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Shell script

To be exact, Shell is a command-line interpreter, and its function is to follow a certain syntax to interpret the input commands and pass them to the system. It provides users with an interface system-level program that sends requests to Linux to run programs. Users can use Shell to start, suspend, stop or even write some programs. Shell itself is a program written in C language, and it is a bridge for users to use Linux. Shell is not only a command language, but also a programming language. As a command language, it interactively interprets and executes commands entered by users; as a programming language, it defines a variety of variables and parameters, and provides many control structures that are unique in high-level languages, including loops and branches. Although it is not part of the Linux system kernel, it invokes most of the functions of the system kernel to execute programs, create documents, and coordinate the running of each program in parallel.

The advantage of shell script is that it handles the business at the bottom of the operating system (all applications within the linux system are completed by shell scripts) because it is supported by a large number of linux system commands. More than 2000 commands are powerful supports for shell scripting, especially grep, awk, sed, and so on. For example: one-click software installation, optimization, monitoring alarm scripts, conventional business applications, shell development is easier and faster, in line with the simple, easy-to-use and efficient principles of operation and maintenance.

Shell script

Open a text editor (you can use the vi/vim command to create a file) and create a new file test.sh with the extension sh

Enter some code, and the first line usually looks like this:

[root@zhaocheng ~] # cat test.sh #! / bin/bashecho "Hello World" [root@zhaocheng ~] # bash test.sh Hello World

"#!" Is a convention tag that tells the system what interpreter the script needs to execute, no matter which Shell is used.

The echo command is used to output text to the window

View the interpreter in the system

[root@localhost ~] # cat / etc/shells / bin/sh/bin/bash/usr/bin/sh/usr/bin/bash/bin/tcsh/bin/csh

Enter echo $SHELL default system display / bin/bash

[root@localhost ~] # echo $SHELL/bin/bash

Enter bash-version to display the shell version

[root@localhost] # bash-versionGNU bash, version 4.2.46 (2)-release (x86_64-redhat-linux-gnu) Copyright (C) 2011 Free Software Foundation, Inc.License GPLv3+: GNU GPL version 3 or later This is free software; you are free to change and redistribute it.There is NO WARRANTY, to the extent permitted by law.

Script writing specification

It is recommended to store the catalogue uniformly to facilitate the management and search of the operation and maintenance staff to carry out.

[root@localhost ~] # mkdir / shell/scripts-pv

The script has a .sh extension

Start by specifying the script interpreter.

Add information such as version copyright at the beginning, and the ~ / .vimrc file can be automatically added.

The script should not be commented in Chinese, but in English as much as possible.

Excellent code writing habits

Write pairs of content at one time to prevent omissions, such as [],'', "", etc.

[] to have spaces at both ends, first enter [], backspace, enter 2 spaces, and then backspace.

The process control statement is written at once, and then the content is added. (if condition; then content; fi) ddd

Make the code readable by indenting.

The quotation marks in the script are all quotation marks in English state, and other characters are also in English status.

Execution of shell script

[root@localhost scripts] # chmod + x test.sh [root@localhost scripts] # lstest.sh [root@localhost scripts] #. / test.sh Hello World [root@localhost scripts] # source test.sh Hello World [root@localhost scripts] # bash test.sh Hello World [root@localhost scripts] # sh test.sh Hello World

* * variables of shell

Variables can be divided into two categories: environment variables (global variables) and ordinary variables (local variables).

Environment variables, also known as global variables, can be used in the Shell that created them and any child process shell derived from them. Environment variables can be divided into custom environment variables and Bash built-in environment variables

Ordinary variables can also be called local variables and can only be used in the Shell function or Shell script that created them. Ordinary variables are generally created by developers and users when they develop script programs.

