Linux man pages : alias (1)
bash, :, ., [, alias, bg, bind, break, builtin, cd, command, compgen,
complete, continue, declare, dirs, disown, echo, enable, eval, exec,
exit, export, fc, fg, getopts, hash, help, history, 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, wait - bash built-in commands, see
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
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, file
names in PATH are used to find the directory containing file-
name. 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
Resume the 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
run when job control is disabled or, when run with job control
enabled, if jobspec was not found or started without job con-
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, bind a key
sequence to a readline function or macro, or set a readline
variable. Each non-option argument is a command as it would
appear in .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.
-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-
-S Display readline key sequences bound to macros and the
strings they output.
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
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 the shell is not executing
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 func-
tionality 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 [-L|-P] [dir]
Change the current directory to dir. The variable HOME is the
default dir. The variable CDPATH defines the search path for
the directory containing dir. 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 fol-
lowed. An argument of - is equivalent to $OLDPWD. The return
value is true if the directory was successfully changed; false
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 file name
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
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
various shell variables set by the programmable completion
facilities, while available, will not have useful values.
The matches will be generated in the same way as if the pro-
grammable completion code had generated them directly from a
completion specification with the same flags. If word is speci-
fied, only those completions matching word will be displayed.
The return value is true unless an invalid option is supplied,
or no matches were generated.
complete [-abcdefgjksuv] [-o comp-option] [-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 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-
The process of applying these completion specifications when
word completion is attempted is described above under Pro-
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:
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 or suppressing trailing spaces). Intended
to be used with shell functions.
nospace Tell readline not to append a space (the
default) to words completed at the end of the
The action may be one of the following to generate a
list of possible completions:
alias Alias names. May also be specified as -a.
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 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.
The filename expansion pattern globpat is expanded to
generate the possible completions.
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 com-
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 it finishes, the possible com-
pletions are retrieved from the value of the COMPREPLY
filterpat is a pattern as used for filename expansion.
It is applied to the list of possible completions gener-
ated by the preceding options and arguments, and each
completion matching filterpat is removed from the list.
A leading ! in filterpat negates the pattern; in this
case, any completion not matching filterpat is removed.
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
other options have been applied.
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.
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 [-afFirtx] [-p] [name[=value]]
typeset [-afFirtx] [-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, additional options are ignored. The -F option inhibits
the display of function definitions; only the function name and
attributes are printed. The -F option implies -f. The follow-
ing options can be used to restrict output to variables with the
specified attribute or to give variables attributes:
-a Each name is an array variable (see Arrays above).
-f Use function names only.
-i The variable is treated as an integer; arithmetic evalua-
tion (see ARITHMETIC EVALUATION ) 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.
-t Give each name the trace attribute. Traced functions
inherit the DEBUG trap from the calling shell. The trace
attribute has no special meaning for variables.
-x Mark names for export to subsequent commands via the
Using `+' instead of `-' turns off the attribute instead, with
the exception that +a may not be used to destroy an array vari-
able. When used in a function, makes each name local, as with
the local command. 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 readonly status for a read-
only variable, an attempt is made to turn off array status for
an array variable, 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
-n Displays the nth entry counting from the right of the
list shown by dirs when invoked without options, starting
-c Clears the directory stack by deleting all of the
-l Produces a longer listing; 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.
The return value is 0 unless an invalid option is supplied or n
indexes beyond the end of the 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 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 always 0. If -n is specified, the trailing
newline is suppressed. If the -e option is given, interpreta-
tion of the following backslash-escaped characters is enabled.
The -E option disables the interpretation of these escape char-
acters, 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 sequences:
\a alert (bell)
\c suppress trailing newline
\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)
\nnn the eight-bit character whose value is the octal value
nnn (one to three octal digits)
\xHH the eight-bit character whose value is the hexadecimal
value HH (one or two hex digits)
enable [-adnps] [-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-
plied, the list printed includes all builtins, with an indica-
tion 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 com-
mand. This command is then read and executed 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 supplied, the shell places a dash at the begin-
ning 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 supplied, the shell passes name as the
zeroth argument to the executed command. If command cannot be
executed 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 can-
not be executed. If command is not specified, any redirections
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 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 encoun-
tered, 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 commands from first
to last is selected from the history list. First and last may
be specified as a string (to locate the last command beginning
with that string) or as a number (an index into the history
list, where a negative number is used as an offset from the cur-
rent 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 spec-
ified it is set to the previous command for editing and -16 for
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, 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 typing ``r cc'' runs the last command
beginning with ``cc'' and typing ``r'' re-executes the last com-
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-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
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 [-lr] [-p filename] [-dt] [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 locations. The -d 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 arguments are
supplied with -t, the name is printed before the hashed full
pathname. The -l option causes output to be displayed in a for-
mat that may be reused as input. If no arguments are given, or
if only -l is supplied, 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 information
displayed to a short usage synopsis. 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 filename is supplied, it is
used as the name of the history file; if not, the value of HIST-
FILE is used. Options, if supplied, have the following mean-
-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 use them as the
-w Write the current history to the history file, overwrit-
ing the history file's contents.
-p Perform history substitution on the following args and
display the result on the standard 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 single 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 writing the history file, an
invalid offset is supplied 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.
