shell特殊變量：Shell $0, $#, $*, $@, $?, $$和命令行參數(shù)
https://www.cnblogs.com/davygeek/p/5670212.html
What are PID and?PPID?
https://linux.cn/article-5051-1.html
https://riptutorial.com/bash/example/16878/-ppid
https://delightlylinux.wordpress.com/2012/06/25/what-is-pid-and-ppid/
shell變量的初始值賦值
https://blog.csdn.net/xy8310292/article/details/80671664
https://blog.csdn.net/joe_007/article/details/8773594
shell腳本里面PS1="${x##*/}\$"的意思是什么？
https://zhidao.baidu.com/question/746509459296838252.html
What is the meaning of “${1#*-}” in BASH搀别？
https://stackoverflow.com/questions/41806725/what-is-the-meaning-of-1-in-bash
https://wiki.bash-hackers.org/syntax/pe
http://www.reibang.com/p/10d7405fc36b
Linux shell：${var1##*：} ${bz1%，*}的意思
https://blog.csdn.net/wmjcode/article/details/80662501
Linux 中 if [ "x${var}" = "x" ] 什么意思?
https://zhidao.baidu.com/question/510807608.html
關(guān)于shell腳本中shift 用法
Linux shell腳本中shift的用法說明
https://www.cnblogs.com/image-eye/archive/2011/08/20/2147153.html
https://blog.csdn.net/zhu_xun/article/details/24796235
https://reb12345reb.iteye.com/blog/2118179
