gistfile1.txt

class Turing
  def initialize(file, tape=nil)
    @tape = Hash.new('_')
    @head = 0

    # initialize tape
    tape.split(//).each_with_index {|c,i| @tape[i] = c } if tape

    # read program instructions
    @program = Hash[
      File.readlines(file)
        .map {|line| line.gsub(/#.*$/, '') } # remove comments
        .map(&:strip).reject(&:empty?) # skip blank lines
        .map {|line| line.split(/\s+/) }
        .map {|line| [line[0..1], line[2..4]] }
    ]

    # set the initial state
    @state = @program.first[0][0]
  end

  def run
    while next_state = @program[[@state, @tape[@head]]]
      @state, @tape[@head], dir = next_state
      @head += (dir == 'R') ? 1 : -1
    end

    puts @tape.sort.map {|_,v| v}.join.gsub(/^_*|_*$/, '')
  end
end

Turing.new(ARGV.shift, ARGV.shift).run if __FILE__ == $0