Shulou(Shulou.com)06/01 Report--

Today, I will talk to you about the basic applications of shell, which may not be well understood by many people. in order to make you understand better, the editor has summarized the following content for you. I hope you can get something according to this article.

What is shell?

Shell is the interpreter program between you and the user in linux, which usually refers to bash, which is responsible for translating to the kernel and communicating user / program instructions.

How to use Shell:

1. Interactive execution of instructions: manual intervention, low execution efficiency.

two。 Non-interactive execution of instructions: quiet execution in the background, efficient execution, easy to write scripts.

Cat / etc/shell view all explanations on the machine

Yum-y install ksh installs a new interpreter

Advantages of bash

Tab complete alias shortcut history command pipe redirection

Writing Shell script specification

1. Declaration interpreter

#! / bin/bash

two。 Comments, which can explain the function of the script, the role of variables, etc.

3. Execute the code

+ x permissions

Execute directly with the interpreter, execute with the new interpreter (open child processes)

Use the source (or. + spaces) command to execute, and use the current interpreter to execute (do not start child processes) / / source test01.sh

Deploy the yum repository script:

#! / bin/bash

# deploy yum

Echo "[adc]

Name=adc

Baseurl= http://content.example.com/rhel7.0/x86_64/dvd

Enabled=1

Gpgcheck=0 "> / etc/yum.repos.d/adc.repo

Exchange rate query http://www.gendan5.com/exrate.html

Deploy the ftp script:

#! / bin/bash

Yum-y install vsftpd & > / dev/null

Systemctl restart vsftpd

Systemctl enable vsftpd

Constant: fixed

Variables: flexible, more use of variables in scripts can increase performance

Types of variables

1. Custom variable

Variable name = value of a variable the process of defining the value of a variable is called assignment. Names can be defined with uppercase and lowercase letters, numbers, underscores, cannot start with numbers, and cannot use special symbols.

Await 20 / / define variables

Echo $a / / call variable

A1: 20

1a=20 / / definition failed

Axia1: 20

Failed to define 20 / /

Axia40

Echo $a RMB

Unset a / / Undefine a variable

Environment variable

UID current user's ID USER current user name SHELL current user's interpreter HOSTNAME hostname HOME current user's home directory PWD location where PATH stores commands

PS1 first level prompt PS2 second level prompt

Extended application of variables

"" define the scope

Define the scope and shield the special symbols

``reverse apostrophe, you can get the result of command execution = = $()

Stty-echo / / screen echo

Stty echo / / restore echo

Axi20

Export a local variable-> global variable

Export-na global variable-> local variable

Calculate

Method one

Expr 1 + 1

Expr 1-1

Expr 1 / 1

Expr 1\ * 1 1'*'1\ the special meaning of a character after the escape symbol mask

Expr 5% 2 > 1 find the module and take the remainder

Method two

Echo $[1x 1]

Echo$ [Avoca]

Method three

The results of let operations are not displayed, and are usually used to define the values of variables, or to add or subtract variables.

Let axiom +

Let a muri-

Let axioms 2

Let a murmur 2

Method 4

Bc calculator, which can calculate decimals

Echo 1.15 to 5.04 | bc

Echo scale=3;10/3 | bc / / scale defines a few places after the decimal point

After reading the above, do you have any further understanding of the basic application of shell? 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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