PHP: shortest and easiest GeoIP (IP to Country)

Without using a database of IP addresses or an "external API" (not completely true), this is the shortest method of determining the country of an IP addresss.

The one-liner issues a shell_exec() to the whois command and parses the two letter country code from it.

if(preg_match('/^(\d+\.?){4}$/',$ip)) {
  $country = trim(shell_exec('whois '.$ip.' -H | grep country | awk \'{print $2}\''));
}

The preg_match() is of course optional, but for your own good, because as you may know, shell_exec() is VERY DANGEROUS.

Note: This does not work on all versions of WHOIS!

Also note that there is a daily query limit to the RIPE.NET database, so it's good to cache the results. It's not like that information gets changed often.