设计并实现一个简单的命令处理程序，名字为smallshell。要求具备以下基本功能：

1.支持交互式的用户界面

2.支持内置命令：cd，exit，设置搜索路径path等。

3.支持可执行文件的运行

4.支持输入输出重定向功能

5.支持管道功能-Design and implement a simple command handler, named smallshell. Requires the following basic functions: 1. Support an interactive user interface (2) support built-in commands: cd, exit, set the search path path and so on. 3 support the executable file to run 4 Support input and output redirection 5 feature support for the pipeline