在C- Piping和外部命令中创建外壳

Question

我正在尝试使用C创建一个小的shell，目前我正在尝试弄清楚管道和外部命令。即使在看了各种youtube视频后，我还是被困在了他们两个人身上。我指的是MAN甚至是Advanced Linux Programming

我可以改变什么来改进和使实现工作？

这是检查命令、args := tokenisation by whitespace、commLHS := will be used to store args before | and commRHS will be used to store args after |和indexT refers to the number of arguments inputted的一部分

else if((check4pipe(args, commLHS, commRHS, indexT) != 0))
    {
        return runPipeComm(commLHS, commRHS);
        //fprintf(stderr, "%s: command not found\n", args[0]);
    }

这将执行外部命令

void externalCommands(char **args)
{
    // fork-plus-exec pattern 
    // https://www.percona.com/community-blog/2021/01/04/fork-exec-wait-and-exit/

    /*
        First we Fork
        Then we Exec
        Then we Wait
        Then we Exit
    */
    int status;
    
    pid_t pip = fork();

    if (pip == -1) 
    {
        perror("Error - fork()");
    }
    else if (pip == 0) 
    {   
        //If PID is the child process
        //Launches the process.
        
        if (execvp(args[0], args) < 0) 
        {
            perror("Error - execvp()");
        }
    }
    else 
    { //If PID is the parent process.
        //Waits for the child process and returns exit code if waitpid() is successful.
            if(waitpid(pip, &status, WUNTRACED) == -1)
            {
                perror("Error occured during waitpi");
            }
            else
            {   
                //set_exitcode(status); //Sets the exitcode environment variable.
            }
    }
    
}

这是为了在标记化之后检查用户输入的参数中的|。

int check4pipe(char **args, char **pipeLHS, char **pipeRHS, int indexT)
{
    bool foundPipe = false;

    for(int i = 0; i < indexT; i++)
    {
        if(strcmp(args[i], "|") == 0)
        {
            foundPipe = true;

            memcpy(pipeLHS, args, (i+1) * sizeof(char*));
            pipeLHS[i] = NULL;

            memcpy(pipeLHS, args+(i+1), ((indexT-i)+1) * sizeof(char*));
            pipeRHS[i]= NULL;
        }
        else
        {
            continue;
        }
    }

    if(foundPipe == true)
    {
        return 1;
    }
    else
    {
        return 0;
    }
}

这将运行管道命令

int runPipeComm(char **commLHS, char **commRHS)
{
    int userPipe[2];
    
    pid_t pip1; // Pipe ID 1
    pid_t pip2; // Pipe ID 2

    if(pipe(userPipe) < 0)
    {
        perror("Error Occurred while piping: ");
    }

    // Start Process 
    pip1 = fork();

    if(pip1 == -1)
    {
        perror("Error Occurred while forking: ");
    }
    else if(pip1 == 0)
    {
        dup2(userPipe[1], STDOUT_FILENO);
        close(userPipe[1]);

        //run

        exit(0);
    }
    else
    {
        pip2 = fork();

        if(pip2 == -1)
        {
            perror("Error Occurred while forking: ");
        }
        else if(pip2 == 0)
        {
            dup2(userPipe[0], STDOUT_FILENO);
            close(userPipe[1]);

            //run

            exit(0);
        }
        else
        {
            close(userPipe[0]);
            close(userPipe[1]);

            wait(NULL);
            wait(NULL);
        }
    }

    return 1;
}

Answer 1

在程序中复制代码片段时，您忘记了更改某些内容。

错误：

            memcpy(pipeLHS, args+(i+1), ((indexT-i)+1) * sizeof(char*));
            pipeRHS[i]= NULL;

右图：

            memcpy(pipeRHS, args+(i+1), (indexT-(i+1)) * sizeof (char*));
            pipeRHS[indexT-(i+1)] = NULL;

错误：

            dup2(userPipe[0], STDOUT_FILENO);
            close(userPipe[1]);

右图：

            dup2(userPipe[0], STDIN_FILENO);
            close(userPipe[0]);

在第一个//run行之后，添加缺少的

        execvp(*commLHS, commLHS);
        perror("Error - execvp()");

在第二个//run行之后，添加缺少的

            execvp(*commRHS, commRHS);
            perror("Error - execvp()");

最后，在父进程中必须关闭管道的写入端，因此将close()移到那里：

        close(userPipe[1]);
        pip2 = fork();