Is there a GUI program that can help debug and explain regular expressions?
Yes there is. Check out the excellent Regex Coach package: »www.weitz.de/regex-coach/ It was written by Dr. Edmund Weitz, runs on Windows and Linux/x86, and is very helpful for the novice to the advanced regular expression programmer. It allows you to type in regular expressions, sample text, replacement strings, and have the regex engine step through them. It can also display the parse tree. This is a must-have utility for anyone who programs frequently with regular expressions.