23.rb

line = (<<-END).strip.chars.to_a
'"'hello world"\\", he" said, whil'e \\opening\\' "the door"
END

elements = [""]
mode = nil

while char = line.shift
  puts char
  case mode
  when :double
    case char
    when '"'
      mode = nil
    when "\\"
      line.shift # to also eat the "
      elements[-1] = elements.last + '"'
    else
      elements[-1] = elements.last + char
    end
  when :single
    case char
    when "'"
      mode = nil
    else
      elements[-1] = elements.last + char
    end
  else
    case char
    when '"'
      puts 'switch to double'
      mode = :double
    when "'"
      mode = :single
    when " "
      elements << ""
    else
      elements[-1] = elements.last + char
    end
  end
end

elements.each { |i| puts i }