On his codediesel.com blog today Sameer Borate has a quick post looking at URL manipulation with the help of the Net_URL2 PEAR package.

Whether you are dynamically creating urls or changing existing ones, manipulation of urls is a frequent coding requirement during development; doing the same on short urls is easy, but quickly becomes complex for urls which have larger query parameters.

He shows how to use the package to parse the current URL into its respective parts (host, port, path, etc) and how to automatically change certain parameters in the current URL and push the updated version back out the other side. There's also a bit there at the end on normalizing URLs.