converts english into morse code

morse code converter

str = ''
counter = 1
ARGV.each do |a|
  counter = counter + 1
  a.each_char do |char|
    char = char.to_s.downcase
    case char
      when 'a'
        str += '.-'
      when 'b'
        str += '-...'
      when 'c'
        str += '-.-.'
      when 'd'
        str += '-..'
      when 'e'
        str += '.'
      when 'f'
        str += '..-.'
      when 'g'
        str += '--.'
      when 'h'
        str += '....'
      when 'i'
        str += '..'
      when 'j'
        str += '.---'
      when 'k'
        str += '-.-'
      when 'l'
        str += '.-..'
      when 'm'
        str += '--'
      when 'n'
        str += '-.'
      when 'o'
        str += '---'
      when 'p'
        str += '.--.'
      when 'q'
        str += '--.-'
      when 'r'
        str += '.-.'
      when 's'
        str += '...'
      when 't'
        str += '-'
      when 'u'
        str += '..-'
      when 'v'
        str += '...-'
      when 'w'
        str += '.--'
      when 'x'
        str += '-..-'
      when 'y'
        str += '-.--'
      when 'z'
        str += '--..'
      when '1'
        str += '.----'
      when '2'
        str += '..---'
      when '3'
        str += '...--'
      when '4'
        str += '....-'
      when '5'
        str += '.....'
      when '6'
        str += '-....'
      when '7'
        str += '--...'
      when '8'
        str += '---..'
      when '9'
        str += '----.'
      when '0'
        str += '-----'
      when ' '
        str += ' '
    end
  end
  str += ' ' unless ARGV.size - counter < 1
end

puts str