自己编写的Linux下的C程序，实现ls命令的功能。

可选参数有-a -l -al

后面可以加上目录或文件名，也可不加。不写路径的默认是当前目录。

输入错误命令会提示正确的命令格式。-A C program under Linux to achieve ls commands.

Optional parameters are-a-l and-al

Can be followed with the directory or file name.

If the command doesn t contain the path, the default is the current directory path.

Correct command format will be displayed if inputed incorrect commands.