How to validate credit cards using a regular expression?

 Again, you should rely on other methods since the regular expressions here will only validate the format. Make use of the Luhn algorithm to properly validate a card.

VISA:

^4[0-9]{12}(?:[0-9]{3})?$

MasterCard:

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

American Express:

^3[47][0-9]{13}$

Diners Club:

^3(?:0[0-5]|[68][0-9])[0-9]{11}$

Discover:

^6(?:011|5[0-9]{2})[0-9]{12}$

JCB:

^(?:2131|1800|35\d{3})\d{11}$