Regular Expressions (Regex) are expressions that define a search pattern. Regex can be implemented in various tasks including searching, replacing, validation and text processing/parsing. It is mostly known in the combination with the programming language Perl, but Regex are also supported by most other languages.
If you every want to really dive deep into the world of Regular Expressions, I'd recommend the book "Mastering Regular Expressions " by Jeffrey E.F. Friedl.
Testing your regular expressions
There are times in which you can't test your Regex while programming. Or you might just want to play around and test your Regex.
In any case, there are a few Regex tester online, where you can add sample data and build or test your regex. Some of them are:
