What are Regular Expression?
Regular expressions are a series of special characters that looks like your cat has walked over your keyboard.
For example /\w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*/
What the above does is match email adresses from a given string (block of text) using a set pattern.
Regular Expressions can be difficult to learn but it's worth the effort. Using regular expressions can save you loads of time if you need to do a lot of text manipulation.
Use the above form to test your regular expressions. Either enter your own into the space provided or select a pre defined one from the list. Enter the thect you want to search into the textarea and click on the TestExpression button.Some Special Characters and their meaning
|^||Start of a line|
|$||End of a line|
|.||Any character except for newline character (if used without parameter " /.../s")|
|[ ... ]||
Match any characters between the 
|[^ ... ]||Doesn't Match any of the characters between the |
Escape spaecial characters to use as literal for example, $ is a special character if you want to match a $ in your text escape it with a backslash \$
|\b|| Word boundary -
|\B|| Non word Boundary -
|\n||Match linefeed or new line character|
|\r||Match Carriage Return|
|\s||A whitespace character (tab/space /cr/lf)|
|\S||Not a whitespace character|
|\w||Match a word character - letters digits and underscore|
|\W||A non-word character - including spaces|
|\D||Not a digit|