is a program that allows you to interactively examine and test regular expressions. It shows you what your regular expressions match as you type on a sample text you provide. You can set the colour RegExhibit uses for this, and whether it should underline matches and captures. It also provides full details on successful matches.
As RegExhibit uses Perl to interpret your regular expressions, you get access to one of the most complete regular expression dialects around. RegExhibit will even allow you to use Perl code inside a regular expression.