Regex for MasterCard

Question

I found the following regex for credit card type MasterCard

public static readonly string CreditMasterCard = @"^(5[1 - 5][0 - 9]{14})$";

then I wrote the following code:

Regex regexMasterCard = new Regex(CommonLibrary.RegexCreditCardStrings.CreditMasterCard);

if (regexMasterCard.IsMatch(number)) return CommonLibrary.CreditCardType.mastercard;

But when I set number='5308171154251187' it's wrong. What is incorrect in regex?

Answer 1

You just need to remove the spaces inside the character classes:

^5[1-5][0-9]{14}$

Those spaces are always meaningful inside a character class (even if you specify the RegexOptions.IgnorePatternWhitespace flag) and in your case they created ranges from space to space, not from 1 to 5 and 0 to 9 digits. Also, there is no need in the outer parentheses, you do not need to capture the whole pattern (you can always refer to the whole match with $0 backreference or match.Value).

See the regex demo.

As per @saj comment, you may now use

^(?:5[1-5][0-9]{2}|222[1-9]|22[3-9][0-9]|2[3-6][0-9]{2}|27[01][0-9]|2720)[0-9]{12}$

See the regex demo

Details:

• ^ - start of string
• (?:5[1-5][0-9]{2}|222[1-9]|22[3-9][0-9]|2[3-6][0-9]{2}|27[01][0-9]|2720) - any of the alternatives:
  • 5[1-5][0-9]{2} - 5, a 1 to 5 and any 2 digits (5100 to 5599)
  • 222[1-9] - 2221 to 2229
  • 22[3-9][0-9] - 2230 to 2299
  • 2[3-6][0-9]{2} - 2, then 3 to 6 and any 2 digits (2300 till 2699)
  • 27[01][0-9] - 2700 till 2719
  • 2720 - 2720
• [0-9]{12} - any 12 digits
• $ - end of string.