Regex to Extract Domain Names

This regex extracts domain names from URLs or plain text. Here is the token-by-token breakdown:

(?:https?://)? — An optional non-capturing group that matches the protocol portion (http:// or https://). The entire group is optional thanks to the trailing ?, so the regex works on both full URLs and bare domain names.

(?:www.)? — Another optional non-capturing group matching the 'www.' prefix. Many domains are written with or without this prefix, so making it optional ensures both forms are captured.

( — Opens the first capturing group, which will contain the actual domain name we want to extract.

[a-zA-Z0-9-]+ — Matches the main part of the domain name. It allows letters, digits, and hyphens, requiring at least one character. This covers domain names like 'example', 'my-site', or 'shop123'.

(?:.[a-zA-Z]{2,})+ — A non-capturing group that matches a dot followed by two or more letters, repeated one or more times. This captures the TLD and allows for compound TLDs like .co.uk or .com.au.

) — Closes the capturing group.

The g flag enables global matching to find all domains in the text, and the i flag makes it case-insensitive. The first capturing group isolates the domain name without the protocol or www prefix, making extraction straightforward.