Environment variable

You can get the environment variables in the system through env or export * *

[root@localhost scripts] # envXDG_SESSION_ID=141785HOSTNAME=zhaochengSHELL=/bin/bashTERM=xtermHISTSIZE=3000

Output variables in the system

[root@localhost scripts] # echo $HOME/root [root@localhost scripts] # echo $USERroot [root@localhost scripts] # echo $HISTSIZE3000 [root@localhost scripts] # echo $PATH/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/date/soft/logstash-7.5.0/bin:/root/bin

Ordinary variable

It is generally set and executed locally, but it is not valid to execute it in a script

[root@localhost scripts] # xiaoming=26 [root@localhost scripts] # echo $xiaoming26 [root@localhost scripts] # cat test.sh #! / bin/bashecho $xiaoming [root@localhost scripts] # bash test.sh

You can't get an ordinary variable in this way, because it's a local variable value, and if you add it to the system variable, of course, you get it.

And just now through the export command to see that $PATH is the system variable, of course, our execution can call this variable directly in our script.

[root@localhost scripts] # cat test.sh #! / bin/bashecho $PATH [root@localhost scripts] # bash test.sh / usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/date/soft/logstash-7.5.0/bin:/root/bin

Now we add the variables we usually define to the shell. Generally, when developing some scripts, it is convenient to manage and directly call the variables in our global variables to improve the efficiency and clarity of the script. The variables are capitalized, which is not recommended. When you exit, the variables will become invalid. It is recommended to write them into the script.

To view the variables added by our system, you can use export to view

[root@localhost scripts] # export XIAOMING=26 [root@localhost scripts] # cat test.sh #! / bin/bashecho $XIAOMING [root@localhost scripts] # bash test.sh 26

Simple exampl

Define variables import variables into system variables

[root@localhost scripts] # export TENGXUN=mahuateng [root@localhost scripts] # export ALI=mayun [root@localhost scripts] # export BAIDU=liyanhong [root@localhost scripts] # cat test.sh #! / bin/bashecho $TENGXUNecho $BAIDUecho $ALI

The execution effect is to call our system variables directly, without the need to write the above syntax in the script, but you can use it according to your own habits.

[root@localhost scripts] # bash test.sh mahuatengliyanhongmayun

In addition, if it is not written into the system variable, it can also be called, you can use source, so you can also get the

[root@localhost scripts] # LIHONGLEI=lei [root@localhost scripts] # cat test.sh #! / bin/bashecho $LIHONGLEI [root@localhost scripts] # source test.sh lei

You can also add this to / etc/profile or execute it.

[root@localhost scripts] # cat test.sh #! / bin/bashecho $PING [root@localhost scripts] # tail-1 / etc/profilePING=guo

This can only be obtained by source / etc/profile.

[root@localhost scripts] # source / etc/profile [root@localhost scripts] # source test.sh guo

In general, when the linux system starts, the system will launch a user shell. This shell can directly use the shell command or declare variables, for example, define a declared variable, but this output is empty in the script, and you need to add $to the local variable to reference.

[root@localhost scripts] # name=lili [root@localhost scripts] # echo namename [root@localhost scripts] # echo $namelili

* * Why use the export command?

In fact, the main reason is that when we define a variable, it can be called in the child shell without having to repeat it, but it will exit automatically at the end of shell execution, and the environment variable cannot be used any more.

Use of variables in quotation marks

Generally speaking, you need to use''when it is a special character. If you are referring to a system variable, you must use' * *'.

[root@tengxunyun ~] # name1=pingguo [root@tengxunyun ~] # name2='li' [root@tengxunyun ~] # name3= "juzi" [root@tengxunyun ~] # name4=' ^'[root@tengxunyun ~] # name5='&&& $SHELL' [root@tengxunyun ~] # name6= "kkk # SHELL" [root@tengxunyun ~] # echo $name1pingguo [root@tengxunyun ~] # echo $name2li [root@tengxunyun ~] # echo $name3juzi [root@tengxunyun ~] # echo $name4 ^ ^ [root@tengxunyun ~] # echo $name5 & $SHELL [root@tengxunyun ~] # echo $name6kkk # / bin/bash

Variables are assigned in backquotes

If it is a variable, be sure to add $or it thinks it is an ordinary file, and the variable with _ underscore needs to add the preceding variable {}.

