Regular expression to validate hex string

Question

I'm using this simple regular expression to validate a hex string:

^[A-Fa-f0-9]{16}$

As you can see, I'm using a quantifier to validate that the string is 16 characters long. I was wondering if I can use another quantifier in the same regex to validate the string length to be either 16 or 18 (not 17).

Answer 1

I believe

^([A-Fa-f0-9]{2}){8,9}$

will work.

This is nice because it generalizes to any even-length string.

Answer 2

That's just a 16 character requirement with an optional 2 character afterwards:

^[A-Fa-f0-9]{16}([A-Fa-f0-9]{2})?$

The parentheses may not be required - I'm not enough of a regex guru to know offhand, I'm afraid. If anyone wants to edit it, do feel free...

Answer 3

^(?:[A-Fa-f0-9]{16}|[A-Fa-f0-9]{18})$