It's also a good idea to use \w instead of
[a-z], even if that also catches upper case
and underscores. Random escaped regexp characters are much
harder to sync up in your mind than character ranges. So
your regexp looks like this:
By the way, obfuscation is fun because it forces you to learn the more 'obscure' parts of Perl. Half the fun is trying to figure out how it works, and then diving into the library to fill in the gaps. You can find out about all the predefined variables this way too.