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

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")