to be ignored in an
interactive shell (see COMMENTS above).
This option is enabled by default.
lithist If set, and the cmdhist option is enabled,
multi-line commands are saved to the his
tory with embedded newlines rather than
using semicolon separators where possible.
GNU 1996 Mar 20 22
BASH_BUILTINS(1) BASH_BUILTINS(1)
mailwarn
If set, and a file that bash is checking
for mail has been accessed since the last
time it was checked, the message ``The mail
in mailfile has been read'' is displayed.
no_empty_cmd_completion
If set, and readline is being used, bash
will not attempt to search the PATH for
possible completions when completion is
attempted on an empty line.
nocaseglob
If set, bash matches filenames in a
case-insensitive fashion when performing
pathname expansion (see Pathname Expansion
above).
nullglob
If set, bash allows patterns which match no
files (see Pathname Expansion above) to
expand to a null string, rather than them
selves.
progcomp
If set, the programmable completion facili
ties (see Programmable Completion above)
are enabled. This option is enabled by
default.
promptvars
If set, prompt strings undergo variable and
parameter expansion after being expanded as
described in PROMPTING above. This option
is enabled by default.
restricted_shell
The shell sets this option if it is started
in restricted mode (see RESTRICTED SHELL
below). The value may not be changed.
This is not reset when the startup files
are executed, allowing the startup files to
discover whether or not a shell is
restricted.
shift_verbose
If set, the shift builtin prints an error
message when the shift count exceeds the
number of positional parameters.
sourcepath
If set, the source (.) builtin uses the
value of PATH to find the directory con
taining the file supplied as an argument.
This option is enabled by default.
xpg_echo
If set, the echo builtin expands backslash-
escape sequences by default.
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
GNU 1996 Mar 20 23
BASH_BUILTINS(1) BASH_BUILTINS(1)
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
[ expr ]
Return a status of 0 or 1 depending on the evalua
tion of the conditional expression expr. Each
operator and operand must be a separate argument.
Expressions are composed of the primaries described
above under CONDITIONAL EXPRESSIONS.
Expressions may be combined using the following
operators, listed in decreasing order of prece
dence.
! expr True if expr is false.
( expr )
Returns the value of expr. This may be used
to override the normal precedence of opera
tors.
expr1 -a expr2
True if both expr1 and expr2 are true.
expr1 -o expr2
True if either expr1 or expr2 is true.
test and [ evaluate conditional expressions using a
set of rules based on the number of arguments.
0 arguments
The expression is false.
1 argument
The expression is true if and only if the
argument is not null.
2 arguments
If the first argument is !, the expression
is true if and only if the second argument
is null. If the first argument is one of
the unary conditional operators listed above
under CONDITIONAL EXPRESSIONS, the expres
sion is true if the unary test is true. If
the first argument is not a valid unary con
ditional operator, the expression is false.
3 arguments
If the second argument is one of the binary
conditional operators listed above under
CONDITIONAL EXPRESSIONS, the result of the
expression is the result of the binary test
using the first and third arguments as
operands. If the first argument is !, the
value is the negation of the two-argument
test using the second and third arguments.
If the first argument is exactly ( and the
third argument is exactly ), the result is
the one-argument test of the second argu
ment. Otherwise, the expression is false.
GNU 1996 Mar 20 24
BASH_BUILTINS(1) BASH_BUILTINS(1)
The -a and -o operators are considered
binary operators in this case.
4 arguments
If the first argument is !, the result is
the negation of the three-argument expres
sion composed of the remaining arguments.
Otherwise, the expression is parsed and
evaluated according to precedence using the
rules listed above.
5 or more arguments
The expression is parsed and evaluated
according to precedence using the rules
listed above.
times Print the accumulated user and system times for the
shell and for processes run from the shell. The
return status is 0.
trap [-lp] [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 the sig
nal specified by each sigspec is ignored by the
shell and by the commands it invokes. If arg is
not present and -p has been supplied, then the trap
commands associated with each sigspec are dis
played. If no arguments are supplied or if only -p
is given, trap prints the list of commands associ
ated with each signal number. Each sigspec is
either a signal name defined in <signal.h>, or a
signal number. If a sigspec is EXIT (0) the com
mand arg is executed on exit from the shell. If a
sigspec is DEBUG, the command arg is executed after
every simple command (see SHELL GRAMMAR above).
The -l option causes the shell to print a list of
signal names and their corresponding numbers. Sig
nals 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 any sigspec
is invalid; otherwise trap returns true.
type [-atp] name [name ...]
With no options, indicate how each name would be
interpreted if used as a command name. If the -t
option is used, type prints a string which is one
of alias, keyword, 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 -p option is
used, type either returns the name of the disk file
GNU 1996 Mar 20 25
BASH_BUILTINS(1) BASH_BUILTINS(1)
that would be executed if name were specified as a
command name, or nothing if type -t name would not
return file. If a command is hashed, -p prints the
hashed value, not necessarily the file that appears
first in PATH. If the -a option is used, type
prints all of the places that contain an executable
named name. This includes aliases and functions,
if and only if the -p option is not also used. The
table of hashed commands is not consulted when
using -a. type returns true if any of the argu
ments are found, false if none are found.
ulimit [-SHacdflmnpstuv [limit]]
Provides control over the resources available to
the shell and to processes started by it, on sys
tems 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, both the soft and
hard limits are set. If limit is omitted, the cur
rent 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 are printed before the value. Other options
are interpreted 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
-l The maximum size that may be locked into
memory
-m The maximum resident set size
-n The maximum number of open file descriptors
(most systems do not allow this value to be
set)
-p The pipe size in 512-byte blocks (this may
not be set)
-s The maximum stack size
-t The maximum amount of cpu time in seconds
-u The maximum number of processes available to
a single user
-v The maximum amount of virtual memory avail
able to the shell
If limit is given, it is the new value of the spec
ified 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,
GNU 1996 Mar 20 26
BASH_BUILTINS(1) BASH_BUILTINS(1)
and -n and -u, which are unscaled values. The
return status is 0 unless an invalid option is
encountered, a non-numeric argument other than
unlimited is supplied as limit, or an error occurs
while setting a new limit.
umask [-p] [-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 sym
bolic mode mask similar to that accepted by
chmod(1). If mode is omitted, 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. If the -p option is supplied,
and mode is omitted, the output is in a form that
may be reused as input. 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 each name from the list of defined aliases.
If -a is supplied, all alias definitions are
removed. The return value is true unless a sup
plied name is not a defined alias.
unset [-fv] [name ...]
For each name, remove the corresponding variable or
function. If no options are supplied, or the -v
option is given, each name refers to a shell vari
able. Read-only variables may not be unset. If -f
is specifed, each name refers to a shell function,
and the function definition is removed. Each unset
variable or function is removed from the environ
ment passed to subsequent commands. If any of RAN
DOM, SECONDS, LINENO, HISTCMD, FUNCNAME, GROUPS, or
DIRSTACK are unset, they lose their special proper
ties, even if they are subsequently reset. The
exit status is true unless a name does not exist or
is readonly.
wait [n]
Wait for the specified process and return its ter
mination status. n may be a process ID or a job
specification; if a job spec is given, all pro
cesses 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-existent process or job, the
return status is 127. Otherwise, the return status
is the exit status of the last process or job
waited for.
GNU 1996 Mar 20 27
BASH_BUILTINS(1) BASH_BUILTINS(1)
SEE ALSO
bash(1), sh(1)
GNU 1996 Mar 20 28