docs: def get_output_from_pipe(self, input_file):
          """Executes an external command and get its output. The command
          receives its input_file from the stdin through a pipe
          
          :param input_file: input file
          :return: output of command
          """
          args = shlex.split(self.cmd)
          p = Popen(args, stdout=PIPE, stdin=PIPE)  # | grep es
          p.stdin.write(bytearray(input_file.encode("utf8")))  # echo test |
          return p.communicate()[0].decode("utf8")