我正在创建一个自定义 shell ，目前正在努力让多个管道工作。例如，ls -al | wc -l返回当前目录中所有文件目录的数量。我密切关注这个link的“解决方案代码”。
下面是我的实现，具有非常相似的命令输入结构：

// every command is a 
// struct command
// with their arguments attached
struct command
{
    char **cmd; // argument list for execvp(eg: {"ls", "-al"})
    int numArgs; // number of total arguments in current line 
};

// my implementation of multiple pipes based on link supplied with slight modifications
void runPipedCommands(struct command *commands)
{
    // this code just counds the number of pipes in commands
    int numPipes = 0;
    for (int i = 0; i < commands->numArgs; i++)
    {
        if (!strcmp(commands[i].cmd[0], "|"))
            numPipes++;
    }
    printf("number of pipes: %d\n", numPipes);

    int status;
    int i = 0;
    pid_t pid;

    int pipefds[2 * numPipes];
    // create the pipes
    for (i = 0; i < (numPipes); i++)
    {
        if (pipe(pipefds + i * 2) < 0)
        {
            perror("couldn't pipe");
            exit(EXIT_FAILURE);
        }
    }

    int j = 0;
    int c = 0;
    while (commands[c].cmd)
    {
        // skip the pipe operators
        if (!strcmp(commands[c].cmd[0], "|"))
            c++;
        pid = fork();
        if (pid == 0)
        {

            printf("cmd to execute: %s\n", commands[c].cmd[0]);
            //if not last command
            if (commands[c + 1].cmd[0])
            {
                // everyone even fd gets this, set stdout to write
                // end of pipe
                if (dup2(pipefds[j + 1], STDOUT_FILENO) < 0)
                {
                    perror("dup2");
                    exit(EXIT_FAILURE);
                }
            }
            else
            {
                exit(EXIT_SUCCESS);
            }

            //if not first command&& j!= 2*numPipes
            if (j != 0)
            {
                // every odd fd gets this, set stdin to
                // read end of pipe
                if (dup2(pipefds[j - 2], STDIN_FILENO) < 0)
                {
                    perror(" dup2");
                    exit(EXIT_FAILURE);
                }
            }

            // close dup2ed fds
            for (i = 0; i < 2 * numPipes; i++)
            {
                close(pipefds[i]);
            }
            // execvp
            if (execvp(commands[c].cmd[0], commands[c].cmd) < 0)
            {
                perror(commands[c].cmd[0]);
                exit(EXIT_FAILURE);
            }
        }
        else if (pid < 0)
        {
            perror("error");
            exit(EXIT_FAILURE);
        }

        c++;
        j += 2;
    }
    /**Parent closes the pipes and wait for children*/

    for (i = 0; i < 2 * numPipes; i++)
    {
        close(pipefds[i]);
    }

    for (i = 0; i < numPipes + 1; i++)
        wait(&status);
}

// my main function with my test input:
int main(int argc, char *argv[])
{
    // my parseW function simply returns a list of struct commands
    struct command *results = parseW("ls -al | wc -l");

    runPipedCommands(results);
    return 0;
}

上面的代码省略了parseW，结果是终端输出：

在管道的执行中，一切看起来都是正确的，我已经检查了文件描述符（在我的特定测试用例中只有2个文件描述符）。我不知道我做错了什么。