PHP: How to detect the browser currently used by the user?

Chrome

if (stripos($_SERVER['HTTP_USER_AGENT'],"Chrome"))
        $browser = 'Chrome';

Firefox

if (stripos($_SERVER['HTTP_USER_AGENT'],"Firefox"))
        $browser = 'Firefox';

Safari

if (stripos($_SERVER['HTTP_USER_AGENT'],"Safari"))
        $browser = 'Safari';