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if ($zip !~ /^\d+(\-\d{4})?$/)
{
     $error{zip} = "Invalid postal code.";
}

sub valid_ip
{
     my $bit = '[01]?\d\d?|2[0-4]\d|25[0-5]';
     return $_[0] =~ /^($bit)(\.($bit)){3}/;
}

sub valid_ip
{
        my $bits = 0;
...

        return $bits == 4;
}

use Net::IPv6Addr;

sub valid_ipv6 
{
     return Net::IPv6Addr::ipv6_parse($_[0]);
}