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These subroutines tell you whether a credit card number is
self-consistent -- whether the last digit of the number is
a valid checksum for the preceding digits.
The validate() subroutine returns 1 if the card number
provided passes the checksum test, and 0 otherwise.
The cardtype() subroutine returns a string containing the
type of card: "MasterCard", "VISA", and so on. My list is
not complete; I welcome additions.
The generate_last_digit() subroutine computes and returns
the last digit of the card given the preceding digits.
With a 16-digit card, you provide the first 15 digits; the
subroutine returns the sixteenth.
This module does not tell you whether the number is on an
actual card, only whether it might conceivably be on a
real card. To verify whether a card is real, or whether
it's been stolen, or what its balance is, you need a
Merchant ID, which gives you access to credit card
databases. The Perl Journal
(http://work.media.mit.edu/tpj) has a Merchant ID so that
I can accept MasterCard and VISA payments; it comes with
the little pushbutton/slide-your-card-through device
you've seen in restaurants and stores. That device
calculates the checksum for you, so I don't actually use
this module.
These subroutines will also work if you provide the
arguments as numbers instead of strings, e.g.
validate(5276440065421319).
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