UNIX管道子进程之间 [英] UNIX Pipes Between Child Processes

问题描述

我想编写一个程序，将产生子进程和管道之间，类似的命令行管道任意数量。就我而言，我试图做的ls -l命令|更多。并输出到标准输出，然后让父母继续执行多个命令

I'm trying to write a program that will spawn an arbitrary number of child processes and pipe between them, similar to a command line pipeline. In my case I'm trying to do "ls -l | more" and output that to stdout, then have the parent continue executing more commands.

我有以下的code作为一个小例子：

I have the following code as a minimal example:

int main (int argc, const char * argv[]) {
    int fd[2];
    pipe(fd); 
    chdir("/directory/with/lots/of/files");

    // Create one child process for more
    int pid = fork();
    if (pid == 0) {
        close(fd[1]);
        int ret = dup2(fd[0],0);
        if (ret < 0) perror("dup2");
        char *argv[10];
        argv[0] = "more";  argv[1] = NULL;
        execvp("more", argv);
    } 
    // Create another child process for ls
    int pid2 = fork();
    if (pid2 == 0) {
        int ret = dup2(fd[1],1);
        if (ret < 0) perror("dup2");
        char *argv[10];
        argv[0] = "ls";    argv[1] = "-l";   
        argv[2] = NULL;
        execvp("ls", argv);
    }

    // wait for the more process to finish
    int status;
    waitpid(pid, &status, 0);

    printf("Done!\n");
    return 0;
}

现在，当我执行程序（用当然是一个main（）函数）我结了比较，预计。我会打D向下翻页更多的产出和u上去，似乎很好地工作。但是，当我到达的不是退出更喜欢做底，它只是留下一个空行。按Ctrl-C的工作，退出它，但它退出整个程序，这意味着DONE！线永远不会被打印出来。电影可以这里，说明发生了什么（请注意，在最后我preSS按Ctrl-C要回的bash）

Now, when I execute the program (enclosed in a main() function of course) what I end up with is more, which is expected. I'll hit "d" to page down more's output and "u" to go up, and it seems to work fine. But when I reach the bottom, instead of exiting like more does, it just leaves a blank line. Ctrl-C works to exit it but it exits the entire program, meaning the "Done!" line never gets printed. A movie is available here that illustrates what happens (note that at the very end I press Ctrl-C to get back to bash).

在这个有什么想法？我只是想弄清楚如何将其更改为，而不是经过到达底部，更多的退出并返回到父进程将一个空行，因此它可以继续执行。

Any thoughts on this? I'm just trying to figure out how to change it to where instead of going to a blank line after more reaches the bottom, more quits and returns to the parent process so it can continue executing.

推荐答案

您需要的close（）至少你管的书写端，否则更多将永远不会看到EOF。例如：

You need to close() at least the writing end of your pipe, otherwise more will never see EOF. For example:

    ...

    // close parent's pipes
    close(fd[0]);
    close(fd[1]);

    // wait for the more process to finish
    int status;
    waitpid(pid, &status, 0);

    printf("Done!\n");
    return 0;
}

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