Create a shell variable and set it equal to some value.

      set [--abefhkmnptuvxBCHP] [-o option] [arg ...]

   -a   Automatically mark variables and functions which are modified or created for export to
        the environment of subsequent commands.
   -b   Report the status of terminated background jobs immediately, 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) exits with 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 a && or || list, or if the command's return value is being inverted via !.  A
        trap on ERR, if set, is executed before the shell exits.
   -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).  Background processes run in a
        separate process group and a line containing their exit status is printed upon their
   -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.
   -o option-name
                 The option-name can be one of the following:
                 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.  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 (posix mode).
                 privileged  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 output.

   -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 ids.
   -t      Exit after reading and executing one command.
   -u      Treat unset variables as an error when performing parameter 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, for command, case  command,  select  command,  or
           arithmetic for command, display the expanded value of PS4, followed by the command and
           its expanded arguments or associated word list.
   -B      The shell performs brace expansion  (see  Brace  Expansion  above).   This  is  on  by
   -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 redirection
           operator >| instead of >.
   -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. This option is on by default when the shell is
   -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.
   -T      If  set,  any traps 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 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 positional
           parameters remain unchanged.

The options are off by default unless otherwise noted. Using + rather than - causes these options to be turned off.

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.

Read-only variables cannot be reset.
In posix mode, only shell variables are listed.
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, ...

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.
set is a bash builtin command.

“Have no friends not equal to yourself” ~ Confucious (Analects)


echo - Display text (or variables) on screen
unset - Remove variable or function names

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