Introductory Guide to regular expressions
Regular Expressions and Patterns
Regular expressions are very powerful tools for performing pattern matches. PERL programmers and UNIX shell programmers have enjoyed the benefits of regular expressions for years. Once you master the pattern language, most validation tasks become trivial. You can perform complex tasks that once required lengthy procedures with just a few lines of code using regular expressions.
1) Using literal syntax.
The literal syntax looks something like:
var RegularExpression = /pattern/
while the RegExp() constructor method looks like
var RegularExpression = new RegExp("pattern");
The RegExp() method allows you to dynamically construct the search pattern as a string, and is useful when the pattern is not known ahead of time.
To use regular expressions to validate a string you need to define a pattern string that represents the search criteria, then use a relevant string method to denote the action (ie: search, replace etc). Patterns are defined using string literal characters and metacharacters. For example, the following regular expression determines whether a string contains a valid 5-digit US postal code (for sake or simplicity, other possibilities are not considered):
Lets deconstruct the regular expression used, which checks that a string contains a valid 5-digit number, and ONLY a 5-digit number:
Translated to English, this pattern states: "Starting at the beginning of the string there must be nothing other than 5 digits. There must also be nothing following those 5 digits."
Now that you've got a taste of what regular expressions is all about, lets formally look at its syntax, so you can create complex expressions that validate virtually anything you want.