Regex for a promo code that has the following rules

Question

I need to build a regex that have the following:

Rules to be applied:

• exactly 14 characters
• only letters (latin characters) and numbers
• at least 3 letters

Regex still confuses me so I am struggling to get the correct output. I want to use it with swift and swiftui in an app I am making

(?=(.*[a-zA-Z]){3,}([0-9]){0,}){14,14}$

I tried this. But I know it is not the way

Answer 1

I would use a positive lookahead for the length requirement:

^(?=.{14}$)(?:[A-Za-z0-9]*[A-Za-z]){3}[A-Za-z0-9]*$

This pattern says to match:

• ^ from the start of the input
• (?=.{14}$) assert exact length of 14
• (?:
  • [A-Za-z0-9]*[A-Za-z] zero or more alphanumeric followed by one alpha
• )
• [A-Za-z0-9]* any alphanumeric zero or more times
• $ end of the input

Answer 2

You need to use

^(?=(?:[0-9]*[a-zA-Z]){3})[a-zA-Z0-9]{14}$

Details

• ^ - start of string
• (?=(?:[0-9]*[a-zA-Z]){3}) - at least three repeations of a letter after any zero or more digits sequence required
• [a-zA-Z0-9]{14} - fourteen letters/digits
• $ - end of string.

See the regex demo.