The third of the shell

Chapter 1th whileLooping Statements

in a programming language , a while loop is a statement of a control flow that uses an expression that returns a Boolean value that, when the return value of the expression is true , repeats the condition of the loop If the return value of the expression is False , the condition of the loop is not executed

1.1 WhileGrammar:

while conditions

Do

Command

Done

1.2 WhileUsage Scenarios: 1.2.1more for creating daemons

[email protected] tmp]# cat test.sh

#!/bin/bash

##############################################################

# File Name:test.sh

# version:v1.0

# Author:da Ya

# Organization: [Email protected]

# Created time:2018-03-24 19:48:06

# Description:

##############################################################

While True

Do

echo "OK" | NC-L 81

Done

[Email protected] tmp]# sh test.sh

get/http/1.1

user-agent:curl/7.29.0

host:10.0.0.31:81

Accept: */*

get/http/1.1

user-agent:curl/7.29.0

host:10.0.0.31:81

Accept: */*

1.2.2You can create a timed task,scheduled tasks with less than one minute execution time

[email protected] tmp]# cat test.sh

#!/bin/bash

While true causes the return value to always be true , so it always loops

Do

Uptime

Sleep 1

Done

[Email protected] tmp]# sh test.sh

19:48:45 up 2 days, 4:12, 4 users, load average:0.08, 0.04, 0.05

19:48:46 up 2 days, 4:12, 4 users, load average:0.08, 0.04, 0.05

19:48:47 up 2 days, 4:12, 4 users, load average:0.08, 0.04, 0.05

19:48:48 up 2 days, 4:12, 4 users, load average:0.07, 0.04, 0.05

^c

1.3 Whilefunction:

Replenish Scheduled Tasks to perform tasks that are less than one second

Loop through certain actions , such as fruit menu

1.4traverse each line in a file: 1.4.1Method One:

While read I

Do

echo "$i"

Done </etc/hosts

[Email protected] scripts]# sh test.sh

127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4

:: 1 localhost localhost.localdomain localhost6 localhost6.localdomain6

192.168.16.200 mirrors.aliyun.com

1.4.2Method Two:

Cat/etc/hosts|while Read I

Do

echo "$i"

Done

1.4.3Method Three:

EXEC </etc/hosts

While read I

Do

echo "$i"

Done

Get each word in a row

While read I

Do

echo "$i"

For W in $i

Do

echo "$w"

Done

Done </etc/hosts

1th Chapterloop Control Scripts1.1Example: Break

For i in {1..5}

Do

If ["$i"-eq 2];then

Break

Fi

echo "$i"

Done

Echo OK

[Email protected] scripts]# sh test.sh

1

Ok

1.2Example: Continue

For i in {1..5}

Do

If ["$i"-eq 2];then

Continue

Fi

echo "$i"

Done

Echo OK

[Email protected] scripts]# sh test.sh

1

3

4

5

Ok

1.3Example: Exit

For i in {1..5}

Do

If ["$i"-eq 2];then

Exit

Fi

echo "$i"

Done

Echo OK

[Email protected] scripts]# sh test.sh

1

2nd Chapter ShellArray

The simple answer is: An array is a combination of multiple variables

[Email protected] scripts]# name= (Jiang Bo Yang)

[[email protected] scripts]# echo ${name[1]}

Bo

[[email protected] scripts]# echo ${name[2]}

Yang

[Email protected] scripts]# unset name[1]

[[email protected] scripts]# echo ${name[1]}

[[email protected] scripts]# echo ${name[*]}

Jiang Yang

[[email protected] scripts]# echo ${name[@]}

Jiang Yang

[Email protected] scripts]# Name[1]=bo

[[email protected] scripts]# echo ${name[@]}

Jiang Bo Yang

1th Chapter Shellfunction1.1Defining Functions:

Jiang () {

Echo Nihao

}

Jiang means calling the function defined above

[Email protected] scripts]# sh test.sh

Nihao

1.2extended usage of functions:Add a command

[Email protected] scripts]# source test.sh

Nihao

[email protected] scripts]# Jiang

Nihao

1.3parameters of a function

Jiang () {

Echo Nihao $

}

Daya () {

Echo Buhao $

}

Jiang $

Daya $

[[Email protected] scripts]# sh test.sh 1

Nihao 1

Buhao 1

1.4 basenameUse of Commands

[Email protected] scripts]# basename/server/scripts/test.sh

test.sh

[Email protected] scripts]# basename/server/scripts/test.sh. sh

Test

2nd Chapter ShellDebugging Tips: 2.1Power -down commissioning:

Jiang () {

Echo Nihao $

}

Daya () {

Echo Buhao $

}

Jiang

Exit Add exit where there may be a problem , not continue to execute script down , narrow down the scope of the investigation

Daya

2.2Use-XParameters:

[Email protected] scripts]# sh-x test.sh

+ Jiang

+ Echo Nihao

Nihao

+ Daya

+ Echo Buhao

Buhao

2.3specifying the debug scope:

[Email protected] scripts]# sh test.sh

Nihao

+ Daya

+ Echo Buhao

Buhao

+ Set +x

The third of the shell