Believe it or not, this is a FAQ. And it's been asked here several times. You can find the answer in perlfaq4; it's the FIRST question in there.
Jeff japhy Pinyan,
P.L., P.M., P.O.D, X.S.:
Perl,
regex,
and perlhacker How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart