Question

The user should be able to write it in any of the below formats

http://www.microsoft.com
or
https://www.microsoft.com
or
http://www.microsoft.com

Programming Language : C#

Answer 1

This should work for most regex processors:

/((?:https?\:\/\/|www\.)(?:[-a-z0-9]+\.)*[-a-z0-9]+.*)/i

What this matches:

• Anything that starts with http://, https://, or www.
• Followed by at least one or more valid domain characters (a-z, 0-9, or -)
• Matches without case sensitivity (/i)
• It does not enforce white space, so it will match this: blahwww.domain.com, and return www.domain.com If you want to enforce space, add \s to the beginning, but then you have to ensure that you add a space to the beginning of the string to match.

The (?:) blocks are non-matching groups. They prevent those specific groups of characters from being assigned a number. They can be replaced with matching groups () if your regex processor has trouble. Group 1 is always the entire URL.

It’s not terribly strict, but it matches all standard domain names (but might let slip through some invalid ones).

Also, next time, you might want to include the programming language or context, because regex processors vary greatly in feature support.