Try doing this:

my $grepped = grep(...
print $grepped, "\n";
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That will tell you if the data is being overridden or if you're just retrieving the same data each time.

You could also help yourself by tidying up your code (see perlstyle) so you can read it more easily.

Another thing you can do is choose better variable names: using $filename and $file_name is just asking for trouble.