gistfile1.rb

def String.random(size, option={})
  option = {
    :capital => false,
    :exclude => []
  }.merge(option)

  alphanumerics = ('a'..'z').to_a + ('0'..'9').to_a
  alphanumerics += ('A'..'Z').to_a if option[:capital]
  alphanumerics -= option[:exclude].to_a

  Array.new(size){ alphanumerics.choice }.join
end