Shell command interpreter: between the system kernel—>Command interpreter—>Peripheral application: Application/Command/Service
Shell programming: bash programming
1. Command interpreter
| bash | The most widely used command interpreter at present, Red Hat series (default), Debain, Unbantu, BASH full name: Bourne-Again Shell |
| dash | Generally, the default Debain/Unbantu system is used, and it is recommended to use bash when running scripts. |
| csh,tcsh | Some Unix systems use |
| zsh | More features and more plug-ins to look better |
2. Programming language classification
| Analysis: Direct parsing | After writing the code, the shell, python, run it through the corresponding parser |
| Compilation: Need to be compiled and run | C,C++ |
Explanation
[root@localhost ~]# vim
[root@localhost ~]# cat
print("hrllo world!")
[root@localhost ~]# python
hrllo world!3. Shell script execution method
1Execute via sh or bash
[root@localhost shell]# vim [root@localhost shell]# cat hostname pwd whoami [root@localhost shell]# sh /root/shell root [root@localhost shell]# bash /root/shell root [root@localhost shell]# ll `which sh bash` -rwxr-xr-x. 1 root root 964544 Apr 10 2018 /usr/bin/bash lrwxrwxrwx. 1 root root 4 Mar 23 05:59 /usr/bin/sh -> bash
2Execute via source or .
[root@localhost shell]# . /root/shell root [root@localhost shell]# source /root/shell root
3 Execute through absolute or relative paths
[root@localhost shell]# ./ -bash: ./: Permission denied [root@localhost shell]# chmod +x ./ [root@localhost shell]# ls -l total 4 -rwxr-xr-x. 1 root root 21 May 6 01:15 [root@localhost shell]# ./ /root/shell root
4 Run by redirection symbol
[root@localhost shell]# sh < /root/shell root [root@localhost shell]# bash < /root/shell root
4. Application scenarios
Applications and scenarios
| Execute via sh or bash | The most common way to write scripts is in other non-Red Hat systems. It is recommended to use bash to run scripts |
| By.or source | Loading/configuring effective files (environment variables, alias) can be used to implement include function, and eight other scripts are referenced to the current script. |
| By relative or absolute path | This is generally not recommended, system scripts/services use scripts (plus execution permissions) |
| Enter a redirector | Not recommended |