@OP

You could also write the conditional as

if ($range >= 300 and $range <= 400)
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In this case it actually does not make a difference which one you use, but

open my $fh, '<', $filename
  || die;
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and

open my $fh, '<', $filename
  or die;
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are two totally different things due to different order of precedence. (A verbose explanation can be found at 'or' vs '', '&&' vs 'and'.)