bash defines the following built-in commands: :, ., [, alias, bg, bind,
break, builtin, case, cd, command, compgen, complete, continue,
declare, dirs, disown, echo, enable, eval, exec, exit, export, fc, fg,
getopts, hash, help, history, if, jobs, kill, let, local, logout, popd,
printf, pushd, pwd, read, readonly, return, set, shift, shopt, source,
suspend, test, times, trap, type, typeset, ulimit, umask, unalias,
unset, until, wait, while.
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. The :, true, false, and test builtins do not accept options
and do not treat -- specially. The exit, logout, break, continue, let,
and shift builtins accept and process arguments beginning with - with-
out requiring --. Other builtins that accept arguments but are not
specified as accepting options interpret arguments beginning with - as
invalid options and require -- to prevent this interpretation.
No effect; the command does nothing beyond expanding arguments
and performing any specified redirections. A zero exit code is
. 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 exe-
cuted from filename. If filename does not contain a slash,
filenames in PATH are used to find the directory containing
filename. The file searched for in PATH need not be executable.
When bash is not in posix mode, 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 posi-
tional parameters when filename is executed. Otherwise the
positional 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 sup-
plied, the name and value of the alias is printed. Alias
returns true unless a name is given for which no alias has been
bg [jobspec ...]
Resume each suspended job 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
variable. Each non-option argument is a command as it would
appear in .inputrc, but each binding or command must be passed
as a separate argument; e.g., '"\C-x\C-r": re-read-init-file'.
Options, if supplied, have the following meanings:
Use keymap as the keymap to be affected by the subsequent
bindings. Acceptable keymap names are emacs, emacs-stan-
dard, 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.
-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.
-s Display readline key sequences bound to macros and the
strings they output in such a way that they can be re-
-S Display readline key sequences bound to macros and the
strings they output.
-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.
Read key bindings from filename.
Query about which keys invoke the named function.
Unbind all keys bound to the named function.
Remove any current binding for keyseq.
Cause shell-command to be executed whenever keyseq is
entered. When shell-command is executed, the shell sets
the READLINE_LINE variable to the contents of the read-
line line buffer and the READLINE_POINT variable to the
current location of the insertion point. If the executed
command changes the value of READLINE_LINE or READ-
LINE_POINT, those new values will be reflected in the
-X List all key sequences bound to shell commands and the
associated commands in a format that can be reused as
The return value is 0 unless an unrecognized option is given or
an error occurred.
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 n is not greater than or
equal to 1.
builtin shell-builtin [arguments]
plied as expr, caller displays the line number, subroutine name,
and source file corresponding to that position in the current
execution call stack. This extra information may be used, for
example, to print a stack trace. The current frame is frame 0.
The return value is 0 unless the shell is not executing a sub-
routine call or expr does not correspond to a valid position in
the call stack.
cd [-L|[-P [-e]] [-@]] [dir]
Change the current directory to dir. if dir is not supplied,
the value of the HOME shell variable is the default. Any addi-
tional arguments following dir are ignored. The variable CDPATH
defines the search path for the directory containing dir: each
directory name in CDPATH is searched for 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 causes cd to use the physical directory
structure by resolving symbolic links while traversing dir and
before processing instances of .. in dir (see also the -P option
to the set builtin command); the -L option forces symbolic links
to be followed by resolving the link after processing instances
of .. in dir. If .. appears in dir, it is processed by removing
the immediately previous pathname component from dir, back to a
slash or the beginning of dir. If the -e option is supplied
with -P, and the current working directory cannot be success-
fully determined after a successful directory change, cd will
return an unsuccessful status. On systems that support it, the
-@ option presents the extended attributes associated with a
file as a directory. An argument of - is converted to $OLDPWD
before the directory change is attempted. If a non-empty direc-
tory name from CDPATH is used, or if - is the first argument,
and the directory change is successful, the absolute pathname of
the new working directory is written to the standard output.
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 indicating the command or filename
used to invoke command 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 can-
not be found, the exit status is 127. Otherwise, the exit sta-
tus of the command builtin is the exit status of command.
compgen [option] [word]
Generate possible completion matches for word according to the
or no matches were generated.
complete [-abcdefgjksuv] [-o comp-option] [-DE] [-A action] [-G glob-
pat] [-W wordlist] [-F function] [-C command]
[-X filterpat] [-P prefix] [-S suffix] name [name ...]
complete -pr [-DE] [name ...]
