for (;;) {
   defined(read($fh1, my $buf1='', 4096)) or die $!;
   defined(read($fh2, my $buf2='', 4096)) or die $!;
   if ($buf1 ne $buf2) {
      print("Different\n");
      exit(1);
   }
   last if !length($buf1);
}
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Why not File::Compare?