教程 http://c.biancheng.net/cpp/view/6994.html
shell编程空格的使用:https://blog.csdn.net/lee244868149/article/details/38724943
shell运算:https://blog.csdn.net/shimazhuge/article/details/38703523
shell脚本中使用for循环开启并行方法:https://blog.csdn.net/zcb_data/article/details/80533808