Question

Wanna write a RegEx to validate a driving license.

if it doesn’t start with (US, CA, CN) then it has to be followed with XX and after that with any number of Alpha numeric letters.

So for example if the driving license starts with GB then it has to be followed with XX GBXX12345363 However if it starts with US then we don’t care what comes after it. USLA039247230

Answer 1

Remember not everyone is familiar with that driving license notation, I’m assuming that what follows is the precise specification (you should really try to be very precise when asking for a regex else you’ll get things you don’t want):

• Has to start with two capital letters
• If those first two letters are either US, CA or CN, the rest has to be alphanumeric and of unspecified length

• If those first two letters are none of US, CA or CN, then the next two letters have to be X, the rest after that has to be alphanumeric and of unspecified length

  ((US|CA|CN)[A-Za-z0-9]+|(?<!(US|CA|CN))[A-Z]{2}XX[A-Za-z0-9]+)

First part:

• Matches one of US, CA or CN
• One or more alphanumeric characters

Second part:

• Negative lookbehind, doesn’t start with US CA CN
• Has two uppercase letters
• There are two X characters
• One or more alphanumeric characters

And it matches either the first part or the second one