$_SERVER["SERVER_NAME"] not showing www.example.com

Question

Why does $_SERVER["SERVER_NAME"] not echo the www in www.example.com but it does work when I echo it from a sub domain like test.example.com?

Answer 1

I don’t know why it doesn’t contain the expected value. But try $_SERVER['HTTP_HOST'] instead, that contains the value provided by the client in the HTTP header field Host. But see Chris Shiftlett’s SERVER_NAME Versus HTTP_HOST for security considerations.