Make shopt change local to function

Question

I\'m trying to write a bash function that uses nocasematch without changing the callers setting of the option. The function definition is:

is_he         


        

Answer 1

Use a RETURN trap

Commands specified with an RETURN trap are executed before execution resumes after a shell function ... returns...

The -p option [to shopt] causes output to be displayed in a form that may be reused as input.

– https://www.gnu.org/software/bash/manual/bash.html

foobar() {
    trap "$(shopt -p extglob)" RETURN
    shopt -s extglob

    # ... your stuff here ...

}

For test

foobar() {
    trap "$(shopt -p extglob)" RETURN
    shopt -s extglob

    echo "inside foobar"
    shopt extglob # Display current setting for errexit option
}

main() {
    echo "inside main"
    shopt extglob # Display current setting for errexit option
    foobar
    echo "back inside main"
    shopt extglob # Display current setting for errexit option
}

Test

$ main
inside main
extglob         off
inside foobar
extglob         on
back inside main
extglob         off

Variation: To reset all shopt options, change the trap statement to:

trap "$(shopt -p)" RETURN

Variation: To reset all set options, change the trap statement to:

trap "$(set +o)" RETURN

Note: Starting with Bash 4.4, there's a better way: make $- local.

Variation: To reset all set and all shopt options, change the trap statement to:

trap "$(set +o)$(shopt -p)" RETURN

NOTE: set +o is equivalent to shopt -p -o:

+o Write the current option settings to standard output in a format that is suitable for reinput to the shell as commands that achieve the same options settings.

– Open Group Base Specifications Issue 7, 2018 edition > set