Get a Domain from a URL in PHP

gistfile1.txt

/**
 * Get the "domain" from a URL. By domain, we mean the host name, minus any subdomains. So just the domain and TLD.	 
 *
 * @param string $url The URL to parse. (generally pass site_url() in WP)
 * @return string The domain.
 */
function getDomainFromURL($url = NULL)
{
	$domainparts = parse_url($url);
	$domainparts = explode(".", $domainparts['host']);
	if(count($domainparts) > 1)
	{
		//check for ips
		$isip = true;
		foreach($domainparts as $part)
		{
			if(!is_numeric($part))
			{
				$isip = false;
				break;
			}
		}
		
		if($isip)
		{
			//ip, e.g. 127.1.1.1
			$domain = implode(".", $domainparts);
		}
		else
		{			
			//www.something.com, etc.
			$domain = $domainparts[count($domainparts)-2] . "." . $domainparts[count($domainparts)-1];
		}
	}
	else
	{
		//localhost or another single word domain
		$domain = $domainparts[0];	
	}
	
	return $domain;
}