How to always execute a command when a shell script function finishes?

Question

I need to write a zsh function with multiple exit points and execute the same clean-up command at every one of them:

function foo {
    if ... ; then
        ...
        run_cleanup
        return
    elif ... ; then
        some_command || (run_cleanup ; return 1)
    else
        ...
    fi
    ...
    run_cleanup
}

Is there a way to avoid repeating run_cleanup at every exit point (which is very error-prone)?

Answer 1

The solution is to use trap EXIT, which registers a clean-up action to be run automatically when the function finishes:

function foo {
    trap run_cleanup EXIT
    if ... ; then
        ...
        return
    elif ... ; then
        some_command || return 1
    else
        ...
    fi
    ...
}

Note that using trap ... EXIT in functions is zsh-specific:

If sig is 0 or EXIT and the trap statement is executed inside the body of a function, then the command arg is executed after the function completes. ... If sig is 0 or EXIT and the trap statement is not executed inside the body of a function, then the command arg is executed when the shell terminates.

In bash the command is trap ... RETURN.

If a sigspec is EXIT (0) the command arg is executed on exit from the shell ... If a sigspec is RETURN, the command arg is executed each time a shell function or a script executed with the . or source builtins finishes executing.