I had a mod_rewrite problem that was really tough, tough enough that I needed to break down my Regular Expression step by step and see what was matching. I’m not a huge fan of doing this in Terminal, and I work on a Mac so Editpad Pro was out, (it’s good to use on a PC). So, I built a web-based tool to see how my regular expression was matched against a string. It’s available here.
To use it enter a Regular Expression, and a string to match it against. It’ll tell you if the regex matches the string and if so it’ll show you the substring that matches the regex, (if it is a substring), and any parenthetical substring matches.
This little script uses PHP’s native preg_match() function to determine matches, I believe its matching engine is very, very, close to Apache’s engine used in mod_rewrite so it should work well.
So, did this help me solve my problem? Yes it did. It told me that the problem wasn’t in the rewrite rule that I thought it was in.
Try out the Regular Expression Testing Tool.
Update 29 December 2010: I posted a small update to make the input fields larger and corrected some text when the regex does not match.