exec을 실행시킨 프로세스가 바로 죽어버립니다..

            if(pid < 0)
    36      {
    37          perror("fork err");
    38          exit(1);
    39      }
    40      else if(pid == 0)
    41      {
    42          close(0);
    43          close(1);
    44          dup2(w_pipe[0], 0);
    45          close(w_pipe[0]);
    46          close(w_pipe[1]);
    47
    48          dup2(r_pipe[1], 1);
    49          close(r_pipe[0]);
    50          close(r_pipe[1]);
    51
    52          execl("/bin/sh", "sh", NULL);
    53
    54          fprintf(stderr, "fail exec\n");
    55          exit(0);
    56      }
    57      else
    58      {
    59          waitpid(-1, NULL, WNOHANG);
    60
    61          close(w_pipe[0]);
    62          close(r_pipe[1]);
    63
    64          if(pthread_create(&tid1, NULL, (void *)read_bash, NULL)  == -1)
    65          {
    66              printf("p_c fail\n");
    67          }
    68          if(pthread_create(&tid2, NULL, (void *)write_bash, NULL)  == -1)
    69          {
    70              printf("p_c fail\n");
    71          }
    72
    73          pthread_join(tid1, NULL);
    74          pthread_join(tid2, NULL);
    75      }