Specify how arguments to each name should be completed. If the
-p option is supplied, or if no options are supplied, existing
completion specifications are printed in a way that allows them
to be reused as input. The -r option removes a completion spec-
ification for each name, or, if no names are supplied, all com-
pletion specifications. The -D option indicates that the
remaining options and actions should apply to the ``default''
command completion; that is, completion attempted on a command
for which no completion has previously been defined. The -E
option indicates that the remaining options and actions should
apply to ``empty'' command completion; that is, completion
attempted on a blank line.
The process of applying these completion specifications when
word completion is attempted is described above under Program-
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 expan-
sion before the complete builtin is invoked.
The comp-option controls several aspects of the comp-
spec's behavior beyond the simple generation of comple-
tions. comp-option may be one of:
Perform the rest of the default bash completions
if the compspec generates no matches.
default Use readline's default filename completion if
the compspec generates no matches.
Perform directory name completion if the comp-
spec generates no matches.
Tell readline that the compspec generates file-
names, so it can perform any filename-specific
processing (like adding a slash to directory
names, quoting special characters, or suppress-
ing trailing spaces). Intended to be used with
noquote Tell readline not to quote the completed words
if they are filenames (quoting filenames is the
nospace Tell readline not to append a space (the
default) to words completed at the end of the
After any matches defined by the compspec are
command Command names. May also be specified as -c.
Directory names. May also be specified as -d.
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.
Names of shell functions.
group Group names. May also be specified as -g.
Help topics as accepted by the help builtin.
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
running Names of running jobs, if job control is active.
service Service names. May also be specified as -s.
setopt Valid arguments for the -o option to the set
shopt Shell option names as accepted by the shopt
signal Signal names.
stopped Names of stopped jobs, if job control is active.
user User names. May also be specified as -u.
Names of all shell variables. May also be spec-
ified as -v.
command is executed in a subshell environment, and its
output is used as the possible completions.
The shell function function is executed in the current
shell environment. When the function is executed, the
first argument ($1) is the name of the command whose
arguments are being completed, the second argument ($2)
is the word being completed, and the third argument ($3)
is the word preceding the word being completed on the
current command line. When it finishes, the possible
completions are retrieved from the value of the COMPRE-
PLY array variable.
The pathname expansion pattern globpat is expanded to
generate the possible completions.
prefix is added at the beginning of each possible com-
pletion after all other options have been applied.
suffix is appended to each possible completion after all
A leading ! in filterpat negates the pattern; in this
case, any completion not matching filterpat is removed.
The return value is true unless an invalid option is supplied,
an option other than -p or -r is supplied without a name argu-
ment, 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.
compopt [-o option] [-DE] [+o option] [name]
Modify completion options for each name according to the
options, or for the currently-executing completion if no names
are supplied. If no options are given, display the completion
options for each name or the current completion. The possible
values of option are those valid for the complete builtin
described above. The -D option indicates that the remaining
options should apply to the ``default'' command completion; that
is, completion attempted on a command for which no completion
has previously been defined. The -E option indicates that the
remaining options should apply to ``empty'' command completion;
that is, completion attempted on a blank line.
The return value is true unless an invalid option is supplied,
an attempt is made to modify the options for a name for which no
completion specification exists, or an output error occurs.
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 n is not greater
than or equal to 1.
declare [-aAfFgilnrtux] [-p] [name[=value] ...]
typeset [-aAfFgilnrtux] [-p] [name[=value] ...]
Declare variables and/or give them attributes. If no names are
given then display the values of variables. The -p option will
display the attributes and values of each name. When -p is used
with name arguments, additional options, other than -f and -F,
are ignored. When -p is supplied without name arguments, it
will display the attributes and values of all variables having
the attributes specified by the additional options. If no other
options are supplied with -p, declare will display the
attributes and values of all shell variables. The -f option
will restrict the display to shell functions. The -F option
inhibits the display of function definitions; only the function
name and attributes are printed. If the extdebug shell option
is enabled using shopt, the source file name and line number
where the function is defined are displayed as well. The -F
option implies -f. The -g option forces variables to be created
or modified at the global scope, even when declare is executed
in a shell function. It is ignored in all other cases. The
following options can be used to restrict output to variables
-n Give each name the nameref attribute, making it a name
reference to another variable. That other variable is
defined by the value of name. All references and assign-
ments to name, except for changing the -n attribute
itself, are performed on the variable referenced by
name's value. The -n attribute cannot be applied to
-r Make names readonly. These names cannot then be assigned
values by subsequent assignment statements or unset.
