Regex to Match IPv4 Addresses

This regex validates IPv4 addresses by ensuring each of the four octets falls within the range 0 to 255. Here is the token-by-token breakdown:

\b — A word boundary anchor that ensures the match starts at a boundary between a word character and a non-word character. This prevents partial matches within longer numbers.

(?: — Opens a non-capturing group for the first three octets (each followed by a dot).

(?:25[0-5]|2[0-4]\d|[01]?\d\d?) — A non-capturing group with three alternatives to match numbers 0-255:

• 25[0-5] matches 250-255
• 2[0-4]\d matches 200-249
• [01]?\d\d? matches 0-199. The [01]? optionally matches a leading 0 or 1, \d matches one digit, and \d? optionally matches a second digit.

. — Matches a literal dot separating the octets.

){3} — Closes the non-capturing group and repeats it exactly three times, matching the first three octets with their trailing dots.

(?:25[0-5]|2[0-4]\d|[01]?\d\d?) — The same alternation pattern again for the fourth and final octet, but without a trailing dot.

\b — Another word boundary anchor at the end.

The g flag enables global matching to find all IPv4 addresses in the text. This pattern is highly accurate because it validates the numeric range of each octet rather than just matching digit patterns.