set

Manipulate shell variables and functions.

Syntax
      set [--abBCefhHkmnpPtuvx] [-o option] [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. When options are supplied, they set or unset shell attributes.

Options

Using + rather than - will cause the option to be turned off. 

   -a  Mark variables which are modified or created for export. -o allexport     

   -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 may be used
       to check a script for syntax errors. 
       This option is ignored by interactive shells. -o noexec

   -o option-name
          Set the option corresponding to `option-name'
          The `option-names' are listed above and below (in bold)      

          emacs     : Use an emacs-style line editing interface . 
          history   : Enable command history,
                      this option is on by default in interactive shells. 
          ignoreeof : An interactive shell will not exit upon reading EOF. 
          posix     : Change the behavior of Bash to match the POSIX 1003.2 standard. 
          vi        : Use a vi-style line editing interface. 

   -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.

Examples

Set the variable 'mydept' equal to 'Sales' :

 mydept=Sales

To make the change permanent:

 export mydept

Symbolic Links

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

Debugging part of a script:

set -x			# activate debugging 
# your commands go here...
set +x # stop debugging

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.

set is a POSIX `special' builtin. The return status is always zero unless an invalid option is supplied.

"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

Related bash commands:

env
- Display, set, or remove environment variables
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
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 NT environment variables


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