Swaps a with b. An old assembly idiom... ^= will also get what you want... =)

Update: used to be common... when i learnt assembly no teacher knew it. I found that in some perl tut actually, which i skimmed for a friend. It discussed something along "while that trick may have been common for swapping registers in assembly, in perl you can do ($a,$b) = ($b, $a) instead.

-nuffin
zz zZ Z Z #!perl