Shell Basics-variables, judgments, loops

1. Shell basic format, variable

# Add an interpreter to the shell script #! /bin/bash

# Print out Hello world with a script

#! /bin/bash

echo "Hello World"

Exit

Parameters: A parameter is an entity that stores real values that are typically referenced in a script

#利用变量回显hello World, the following example will echo two Hello world.

#! /bin/bash

A= "Hello World"

Echo $a

echo "Hello World"

Exit

If additional content is appended to the argument, you need to use {}

#! /bin/bash

A= "Hello World"

Echo ${a},i am coming

Exit

Echo Result:

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#计算字符串长度, hello World with spaces, total 11

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2. Script exit

#一个执行成功的脚本返回值为0, unsuccessful for non 0

[Email protected] script]# Clear

[Email protected] script]# sh hello.sh

Hello world,i am Coming

11

[[email protected] script]# echo $?

0

#判断一个目录内是否有某个文件, there is a echo of file Exsit, no return 1

[email protected] script]# cat test.sh

#! /bin/bash

Cd/home

If [-F file];then

echo "File Exsit"

Else

Exit 2

Fi

[Email protected] script]# sh test.sh

[[email protected] script]# echo $?

2

[[Email Protected]ost script]#

3. Test statement, if statement

test-d XX directory is present

test-f xx file is present

Test-b xx is a block file

Test-x xx is an executable file

A-eq B determine equality

A-ne B judged unequal

A-le B is less than or equal to

A-lt B is less than

A-GT B is greater than

#if条件判断语句

if [];then

......

Else

......

Fi

#if语句嵌套

if [];then

.......

elif [];then

.......

elif [];then

.......

Else

......

Fi

#test举例, determine whether the test file exists if there is a backup operation for it. If the message is not echoed

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#例子: Enter a numeric value to determine which interval it is in. Less than 80, greater than 100, located between 80 and 100, with the IF nesting!

[email protected] script]# cat if.sh

#! /bin/bash

Read-p "plz input a $num:" num

If [$num-le];then

echo "Num is less 80"

elif [$num-ge] && [$num-le];then

echo "Num between and 100"

Else

echo "num is greater than 100"

Fi

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4. Loop statement for, while

For Var in $var 1 $var 2 $var 3 VAR4 ... $var

Do

......

......

Done

#例子: Print 1 to 10 digits

[email protected] home]# cat for1.sh

#! /bin/bash

For Var in {1..10}

Do

echo "$var"

Sleep 2

Done

[Email protected] home]# sh for1.sh

1

2

3

4

5

6

7

8

9

10

[Email protected] home]#

#打印方块内容 for nesting

[Email protected] home]# sh for2.sh

*********

*********

*********

*********

*********

*********

*********

*********

*********

[email protected] home]# cat for2.sh

#! /bin/bash

For ((i=1;i<10;i++))

Do

For ((j=1;j<10;j++))

Do

Echo-n "*"

Done

echo ""

Done

# while loop, mostly for loops, plus continue (jump out of continue below, return to top command line), break (Stop, exit Loop)

#while语句

While [conditional judgment]

Do

......

......

Done

#例子: According to the conditions, output 1-10

[email protected] script]# cat while.sh

#! /bin/bash

Var=1

While [$var-le 10]

Do

Echo $var

var=$[$var +1]

Done

[Email protected] script]# sh while.sh

1

2

3

4

5

6

7

8

9

10

[[email protected] script]# echo $?

0

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Shell Basics-variables, judgments, loops