Handling extglob in library scripts that are sourced at login

Having posted a question about debugging a bash script, the solution involved setting the command shopt -s extglob.

I have been sourcing some library scripts at login for use interactively. I introspected the possibility of calling shopt -s extglob at the beginning of each file and unsetting at the end of each file.

It was explained that I could use the current status of a shopt flag. The command shopt -p extglob also outputs a string one can eval to get back the current setting.

Can I get some further elaborations and some tests and useful implementations I can check out?

The code would look something like this:

savestate=$(shopt -p extglob) # save old extglob setting
shopt -s extglob # enable extglob
# do something that requires extended globbing
eval "$savestate" # restore the old extglob setting

You could put the first two lines at the beginning of the script, and the last line at the end. The rest of the script would be the "do something" part.

> I introspected the possibility of calling shopt -s extglob at the beginning of each file and unsetting at the end of each file.

You could write a function, something like:

enable_extlob(){ 
  if ! shopt -q extglob; then
    shopt -s extglob
  fi
}

disable_extglob(){
  if shopt -q extglob; then
    shopt -u extglob
  fi
}

For both start and end of the script/files, something like

extglob_boolean(){ 
  if ! shopt -q extglob; then
     shopt -s extglob
  else
    shopt -u extglob
  fi
}

• Add that at the beginning and at the end of your script/files.

• The function checks if extglob is NOT on, enable it otherwise disable it.

• The downside of this is if the script you're calling needs extglob like what @Barmar said from his comment post. So make sure you really need this.