Someone once said:
Some people, when confronted with a problem, think “I know, I’ll use regular expressions.” Now they have two problems.
Regular expressions are incredibly powerful, but can also be extremely confusing and hard to use. This free online tool is, by far, the best thing I’ve ever found to build, refine, debug, and understand them. It will even help you generate code to use them in various languages. If you find it helpful you can donate using the “$” icon at the bottom to help keep the lights on.