#include 
    
     #include 
     
      #include 
      
       #include 
       
         int main(int argc, char **argv){
       int fd[2];    int pid;    pipe(fd);    int rpipe = fd[0];    int wpipe = fd[1];    pid = fork();    if (pid == 0)    {
              /* 子进程关掉读的那端，只用写的一端 */        close(rpipe);          /* 把标准输入指向pipe的写的一端 */        dup2(wpipe, STDOUT_FILENO);         /* 执行pwd */        execl("/bin/pwd",".",NULL);         /* 嗯 */        exit(0);    }       else    {
              /* 父进程关掉写的那端，只用读的一端 */        close(wpipe);         printf("begin parent process\n");        char readbuffer[1024];         /* 从读的这端读出pwd的输出 */        int nbytes = read(rpipe, readbuffer, sizeof(readbuffer));         printf("Received string: %s | %d\n", readbuffer, nbytes);        printf("end parent process\n");         wait(&pid);    }       return 0;}