The way of Learning (II.): Bash and its features, command history and user management and permissions, shell types

After a week, the progress seems a little slack, but after the weekend rally
Shell (Shell)
Gui:gnome,kde,xfce
Cli:sh,csh,ksh,bash
Bash (parent process)-----Bash (child process) they are independent of each other.
Command history: Historical
Quotes supported by bash:
"Command Replacement (keyboard ~ key)
"" Weak reference, you can implement variable substitution
Strong reference, do not complete variable substitution
Wildcard characters for file names:

• : Any character
  ? : Any single character
  []: matches any single character within the specified range
  Bash's configuration file
  Global configuration
  /etc/profile;/etc/profile.d/. Sh;/etc/bahsrc
  Personal configuration
  ~/.bash_profile; ~/.BASHRC
  Profile class file:
  Setting environment variables
  Run commands or scripts (commands or scripts that are displayed on the boot)
  Files of the BASHRC class:
  Setting Local Variables
  Defining command aliases
  Log-in Shell read configuration file:
  /etc/profile---->/etc/profile.d/sh---->~/.bash_profile---->~/.BASHRC---->/ETC/BASHRC
  Non-login Shell read configuration file:
  ~/.BASHRC----->/ETC/BASHRC------>/etc/profile.d/*.sh

    权限r w x    文件： r可读            w可写               x可执行    目录： r可对此目录执行ls列出内部文件                w可以在此目录创建文件                x可使用cd切换进此目录   用户：UID；/etc/passwd组   ：GID；/etc/group    影子口令：                   用户：/etc/shadow                   组   ：/etc/gshadow    用户类别：    管理员：    普通用户：系统用户1-499                      一般用户500-60000    用户组类别：                        私有组；基本组；附加组    加密方法：                        对称加密；公钥加密；单向加密；

    用户管理：                    useradd; useradel; usermod; passwd; chsh; chfn; finger; id; chage    组管理：                                                groupadd; groupdel; groupmod; gpasswd    权限管理：                    chown; chgrp; chmod    /etc/passwd（列表含义）    用户名：密码：UID：GID：注释：家目录：默认SHELL   /etc/group    组名：密码：GID：附加组的用户   /etc/shadow     用户名：密码：最近一次修改密码时间：最短使用日期：最长使用期限：警告时间：非活动时间：过期时间

The way of Learning (II.): Bash and its features, command history and user management and permissions, shell types