def `(command)
      result    = super(command)
      exit_code = $?.to_i
      raise Error::CommandFailed.new(result, exit_code) unless exit_code == 0
      result
    end
def `(command)
      result    = super(command)
      exit_code = $?.to_i
      raise Error::CommandFailed.new(result, exit_code) unless exit_code == 0
      result
    end
Actions have a backticks command that raises a CommandFailed exception
 on failure, so that processing doesn't just blithely continue.