Lets consider an example where the user is asked to enter their Email ID and we have to validate it using RegEx. The format of an email is as follow:

Personal details/local part like john123 [only . and _ allowed]

Single @

Domain Name like gmail/yahoo/hotmail/rediffmail/vitstudent [minimum 4 characters]

Sol85:

To validate an email using RegEx with the format described, we can use the following pattern:

^[a-zA-Z0-9._]+@[a-zA-Z0-9]{4,}.[a-zA-Z0-9]+$

Breaking down the pattern:

• ^ : start of string
• [a-zA-Z0-9.]+ : one or more characters of alphabets (both upper and lower case), digits, period (.), and underscore (), for the personal details
• @ : a single @ symbol
• [a-zA-Z0-9]{4,} : four or more characters of alphabets and digits, for the domain name
• . : a period (escaped with backslash since it is a special character in RegEx)
• [a-zA-Z0-9]+ : one or more characters of alphabets and digits, for the top-level domain
• $ : end of string

So, for example, the email john123@gmail.com would match this pattern, while john123@hotmail would not match (since it does not have a top-level domain).

We can use this pattern in our code to validate user input for an email address.