Doing a phpinfo() will tell you about display_errors, error_reporting, etc.
On my production server, I log errors instead of displaying them. When I want to debug a script in-place, rather than moving it to a development server (and therefore taking it out of the environment that's causing the errors), I simply place include 'debug.php' at the top of the script, because in my defualt includes directory, I've created debug.php that looks like this:
<?php
ini_set('log_errors', 'Off');
ini_set('display_errors', 'On');
error_reporting(E_ALL);
?>