[root@tengxunyun ~] # time= `date` [root@tengxunyun ~] # echo timetime [root@tengxunyun ~] # echo $timeThu Feb 20 13:34:26 CST 2020 [root@tengxunyun ~] # file= `ll` [root@tengxunyun ~] # echo $filetotal 4-rw-r--r-- 1 root root 26 Feb 20 12:07 test.sh [root@tengxunyun ~] # echo ${time} _ dayThu Feb 20 13:34:26 CST 20 _ day [root @ tengxunyun ~] # echo $time-dayThu Feb 20 13:34:26 CST 2020-day

* * when writing a script, we need to add comments to the beginning of the script, so that we can increase the specification of our script.

Use vimrc files * *

[root@zhaocheng ~] # cat .vimrc autocmd BufNewFile * .py,*.cc,*.sh,*.java exec ": call SetTitle ()" func SetTitle () if expand ("%: e") = = 'sh' call setline (1, "#! / bin/bash") call setline (2 "# #") call setline (3, "# File Name:" .clients ("%")) call setline (4, "# Version: V1.0") call setline (5 "# Author: clsn") call setline (6, "# Organization: http://blog.znix.top") call setline (7," # Created Time: ".strftime ("% F% T ") call setline (8," # Description: ") call setline (9 "# #") call setline (10, ") endifendfunc

Location variable

$0 gets the file name of the current shell script, $1 is the second parameter obtained, $2 is the second parameter obtained, and ${11} needs to be caused by {} when the parameter exceeds 9.

[root@zhaocheng ~] # cat test.sh #! / bin/bashecho $0echo "first parameter:" $1echo "second parameter:" $2echo "11th parameter:" ${11} [root@zhaocheng ~] # bash test.sh 1 3 3 5 6 78 8 89 9 654 77test.sh first parameter: 1 second parameter: 3 11th parameter: 77

$# is equivalent to listing the total number of parameters

[root@zhaocheng ~] # cat test.sh #! / bin/bashecho $0echo "first parameter:" $1echo "second parameter:" $2echo "11th parameter:" ${11} echo "lists how many parameters are there:" $# [root@zhaocheng ~] # bash test.sh 66 99 00 9990test.sh first parameter: 66 second parameter: 99 11th parameter: list how many parameters are listed: 4

* $is equivalent to listing all the parameters * *

[root@zhaocheng ~] # cat test.sh #! / bin/bashecho $0echo "first parameter:" $1echo "second parameter:" $2echo "11th parameter:" ${11} echo "lists how many parameters are listed:" $# echo "lists all output parameters:" $* [root@zhaocheng ~] # bash test.sh 99 00 88 77 66 44 33test.sh first parameter: 99 second parameter: 00 11th parameter: list How many parameters are there: 8 list all output parameters: 99 00 88 77 66 55 44 33

* $and ¥@ contrast * *

[root@zhaocheng ~] # set-- "It's" a nice day today [root@zhaocheng] # echo $1It's [root@zhaocheng ~] # echo $2a [root@zhaocheng ~] # echo $3nice [root@zhaocheng] # echo $4day [root@zhaocheng ~] # echo $5today [root@zhaocheng ~] # for i in $1 ETS [root@zhaocheng ~] # for i in $2ten do echo $itera [root@zhaocheng ~] # for i in $*; do echo $I DoneIt'sanicedaytoday [root@zhaocheng ~] # for i in $#; do echo $iTinct 5 [root@zhaocheng ~] # for i in $@; do echo $iTrue [root@zhaocheng] # for i in "$@"; do echo $Itinctingsanicedayday

Process state variable

Shell process special state variables

* * define variable mode

1. Direct assignment

2. Transfer parameters

3. Set variables interactively, using the read command

Use of read on the command line * *

[root@zhaocheng ~] # read999 [root@zhaocheng ~] # echo $REPLY999 [root@zhaocheng ~] # read kele [root@zhaocheng] # read keleniunai [root@zhaocheng ~] # echo $keleniunai [root@zhaocheng ~] # echo $REPLY999

Use in script

[root@zhaocheng] # cat echo.sh #! / bin/bashread-p "Please enter:" iecho $I [root@zhaocheng ~] # bash echo.sh Please enter: chengzhichengzhi

The use of assignment, CHA defines the variable ls, this is our shell command needs to use backquotes to quote, generally longer directories can be directly written in the form of variables, directly referenced in the shell script, so it looks relatively simple, here is to find out the file under this file ending in .yaml and count the size and sort backwards

[root@zhaocheng ~] # cat fuzhi.sh #! / bin/bashCHA= `ls`DIR = / opt/k8s/ansibleecho $CHAfind $DIR-name "* .yaml" | xargs du-sh | sort-nr [root@zhaocheng ~] # bash fuzhi.sh canshu.sh echo.sh fuzhi.sh tianqi.sh yum.sh8.0K / opt/k8s/ansible/ansible-k8s/ansible-install-k8s/roles/addons/files/kubernetes-dashboard.yaml8.0K / opt/k8s/ansible/ansible-k8s/ansible-install-k8s/roles/ Addons/files/kube-flannel.yaml8.0K / opt/k8s/ansible/ansible-k8s/ansible-install-k8s/roles/addons/files/ingress-controller.yaml8.0K / opt/k8s/ansible/ansible-k8s/ansible-install-k8s/roles/addons/files/coredns.yaml4.0K / opt/k8s/ansible/ansible-k8s/ansible-install-k8s/roles/master/files/kubelet-bootstrap-rbac.yaml4.0K / opt/k8s/ansible/ansible-k8s/ Ansible-install-k8s/roles/master/files/apiserver-to-kubelet-rbac.yaml

Interactive setting variable read

Common parameters

-p: give a prompt. "\ n" line feeds are not supported by default

-s: silent mode. The input will not be echoed on the screen

-t: gives the timeout. When the timeout is reached, read exits and returns an error.

-n: a limit of N characters will automatically end the reading. If you press enter or encounter a newline character before reading N characters, it will also end the reading.

-N: it is strictly required to finish reading automatically after reading N characters, even if you press enter or encounter a newline character. Where the newline character or carriage return is one character

-a: stores the split fields in the specified array in turn, starting with the index=0 of the array

-p: give the prompt

The basic usage of read

[root@zhaocheng] # cat read.sh #! / bin/bashread-p "Please enter your name:" lakeyread-s-p "Please enter your gender:" girlread-s-p "Please enter whether you have a date:" gggechoecho-e "\ 033 [35m your name is: $lakey\ 033 [0m" echo-e "\ 033 [35m your gender is: $girl\ 033 [0m" echo-e "\ 033 [35m No, you can't have a date: $ggg\ 033 [0m"

The usage of expr in shell

Determine whether the input is an integer, and the non-integer return value is 2

Calculate the length of a variable

[root@zhaocheng ~] # expr 1: 1

1-1

[root@zhaocheng ~] # expr 1 + 1

two

[root@zhaocheng ~] # expr 1 1

Expr: syntax error

[root@zhaocheng ~] # expr 1 * 1

one

[root@zhaocheng ~] # expr 1\ 3

three

Example of a non-integer return value of 2

[root@zhaocheng] # expr-1 + 1

0

[root@zhaocheng] # echo $?

one

[root@zhaocheng ~] # echo a + 1

A + 1

[root@zhaocheng ~] # expr a + 1

Expr: non-integer argument

[root@zhaocheng] # echo $?

two

$[] operator

[root@zhaocheng ~] # echo $[1x 2]

three

[root@zhaocheng ~] # echo $[122]

one hundred and twenty two

[root@zhaocheng ~] # echo $[1-2]

-1

[root@zhaocheng ~] # echo $[1x 2]

two

[root@zhaocheng ~] # echo $[1Acer 2]

0

File judgment in shell

Common file test operators

Judge whether the file exists. If it exists, the output 0 will be true and 1 will be false.