-t Give each name the trace attribute. Traced functions
inherit the DEBUG and RETURN traps from the calling
shell. The trace attribute has no special meaning for
-u When the variable is assigned a value, all lower-case
characters are converted to upper-case. The lower-case
attribute is disabled.
-x Mark names for export to subsequent commands via the
Using `+' instead of `-' turns off the attribute instead, with
the exceptions that +a may not be used to destroy an array vari-
able and +r will not remove the readonly attribute. When used
in a function, declare and typeset make each name local, as with
the local command, unless the -g option is supplied. If a vari-
able name is followed by =value, the value of the variable is
set to value. When using -a or -A and the compound assignment
syntax to create array variables, additional attributes do not
take effect until subsequent assignments. 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 variable 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 read-
only status for a readonly variable, an attempt is made to turn
off array status for an array variable, or an attempt is made to
display a non-existent function with -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.
-c Clears the directory stack by deleting all of the
-l Produces a listing using full pathnames; the default
listing 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, pre-
fixing each entry with its index in the stack.
+n Displays the nth entry counting from the left of the list
shown by dirs when invoked without options, starting with
marked so that SIGHUP is not sent to the job if the shell
receives a SIGHUP. If no jobspec is supplied, the -a option
means to remove or mark all jobs; the -r option without a job-
spec 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 0 unless a write error occurs. If -n is
specified, the trailing newline is suppressed. If the -e option
is given, interpretation of the following backslash-escaped
characters is enabled. The -E option disables the interpreta-
tion of these escape characters, even on systems where they are
interpreted by default. The xpg_echo shell option 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
\a alert (bell)
\c suppress further output
\E an escape character
\f form feed
\n new line
\r carriage return
\t horizontal tab
\v vertical tab
\0nnn the eight-bit character whose value is the octal value
nnn (zero to three octal digits)
\xHH the eight-bit character whose value is the hexadecimal
value HH (one or two hex digits)
\uHHHH the Unicode (ISO/IEC 10646) character whose value is the
hexadecimal value HHHH (one to four hex digits)
the Unicode (ISO/IEC 10646) character whose value is the
hexadecimal value HHHHHHHH (one to eight hex digits)
enable [-a] [-dnps] [-f filename] [name ...]
Enable and disable builtin shell commands. Disabling a builtin
allows a disk command which has the same name as a shell builtin
to be executed without specifying a full pathname, even though
the shell normally searches for builtins before disk commands.
If -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, run ``enable -n test''.
The -f option means to load the new builtin command name from
shared object filename, on systems that support 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 supplied,
a list of shell builtins is printed. With no other option argu-
ments, the list consists of all enabled shell builtins. If -n
is supplied, only disabled builtins are printed. If -a is sup-
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 supplied, the shell places a dash at the begin-
ning of the zeroth argument passed to command. This is what
login(1) does. The -c option causes command to be executed with
an empty environment. If -a is supplied, the shell passes name
as the zeroth argument to the executed command. If command can-
not be executed for some reason, a non-interactive shell exits,
unless the execfail shell option is enabled. In that case, it
returns failure. An interactive shell returns failure if the
file cannot be executed. If command is not specified, any redi-
rections take effect in the current shell, and the return status
is 0. If there is a redirection error, the return status is 1.
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]] ...
The supplied names are marked for automatic export to the envi-
ronment 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 names of all exported
variables is printed. The -n option causes the export property
to be removed from each name. If a variable name is followed by
=word, the value of the variable is set to word. 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 sup-
plied with a name that is not a function.
fc [-e ename] [-lnr] [first] [last]
fc -s [pat=rep] [cmd]
The first form selects a range of commands from first to last
from the history list and displays or edits and re-executes
them. 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 history 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 other-
wise. If first is not specified it is set to the previous com-
mand 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. Other-
wise, 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, vi is used. When editing is com-
plete, the edited commands are echoed and executed.
form is used, the return status is that of the command re-exe-
cuted, unless cmd does not specify a valid history line, in
which case fc returns failure.
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 spec-
ify 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 parame-
ters. optstring contains the option characters to be recog-
nized; if a character is followed by a colon, the option is
expected to have an argument, which should be separated from it
by white space. The colon and question mark characters 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 automati-
cally; it must be manually reset between multiple calls to
getopts within the same shell invocation if a new set of parame-
ters 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, diagnostic 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 dis-
played, even if the first character of optstring 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 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
option causes the shell to forget the remembered location of
each name. If the -t option is supplied, the full pathname to
which each name corresponds is printed. If multiple name argu-
ments are supplied with -t, the name is printed before the
hashed full pathname. The -l option causes output to be dis-
played in a format that may be reused as input. If no arguments
are given, or if only -l is supplied, information about remem-
bered commands is printed. The return status is true unless a
name is not found or an invalid option is supplied.
help [-dms] [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.
