If u have developed some parser in Perl,Ruby, Shell script ans Python , then you must have came across regular expression (regex).
Regular expression is consider strength of these scripting language.
If you want to test your regular expression for the test you have to parse or to develop a regular expression that can get or match your specific condition ... rubular can be handy tool to do this job.
It has text box to input your regular expression and box to give ur sample test text.
Give a try friends.