shell related reference materials

1. https://blog.csdn.net/sunny05296/article/details/71173467

2.https://blog.csdn.net/wanxiaoderen/article/details/82388091

3.https://blog.csdn.net/wangcg123/article/details/50667883

4.https://blog.csdn.net/mzc11/article/details/79584901

5.https://blog.csdn.net/zl87758539/article/details/77481679