This is a simple commandline tool I wrote to help debug perl regular expressions. It works by highlighting the part(s) of a test string which match a given regular expression.
Check out these examples of how rred works, or read the perldoc documentation embedded in the script for a full description.
You can download rred here and try it out. It has no dependencies other than perl.
This code is in the public domain. Permission is granted to anyone to use it for any purpose.
If you find rred useful (or even if you don't, and have something to say about it), let me know!
A somewhat similar tool is rtest.
The Komodo IDE, sold by ActiveState, includes a regular expression test tool providing similar functionality in a GUI environment.
I like dogs, but rred is not affiliated with the Rhodesian Ridgeback Enthusiasts of Dallas.