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  if ( ($a,$b,$c,$d) = m/^(\d+)\.(\d+)\.(\d+)\.(\d+)$/ ) {
      if ( $a < 256 && $b < 256 && $c < 256 && $d < 256 ) {
...
      }
  }
  return 0;

  0.0.0.0:         "0" | "0" | "0" | "0"         eq "0"    OK
  255.255.255.255: "255" | "255" | "255" | "255" eq "255"  OK
  127.0.0.1:       "127" | "0" | "0" | "1"       eq "127"  OK

      return 1 if (0+$a|0+$b|0+$c|0+$d) < 256;

      return 1 if (0|$a|$b|$c|$d) < 256;