C++ 模拟shell并运行.sh文件

我有一个模拟shell，具有运行bash文件的能力，需要shell支持！！，echo和exit，这就是我到目前为止所做的:

void run_file(char* file){
    int i;
    char* echo = "echo";
    char* ex = "exit";
    char* prev_f = (char*)malloc(sizeof(char)*MAX_CMD_BUFFER);
    char* nline = "\n";
    char* bang = "!!";
    char check[5];
    char c_bang[3];
    char c_nline[2];
    
    c_nline[1] = '\0';
    FILE *fp = fopen(file, "r");
    char line[MAX_CMD_BUFFER];
    size_t len = 0;
    ssize_t read;
    if (fp == NULL)
        exit(EXIT_FAILURE);
    while((read = getline(&line, &len, fp)) != -1){
        for(i = 0; i < 4; i++){
            check[i] = line[i];
            if(i < 2){
                c_bang[i] = line[i];
            }
        }
        c_nline[0]=line[0];
        check[4] = '\0';
        c_bang[3] = '\0';
        if(strcmp(c_nline, nline) == 0){continue;}
        else if(strcmp(check, echo) == 0){
            i = 5;
            if (line[5] =='\n')
            {
                continue;
            }
            while(line[i] != '\n'){
                printf("%c", line[i]);
                i++;
            }
            strcpy(prev_f, line);
        }
        else if(strcmp(c_bang, bang) == 0){
            if(*prev_f == NULL){continue;}
            i = 0;
            for(i = 0; i < 4; i++){
                check[i] = prev_f[i];
            }
            check[4] = '\0';
            if(strcmp(check, echo) == 0){
                i = 5;
                if (prev_f[5] == '\n'){
                    continue;
                }
                while(prev_f[i] != '\n'){
                    printf("%c", prev_f[i]);
                    i++;
                }
            }
            else if(strcmp(check, ex) == 0){
                char val[3];
                for(i = 5; i < 8; i++){
                    val[i - 5] = prev_f[i];
                }
                int v = atoi(val);
                if(v > 255){v = 255;}
                printf("bye!\n");
                exit(v);
            }
            else{
                printf("invalid previous command");
            }
        }
        else if(strcmp(check, ex) == 0){
            char val[3];
            for(i = 5; i < 8; i++){
                val[i - 5] = line[i];
            }
            int v = atoi(val);
            if(v > 255){v = 255;}
            printf("$ echo $?\n");
            printf("%d\n$", v);
            strcpy(prev_f, line);
            exit(v);
        }
    }
    fclose(fp);
    free(prev_f);
}

然而，getline()没有正确存储该行的数据，因此我无法正确运行命令.有什么方法可以克服这个问题吗？或者我需要手动将文件读取到缓冲区，然后查看缓冲区中有什么命令？ 我不知道有什么简单的替代办法/解决办法

谢谢