How to know if the visitor is the Google bot, or Facebook bot

Question

Have some way, via PHP, to know if who is visiting my page is Google bot and Facebook bot?

Answer 1

Google

if (strstr(strtolower($_SERVER['HTTP_USER_AGENT']), "googlebot")) {
    // Provavelmente proveio do google.
    // Aqui você implementa as suas firulas.
}

Facebook:

if (
    strpos($_SERVER["HTTP_USER_AGENT"], "facebookexternalhit/") !== false ||          
    strpos($_SERVER["HTTP_USER_AGENT"], "Facebot") !== false
) {
    // Provavelmente proveio do facebook.
    // Aqui você implementa as suas firulas.
}

Note: Be aware that it is easy to manipulate HTTP_USER_AGENT. Anyone can create a script that identifies itself as googlebot, for example. So do not trust this parameter 100%.

To ensure greater integrity you will need to do reverse DNS checks, IP origin, etc.