UNIX 管道操作小Demo

/* 摘自 
    "UNIX SYSTEMS Programming: Communication, 
    Concurrency, and Threads", by Kay a. Robbins, 
    and Steven Robbins. 第190页
*/

#include 
#include 
#include 
#include 

int main(void)
{
  pid_t childpid;
  int fd[2];

  if ((pipe(fd) == -1) || ((childpid = fork()) == -1)) {
    perror("failed to setup pipeline");
    return 1;
  }
  
  if (childpid == 0) {
    if (dup2(fd[1], STDOUT_FILENO) == -1)
      perror("Failed to redirect stdou of ls");
    else if ((close(fd[0]) == -1) || (close(fd[1]) == -1))
      perror("Failed to close extra pipe descriptors on ls");
    else {
      execl("/bin/ls","ls","-l", NULL);
      perror("Failed t exec ls");
    }
    return 1;
  }

  if (dup2(fd[0], STDIN_FILENO) == -1)
    perror("Failed to redirect stdin of sort");
  else if ((close(fd[0]) == -1) || (close(fd[1]) == -1))
    perror("Failed to close extra pipe file descriptors on sort");
  else {
    execl ("/bin/sort","sort", "-n","+4",NULL);
    perror("Faile dot exec sort");
  }
  return 1;
}