bash-hackers-wiki/original_source/commands/builtin/set.txt

====== The set builtin command ======

FIXME incomplete - text, examples, maybe extended description

===== Synopsis =====

<code>
set [--abefhkmnptuvxBCHP] <-o OPTIONNAME> [-][--] <POSPARAMS>
</code>

===== Description =====

''set'' is primarily made to
  * set the positional parameters (see [[scripting:posparams | handling positional parameters]]) to ''<POSPARAMS>''
  * set shell attributes with short options (see below)
  * set shell attributes with long option names (see below)

Without any options, ''set'' displays all shell- and environment-variables (only is POSIX-mode) in a re-usable format ''NAME=VALUE''.

==== Attributes ====

All attributes below can be switched on using ''-X'' and switched off using ''+X''. This is done because of the historical meaning of the ''-'' to set flags (true for most commands on UNIX(r)).

^Flag^Optionname^Description^
|''-a''|''allexport''|Automatically mark new and altered variables to be exported to subsequent environments.|
|''-b''|''notify''|Don't wait for the next prompt to print when showing the reports for a terminated background job (only with job control)|
|''-e''|''errexit''|When set, the shell exits when a simple command in a command list exits non-zero (''FALSE''). This is not done in situations, where the exit code is already checked (''if'', ''while'', ''until'', ''<nowiki>||</nowiki>'', ''<nowiki>&&</nowiki>'')|
|''-f''|''noglob''|Disable [[syntax:expansion:globs | pathname expansion]] (globbing)|
|''-h''|''hashall''|Remembers the location of commands when they're called (hashing). Enabled by default.|
|''-k''|''keyword''|Allows to place environment-assignments everywhere in the commandline, not only infront of the called command.|
|''-m''|''monitor''|**Monitor mode**. With job control, a short descriptive line is printed when a backgroud job ends. Default is "on" for interactive shells (with job control).|
|''-n''|''noexec''|Read and parse but **do not execute commands** - useful for checking scripts for syntax errors. Ignored by interactive shells.|
|''-o''| |Set/unset attributes with long option names, e.g. ''set -o noglob''. The long option names are in the second column of this table. If no option name is given, all options are printed with their current status.|
|''-p''|''privileged''|Turn on privileged mode.|
|''-t''|''onecmd''|Exit after reading and executing **one** command.|
|''-u''|''nounset''|Treat unset variables as an error when performing parameter expansion. Non-interactive shells exit on this error.|
|''-v''|''verbose''|Print shell input lines as they are read - useful for debugging.|
|''-x''|''xtrace''|Print commands just before execution - with all expansions and substitutions done, and words marked - useful for debugging.|
|''-B''|''braceexpand''|The shell performs [[syntax:expansion:brace | brace expansion]] This is on by default.|
|''-C''|<BOOKMARK:tag_noclobber>''noclobber''|Don't overwrite files on redirection operations. You can override that by specifying the ''>|'' redirection operator when needed. See [[syntax:redirection | redirection]]|
|''-E''|''errtrace''|''ERR''-traps are inherited by by shell functions, command substitutions, and commands executed in a subshell environment.|
|''-H''|''histexpand''|Enable ''!''-style history expansion. Defaults to ''on'' for interactive shells.|
|''-P''|''physical''|Don't follow symlinks when changing directories - use the physical filesystem structure.|
|''-T''|''functrace''|''DEBUG''- and ''RETURN''-traps are inherited by subsequent environments, like ''-E'' for ''ERR'' trap.|
|''-''| |"End of options" - all following arguments are assigned to the positional parameters, even when they begin with a dash. ''-x'' and ''-v'' options are turned off. Positional parameters are unchanged (unlike using ''<nowiki>--</nowiki>''!) when no further arguments are given.|
|''<nowiki>--</nowiki>''| |If no arguments follow, the positional parameters are unset. With arguments, the positional parameters are set, even if the strings begin with a ''-'' (dash) like an option.|
^^Long options usable with ''-o'' without a short equivalent ^^
| |''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'' option.|
| |''history''|If set, command historization is done (enabled by default on interactive shells)|
| |''ignoreeof''|The effect is as if the shell command ''IGNOREEOF=10'' had been executed. See [[syntax:shellvars | shell variables]].|
| |''nolog''|**(currently ignored)**|
| |''pipefail''|If set, the exit code from a pipeline is different from the normal ("last command in pipeline") behaviour: ''TRUE'' when no command failed, ''FALSE'' when something failed (code of the rightmost command that failed)|
| |''posix''|When set, Bash runs in POSIX mode.|
| |''vi''|Enables a ''vi''-style command line editing interface.|

===== Examples =====

Tag a part of a shell script to output debugging information (''-x''):
<code bash>
#!/bin/bash
...
set -x # on
...
set +x # off
...
</code>

===== Portability considerations =====

''set'' and its basic behaviour and options are specified by POSIX(r). However, options that influence Bash-specific things are not portable, naturally.

===== See also =====

  * Internal: [[commands:builtin:shopt | The shopt builtin command]]