while ($line = <MAIN_FILE1>){
chomp $line;

  if (exists $hash2{$entry}) {
        print OUTPUT2 "$filename\n";
        next;
    }
  # either exists in %hash1,
  # or not in either,
  # so output to OUTPUT1
  print OUTPUT1 "$filename\n";
  next;
}

close(MAIN_FILE1)