or download this
WARNING: Once Perl sees that you need one of $&, $`, or $' anywhere in
the program, it has to provide them for every pattern match. This may
substantially slow your program. Perl uses the same mechanism to produ
+ce
...
but if you can't (and some algorithms really appreciate them), once
you've used them once, use them at will, because you've already paid t
+he
price. As of 5.005, $& is not so costly as the other two.