How do I sanitize title URIs with PHP?

Question

I am programming a blog and I want the URIs to be the title like the question title here in stackoverflow or like wordpress.
What are the rules for sanitizing a URI?

Answer 1

This might be the shortest way to replace any non alphanumeric character with a single hyphen:

trim(preg_replace('/[^a-z0-9-]+/', '-', strtolower($str)), '-')