-d Display a short description of each pattern
-m Display the description of each pattern in a manpage-like
-s Display only a short usage synopsis for each pattern
The return status is 0 unless no command matches pattern.
history -d offset
history -anrw [filename]
history -p arg [arg ...]
history -s arg [arg ...]
With no options, display the command history list with line num-
bers. Lines listed with a * have been modified. An argument of
n lists only the last n lines. If the shell variable HISTTIME-
FORMAT is set and not null, it is used as a format string for
strftime(3) to display the time stamp associated with each dis-
played history entry. No intervening blank is printed between
the formatted time stamp and the history line. 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
-c Clear the history list by deleting all the entries.
Delete the history entry at position offset.
-a Append the ``new'' history lines (history lines entered
since the beginning of the current bash session) to the
-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 append them to
the current history list.
-w Write the current history list to the history file, over-
writing the history file's contents.
-p Perform history substitution on the following args and
display the result on the standard output. Does not
unless an invalid option is encountered, an error occurs while
reading or writing the history file, an invalid offset is sup-
plied as an argument to -d, or the history expansion supplied as
an argument to -p fails.
jobs [-lnprs] [ jobspec ... ]
jobs -x command [ args ... ]
The first form lists the active jobs. The options have the fol-
-l List process IDs in addition to the normal information.
-n Display information only about jobs that have changed
status since the user was last notified of their status.
-p List only the process ID of the job's process group
-r Display only running jobs.
-s Display only stopped jobs.
If jobspec is given, output is restricted to information 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 corresponding 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 processes
named by pid or jobspec. sigspec is either a case-insensitive
signal name such as SIGKILL (with or without the SIG prefix) or
a signal number; signum is a signal number. 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
status of a process terminated by a signal. kill returns true
if at least one signal was successfully sent, or false if an
error occurs or an invalid option is encountered.
let arg [arg ...]
Each arg is an arithmetic expression to be evaluated (see ARITH-
METIC EVALUATION above). If the last arg evaluates to 0, let
returns 1; 0 is returned otherwise.
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 func-
tion 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 function. The return status is 0 unless
local is used outside a function, an invalid name is supplied,
-n Copy at most count lines. If count is 0, all lines are
-O Begin assigning to array at index origin. The default
index is 0.
-s Discard the first count lines read.
-t Remove a trailing newline from each line read.
-u Read lines from file descriptor fd instead of the stan-
-C Evaluate callback each time quantum lines are read. The
-c option specifies quantum.
-c Specify the number of lines read between each call to
If -C is specified without -c, the default quantum is 5000.
When callback is evaluated, it is supplied the index of the next
array element to be assigned and the line to be assigned to that
element as additional arguments. callback is evaluated after
the line is read but before the array element is assigned.
If not supplied with an explicit origin, mapfile will clear
array before assigning to it.
mapfile returns successfully unless an invalid option or option
argument is supplied, array is invalid or unassignable, or if
array is not an indexed array.
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 follow-
-n Suppresses the normal change of directory when removing
directories from the stack, so that only the stack is
+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
If the popd command is successful, a dirs is performed as well,
and the return status is 0. popd returns false if an invalid
option is encountered, the directory stack is empty, a non-exis-
tent directory stack entry is specified, or the directory change
printf [-v var] format [arguments]
Write the formatted arguments to the standard output under the
control of the format. The -v option causes the output to be
assigned to the variable var rather than being printed to the
format that can be reused as shell input.
causes printf to output the date-time string resulting
from using datefmt as a format string for strftime(3).
The corresponding argument is an integer representing the
number of seconds since the epoch. Two special argument
values may be used: -1 represents the current time, and
-2 represents the time the shell was invoked. If no
argument is specified, conversion behaves as if -1 had
been given. This is an exception to the usual printf
Arguments to non-string format specifiers are treated as C con-
stants, except that a leading plus or minus sign is allowed, and
if the leading character is a single or double quote, the value
is the ASCII value of the following character.
