管道实现ps -aux | grep a.out

/*************************************************************************
 * File Name: ps_aux.c
 * Author: lixiaogang
 * Mail: [e-mail] 
 * Created Time: 2017年06月08日 星期四 21时13分08秒
 ************************************************************************/

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/types.h>
#include<fcntl.h>
#include<unistd.h>

void sys_err(const char *str,int num)
{
    perror(str);
    exit(num);
}

int main(int argc,char *argv[])
{
    int fd[2];
    pid_t pid;
    if(pipe(fd) != 0){
        sys_err("pipe",-1);
    }
    pid = fork();
    if(pid < 0){
        sys_err("fork",-1);
    }else if(pid == 0){
        //ps -aux | grep a.out
        close(fd[0]);
        dup2(fd[1],STDOUT_FILENO);
        close(fd[1]);
        execlp("ps","ps","aux",NULL);
        return -3;
    }


    pid = fork();
    if(pid < 0){
        sys_err("fork",-1);
    } else if(pid == 0){
        close(fd[1]);
        dup2(fd[0],STDIN_FILENO);
        close(fd[0]);
        execlp("grep","grep","a.out",NULL);
    }

    wait(NULL);
    wait(NULL);

    close(fd[0]);
    close(fd[1]);

    return 0;
}