A few additional observations:

• In the foreach loop there is no need for explicit indices, since these are used only to identify array elements. It’s simpler and clearer to loop directly over the elements themselves: for (@outputlist) { This has the additional benefit that you don’t need to use the binding operator (=~) explicitly, because $_ is “understood”:

  for (@outputlist) {
      print ... if /.../;
  }
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• Testing that a string matches /^0/ and then testing that it matches a longer pattern beginnning with /^0.../ is fairly pointless here.

• The input line:

  "    0            258520344       520344                    0"
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  will not match any pattern beginning /^0.../ because there is whitespace before the zero digit. You need something like this:

  / ^ \s* 0 \s+ (\d+) \s+ (\d+) \s+ 0 \s $ /x
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  Note the quantifiers: * means zero or more, + means one or more. See “Quantifiers” in perlre. (The /x modifier just makes the regex easier to read.)

Hope that helps,