Shell Script Introduction

1. When a string is used more frequently in a script and the string length is long, you should use a variable instead

2. Variables are essential when using conditional statements

3. When referencing the result of a command, replace it with a variable

4. Variables are also necessary when writing scripts for user interaction

Built-in variables, $ ...

Mathematical Operation a=1;b=2; c=$ (($a + $b)) or $[$a + $b]

Test Sample: Write an interactive script:

[Email protected] shell]# vim 2.sh

#!/bin/bash

Read-p "Please input anumber:" Number

Echo $number

[Email protected] shell]# sh 2.sh #输入什么就输出什么

Please input anumber:99999

99999

[Email protected] shell]# vim 2.sh

#!/bin/bash

Read-t 3-p "Please input anumber:" Number # "-T 3" join wait 3 seconds

Echo $number

[Email protected] shell]# sh 2.sh #超时会跳出

Please input anumber:

[Email protected] shell]#

---------------------Split Line------------------------------

[Email protected] shell]# vim 3.sh

#!/bin/bash

##

##

Echo $ $

[[Email protected] shell]# sh 3.sh

3.sh

[Email protected] shell]# vim 3.sh

#!/bin/bash

##

##

echo "\$1=$1"

echo "\$2=$2"

echo "\$0=$0"

echo "\$3=$3"

[[Email protected] shell]# sh 3.sh

$1=

$2=

$0=3.sh

$3=

[[Email protected] shell]# SH 3.sh 11 22 33

$1=11

$2=22

$0=3.sh

$3=33

[Email protected] shell]# sh 3.sh #写两个值

$1=11

$2=22

$0=3.sh

$3=

Mathematical operations

[Email protected] shell]# a=1;b=2

[Email protected] shell]# c= $a + $b

[Email protected] shell]# echo $c

1+2

[Email protected] shell]# c=$[$a + $b] #数学运算应该这样写

[Email protected] shell]# echo $c

3

------------------------Split Line------------------------------

If statement

[Email protected] shell]# vim if.sh

#!/bin/bash

A=5

If [$a-gt 3] #-gt greater than < less than-lt = = equals-eq! = is not equal to-ne >= greater than or equal to-ge <= less than or equal to-le

Then

echo "A>3"

Fi

[Email protected] shell]# sh if.sh

A>3

[[email protected] shell]# sh-x if.sh #-X View detailed procedure

+ a=5

+ ' [' 5-gt 3 '] '

+ Echo ' a>3 '

A>3

[Email protected] shell]# vim if.sh

#!/bin/bash

A=5

If [$a-gt] #如果

Then

echo "A>10"

else #否则

echo "a<=10"

Fi

~

[Email protected] shell]# sh if.sh

a<=10

[Email protected] shell]# vim if.sh

#!/bin/bash

A=5

If [$a-gt 10]

Then

echo "A>10"

elif [$a-lt 4]

Then

echo "A<4"

Else

echo "4<a<10"

Fi

[Email protected] shell]# sh-x if.sh

+ a=5

+ ' [' 5-gt 10 '] '

+ ' [' 5-lt 4 '] '

+ Echo ' 4<a<10 '

4<a<10

-------------------------Split Line-----------------------

Several uses of if:

[-F file] Determines if it is a normal file, and there is

[-D file] Determines if it is a directory and exists

[-E file] to determine whether files or directories exist

[-R File] to determine if the document is readable

[-W file] Determines whether the file is writable

[-X file] Determines whether the file is executable

[[Email protected] shell]# if [-f 1.txt]; then echo OK; Fi

[[email protected] shell]# Touch 1.txt

[[Email protected] shell]# if [-f 1.txt]; then echo OK; Fi #判断是否存在1. txt

Ok

[[Email protected] shell]# if [-R 1.txt]; then echo OK; Fi #-R to determine if the file is readable

Ok

[Email protected] shell]# if [-d/tmp/]; then echo OK; Fi #判断是否存在 Directory

Ok

[Email protected] shell]# vim if2.sh

#!/bin/bash

Read-p "Please input a number:" N

M= ' echo $n |sed ' s/[0-9]//g '

If [-N ' $m '] #-n Indicates whether the variable is not empty

Then

echo "The character you input was not a number,please retry."

Else

Echo $n

Fi

[Email protected] shell]# sh if2.sh

Please input a NUMBER:IIIIIIIIII

The character you input is a number,please retry.

[Email protected] shell]# sh if2.sh

Please input a number:90909090

90909090

[Email protected] shell]# sh-x if2.sh #实例分解

+ read-p ' Please input a number: ' N

Please input a number:oiu00909

+ + echo oiu00909

+ + sed ' s/[0-9]//g '

+ M=oiu

+ ' ['-N Oiu '] '

+ Echo ' The character you input is not a number,please retry. '

The character you input is a number,please retry.

[Email protected] shell]# sh-x if2.sh #实例分解

+ read-p ' Please input a number: ' N

Please input a number:9909090909

+ + sed ' s/[0-9]//g '

+ + echo 9909090909

+ m=

+ ' ['-N '] '

+ Echo 9909090909

9909090909

[Email protected] shell]# vim if2.sh

#!/bin/bash

Read-p "Please input a number:" N

M= ' echo $n |sed ' s/[0-9]//g '

If [-Z ' $m '] #- Z Indicates whether the variable is empty and is the opposite of-N.

