Regex tool for Linux
I use Kiki, it's simple but does the job.
Written in Python and there's an ubuntu package named kiki.
See my answer to How do you write and test your regular expressions? on StackOverflow.
Don't use Regex Buddy, nor any similar tool.
Spend a bit of time learning how regular expressions work.
They are actually much simpler than people think.
I usually use emacs with regex-tool. It get's the job done.
Here's someone's blog entry about it http://bc.tech.coop/blog/071103.html