Have you checked to see if an error has occurred e.g

defined(my $size = -s $filename) or die "ack: $!";
# or using stat()
defined(my $size = [stat $filename]->[7]) or die "ack: $!";
[download]

As this is the most likely cause of your missing filesize.
HTH

_________
broquaint

update: changed code to check definedness instead of the truthfulness of size ... hmm I'm sure there's a joke in their somewhere