The format is reused as necessary to consume all of the argu-
ments. If the format requires more arguments than are supplied,
the extra format specifications behave as if a zero value or
null string, as appropriate, had been supplied. The return
value is zero on success, non-zero on failure.
pushd [-n] [+n] [-n]
pushd [-n] [dir]
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. Arguments,
if supplied, have the following meanings:
-n Suppresses the normal change of directory when adding
directories to the stack, so that only the stack is
+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.
dir Adds dir to the directory stack at the top, making it the
new current working directory as if it had been supplied
as the argument to the cd builtin.
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 direc-
tory stack is empty, a non-existent directory stack element is
specified, or the directory change to the specified new current
Print the absolute pathname of the current working directory.
The pathname printed contains no symbolic links if the -P option
is supplied or the -o physical option to the set builtin command
words read from the input stream than names, the remaining names
are assigned empty values. The characters in IFS are used to
split the line into words using the same rules the shell uses
for expansion (described above under Word Splitting). The back-
slash character (\) may be used to remove any special meaning
for the next character read and for line continuation. Options,
if supplied, have the following meanings:
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
The first character of delim is used to terminate the
input line, rather than newline.
-e If the standard input is coming from a terminal, readline
(see READLINE above) is used to obtain the line. Read-
line uses the current (or default, if line editing was
not previously active) editing settings.
If readline is being used to read the line, text is
placed into the editing buffer before editing begins.
read returns after reading nchars characters rather than
waiting for a complete line of input, but honor a delim-
iter if fewer than nchars characters are read before the
read returns after reading exactly nchars characters
rather than waiting for a complete line of input, unless
EOF is encountered or read times out. Delimiter charac-
ters encountered in the input are not treated specially
and do not cause read to return until nchars characters
Display prompt on standard error, without a trailing new-
line, 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 character. The back-
slash is considered to be part of the line. In particu-
lar, a backslash-newline pair may not be used as a line
-s Silent mode. If input is coming from a terminal, charac-
ters are not echoed.
Cause read to time out and return failure if a complete
line of input (or a specified number of characters) is
not read within timeout seconds. timeout may be a deci-
mal number with a fractional portion following the deci-
mal point. This option is only effective if read is
reading input from a terminal, pipe, or other special
file; it has no effect when reading from regular files.
If read times out, read saves any partial input read into
the specified variable name. If timeout is 0, read
readonly [-aAf] [-p] [name[=word] ...]
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 indexed
arrays; the -A option restricts the variables to associative
arrays. If both options are supplied, -A takes precedence. If
no name arguments are given, or if the -p option is supplied, a
list of all readonly names is printed. The other options may be
used to restrict the output to a subset of the set of readonly
names. The -p option causes output to be displayed in a format
that may be reused as input. If a variable name is followed by
=word, the value of the variable is set to word. 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.
Causes a function to stop executing and return the value speci-
fied by n to its caller. If n is omitted, the return status is
that of the last command executed in the function body. If
return is 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 n is supplied, the return value is its least
significant 8 bits. The return status is non-zero if return is
supplied a non-numeric argument, or is used outside a function
and not during execution of a script by . or source. Any com-
mand associated with the RETURN trap is executed before execu-
tion resumes after the function or script.
set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
Without options, the name and value of each shell variable are
displayed in a format that can be reused as input for setting or
resetting the currently-set variables. Read-only variables can-
not be reset. In posix mode, only shell variables are listed.
The output is sorted according to the current locale. When
options are specified, they set or unset shell attributes. Any
arguments remaining after option processing are treated as val-
ues for the positional parameters and are assigned, in order, to
$1, $2, ... $n. Options, if specified, have the following
-a Automatically mark variables and functions which are
modified or created for export to the environment of
-b Report the status of terminated background jobs immedi-
ately, rather than before the next primary prompt. This
is effective only when job control is enabled.
-e Exit immediately if a pipeline (which may consist of a
single simple command), a list, or a compound command
(see SHELL GRAMMAR above), exits with a non-zero sta-
ronment separately (see COMMAND EXECUTION ENVIRONMENT
above), and may cause subshells to exit before executing
all the commands in the subshell.
If a compound command or shell function executes in a
context where -e is being ignored, none of the commands
executed within the compound command or function body
will be affected by the -e setting, even if -e is set
and a command returns a failure status. If a compound
command or shell function sets -e while executing in a
context where -e is ignored, that setting will not have
any effect until the compound command or the command
containing the function call completes.
-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 interactive shells on systems that
support it (see JOB CONTROL above). All processes run
in a separate process group. When a background job com-
pletes, the shell prints a line containing its exit sta-
-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.
The option-name can be one of the following:
Same as -a.
