How to use PHP to get information about the user

What kinds of information can PHP get about users? I would like to make a web page that shows information about whoever goes to it, lik开发者_开发百科e their IP address.

You can get anything in $_SERVER.

well, run
phpinfo(); to find all the variables that may be interesting.

to get more, you should think about using cookies to see if the user is here for the first time. And use javascript to get some other stuff, like screen resolution, etc.

IP Address, User-Agent, Geo-Location based on IP Address, and that's about it without cookies and other data from other sites or properties.