Comment by plesner

This is a fine introduction to automata-based regexps but the framing of comparing "good" automata with "bad" perl-style is misguided. Automata and perl-style regexps are different beasts and solve different problems. The problem seems to be one of terminology: the perl style should never have been called regexps. That's not what they are. It's a pattern language that happens to have a variant of regexps as a subset.