Same as -B.
emacs Use an emacs-style command line editing inter-
face. This is enabled by default when the shell
is interactive, unless the shell is started with
the --noediting option. This also affects the
editing interface used for read -e.
errexit Same as -e.
Same as -E.
Same as -T.
hashall Same as -h.
Same as -H.
history Enable command history, as described above under
HISTORY. This option is on by default in inter-
The effect is as if the shell command
``IGNOREEOF=10'' had been executed (see Shell
If set, the return value of a pipeline is the
value of the last (rightmost) command to exit
with a non-zero status, or zero if all commands
in the pipeline exit successfully. This option
is disabled by default.
posix Change the behavior of bash where the default
operation differs from the POSIX standard to
match the standard (posix mode). See SEE ALSO
below for a reference to a document that details
how posix mode affects bash's behavior.
Same as -p.
verbose Same as -v.
vi Use a vi-style command line editing interface.
This also affects the editing interface used for
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
current option settings is displayed on the standard
-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,
BASHOPTS, CDPATH, and GLOBIGNORE variables, if they
appear in the environment, are 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 sup-
plied 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 command.
-u Treat unset variables and parameters other than the spe-
cial parameters "@" and "*" as an error when performing
parameter expansion. If expansion is attempted on an
unset variable or parameter, the shell prints an error
message, and, if not interactive, exits with a non-zero
-v Print shell input lines as they are read.
-x After expanding each simple command, for command, case
command, select command, or arithmetic for command, dis-
play the expanded value of PS4, followed by the command
and its expanded arguments or associated word list.
-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 redi-
rection operator >| instead of >.
-E If set, any trap on ERR is inherited by shell functions,
shell functions, command substitutions, and commands
executed in a subshell environment. The DEBUG and
RETURN traps are normally not inherited in such cases.
-- If no arguments follow this option, then the positional
parameters are unset. Otherwise, the positional parame-
ters 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 parameters. The -x and -v
options are turned off. If there are no args, the posi-
tional 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 specified 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 encoun-
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-negative 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 settings controlling optional shell behav-
ior. The settings can be either those listed below, or, if the
-o option is used, those available with the -o option to the set
builtin command. With no options, or with the -p option, a list
of all settable options is displayed, with an indication of
whether or not each is set. The -p option causes output to be
displayed 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 multi-
ple optname arguments are given with -q, the return sta-
tus is zero if all optnames are enabled; non-zero other-
-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 arguments, shopt
shows only those options which are set or unset, respectively.
Unless otherwise noted, the shopt options are disabled (unset)
The return status when listing options is zero if all optnames
are enabled, non-zero otherwise. When setting or unsetting
cdspell If set, minor errors in the spelling of a directory com-
ponent in a cd command will be corrected. The errors
checked for are transposed characters, a missing charac-
ter, and one character too many. If a correction is
found, the corrected filename is printed, and the com-
mand proceeds. This option is only used by interactive
If set, bash checks that a command found in the hash ta-
ble exists before trying to execute it. If a hashed
command no longer exists, a normal path search is per-
If set, bash lists the status of any stopped and running
jobs before exiting an interactive shell. If any jobs
are running, this causes the exit to be deferred until a
second exit is attempted without an intervening command
(see JOB CONTROL above). The shell always postpones
exiting if any jobs are stopped.
If set, bash checks the window size after each command
and, if necessary, updates the values of LINES and COL-
cmdhist If set, bash attempts to save all lines of a multiple-
line command in the same history entry. This allows
easy re-editing of multi-line commands.
If set, bash changes its behavior to that of version 3.1
with respect to quoted arguments to the [[ conditional
command's =~ operator and locale-specific string compar-
ison when using the [[ conditional command's < and >
operators. Bash versions prior to bash-4.1 use ASCII
collation and strcmp(3); bash-4.1 and later use the cur-
rent locale's collation sequence and strcoll(3).
If set, bash changes its behavior to that of version 3.2
with respect to locale-specific string comparison when
using the [[ conditional command's < and > operators
(see previous item).
If set, bash changes its behavior to that of version 4.0
with respect to locale-specific string comparison when
using the [[ conditional command's < and > operators
(see description of compat31) and the effect of inter-
rupting a command list. Bash versions 4.0 and later
interrupt the list as if the shell received the inter-
rupt; previous versions continue with the next command
in the list.
If set, bash, when in posix mode, treats a single quote
in a double-quoted parameter expansion as a special
character. The single quotes must match (an even num-
ber) and the characters between the single quotes are
considered quoted. This is the behavior of posix mode
in shell variable references in words to be completed.
