The development web server built in to PHP 5.4+ does not work in the way you want. That is, it's not a PHP process, and you can't have it run code for you.
It's designed to serve PHP applications and content from the specified directory. The output of the server process is the access log. You can write to the log using the error_log
function, with a value of 4 as the message_type
. So, in theory, you could do something like
ob_start();
var_dump($_POST);
error_log(ob_get_clean(), 4);
It sounds like you're trying to perform some debugging. You should be using real debugging tools instead of cobbling something together.