Wow, that's an impressive module. Thanks for the tip on that. Out of curiosity, I benchmarked it against the hash solution, and the hash is faster of course, but only 13 times faster. As you say, there will be times when you can't use a standard hash lookup, so something like this is a good alternative. I had it print out the regex it built for 10,000 different keys (all 7-char random lowercase letters) and it was huge, yet it only took a little over a second to compare it to 50,000 different strings on my system. The Perl regex machine is amazing.