(PHP3 , PHP4 )
string getenv (string varname)
string getenv
Returns the value of the environment variable varname, or false on an error.
$ip = getenv ("REMOTE_ADDR"); // get the ip number of the user
You can see a list of all the environmental variables by using phpinfo(). You can find out what many of them mean by taking a look at the CGI specification, specifically the page on environmental variables.