PHP 3.0.13 and up, php://output and php://input since PHP 4.3
php://stdin, php://stdout and php://stderr allow access to the corresponding input or output stream of the PHP process.
php://input allows you to read raw POST data. It is a less memory intensive alternative to $HTTP_RAW_POST_DATA and does not need any special php.ini directives.
php://stdin and php://input are read-only, whereas php://stdout, php://stderr and php://output are write-only.