I recommend using the 'in-place' command line parameter (like mentioned in in-place edit, regex, one-liner and covered extensivly in perlrun.

As a sidenote: flock is pretty handy :)

Update: Ok, I obviously misread the question (could it be the formatting??). Anyway, look at merlyn's answer.

Greetz
Beatnik
... Quidquid perl dictum sit, altum viditur.