I don't see anything wrong with your original version (and, in fact, it runs as expected on my box).

I see a couple opportunities for things to get fouled up:
1. Where does @filenames come from? Are you sure it's not empty?
2. Your original doesn't check whether or not the open() succeeds, so it might just have been silently failing to open anything in @filenames.

If your original version is still failing, try printing out what's in @filenames and/or $file each time through; and do add the 'or warn $!' after your open(). The infamous 'use strict' and -w might also help you out if the problem turns out to be something simple, like variable name typos.