An [url=http://enterprise.linux.com/article.pl?sid=04/12/22/0028257]article on linux.com[/url] shows a couple of examples of using PHP scripting to perform sysadmin tasks on servers.

More info can be found on the [url=http://www.php.net/manual/en/features.commandline.php]Command Line manual[/url] page on PHP.net.