-p List only the process ID of the job's process group
-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 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 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 sig-
nals corresponding to the arguments are listed, and the return
status is 0. The exit_status argument to -l is a number speci-
fying either a signal number or the exit status of a process
terminated by a signal. kill returns true if at least one sig-
nal 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). 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,
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 follow-
+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
-n Suppresses the normal change of directory when removing
directories from the stack, so that only the stack is
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 format [arguments]
Write the formatted arguments to the standard output 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 output, and for-
mat specifications, each of which causes printing of the next
successive argument. In addition to the standard printf(1) for-
mats, %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
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] [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 arguments, exchanges the top two directories
and returns 0, unless the directory stack is empty. Arguments,
if supplied, have the following meanings:
+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
dir Adds dir to the directory stack at the top, making it the
new current working directory.
If the pushd command is successful, a dirs is performed as well.
If the first form is used, pushd returns 0 unless the cd to dir
fails. With the second form, pushd returns 0 unless the 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
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] [-u fd] [-t timeout] [-a aname] [-p prompt] [-n nchars] [-d
delim] [name ...]
One line is read from the standard input, or from the file
descriptor fd supplied as an argument to the -u option, and the
first word is assigned to the first name, the second word to the
second name, and so on, with leftover words and their interven-
ing separators assigned to the last name. If there are fewer
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. The backslash character (\) may be
used to remove any special meaning for the next character read
and for line continuation. Options, if supplied, have the fol-
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 returns after reading nchars characters rather than
waiting for a complete line of input.
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 is not read within timeout seconds. This
option has no effect if read is not reading input from
the terminal or a pipe.
-u fd Read input from file descriptor fd.
If no names are supplied, the line read is assigned to the vari-
able REPLY. The return code is zero, unless end-of-file is
encountered, read times out, or an invalid file descriptor is
supplied as the argument to -u.
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 displayed 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.
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 function body. If used outside a function, but
during execution of a script by the . (source) command, it
causes the shell to stop executing that script and return either
n or the exit status of the last command executed within the
script as the exit status of the script. If used 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 mean-
-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 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 !. A trap on ERR, if set, is executed before the
-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). Background pro-
cesses run in a separate process group and a line con-
taining their exit status is printed upon their comple-
-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.
errexit Same as -e.
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
keyword Same as -k.
monitor Same as -m.
Same as -C.
noexec Same as -n.
noglob Same as -f. nolog Currently ignored.
notify Same as -b.
nounset Same as -u.
onecmd Same as -t.
Same as -P.
posix Change the behavior of bash where the default
operation differs from the POSIX 1003.2 standard
to match the standard (posix mode).
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
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
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 supplied, 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
-t Exit after reading and executing one command.
-u Treat unset variables as an error when performing param-
eter 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.
-x After expanding each simple command, display the
expanded value of PS4, followed by the command and its
-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 >.
-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 logical
chain of directories when performing commands which
change the current directory.
-- 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 variables controlling optional shell behav-
ior. With no options, or with the -p option, a list of all set-
table 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 fol-
-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, the dis-
play is limited to those options which are set or unset,
respectively. Unless otherwise 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:
If set, an argument to the cd builtin command 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 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 file name 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 checks the window size after each command
and, if necessary, updates the values of LINES and
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.
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-
extglob If set, the extended pattern matching features described
above under Pathname Expansion are enabled.
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.
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, 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 dis-
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.
If set, bash matches filenames in a case-insensitive
fashion when performing pathname expansion (see Pathname
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 variable and parameter
expansion 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. The -f option says not to complain if this is a login
shell; just suspend anyway. The return status is 0 unless the
shell is a login shell and -f is not supplied, or if job control
is not enabled.
[ expr ]
Return a status of 0 or 1 depending on the evaluation 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 precedence.
! expr True if expr is false.
( expr )
Returns the value of expr. This may be used to override
the normal precedence of operators.
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.
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
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 argument. Otherwise, the expression is false.
The -a and -o operators are considered binary operators
in this case.
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.
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 speci-
fied signals are reset to their original values (the values they
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 list of commands associated 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
command 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). If a sigspec is ERR, the command arg
is executed whenever a simple command has a non-zero exit sta-
tus. The ERR trap is not executed if the failed command 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 !. The -l option causes the shell to print a list of signal
names and their corresponding numbers. Signals ignored upon
entry to the shell cannot be trapped or reset. Trapped signals
are reset to their original values in a child process when it is
created. The return status is false if 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, 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. The -f option suppresses shell func-
tion lookup, as with the command builtin. type returns true if
any of the arguments 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 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 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. 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 current hard
limit, the current soft limit, and no limit, respectively. If
limit is omitted, the current value of the soft limit of the
resource is printed, unless the -H option is given. When more
than one resource is specified, the limit name and unit are
printed before the value. Other options are interpreted as fol-
-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
-v The maximum amount of virtual memory available to the
If limit is given, it is the new value of the specified resource
(the -a option is display only). If no option is given, then -f
is assumed. Values are in 1024-byte increments, except for -t,
which is in seconds, -p, which is in units of 512-byte blocks,
and -n and -u, which are unscaled values. The return status is
0 unless an invalid option or argument is supplied, 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] [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 variable. 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 environment passed to subsequent
commands. If any of RANDOM, 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 for the specified process and return its termination sta-
tus. n may be a process ID or a job specification; if a job
spec is given, all processes in that job's pipeline are waited
for. If n is not given, all currently active child processes
are waited for, and the return status is zero. If n specifies a
non-existent process or job, the return status is 127. Other-
wise, the return status is the exit status of the last process
or job waited for.
GNU Bash-2.05a 2001 November 27 BASH_BUILTINS(1)