PHP - Using Cronjobs.

How would one do this? I searched on google, but it couldn't find a good tutorial. My host allows the option in the control panel for it to set it up for you, but I want to learn the actual coding part just in case I never have the option available.

How would I run, say, this script every 4 hours for example?

Code: [Select]
<?php

mysql_query("TRUNCATE logs");

?>