Then

Echo $n

Else

echo "The character you input was not a number,please retry."

Fi

[Email protected] shell]# sh-x if2.sh

+ read-p ' Please input a number: ' N

Please input a number:90909090

+ + sed ' s/[0-9]//g '

+ + echo 90909090

+ m=

+ ' ['-Z '] '

+ Echo 90909090

90909090

[Email protected] shell]# sh-x if2.sh

+ read-p ' Please input a number: ' N

Please input a number:jki0000

+ + sed ' s/[0-9]//g '

+ + echo jki0000

+ M=jki

+ ' ['-Z jki '] '

+ Echo ' The character you input is not a number,please retry. '

The character you input is a number,please retry.

---------------------Split Line-------------------------------

Case usage: not too common. More in startup scripts.

---------------------Split Line-------------------------------

For loop:

[Email protected] shell]# vim for.sh

#!/bin/bash

For i in ' SEQ 1 10 '

Do

Echo $i

Done

[Email protected] shell]# sh for.sh

1

2

3

4

5

6

7

8

9

10

[Email protected] shell]# vim for.sh

#!/bin/bash

Sum=0

For i in ' SEQ 1 10 '

Do

sum=$[$sum + $i]

Done

Echo $sum

~

[Email protected] shell]# sh-x for.sh

+ sum=0

+ + SEQ 1 10

+ for I in ' SEQ 1 10 '

+ Sum=1

+ for I in ' SEQ 1 10 '

+ sum=3

+ for I in ' SEQ 1 10 '

+ sum=6

+ for I in ' SEQ 1 10 '

+ sum=10

+ for I in ' SEQ 1 10 '

+ sum=15

+ for I in ' SEQ 1 10 '

+ sum=21

+ for I in ' SEQ 1 10 '

+ sum=28

+ for I in ' SEQ 1 10 '

+ sum=36

+ for I in ' SEQ 1 10 '

+ sum=45

+ for I in ' SEQ 1 10 '

+ sum=55

+ Echo 55

55

---------------------Split Line-------------------------------

While loop

[Email protected] ~]# vim while.sh

#!/bin/bash

N=0

While [$n-le 10]

Do

Echo $n

n=$[$n +1]

Done

~

[Email protected] ~]# sh-x while.sh #测试结果

+ n=0

+ ' [' 0-le 10 '] '

+ Echo 0

0

+ n=1

+ ' [' 1-le 10 '] '

+ Echo 1

1

+ n=2

+ ' [' 2-le 10 '] '

+ Echo 2

2

+ n=3

+ ' [' 3-le 10 '] '

+ Echo 3

3

+ n=4

+ ' [' 4-le 10 '] '

+ echo 4

4

+ n=5

+ ' [' 5-le 10 '] '

+ echo 5

5

+ n=6

+ ' [' 6-le 10 '] '

+ echo 6

6

+ n=7

+ ' [' 7-le 10 '] '

+ echo 7

7

+ n=8

+ ' [' 8-le 10 '] '

+ echo 8

8

+ n=9

+ ' [' 9-le 10 '] '

+ Echo 9

9

+ n=10

+ ' [' 10-le 10 '] '

+ Echo 10

10

+ n=11

+ ' [' 11-le 10 '] '

---------------------Split Line-------------------------------

Shell interrupt continues to exit:

[Email protected] shell]# vim for2.sh

#!/bin/bash

For i in ' SEQ 1 10 '

Do

Echo $i

If [$i-eq 4]

Then

Break

Fi

Echo $i

Done

~

[Email protected] shell]# sh-x for2.sh

+ + SEQ 1 10

+ for I in ' SEQ 1 10 '

+ Echo 1

1

+ ' [' 1-eq 4 '] '

+ Echo 1

1

+ for I in ' SEQ 1 10 '

+ Echo 2

2

+ ' [' 2-eq 4 '] '

+ Echo 2

2

+ for I in ' SEQ 1 10 '

+ Echo 3

3

+ ' [' 3-eq 4 '] '

+ Echo 3

3

+ for I in ' SEQ 1 10 '

+ echo 4

4

+ ' [' 4-eq 4 '] '

+ Break #退出the entire loop

[Email protected] shell]# vim for2.sh

#!/bin/bash

For i in ' SEQ 1 10 '

Do

Echo $i

If [$i-eq 4]

Then

continue #结束this cycle

Fi

Echo $i

Done

echo "for-Done"

~

[Email protected] shell]# sh for2.sh

1

1

2

2

3

3

4

5

5

6

6

7

7

8

8

9

9

10

10

For-Done

[Email protected] shell]# vim for2.sh

#!/bin/bash

For i in ' SEQ 1 10 '

Do

Echo $i

If [$i-eq 4]

Then

Exit

Fi

Echo $i

Done

echo "for-Done"

[Email protected] shell]# sh for2.sh

1

1

2

2

3

3

4

#此处无for done, exit the shell directly

This article is from the "Cbo#boy_linux Road" blog, make sure to keep this source http://20151213start.blog.51cto.com/9472657/1890665

Shell Script Introduction