Question

我一直在尝试编写一个程序来发送和接收命令到bash shell（/ bin / sh）。就像围绕bash shell的包装程序一样。所以，我可以写入stdin“cd~ / Desktop”，然后再次写“ls”，我将收到桌面上的文件列表。我不能让它工作。在这段代码中的第二个写命令中，它将回显我写入stdin的任何内容。我也尝试使用popen（），但只提供输出，不允许我写入stdin。有人可以帮忙解决这个问题吗？感谢

void main()
{
    // Create a pipe and fork
    //
    int fd[2];
    int p = pipe(fd);
    pid_t pid = fork();

    if (pid > 0)
    {
        // Read from the pipe and output the result
        //
        //close(fd[1]);
        char buf[1024] = { 0 };

        read(fd[0], buf, sizeof(buf));

        printf("1 - %s\n", buf);

        write (fd[1], "ifconfig", strlen ("ifconfig") );

        // problem is here, read is returning echo'd bytes from write()

        read(fd[0], buf, sizeof(buf));

        printf("2 - %s\n", buf);    


        // Wait for child to terminate
        int status;
        wait(&status);
    }
    else if (pid == 0)
    {
        // Redirect stdout and stderr to the pipe and execute the shell
        // command
        //
        dup2(fd[0], STDIN_FILENO);
        dup2(fd[1], STDOUT_FILENO);
        dup2(fd[1], STDERR_FILENO);
        //close(fd[0]);
        execl("/bin/sh", "exec sh", "-c", "ls", (char*) NULL );
    }

}

编辑 - 每个第一个答案更新了代码，现在第二个read（）调用没有输出

void main()
{
    // Create a pipe and fork
    //
    int fd[2];

int ChildToParent[2], ParentToChild[2];



    pipe (ParentToChild);
pipe (ChildToParent);

    pid_t pid = fork();

    if (pid > 0)
    {
        // In parent process

        // Read the output of the child from child_to_parent[0]
        // We don't need child_to_parent[1] so close it
        close(ChildToParent[1]);

        // Write output to the child using parent_to_child[1]
        // We don't need parent_to_child[0] so close it
        close(ParentToChild[0]);

        // Read from and write to the child process...
        char buf[1024] = { 0 };

        read(ChildToParent[0], buf, sizeof(buf));   
    printf("1 - %s\n", buf);


    write(ParentToChild[1], "whoami", strlen ("whoami") );

    memset (buf, 0, 1024);

    // this call to read returns nothing
    read(ChildToParent[0], buf, sizeof(buf));
    printf("2 - %s\n", buf);



    }
    else if (pid == 0)
    {
        // Redirect stdout and stderr to the pipe and execute the shell
        // command
        //
    // child_to_parent[1] is were we write output, it's the
        // new standard output, child_to_parent[0] can be closed
        dup2 (ChildToParent[1], STDOUT_FILENO);
        close(ChildToParent[0]);

        // parent_to_child[0] is where we read input from, it's the
        // new standard input, parent_to_child[1] can be closed
        dup2 (ParentToChild[0], STDIN_FILENO);
        close(ParentToChild[1]);

        //close(fd[0]);
        execl("/bin/sh", "exec sh", "-c", "ls", (char*) NULL );
    }

}

Answer 1

请记住，管道是单向通信流。您不能将它用于两个进程之间的双向通信。为此你需要两个管道，每个方向一个。

也许就像这个简单的例子：

// Pipe for the child process to write to the parent process
int child_to_parent[2];

// Pipe for the parent process to write to the child process
int parent_to_child[2];

// Create the TWO pipes
pipe(child_to_parent);
pipe(parent_to_child);

pid_t pid = fork();
if (pid > 0)
{
    // In parent process

    // Read the output of the child from child_to_parent[0]
    // We don't need child_to_parent[1] so close it
    close(child_to_parent[1]);

    // Write output to the child using parent_to_child[1]
    // We don't need parent_to_child[0] so close it
    close(parent_to_child[0]);

    // Read from and write to the child process...
}
else if (pid == 0)
{
    // In child process

    // child_to_parent[1] is were we write output, it's the
    // new standard output, child_to_parent[0] can be closed
    dup2(child_to_parent[1], STDOUT_FILENO);
    close(child_to_parent[0]);

    // parent_to_child[0] is where we read input from, it's the
    // new standard input, parent_to_child[1] can be closed
    dup2(parent_to_child[0], STDIN_FILENO);
    close(parent_to_child[1]);

    // Do whatever the child is supposed to do
}

读/写stdin / out for bash interpreter linux，fork - execl

1 个答案: