Change the value of a shell option and set the positional parameters, or display the names and values of shell variables.
Syntax
set [-abefhkmnptuvxBCEHPT] [-o option-name] [argument …]
set [+abefhkmnptuvxBCEHPT] [+o option-name] [argument …]
If no options or arguments are supplied, set displays the names and values of all shell variables and functions, sorted according to the current locale, in a format that can be reused as input. When options are supplied, they set or unset shell attributes.
Options
Using + rather than - will cause the option to be turned off.
-a Automatically Mark variables which are modified or created for export. -o allexport
See the export page for an example.
-b Cause the status of terminated background jobs to be
reported immediately, rather than before printing the
next primary prompt. -o notify
-B The shell will perform brace expansion.
This option is on by default. -o braceexpand
-C Prevent output redirection using '>', '>&',
and '<>' from overwriting existing files. -o noclobber
-e Exit immediately if a simple command exits with a non-zero status, unless
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 status
is being inverted using !. -o errexit
-f Disable file name generation (globbing). -o noglob
-h Locate and remember (hash) commands as they are looked
up for execution. This option is enabled by default. -o hashall
-H Enable '!' style history substitution
This option is on by default for interactive shells. -o histexpand
-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. -o keyword
-m Job control is enabled. -o monitor
-n Read commands but do not execute them; this can be used
to check a script for syntax errors.
This option is ignored by interactive shells. -o noexec
-o 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 output.
-o option-name
Set the option corresponding to 'option-name'
The 'option-names' are listed below (and above in bold):
allexport Same as -a.
braceexpand Same as -B.
emacs Use an emacs-style command line editing interface. This is enabled by default
when the shell is interactive, unless the shell is started with --noediting
errtrace Same as -E.
functrace Same as -T.
errexit Same as -e.
hashall Same as -h.
histexpand Same as -H.
history Enable command history, as described above under HISTORY. This option is on
by default in interactive shells.
ignoreeof The effect is as if the shell command 'IGNOREEOF=10' had been executed
keyword Same as -k.
monitor Same as -m.
noclobber 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.
physical Same as -P.
pipefail 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.
By default, pipelines only return a failure if the last command errors.
When used in combination with set -e, pipefail will make a script exit if any command
in a pipeline errors.
posix Change the behavior of bash where the default operation differs from the POSIX
standard to match the standard (posix mode).
privileged Same as -p.
verbose Same as -v.
vi Use a vi-style command line editing interface.
xtrace Same as -x.
-p Turn on privileged mode.
In this mode, the $BASH_ENV and $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 ids. -o privileged
-P If set, do not follow symbolic links when performing commands.
The physical directory is used instead. -o physical
-t Exit after reading and executing one command. -o onecmd
-u Treat unset variables as an error when performing
parameter expansion. An error message will be written
to the standard error, and a non-interactive shell will exit. -o nounset
-v Print shell input lines as they are read. -o verbose
-x Print a trace of simple commands and their arguments
after they are expanded and before they are executed. -o xtrace
-- If no arguments follow this option, then the positional parameters are unset.
Otherwise, the positional parameters are set to the arguments,
even if some of them begin with a '-'.
- Signal the end of options, cause all remaining arguments to be
assigned to the positional parameters. The '-x' and '-v'
options are turned off. If there are no arguments, the positional parameters
remain unchanged.
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.
When options are specified, they set or unset shell attributes.
If no options are specified, then the set command will set the positional parameters $1, $2 etc.
Read-only variables cannot be reset.
By default, unset variables are evaluated as an empty string which can have unexpected and undesirable effects.
When writing and debugging shell scripts it is good practice to set both -e and -u so that the script will exit on an Error or if an Unset variable is referenced : set -eu
The options can also be specified as arguments to an invocation of the shell. The current set of options may be found in $-.
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.
The special parameter # is set to N.
By default, Bash follows the logical chain of directories when performing commands which change the current directory. e.g.
If '/usr/sys' is a symbolic link to '/usr/local/sys' then: $ cd /usr/sys; echo $PWD /usr/sys $ cd ..; pwd /usr If set -P is on (do not follow symbolic links), then: $ cd /usr/sys; echo $PWD /usr/local/sys $ cd ..; pwd /usr/local
In posix mode, only shell variables are listed.
The output is sorted according to the current locale.
The return status is always zero unless an invalid option is supplied.
This is a BASH shell builtin, to display your local syntax from the bash prompt type: help set
Set both -e and -u so that the script will exit on an Error or if an Unset variable is referenced. This is good practice when writing and debugging shell scripts.
#!/bin/bash
# an example bash script
set -eu
Set pipefail so that any failure in a pipeline will return an error:
#!/bin/bash
set -o pipefail
Set both -e and -u and pipefail:
#!/bin/bash
set -eu -o pipefail
Set all of the above for maximum error trapping within a script:
#!/bin/bash
set -euo pipefail
Set the positional parameters $1, $2 and $3 to Alpha Beta and Gamma, the '--' ensures that nothing which follows will be interpreted as an option:
$ set -- Alpha Beta Gamma
$ echo $1
Alpha
$ echo $2
Beta
$ echo $3
Gamma
Turn ON the allexport option:
set -o allexport
Turn OFF the allexport option:
set +o allexport
Set the shell variable 'MYDEPT' equal to 'Sales':
MYDEPT=Sales
echo $MYDEPT
To make the change permanent, you can export this as an environment variable:
export $MYDEPT
Debug part of a script:
set -x # Activate debugging
# your commands go here...
set +x # stop debugging
Disable strict mode while you source a file:
set +u # Disable variable strictness
source ss64file.env
set -u # re-enable variable strictness
“I can understand there are things like shadows they need to fix after a shoot, but it’s unfair to represent an image of yourself if it’s not true. They're gonna see what you look like on film anyway, so why try to cover all your wobbly bits in a photo?” ~ Emily Blunt
env - Display, set, or remove environment variables.
export - Set an environment variable.
groups - Print group names a user is in.
hostname - Print or set system name.
id - Print user and group id’s.
logname - Print current login name.
printenv - Print environment variables.
readonly - Mark variables/functions as readonly.
Bash shell variables
shift - Shift positional parameters.
shopt - Shell Options.
uname - Print system information.
users - Print login names of users currently logged in.
unset - Remove variable or function names.
who - Print who is currently logged in.
Equivalent Windows commands: SET - Display, set, or remove Windows environment variables.