Regular expressions were simple and straightforward tools until Perl. They were originally intended to be equivalent to finite state machines, but, thanks to Pe

Regular expressions were simple and straightforward tools until Perl. They were originally intended to be equivalent to finite state machines, but, thanks to Perl, you can write regexes that may or may not halt, and no one can can ever prove one way or the other. If you want to take the best parts of regexes and leave the rest, don't bother with all of the Perl extensions and just study the basics.