code: func (d *Dataset) PipeAsArgs(name, code string) *Dataset {
  	ret, step := add1ShardTo1Step(d)
  	step.IsPipe = true
  	step.SetInstruction(name, instruction.NewPipeAsArgs(code))
  	return ret
  }
docs: // PipeAsArgs takes each row of input, bind to variables in parameter
  // code. The variables are specified via $1, $2, etc. The code is
  // run as the command for an external program for each row of input.
  //
  // Watch for performance impact since it starts one Os process
  // for each line of input.