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Today, I would like to talk to you about how to understand shell-0, many people may not know much about it. In order to make you understand better, the editor has summarized the following contents for you. I hope you can get something from this article.

Shell-0. Introduction

1. Shell scripts are used in those environments.

Application environment: multiple complex parameters are required to execute some commands

Multiple commands are needed to view and maintain the status of the system

Back up the database regularly

Monitor important processes and logs of the system according to specific conditions

Conduct weekly inspection of major systems

Analyze the security of the configuration files of important network equipment, and give the corresponding analysis report.

Detect the equipment in the network, collect relevant asset information, and enter the asset information table

For example:

Through the command: check the syntax and parameters carefully every time

Write detailed system maintenance documents, list the commands to be maintained, and the administrator operates according to the system maintenance documents.

Backup the database at 6: 00 p. M. every day

Perform monitoring, command, or view the system screen every 10 or 15 minutes

The workload is heavy and the data is difficult to organize.

two。 What is Shell?

Shell---- kernel-hardware

Please check

Http://yuanji6699.blog.51cto.com/11568362/1771930

Constituent elements of a 3.Shell script

Notes

System command

Text processing tool (sort,grep,sed,awk...)

Variabl

Conditional judgment

Cyclic structure

Function.

4. Check which shell is supported by the system

Debian:/myshell# cat / etc/shells

# / etc/shells: valid login shells

/ bin/csh

/ bin/sh

/ usr/bin/es

/ usr/bin/ksh

/ bin/ksh

/ usr/bin/rc

/ usr/bin/tcsh

/ bin/tcsh

/ usr/bin/esh

/ bin/bash

/ bin/rbash

So many, basically using bash

5. View the sh type used by the current user

Debian:/myshell# echo $SHELL [Note this may not be correct]

/ bin/bash

You should use [be sure to check before use, individual system versions are not bash by default]

Ls-alh / bin/sh

Root@WebB:/home/log# ls-lah / bin/sh

Lrwxrwxrwx 1 root root 4 Nov 14 15:15 / bin/sh-> dash [actually using dash]

Root@WebB:/home/log# echo $SHELL

/ bin/bash

Solution:

-

So how do you change sh to point to bash?

The most violent way, of course, is to directly change the soft link of / bin/sh to bash.

Such as: ln-s / bin/bash / bin/sh

Check again, ls / bin/sh-al finds that the soft link points to / bin/bash.

-

6. First script (International practice, hello world)

Debian:/# vim first.sh

#! / bin/sh

Echo "Hello world"

Debian:/# sh first.sh

Hello world

Debian:/# chmod + x first.sh

Debian:/#. / first.sh

Hello world

After that

Debian:/myshell# echo $? (described in detail later in this section)

0

If 0, it is normal.

After reading the above, do you have any further understanding of how to understand shell-0? If you want to know more knowledge or related content, please follow the industry information channel, thank you for your support.

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