Tools for writing regular expressions

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In this video we will discuss the basics of regular expressions and then look at some of the tools available to learn, write and test regular expressions.



Basics of Regular Expressions : 

Find the word expression in a given string. This will also match with the word expressions.
expression

To find the word "expression" as a whole word, include \b on either sides of the word expression
\bexpression\b

\d indicates to find a digit. To find a 5 digit number we could use the following
\b\d\d\d\d\d\b

We can avoid the repetition of \d by using curly braces as shown below. \d{5} means repeat \d 5 times.
\b\d{5}\b

The above example can also be rewritten as shown below.
\b[0-9]{5}\b

Find all the words with exactly 5 letters
\b[a-zA-Z]{5}\b

Brackets are used to find a range of characters
[a-z] - Find any of the characters between the brackets
[0-9] - Find any of the digits between the brackets. This is equivalent to \d
(a|b) - Find any of the characters a or b

The page at the following link explains the basics of regular expressions.
https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions

Expresso is one of the free tools available. Here is the link to download.
http://www.ultrapico.com/ExpressoDownload.htm

Regular Expression Library
http://regexlib.com