This means that dollar signs in variable names that
expand to directories will not be quoted; however, any
dollar signs appearing in filenames will not be quoted,
either. This is active only when bash is using back-
slashes to quote completed filenames. This variable is
set by default, which is the default bash behavior in
versions through 4.2.
If set, bash replaces directory names with the results
of word expansion when performing filename completion.
This changes the contents of the readline editing buf-
fer. If not set, bash attempts to preserve what the
If set, bash attempts spelling correction on directory
names during word completion if the directory name ini-
tially supplied does not exist.
dotglob If set, bash includes filenames beginning with a `.' in
the results of pathname expansion.
If set, a non-interactive shell will not exit if it can-
not execute the file specified as an argument to the
exec builtin command. An interactive shell does not
exit if exec fails.
If set, aliases are expanded as described above under
ALIASES. This option is enabled by default for interac-
If set, behavior intended for use by debuggers is
1. The -F option to the declare builtin displays the
source file name and line number corresponding to
each function name supplied as an argument.
2. If the command run by the DEBUG trap returns a
non-zero value, the next command is skipped and
3. If the command run by the DEBUG trap returns a
value of 2, and the shell is executing in a sub-
routine (a shell function or a shell script exe-
cuted by the . or source builtins), a call to
return is simulated.
4. BASH_ARGC and BASH_ARGV are updated as described
in their descriptions above.
5. Function tracing is enabled: command substitu-
tion, shell functions, and subshells invoked with
( command ) inherit the DEBUG and RETURN traps.
6. Error tracing is enabled: command substitution,
shell functions, and subshells invoked with (
command ) inherit the ERR trap.
extglob If set, the extended pattern matching features described
above under Pathname Expansion are enabled.
If set, range expressions used in pattern matching
bracket expressions (see Pattern Matching above) behave
as if in the traditional C locale when performing com-
parisons. That is, the current locale's collating
sequence is not taken into account, so b will not col-
late between A and B, and upper-case and lower-case
ASCII characters will collate together.
If set, the pattern ** used in a pathname expansion con-
text will match all files and zero or more directories
and subdirectories. If the pattern is followed by a /,
only directories and subdirectories match.
If set, shell error messages are written in the standard
GNU error message format.
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.
If set, and readline is being used, a user is given the
opportunity to re-edit a failed history substitution.
If set, and readline is being used, the results of his-
tory substitution are not immediately passed to the
shell parser. Instead, the resulting line is loaded
into the readline editing buffer, allowing further modi-
If set, and readline is being used, bash will attempt to
perform hostname completion when a word containing a @
is being completed (see Completing under READLINE
above). This is enabled by default.
If set, bash will send SIGHUP to all jobs when an inter-
active login shell exits.
If set, 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). This
option is enabled by default.
If set, and job control is not active, the shell runs
the last command of a pipeline not executed in the back-
ground in the current shell environment.
lithist If set, and the cmdhist option is enabled, multi-line
commands are saved to the history with embedded newlines
rather than using semicolon separators where possible.
The shell sets this option if it is started as a login
shell (see INVOCATION above). The value may not be
If set, bash matches patterns in a case-insensitive
fashion when performing matching while executing case or
[[ conditional commands.
If set, bash allows patterns which match no files (see
Pathname Expansion above) to expand to a null string,
rather than themselves.
If set, the programmable completion facilities (see Pro-
grammable Completion above) are enabled. This option is
enabled by default.
If set, prompt strings undergo parameter expansion, com-
mand substitution, arithmetic expansion, and quote
removal after being expanded as described in PROMPTING
above. This option is enabled by default.
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 dis-
cover whether or not a shell is restricted.
If set, the shift builtin prints an error message when
the shift count exceeds the number of positional parame-
If set, the source (.) builtin uses the value of PATH to
find the directory containing the file supplied as an
argument. This option is enabled by default.
If set, the echo builtin expands backslash-escape
sequences by default.
Suspend the execution of this shell until it receives a SIGCONT
signal. A login shell cannot be suspended; the -f option can be
used to override this and force the suspension. The return sta-
tus is 0 unless the shell is a login shell and -f is not sup-
plied, or if job control is not enabled.
[ expr ]
Return a status of 0 (true) or 1 (false) depending on the evalu-
ation of the conditional expression expr. Each operator and op-
erand must be a separate argument. Expressions are composed of
the primaries described above under CONDITIONAL EXPRESSIONS.
test does not accept any options, nor does it accept and ignore
an argument of -- as signifying the end of options.
