Two other regex-understanding tools I've found useful:<p><a href="http://www.regexbuddy.com/" rel="nofollow">http://www.regexbuddy.com/</a><p><a href="http://www.regexio.com/" rel="nofollow">http://www.regexio.com/</a>
I think the ultimate tool for understanding regexps is Russ Cox's notes:<p><a href="http://swtch.com/~rsc/regexp/" rel="nofollow">http://swtch.com/~rsc/regexp/</a><p>When explained well, the big picture of NFAs and DFAs is bog simple. I'm sure some of the details are messy, but I expect they rarely matter.
Unfortunately it doesn't allow me to enter the regular expression found here: <a href="http://www.ex-parrot.com/pdw/Mail-RFC822-Address.html" rel="nofollow">http://www.ex-parrot.com/pdw/Mail-RFC822-Address.html</a>. It's horrendous I but would love to see it visualized.
This is nice for visualizing an NFA and the minimized DFA for asome regular expression (note: regular!!): <a href="http://osteele.com/tools/reanimator/" rel="nofollow">http://osteele.com/tools/reanimator/</a>. The aforementioned tool also lets you give input and highlights the current states of each FA.
awesome. the best would be if you could go in the opposite direction. like if you could create regular expressions in the image view and have it output the text version.<p>this would probably help a lot of people who aren't 'ninjas' like you and me ;?j