操作系统实验：模拟采用二级目录结构的磁盘文件系统中的文件操作。程序简单模拟了一个类unix的shell界面,并完成了实验中所要求的具体内容。运行时需注意问题：初始用户名密码为root,登陆后可输入help命令查看命令格式获取帮助。-Operating System Experiment: Simulate file operations for the two-level directory structure in the file system.　Should pay attention to run it: the initial user name and password are "root", and you can enter command "help" for help.