我可以获得正则表达式信用卡号的最后 4 位数字吗？

Question

I have this regex pattern for an AMEX Credit Card format - (?<?\d)3[47][0-9]{13}(.?\d). Is there a way to get the last 4 characters or digits?

I'm trying to mask a credit card in case a credit card format has been inserted in the form. So instead of credit card being inserted, it will be asked something like **** **** **** 1234

Answer 1

It can be 16 digit credit card or more so you can match it using this regex or You can goto This Link and generate your own regex

Regex  (?i)^((\d+\s+?\d+\s+?\d+\s+?)(\d{4}))

In here accessing the Group2

                var Creditcardno= // Here put your credit card no
                string reg = @"(?i)^((\d+\s+\d+\s+\d+\s+)(\d{4})))";
                Regex r = new Regex(reg, RegexOptions.IgnoreCase);
                Match m = r.Match(Creditcardno);
                int number = m.Groups[2];

You Can get last Four no or anything with grouping the regex.

If you only need last four-digit nothing more

      (.+)([0-9]{4}$) 

use this and from a group 1 you can get the last four no.

Answer 2

Here's a pattern to match the last four digits of an American Express card number.

Pattern

3[47]\d{2}\s?\d{6}\s?\d(\d{4})

See the demo here .

Edit: Per request in the discussion we had in the chat, here's a consolidated pattern based on the patterns of most major card networks that you provided (without any research on the specification myself): consolidated pattern

Sources

• Anatomy of a Credit Card: Cardholder Name, Number, Network and More
• ISO/IEC 7812-1:2017 - Identification cards — Identification of issuers — Part 1: Numbering system