linux 查看命令帮助的几种方法

1，command --help/-h
2，info command
3，man command
4，help command
适用于内部命令
5，whatis command
6，readme
绝大多数程序都有相应的帮助文档，保存在/usr/share/doc文件夹中
7，apropos command

参考文档：
https://www.linuxnix.com/how-to-get-help-on-linuxunix-command/
https://blog.linuxeye.cn/381.html
https://www.thegeekstuff.com/2009/11/5-methods-to-get-quick-help-on-linux-commands/
https://www.ibm.com/support/knowledgecenter/en/SSEPGG_9.7.0/com.ibm.db2.luw.admin.cmd.doc/doc/r0053134.html
https://www.howtogeek.com/108890/how-to-get-help-with-a-command-from-the-linux-terminal-8-tricks-for-beginners-pros-alike/
https://www.linuxnix.com/how-to-get-help-on-linuxunix-command/
https://www.linux.com/learn/intro-to-linux/2017/10/3-tools-help-you-remember-linux-commands
https://www.geeksforgeeks.org/help-command-linux-examples/