```Hi all,
Here's my solution...

(pastie: http://pastie.caboo.se/57591)

regards,
rolando.-

#!/usr/bin/env ruby

# RubyQuiz #122
# Solution by Rolando Abarca M.
# rabarca (at) scio.cl

# small hack to allow intervals as a cc length
class Fixnum
def include?(n)
self == n
end
end

module CChecker
# prefixes taken from wikipedia
# http://en.wikipedia.org/wiki/Credit_card_number
PREFIXES = [
# regexp, length, name, checking algorithm
# length can be a fixnum, array or range.
# the algorithm must be in the CChecker module
[/^(34|37)\d+\$/, 15, "AMEX", :luhn],
[/^30[0-5]\d+\$/, 14, "Diners Club Carte Blanche", :luhn],
[/^36\d+\$/, 14, "Diners Club International", :luhn],
[/^55\d+\$/, 16, "Diners Club US & Canada", :luhn],
[/^(6011|65)\d+\$/, 16, "Discover", :luhn],
[/^35\d+\$/, 16, "JCB", :luhn],
[/^(1800|2131)\d+\$/, 15, "JCB", :luhn],
[/^(5020|5038|6759)\d+\$/, 16, "Maestro", :luhn],
[/^(51|54|55)\d+\$/, 16, "Mastercard", :luhn],
[/^(6334|6767)\d+\$/, [16,19], "Solo", :luhn],
[/^4\d+\$/, [13,16], "Visa", :luhn],
[/^(417500|4917|4913)\d+\$/, 16, "Visa Electron", :luhn]
]
UNKNOWN_PREFIX = [nil, 0, "Unknown", :luhn]

def CChecker.usage(doexit = false)
puts "usage: cchecker.rb <ccnumber>"
exit if doexit
end

# try to identify the card
def CChecker.check_prefix(ccnumber)
pr = PREFIXES.detect {|p| p[0].match(ccnumber) &&
p[1].include?(ccnumber.length)}
(pr.nil?) ? UNKNOWN_PREFIX : pr
end

# do the complete check of the cc:
# 1.- try to identify
# 2.- apply algorithm (should return true/false)
# returns an array: [isvalid, card_identifier]
def CChecker.check(ccnumber)
ccnumber = ccnumber.to_s.delete(" ")
pr = check_prefix(ccnumber)
[send(pr[3], ccnumber), pr[2]]
end

# classic Luhn's algorithm
def CChecker.luhn(ccnumber)
sum = 0
ccnumber.reverse.split(//).each_with_index do |c, i|
cx = c[0]-48; # this should be faster than c.to_i, right?
next if cx > 9 || cx < 0 # only numbers, please
if (i+1) & 1 == 0
cx *= 2
cx = (cx/10 + cx%10) if cx > 9
end
sum += cx
end
sum % 10 == 0
end
end

CChecker::usage(true) if ARGV.size != 1
valid, card = CChecker::check(ARGV[0])
if valid
puts "#{card} Valid"
else
puts "#{card} Invalid"
end

```