Question

I am writing a C program which will run Linux commands, like:
cat /etc/passwd | grep list | cut -c 1-5
and i didnt have any result
*here the parent wait for the first child(child_pid) to finish;
and the first child wait for the second(pfils) !!
any idea?
code :

main()
{
    pid_t child_pid;
    int fd[2];
    int pfd[2];
    pipe(pfd);
    child_pid = fork ();

    if (child_pid != 0) 
    {
        wait(child_pid);
        close(pfd[1]);
        dup2(pfd[0],0);
        close(pfd[0]);
        execlp("cut","cut","-c","1-5",NULL);
    }
    else
    {
        pid_t pfils = fork();
        pipe(fd);

        if(pfils == 0)
        {
            close(fd[0]);
            dup2(fd[1],1);
            close(fd[1]);
            execlp("cat", "cat","/etc/passwd",NULL);
        }
        else
        {
            wait(pfils);
            close(fd[1]);
            dup2(fd[0],0);
            close(fd[0]);
            close(pfd[0]);
            dup2(pfd[1],1);
            close(pfd[1]);
            execlp("grep","grep","list",NULL);
        }
    }
}

Answer 1

    pid_t pfils = fork();
    pipe(fd);

Fork will make a copy of the process. An independent copy of the process. So, if you call pipe after fork, each copy of the process gets their own pipe. Put pipe() before fork() and it should work.