Expressions may be combined using the following operators,
listed in decreasing order of precedence. The evaluation
based on the number of arguments.
The expression is false.
The expression is true if and only if the argument is not
If the first argument is !, the expression is true if and
only if the second argument is null. If the first argu-
ment is one of the unary conditional operators listed
above under CONDITIONAL EXPRESSIONS, the expression is
true if the unary test is true. If the first argument is
not a valid unary conditional operator, the expression is
The following conditions are applied in the order listed.
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. The -a
and -o operators are considered binary operators when
there are three arguments. 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 argument. Other-
wise, the expression is false.
If the first argument is !, the result is the negation of
the three-argument expression composed of the remaining
arguments. Otherwise, the expression is parsed and eval-
uated according to precedence using the rules listed
5 or more arguments
The expression is parsed and evaluated according to
precedence using the rules listed above.
When used with test or [, the < and > operators sort lexico-
graphically using ASCII ordering.
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 (and there is a
single sigspec) or -, each specified signal is reset to its
original disposition (the value it had upon entrance to the
shell). If arg is the null string the signal 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 displayed. If no
arguments are supplied or if only -p is given, trap prints the
shopt builtin for details of its effect on the DEBUG trap. If a
sigspec is RETURN, the command arg is executed each time a shell
function or a script executed with the . or source builtins fin-
If a sigspec is ERR, the command arg is executed whenever a a
pipeline (which may consist of a single simple command), a list,
or a compound command returns a non-zero exit status, subject to
the following conditions. The ERR trap is not executed if the
failed command is part of the command list immediately following
a while or until keyword, part of the test in an if statement,
part of a command executed in a && or || list except the command
following the final && or ||, any command in a pipeline but the
last, or if the command's return value is being inverted using
!. These are the same conditions obeyed by the errexit (-e)
Signals ignored upon entry to the shell cannot be trapped or
reset. Trapped signals that are not being ignored are reset to
their original values in a subshell or subshell environment when
one is created. The return status is false if any sigspec is
invalid; otherwise trap returns true.
type [-aftpP] 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 that would be executed if name were speci-
fied as a command name, or nothing if ``type -t name'' would not
return file. The -P option forces a PATH search for each name,
even if ``type -t name'' would not return file. If a command is
hashed, -p and -P print the hashed value, which is not necessar-
ily 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. The -f option suppresses shell
function lookup, as with the command builtin. type returns true
if all of the arguments are found, false if any are not found.
ulimit [-HSTabcdefilmnpqrstuvx [limit]]
Provides control over the resources available to the shell and
to processes started by it, on systems that allow such control.
The -H and -S options specify that the hard or soft limit is set
for the given resource. A hard limit cannot be increased by a
non-root user once it is set; a soft limit may be increased up
to the value of the hard limit. If neither -H nor -S is speci-
fied, both the soft and hard limits are set. The value of limit
can be a number in the unit specified for the resource or one of
the special values hard, soft, or unlimited, which stand for the
-i The maximum number of pending signals
-l The maximum size that may be locked into memory
-m The maximum resident set size (many systems do not honor
-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)
-q The maximum number of bytes in POSIX message queues
-r The maximum real-time scheduling priority
-s The maximum stack size
-t The maximum amount of cpu time in seconds
-u The maximum number of processes available to a single
-v The maximum amount of virtual memory available to the
shell and, on some systems, to its children
-x The maximum number of file locks
-T The maximum number of threads
If limit is given, and the -a option is not used, limit is the
new value of the specified resource. 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 -T, -b, -n, and -u, which are unscaled values. The
return status is 0 unless an invalid option or argument is sup-
plied, 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 symbolic 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 sym-
bolic 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 supplied name is not a defined alias.
unset [-fv] [-n] [name ...]
For each name, remove the corresponding variable or function.
If the -v option is given, each name refers to a shell variable,
and that variable is removed. Read-only variables may not be
unset. If -f is specified, each name refers to a shell func-
tion, and the function definition is removed. If the -n option
is supplied, and name is a variable with the nameref attribute,
name will be unset rather than the variable it references. -n
has no effect if the -f option is supplied. If no options are
supplied, each name refers to a variable; if there is no vari-
waited for. If n is not given, all currently active child pro-
cesses are waited for, and the return status is zero. If the -n
option is supplied, wait waits for any job to terminate and
returns its exit status. 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 Bash-2.05a 2001 October 29 BASH-BUILTINS(7)
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