Your method is fine, you're just doing something extra that you shouldn't be doing. You're ONLY printing the line to the file if it doesn't exist in your %lines hash yet. But then you're printing a newline regardless of that! Either do: 
while (<DUPLICATE>) {
  print DUPremoved if not $lines{$_}++;
}

[download]
or, if you're really adamant about chomp()ing the line first, do: 
while (<DUPLICATE>) {
  chomp;
  print DUPremoved "$_\n" if not $lines{$_}++;
}

[download]
Jeff japhy Pinyan, P.L., P.M., P.O.D, X.S.: Perl, regex, and perl hacker
How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart

In reply to Re: duplicate lines by japhy
in thread duplicate lines by Anonymous Monk

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