A regex to match (optionally zero padded, decimal) dotted-quad IPs is fairly involved.

#!/usr/bin/perl -w
use strict;

my $octet = q[0?\d\d?|1\d\d?|2[0-4]\d?|25[0-5]|2[6-9]]; # MUST BE CONS
+TRAINED
my $ip = q[(?<!\d\.)] . join(q[\.], ( "($octet)" ) x 4) . q[(?!\.\d)];
my $rx = qr/$ip/;
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Even that isn't perfect(!), but it's much closer. To sort by IP, you should capture the octets and feed them to pack "C4", yielding a string that can be used for ASCIIbetical sorting. This is a basically a task that naturally lends itself to a GRT:

my @line;

while(<>) {
    push @line, pack("C5", (@octet = /$rx/ ? 1, @octet : (0) x 5 ) ) .
+ $_;
}

print map substr($_, 5), sort @line;
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Note I'm using C5 here to be able to distinguish lines with no IP at all from those with 0.0.0.0.

Makeshifts last the longest.