Hey, I'm glad I was wrong (well, on some points). That's pretty good actually (as knowledge of m// and y// escaped me for a long time when I started learning perl) and that is how I would've approached it about two years ago. In terms of efficiency, and this is without any benchmarks of this particular problem, but from previous knowledge, your best bet would be to use y// aka tr//.

 
___crazyinsomniac_______________________________________
Disclaimer: Don't blame. It came from inside the void
perl -e "$q=$_;map({chr unpack qq;H*;,$_}split(q;;,q*H*));print;$q/$q;"