validation Getting started with validation Validating whether the user input contain non alpha numeric character

Example

Sometimes, we have to take input from users which should contain only alpha numeric characters.

For example, lets say a Username system which allow only letters and numbers,

Then this can be done with the following Regular Expression

^[a-zA-Z0-9]+$

• ^ is restrict the start
• [a-zA-Z0-9]+ is the main part which allow only small a-z capital A-Z and numbers with a minimum length of 1 to any extend.
• $ restrict the end

This can also done by using

^[\w\d]+$

Here

• \w represent the alphabets
• \d represent the digits

If we want to restrict the length to maximum 20 charactes,

^[a-zA-Z0-9]{1,20}$

• The {1,20} indicate that the length can be between 1 and 20 including both.