How to recognize Facebook User-Agent

Question

When sharing one of my pages on FB, I want to display something different. Problem is, I prefer not to use the og: elements, but to recognize FB user-agent.

What is

Answer 1

And if you want to block facebook bot from accessing your website (assuming you're using Apache) add this to your .htaccess file:

BrowserMatchNoCase "Feedfetcher-Google" feedfetcher
BrowserMatchNoCase "facebookexternalhit" facebook
order deny,allow
deny from env=feedfetcher
deny from env=facebook

It also blocks google's feedfetcher that also can be used for cheap DDoSing.