Parsing domain from a URL

$domain = str_ireplace('www.', '', parse_url($url, PHP_URL_HOST));

This would return the google.com for both http://google.com/... and http://www.google.com/...

Check out parse_url():

$url = 'http://google.com/dhasjkdas/sadsdds/sdda/sdads.html';
$parse = parse_url($url);
echo $parse['host']; // prints 'google.com'

parse_url doesn't handle really badly mangled urls very well, but is fine if you generally expect decent urls.