$SIG{__DIE__} can be used to automatically call code when the program gets a DIE signal. it doesn't generate one. You might want exit or die instead.

As for monitoring the variable, as I understand it the most "straightforward" way to implement this is to tie the variable to an object that monitors the variable's value whenever it's set. Take a look at the perltie documentation .

updated: fixed typo, thanks gaal