Reading environment variables is possible in PHP by using the $_ENV auto-global array. They are named values associated with a process. For example, the value of $_ENV['HOME'] can be used in unix to find the home directory of a user.
Example for Reading an environment variable:
<?php $name = $_ENV['USER']; ?>
Example for Reading user’s home directory
<?php print $_ENV['HOME']; // user's home directory ?>
The $_ENV array is created only if the value of the variables_order configuration directive contains E. If $_ENV isn’t available, use getenv() to retrieve an environment variable.
<?php $path = getenv('PATH'); ?>
The getenv() function isn’t available if you’re running PHP as an ISAPI module.