you got quality answers; just a minor tip to add for my part. If using one letter only var name is a bad thing, using the same letter of a perl perlvar is very bad habit.

Infact @F is the field array used by -a perl's switch. Even if you have it localized in your example i think is a practice to avoid.

pardon my pedantry visiting this node about file speed!

L*

update:fixed perlvar link thanks to pryrt