The environment variables are usually made available to your scripts via $_ENV, just like $_POST, $_GET etc. are. It seems however that the registration by PHP of these kind of variables for use in your scripts is governed by a configuration option called variables_order in the php.ini file. By default many of the latest installs (and associated php.ini’s) of PHP will have this option set to ‘GPCS’, which stands for Get, Post, Cookie and Built-in variables respectively.
Therefore if you find your php_info() function call returning a bucket load of environment related information but yet a print_r($_ENV) returns an empty array () check the aforementioned setting and be sure to add E in there somewhere so as to instruct PHP to make environment variables available to you and your scripts.
While I’m not 100% certain I believe the ordering of the letters is only important when you have the register_globals option set to on. If register_globals is set to on (off by default since 4.2 and ditched in 6.0) then PHP will make all the variable kinds (Post, Get etc.) specified in variables_order available as global variables in the order you specified in that directive. Imagine for instance that you have ‘EGP’ specified in variables_order and register_globals set to on, if you have a variable called ‘Path’ in both the $_ENV and $_POST arrays, the value from the post array will overwrite the value from the environment array and thus the global variable $Path will hold information from $_POST and not $_ENV. If register_globals was turned to off, you would simply access all array indexes by their full name such as $_ENV["Path"] and $_POST["Path"] and thus they will be considered as 100% different variables.