how to identify web crawlers of google/yahoo/msn by PHP?

Question

AFAIK,

$_SERVER[\'REMOTE_HOST\'] should end up with \"google.com\" or \"yahoo.com\".

but is it the most ensuring method?

any other way out?

Answer 1

The best way to do it with well know and behaving robots, like those you mentioned, is by user agent which you can find on $_SERVER['HTTP_USER_AGENT'].