bash: The Set Builtin
4.3.1 The Set Builtin
---------------------
This builtin is so complicated that it deserves its own section. 'set'
allows you to change the values of shell options and set the positional
parameters, or to display the names and values of shell variables.
'set'
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 may be reused as input for
setting or resetting the currently-set variables. Read-only
variables cannot be reset. In POSIX mode, only shell variables are
listed.
When options are supplied, they set or unset shell attributes.
Options, if specified, have the following meanings:
'-a'
Each variable or function that is created or modified is given
the export attribute and marked for export to the environment
of subsequent commands.
'-b'
Cause the status of terminated background jobs to be reported
immediately, rather than before printing the next primary
prompt.
'-e'
Exit immediately if a pipeline (
Pipelines), which may
consist of a single simple command (Simple Commands),
DONTPRINTYET a list (Lists), or a compound command (*noteCompound
DONTPRINTYET a list (Lists), or a compound command (Compound
Commands) returns a non-zero status. The shell does not
exit if the command that fails is part of the command list
immediately following a 'while' or 'until' keyword, part of
the test in an 'if' statement, part of any 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 status is being inverted with '!'. If a
compound command other than a subshell returns a non-zero
status because a command failed while '-e' was being ignored,
the shell does not exit. A trap on 'ERR', if set, is executed
before the shell exits.
This option applies to the shell environment and each subshell
environment separately (Command Execution
Environment), 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 filename expansion (globbing).
'-h'
Locate and remember (hash) commands as they are looked up for
execution. This option 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'
Job control is enabled (Job Control). All processes
run in a separate process group. When a background job
completes, the shell prints a line containing its exit status.
'-n'
Read commands but do not execute them. This may be used to
check a script for syntax errors. This option is ignored by
interactive shells.
'-o OPTION-NAME'
Set the option corresponding to OPTION-NAME:
'allexport'
Same as '-a'.
'braceexpand'
Same as '-B'.
'emacs'
Use an 'emacs'-style line editing interface (
Command Line Editing). This also affects the editing
interface used for 'read -e'.
'errexit'
Same as '-e'.
'errtrace'
Same as '-E'.
'functrace'
Same as '-T'.
'hashall'
Same as '-h'.
'histexpand'
Same as '-H'.
'history'
Enable command history, as described in Bash
History Facilities. This option is on by default in
interactive shells.
'ignoreeof'
An interactive shell will not exit upon reading EOF.
'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. 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
(Bash POSIX Mode). This is intended to make Bash
behave as a strict superset of that standard.
'privileged'
Same as '-p'.
'verbose'
Same as '-v'.
'vi'
Use a 'vi'-style line editing interface. This also
affects the editing interface used for 'read -e'.
'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',
'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 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.
'-t'
Exit after reading and executing one command.
'-u'
Treat unset variables and parameters other than the special
parameters '@' or '*' as an error when performing parameter
expansion. An error message will be written to the standard
error, and a non-interactive shell will exit.
'-v'
Print shell input lines as they are read.
'-x'
Print a trace of simple commands, 'for' commands, 'case'
commands, 'select' commands, and arithmetic 'for' commands and
their arguments or associated word lists after they are
expanded and before they are executed. The value of the 'PS4'
variable is expanded and the resultant value is printed before
the command and its expanded arguments.
'-B'
The shell will perform brace expansion (Brace
Expansion). This option is on by default.
'-C'
Prevent output redirection using '>', '>&', and '<>' from
overwriting existing files.
'-E'
If set, any trap on 'ERR' is inherited by shell functions,
command substitutions, and commands executed in a subshell
environment. The 'ERR' trap is normally not inherited in such
cases.
'-H'
Enable '!' style history substitution (History
Interaction). This option is on by default for interactive
shells.
'-P'
If set, do not resolve symbolic links when performing commands
such as 'cd' which change the current directory. The physical
directory is used instead. By default, Bash follows the
logical chain of directories when performing commands which
change the current directory.
For example, 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, then:
$ cd /usr/sys; echo $PWD
/usr/local/sys
$ cd ..; pwd
/usr/local
'-T'
If set, any trap on 'DEBUG' and 'RETURN' are inherited by
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 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.
Using '+' rather than '-' causes these options to be turned off.
The options can also be used upon invocation of the shell. The
current set of options may be found in '$-'.
The remaining N ARGUMENTS are positional parameters and are
assigned, in order, to '$1', '$2', ... '$N'. The special parameter
'#' is set to N.
The return status is always zero unless an invalid option is
supplied.
Info Catalog
bash: Modifying Shell Behavior
bash: The Shopt Builtin