Many web developers would love to do everything in PHP -- maybe because it was their first web programming language, or because plenty of pre-written code is available online; or maybe just because PHP is actually quite fast.
When the PHP engine is being called by a web server, there's one thing you can't easily do with PHP: administer your system.
The reason? PHP 4.2.0 (and above) can be invoked directly from the command line.
Although many have attempted to use PHP as the “golden hammer” in the past, this strategy often proves highly inconvenient simply because server-based tasks were simply never meant to run over extended periods of time. However, as of PHP version 4.2.0, it’s possible to directly invoke the PHP engine by calling it from the operating system command-line, available via a new SAPI type known as the CLI (Command Line Interface). This new capability opens up the possibility for system administrators to use PHP for managing various server-related tasks, among which include duties pertinent to managing system backups, monitoring system resources, and parsing logs.
The full post shows you how to make sure your system is configured to handle command-line PHP, offers a simple example (timezone adjustment calculator), and answers a few likely questions you might have. No real-world sysadmin example scripts just yet, but (the post promises) those are coming.
If you're super-comfortable with PHP, and would like to stretch your PHP beyond web programming, then the article is a good read.