[PHP] Retrieve the Http Host from the Http Header

[Ministério Público]

I need a way to retrieve the URL typed by anyone visiting the website, so
that I can rerout them to the apropriate folder, does anyone know how to do
this?
 I got a message saying that I should use the phpinfo and use the variables
that are given as response, but the problem is that the variable that is
usefull is the HTTP HEADER HOST and I dont know how to retrieve it. I thank
anyone who can help.
Rodrigo