[root@zhaocheng ~] # [- f / etc/hosts] [root@zhaocheng ~] # echo $? 0 [root@zhaocheng ~] # [- f / etc/hosts2] [root@zhaocheng ~] # echo $? 1

Determine whether the file exists and how it is returned

You can use colors for output

Use the judgment syntax directory in a script

[root@zhaocheng ~] # cat panduan.sh #! / bin/bashDIR=/opt/k8s1COLOR= "\ 033 [33m directory exists [0m" [- d $DIR] & & echo-e $COLOR | | echo "directory does not exist" [root@zhaocheng ~] # bash panduan.sh directory does not exist

String judgment

String operator

-z judge the length of the string

-n interpretation string length

[root@zhaocheng ~] # cat panduanzifu.sh #! / bin/bashZIFU=33 [- z $ZIFU] & & echo "empty output" | | echo "output has content" [root@zhaocheng ~] # bash panduanzifu.sh output has content [root@zhaocheng ~] # cat panduanzifu.sh #! / bin/bashZIFU= [- z $ZIFU] & & echo "output is empty" | echo "output has content" [root@zhaocheng ~] # bash panduanzifu.sh output is empty [root@zhaocheng ~ " ] # cat panduanzifu.sh #! / bin/bashZIFU= [- n $ZIFU] & & echo "output is empty" | | echo "output has content" [root@zhaocheng ~] # bash panduanzifu.sh

Output is empty

Integer judgment

Integer binary comparison operator

To judge whether two numbers are equal, 0 is true and 1 is false.

[root@zhaocheng ~] # [1-eq 0] [root@zhaocheng ~] # echo $? 1 [root@zhaocheng ~] # [1-eq 1] [root@zhaocheng ~] # echo $? 0 [root@zhaocheng ~] # [9-gt 6] & & echo "correct" | echo "wrong"

Correct

Logical symbol

Common logical symbols

The combination of logical operator and integer judgment

45 is not equal to 40 90 equals 90. If the interpretation is correct, it is established [root@zhaocheng ~] # [45-ne 40-a 90-eq 90] & & echo pair | | echo is not correct as long as one of the following is wrong, this is not true [root@zhaocheng ~] # [45-ne 40-a 90-eq 98] & & echo pair | | echo is not correct |

-O if at least one of them is true, return to true.

[root@zhaocheng] # [45-ne 40-o 90-eq 98] & & echo pair | | echo is not correct

! 12, special usage, directly open the 12th command

If conditional statement

Single branch statement

[root@zhaocheng ~] # cat dan.sh #! / bin/bashDIR=/etc/hostsif [- f $DIR] then echo "File exists" [root @ zhaocheng ~] # bash dan.sh file exists

Multi-branch statement

[root@zhaocheng ~] # cat duo.sh #! / bin/bashDIR=/etc/keepalived.confif [- f $DIR] then echo "else echo does not exist" [root@zhaocheng @ zhaocheng ~] # bash duo.sh exists [root@zhaocheng ~] # cat bijiao.sh #! / bin/bashA=19B=8if [$A-gt $B] then echo "$A > $B" else echo "$A

8 [root@zhaocheng ~] # cat bijiao.sh #! / bin/bashA=19B=89if [$A-gt $B] then echo "$A > $B" else echo "$A < $B" fi [root@zhaocheng ~] # bash bijiao.sh 19 < 89

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