How can I match Portuguese license plates in a single regular expression?

Question

I was building a regex to validate Portuguese license plates however, the old ones come in a different format, and I would like to know if it is possible to validate all of the possibilities with just one regex?

These are the possibilities, any other is invalid (i.e.: 00-A0-00):

• 00-00-AA
• AA-00-00
• 00-AA-00

At the moment, I only have this working:

([A-Z]){2}-([0-9]){2}-([0-9]){2}

Answer 1

This works:

((?:[A-Z]{2}-\d{2}-\d{2})|(?:\d{2}-[A-Z]{2}-\d{2})|(?:\d{2}-\d{2}-[A-Z]{2}))

Demo

Anchors are better (with m flag):

(^(?:[A-Z]{2}-\d{2}-\d{2})|(?:\d{2}-[A-Z]{2}-\d{2})|(?:\d{2}-\d{2}-[A-Z]{2})$)

Demo 2

Answer 2

Just Use Alternation

Depending on your regex engine, you may have to vary a few things, but in general the easiest thing to do is to simply provide three alternations. For example:

\d{2}-\d{2}-[[:alpha:]]{2}|[[:alpha:]]{2}\d{2}-\d{2}|\d{2}-[[:alpha:]]{2}-\d{2}

This works fine for me in Ruby against your sample inputs. YMMV.