All the above certainly is good advice, but what I'm puzzled about is the big picture.

What do you want to know the difference for? I'm asking because I'm sensing an un-Perlish way of doing things in your approach. I believe you're better served if you tell us why you need this information so we can advise you on your overall approach, not just part of it.

(To the more versed people: I would also inquire if f.ex I came across someone wanting to use eof - in Perl, it's almost always possible and better to avoid it.)