for (@list)
{
  
my %dmphash;


    unless (exists $dmphash{$_})
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You test the existence of a key in the hash on the very line after you instantiate the hash so there's no way that key will ever exist (so the test always fails and your file is never opened). Nope, wrong logic, ignore this.

BTW that's quite some indentation scheme you have going on there. It might help the clarity of your code to run it through perltidy. However, if I attempt to do that it quite rightly complains about the unbalanced braces. Perhaps an SSCCE would make it clearer?