linux shell 学习记录 case 和 shift:https://blog.csdn.net/immeatea_aun/article/details/89153304 eval 和 set:https://blog.csdn.net/Man_In_The_Night/article/details/86658305 getopt:https://www.jianshu.com/p/6393259f0a13 和 https://www.cnblogs.com/rwxwsblog/p/5668254.html 综合教程:https://www.runoob.com/linux/linux-shell.html