Checking for new content

[netfrugal]

I provide rss feeds for some people, just so they can keep updated with new content I place on my site.

But, my friends has sites they update once in a while, and I want to know when they do update any pages. Yet, they do not provide any method of alerting me of any new content.

How would anyone go about checking for new content on a page, with PHP?

Any ideas?

[bradgrafelman]

Retrieve the RSS feeds and cache them to your server. Set up a cronjob that executes a PHP script every so often (once a day/week/whatever) to retrieve the RSS feed and compare it with the cached version.