This reminds me a bit of what finally pushed me over the edge from bash to Perl many years ago - validating and sorting lists of IP addresses. In hindsight, I bet there's a module for the task, but it was a good exercise. Anyhow, borrowing from that years-old effort: 

use strict;
use warnings;
while(<DATA>){
   chomp;
   my $mask = (split(/\s+/, $_))[2];
   print "Mask $mask is ", &Valid($mask), "\n";
}

sub Valid {
   my @octs;
   local $_  = shift;

   return 0  if !defined $_;
   return 0  if m{(?:(?:^|\.)[^0]\d*\.)(?!255)};
   return 0  if (@octs = split(/\./, $_)) ne 4;
   return 0  if grep {!m/^(?:0|3|7|15|31|63|127|255)$/} @octs;
   return 1;
}
__DATA__
field1 10.1.253.11  0.0.0.0
field1 10.1.254.0  0.0.0.64
field1 10.1.254.128  0.0.0.63
field1 10.1.158.0  15.255.0.255
field1 10.1.160.0  0.0.0.37
field1 10.1.161.0  0.0.146.255
field1 10.1.161.0  0.0.255
field1 10.1.161.0  0.0.255.255
field1 10.1.161.0  255.0.0.0
field1 10.1.158.0  15.255.255.127

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I'm not sure I followed your non-zero/non-255 rule. I interpreted it as, once there's a non-zero octet, all thereafter must be 255.

In reply to Re: Variable initialization / reinitialization by hbm
in thread Variable initialization / reinitialization by Anonymous Monk

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