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.

Give a man a fish:  <%-{-{-{-<

In reply to Re^3: IPv4 regex by AnomalousMonk
in thread IPv4 regex by ryan

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.