Regular Expression validation for frontend(JS) and backend(PHP)

Start with one example:

For validate Name Field: Alphabets, numbers and space(' ') no special characters min 3 and max 20 characters.

var ck_name = /^[A-Za-z0-9 ]{3,20}$/; 

if (!ck_name.test(name))

{
        alert('Enter valid Name.');
        return false;
}

Note: The above code for front end using JavaScript. If you are using PHP use key word preg_match instead of test.

Some important conditions:

[abc]	Find any character between the brackets
[^abc]	Find any character not between the brackets
[0-9]	Find any digit from 0 to 9
[A-Z]	Find any character from uppercase A to uppercase Z

[a-z]

Find any character from lowercase a to lowercase z

{3,10} Check for the string length in between give boundary.

Important Links:

http://www.w3schools.com/jsref/jsref_obj_regexp.asp

http://www.9lessons.info/2009/03/perfect-javascript-form-validation.html