I was looking at implementing a luhn and credit card type check the other day in java and I noticed that there seems to be a lack of code for doing this in ruby. So I figured I would put something together for doing the checks in ruby.

The following function will do a luhn check for a given number (any number not just credit card numbers). The luhn algorithm is fairly simple, if you want to learn more about it check here.

ccNumber = ccNumber.gsub(/D/, ")

cardLength = ccNumber.length

parity = cardLength % 2

sum = 0

for i in 0…cardLength

digit = ccNumber[i] – 48

if i % 2 == parity

digit = digit * 2

end

if digit > 9

digit = digit – 9

end

sum = sum + digit

end

return (sum % 10) == 0

end

Before running the luhn check you may want to verify that you have a valid card type or at least one you want to accept. The following function will do that based on the current bin ranges for the differenct companies as of today (for more on this see the following: credit card number information and BIN range information). N.B. Bin ranges change from time to time so this will become dated. It should be easy enough to find the updated ranges.

ccNumber = ccNumber.gsub(/D/, ")

case ccNumber

when /^3[47]d{13}$/ then return "AMEX"

when /^4d{12}(d{3})?$/ then return "VISA"

when /^5d{15}|36d{14}$/ then return "MC"

when /^6011d{12}|650d{13}$/ then return "DISC"

when /^3(0[0–5]|8[0–1])d{11}$/ then return "DINERS"

when /^(39d{12})|(389d{11})$/ then return "CB"

when /^3d{15}|1800d{11}|2131d{11}$/ then return "JCB"

else return "NA"

end

end

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Tetsuo Namba# more "Ruby way" of writing the same code

parity = ccNumber.length % 2

sum = 0

ccNumber.split(").each_with_index do |c, i|

digit = c.to_i

digit = (digit * 2) % 9 if i % 2 == parity

sum += digit

end

return (sum % 10) == 0

end