[hn92726819]

> I tend to skip the -u flag as bash scripts often interact with global variables that are set outside my scripts.

What? If globals are set outside the scripts, -u still works. If the author means they may or may not be defined outside the script, the ${VAR:-} construct allows it to expand to nothing if unset (just throw VAR=${VAR:-} at the top if you don't want to edit the body)

Also, I do not like the function return based on error code:

    function ... {
      ...
      (( check_level >= current_level ))
    }

Unless I'm reading this wrong, this is a bad idea if using set -e. This is a function and it should instead:

    return $(( check_level < current_level ))