How do I control options for the current bash shell session?

indigowinged

shopt built-in is used with the bash shell , Where as set built-in was traditionally used with other shells, but the functionality still exists in bash. As with both if you need to set options permanently store them in your .bashrc file.

       shopt [-pqsu] [-o] [optname ...]
              Toggle the values of settings controlling optional shell  behav‐
              ior.   The settings can be either those listed below, or, if the
              -o option is used, those available with the -o option to the set
              builtin command.  With no options, or with the -p option, a list
              of all settable options is  displayed,  with  an  indication  of
              whether  or  not each is set.  The -p option causes output to be
              displayed in a form that may be reused as input.  Other  options
              have the following meanings:
              -s     Enable (set) each optname.
              -u     Disable (unset) each optname.
              -q     Suppresses  normal output (quiet mode); the return status
                     indicates whether the optname is set or unset.  If multi‐
                     ple  optname arguments are given with -q, the return sta‐
                     tus is zero if all optnames are enabled; non-zero  other‐
                     wise.
              -o     Restricts  the  values of optname to be those defined for
                     the -o option to the set builtin.

              If either -s or -u is used  with  no  optname  arguments,  shopt
              shows  only  those options which are set or unset, respectively.
              Unless otherwise noted, the shopt options are  disabled  (unset)
              by default.

              The  return  status when listing options is zero if all optnames
              are enabled, non-zero  otherwise.   When  setting  or  unsetting
              options,  the  return  status is zero unless an optname is not a
              valid shell option.

shopt used to set and unset options for the current shell session

DIsplay current settings.

$ shopt
autocd          off
cdable_vars     off
cdspell         off
checkhash       off
checkjobs       off
checkwinsize    on
cmdhist         on
compat31        off
compat32        off
compat40        off
compat41        off
compat42        off
compat43        off
complete_fullquote      on
direxpand       off
dirspell        off
dotglob         off
execfail        off
expand_aliases  on
extdebug        off
extglob         on
extquote        on
failglob        off
force_fignore   on
globasciiranges off
globstar        off
gnu_errfmt      off
histappend      on
histreedit      off
histverify      off
hostcomplete    off
huponexit       off
inherit_errexit off
interactive_comments    on
lastpipe        off
...
...
...

Enable an option. Using the -s option.

$ shopt -s mailwarn
$ shopt mailwarn
mailwarn        on

Disable an option. Using the -u option

$ shopt mailwarn
mailwarn        on
$ shopt -u mailwarn
$ shopt mailwarn
mailwarn        off

To read about all the shopt settings check the bash man page.