Regular expression (or regex) [Wikipedia] are a very powerful method to parse data and extract the information you need. But a regular expression can quickly turn into a nightmare due to its complexity. I often use a memo but testing the regexp live is the quickest way to debug them.
Edmund Weitz wrote a nice tool called “Regex Coach” which does exactly I wanted. The last version of his tool runs only on Windows operating systems. According to the author, the Linux version had less success and took time to be maintained. Sad!
Check http://weitz.de/regex-coach/ for details and installation instructions. A great tool!