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

In the perspective of user-agent modifications on FB side, it is maybe safer to use a regex like that :

You can find more information about Facebook crawler on their doc: https://developers.facebook.com/docs/sharing/webmasters/crawler