Please also see Regexp::Common and Regexp::Common::net.

c:\@Work\Perl\monks>perl -wMstrict -le
"use Test::More 'no_plan';
 use Test::NoWarnings;
 ;;
 VECTOR:
 for my $ar_vector (
   [ '1.133.123.123', 1 ],  [ '1.2.3.4', 1 ],  [ '11.22.33.44', 1 ],
   [ '0.0.0.0', 1 ],  [ '255.255.255.255', 1 ],
   [ '', '' ],  [ '1asdf1.133.123.123', '' ],  [ '12341.133.', '' ],
   [ '0.0.0.256', '' ],  [ 'not at all valid', '' ],
   [ '1.2.3.4.5', '' ],  [ '1111.2.3.1111', '' ],
   ) {
   my ($ip, $valid) = @$ar_vector;
   ;;
   my $status = $valid ? 'valid' : 'INVALID';
   is IP_valid($ip), $valid, qq{'$ip' $status};
   }
 ;;
 done_testing;
 ;;
 ;;
 use Regexp::Common qw(net);
 ;;
 sub IP_valid {
   my ($ip) = @_;
   return $ip =~ m{ \A $RE{net}{IPv4} \z }xms;
   }
"
ok 1 - '1.133.123.123' valid
ok 2 - '1.2.3.4' valid
ok 3 - '11.22.33.44' valid
ok 4 - '0.0.0.0' valid
ok 5 - '255.255.255.255' valid
ok 6 - '' INVALID
ok 7 - '1asdf1.133.123.123' INVALID
ok 8 - '12341.133.' INVALID
ok 9 - '0.0.0.256' INVALID
ok 10 - 'not at all valid' INVALID
ok 11 - '1.2.3.4.5' INVALID
ok 12 - '1111.2.3.1111' INVALID
1..12
ok 13 - no warnings
1..13
[download]

Note that, by design,  $RE{net}{IPv4} is not "anchored", so by itself it will match, e.g.:

c:\@Work\Perl\monks>perl -wMstrict -le
"use Regexp::Common qw(net);
 ;;
 print qq{matches IP of '$1'}
   if '99999.1.2.9999' =~ m{ ($RE{net}{IPv4}) }xms;
"
matches IP of '99.1.2.99'
[download]

which may or may not be what you want. The  \A \z anchors in the example code above address this (quite intentional) feature.

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