```My solution is below.

# file: credit_card.rb
# author: Drew Olson

class CreditCard
def initialize num
@number = num
end

# check specified conditions to determine the type of card
def type
length = @number.size
if length == 15 && @number =~ /^(34|37)/
"AMEX"
elsif length == 16 && @number =~ /^6011/
"Discover"
elsif length == 16 && @number =~ /^5[1-5]/
"MasterCard"
elsif (length == 13 || length == 16) && @number =~ /^4/
"Visa"
else
"Unknown"
end
end

# determine if card is valid based on Luhn algorithm
def valid?
digits = ''
# double every other number starting with the next to last
# and working backwards
@number.split('').reverse.each_with_index do |d,i|
digits += d if i%2 == 0
digits += (d.to_i*2).to_s if i%2 == 1
end

# sum the resulting digits, mod with ten, check against 0
digits.split('').inject(0){|sum,d| sum+d.to_i}%10 == 0
end
end

if __FILE__ == \$0
card = CreditCard.new(ARGV.join.chomp)
puts "Card Type: #{card.type}"
if card.valid?
puts "Valid Card"
else
puts "Invalid Card"
end
end

--
Posted via http://www.ruby-forum.com/.

```