Given a string, I'd like to check syntactically whether it can be valid domain name or IP. I've found this post by merlyn in 2000: Test the syntactic validity of a domain name, it seems to be a little too strict, as pointed by others (e.g, misses 411.com). Is there a more "correct" solution, both in terms of speed and what it does. Currently I'm using the following code, which also includes some test cases, are there other cases? 
use strict;
use Test::More 'no_plan';

my @good=("www.foo.com","www.411.com","123.34.3.5","web.foo.info",
 "www.foo.co.uk","aaaa-4-bbbb.cCc.COM");
my @bad = ("foo.23.4.2","foo","23","234.12.4.5.4","2345.23.4.43");

ok(is_valid($_)) foreach @good;
ok(!is_valid($_)) foreach @bad;

sub is_valid{
    my $name = shift;
    my $name = lc $name;
    return ($name
            && $name =~ /^[-\.\w]+\.\w+$/ #at least two levels
            && ($name !~ /\.\d+$/ || $name =~ /^\d{1,3}\.\d{1,3}\.\d{1
+,3}\.\d{1,3}$/) #if last part is digit, better be ip
            );
}

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In reply to Syntactically check domain name/IP by johnnywang

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