经典C.使用在execvp的功能，stdin和stdout重定向管道 [英] Classic C. Using pipes in execvp function, stdin and stdout redirection

问题描述

我想使用管道和execvp函数我的Linux C程序来模拟庆典。例如

I want to simulate bash in my Linux C program using pipes and execvp function. e.g

ls -l | wc -l  

有是我的程序：

if(pipe(des_p) == -1) {perror("Failed to create pipe");}

if(fork() == 0) {    //first fork
  close(1);          //closing stdout
  dup(des_p[1]);     //replacing stdout with pipe write 
  close(des_p[0]);   //closing pipe read
  close(des_p[1]);   //closing pipe write

  if(execvp(bash_args[0], bash_args)) // contains ls -l
    /* error checking */
}
else {
  if(fork() == 0) {  //creating 2nd child
    close(0);        //closing stdin
    dup(des_p[0]);   //replacing stdin with pipe read
    close(des_p[1]); //closing pipe write
    close(des_p[0]); //closing pipe read

    if(execvp(bash_args[another_place], bash_args)) //contains wc -l
      /* error checking */
  }

  close(des_p[0]);
  close(des_p[1]);
  wait(0);
  wait(0);
}

这code实际运行，但不会做正确的事。
有什么不对的code？这不是工作，我没有线索，为什么。

This code actually runs, but doesn't do the right thing. What's wrong with this code? That's not working and I don't have a clue why.

推荐答案

您需要关闭管道FDS的父母，或孩子不会收到EOF，因为管道的开放仍然在父写作。这将导致第二个等待（）挂起。对我的作品：

You need to close the pipe fds in the parent, or the child won't receive EOF, because the pipe's still open for writing in the parent. This would cause the second wait() to hang. Works for me:

#include <unistd.h>
#include <stdlib.h>


int main(int argc, char** argv)
{
        int des_p[2];
        if(pipe(des_p) == -1) {
          perror("Pipe failed");
          exit(1);
        }

        if(fork() == 0)            //first fork
        {
            close(STDOUT_FILENO);  //closing stdout
            dup(des_p[1]);         //replacing stdout with pipe write 
            close(des_p[0]);       //closing pipe read
            close(des_p[1]);

            const char* prog1[] = { "ls", "-l", 0};
            execvp(prog1[0], prog1);
            perror("execvp of ls failed");
            exit(1);
        }

        if(fork() == 0)            //creating 2nd child
        {
            close(STDIN_FILENO);   //closing stdin
            dup(des_p[0]);         //replacing stdin with pipe read
            close(des_p[1]);       //closing pipe write
            close(des_p[0]);

            const char* prog2[] = { "wc", "-l", 0};
            execvp(prog2[0], prog2);
            perror("execvp of wc failed");
            exit(1);
        }

        close(des_p[0]);
        close(des_p[1]);
        wait(0);
        wait(0);
        return 0;
}

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