I often generate regexes on the fly. Have a look at the regex that matches URLs at http://www.foad.org/~abigail/Perl/url3.regex, which was generated by the program found at http://www.foad.org/~abigail/Perl/url3.pl. And then there's the Regexp::Common module as found on CPAN. Many of its regexes are generated.

Abigail