One array

1.1 Definition of array

• An array is a collection of data of the same type , It opens up a continuous space in memory , Usually used together with recycling
• The type of array

Normal array ： Direct definition without declaration , Subscript index can only be an integer
Associative array ： Need to use declare -A Otherwise, the system does not recognize it , The index can be a string

1.2 How to define an array

A="1 2 3 456"       // Define string 
A=(1 2 3 4 456)		// Define an array （ Each number inside is also called an element ）
   0 1 2 3 4		// Below it ,0 As the starting point （ Also known as array subscript , Index subscript ）

The first one is ：

Directly enclose the elements to be added to the array in parentheses , Separate... With spaces in the middle

 Array name =(value0 value1 value2)

num=(11 22 33 44)
echo ${
    #num}     ## Displays the length of a single string 
2
[[email protected] ~]# echo ${num[*]} ## Show detailed string （ Array ） Content ,# Number change @ It can also have the same effect 
11 22 33 44
[[email protected] ~]# echo ${#num[*]} ## Show all strings （ Array ） length ,# Number change @ It can also have the same effect 
4

The second kind ：

Precisely define a value for each subscript index and add it to the array , Index numbers can be discontinuous

 Array name =([0]=value [1]=value [2]value ...)

num=([0]=55 [1]=66 [2]77 [4]88)

[[email protected] ~]# echo ${num[*]}
[0]55 [1]66 [2]77 [3]88

The third kind of ：

First assign all the elements to be added to the array to a variable , Then reference this variable and add it to the array

 List name ="value0 value1 value2...."
 Array name =($ List name )

list="11 12 13 14"
num=($list)
[[email protected] ~]# echo ${num[*]}
11 12 13 14 
[[email protected] ~]# echo ${#num[*]}
4

A fourth ：

Define according to the subscript

 Array name [0]="11"
 Array name [0]="22"
 Array name [0]="33"

 Array name [0]="value"
 Array name [0]="value"
 Array name [0]="value"

1.3 The data types included in the array

• value type

• Character type ： Use " " or ’ ’ Definition

1. Get array length

num=(11 22 33 44)
[[email protected] ~]# echo ${#num[*]} ## Show all strings （ Array ） length ,# Number change @ It can also have the same effect 
4
[[email protected] ~]# echo ${#num[@]}
4

2. Get the data list

num=(11 22 33 44)
[[email protected] ~]# echo ${num[*]} ## Show detailed string （ Array ） Content ,# Number change @ It can also have the same effect 
11 22 33 44
[[email protected] ~]# echo ${#num[@]}
11 22 33 44

3. Array element traversal

#!/bin/bsah
arr=(1 2 3 4 5)
for i in ${arr[*]}   
do
echo $i
done
[[email protected] ~]# sh 4.sh
1
2
3
4
5

4. Element slice

[[email protected] ~]# ky20-zy=(4 7 9 5 2) ## Define an array 
[[email protected] ~]# echo ${ky20-zy[*]} ## Output the elements in the array 
4 7 9 5 2
0 1 2 3 4    ## Index subscript 
[[email protected] ~]# echo ${ky20-zy[*]:2:3} ## Extract subscript from index 2 At the beginning 3 Elements 
9 5 2
[[email protected] ~]# echo ${ky20-zy[*]:2:2} ## Extract subscript from index 2 At the beginning 2 Elements 
9 5
[[email protected] ~]# echo ${ky20-zy[*]:3:2} ## Extract subscript from index 3 At the beginning 2 Elements 
5 2
[[email protected] ~]# echo ${ky20-zy[*]:1:2} ## Extract subscript from index 1 At the beginning 2 Elements 
7 9

5. Array element replacement

[[email protected] ~]# mqj=(36 35 34 33 32 31) ## Define an array 
[[email protected] ~]# echo ${mqj[*]} ## Output the elements in the array 
36 35 34 33 32 31
[[email protected] ~]# echo ${mqj[*]/3/55} ## There will be 3 Replace or add a specified value to the element of 55, Just covering , Not a permanent replacement （ Replace only the first match of each element ）
556 555 554 553 552 551

6. Array delete

[[email protected] ~]# jmq=(34 45 55 12)
[[email protected] ~]# echo ${jmq[*]}
34 45 55 12
[[email protected] ~]# unset jmq ## Delete array 
[[email protected] ~]# echo ${jmq[*]}

[[email protected] ~]# jmq=(34 45 55 12)
[[email protected] ~]# echo ${jmq[*]}
34 45 55 12
[[email protected] ~]# unset jmq[3] ## Delete the fourth element , The index subscript in brackets , After deletion, only elements are not displayed , But it will become a space occupying the index subscript , If you check the length, it will be reduced 
[[email protected] ~]# echo ${jmq[*]}
34 45 55 

1. example ： Define random roll calls in an array

[[email protected] opt]# vim w ## Create and edit a file, write the name and corresponding number 
1 Big lion 
2 Little rabbit 
3 Little dolphin 
4 Butterfly 
5 Sparrow 

[[email protected] opt]# vim w.sh ## Write array script 
#!/bin/bash
bu=`cat /opt/w`        ## Defining variables 
arr=($bu)             ## Define array variables 
for i in ${arr[*]}    ## Cycle through the content array in 
do
a=$[$RANDOM%5]       ## Define variables to take random numbers 
done
echo " The number and name of the small animal is : ${arr[$a]}"   ## Output the number and name corresponding to the random number 

[[email protected] opt]# sh w.sh
 The number and name of the small animal is : 1 Big lion 

 Simple method 
#!/bin/bash
bu=`cat /opt/w`
arr=($bu)
a=$[$RANDOM%5]
echo " The number and name of the small animal is : ${arr[$a]}"

Two 、 Array sorting algorithm （ Bubble sort ）

It's like a bubble rising , Move the data forward continuously from small to large or from large to small in the array

• The basic idea

The basic idea of bubble sorting is to compare the values of two adjacent elements , Exchange element values if conditions are met , Move the smaller elements to the front of the array , Move the larger elements behind the array （ That is, to exchange the positions of two elements ）, So the smaller elements rise from the bottom to the top like bubbles

• Algorithm ideas

The bubbling algorithm is realized by two-layer loops , The external loop is used to control the number of sorting rounds , Generally, the length of the array to be sorted minus 1 Time , Because there's only one array element left in the last loop , There's no need to compare , At the same time, the array has been sorted

The inner loop is mainly used to compare the size of each adjacent element in the array , To determine whether to exchange position comparison and exchange times decrease with the number of sorting rounds

• example ： hope a and b Adjust the position of the value of

a=10
b=20

dxz=$a     ## Add custom variables dxz Purpose , It's to make a The assignment of custom variables is idle , It's easy to exchange later 
a=$b
b=$dxz

##dxz=$a
dxz=10
a=10
b=20

##a=$b
dxz=10
a=20
b=20

##b=$a
dxz=10
a=20
b=10

a=20
b=10

## Bubble sort element exchange 
dxz=(10 20)
echo ${dxz[*]}

## Swap places 
xtz=`echo ${dxz[0]}`

dxz[0]=`echo ${dxz[1]}`

dxz[1]=$xtz

echo ${dxz[*]}

[[email protected] ~]# sh 7.sh
10 20
20 10

##a=$b
dxz=10
a=20
b=20

##b=$a
dxz=10
a=20
b=10

a=20
b=10

## Bubble sort element exchange
dxz=(10 20)
echo ${dxz[*]}

## Swap places
xtz=echo ${dxz[0]}

dxz[0]=echo ${dxz[1]}

dxz[1]=$xtz

echo ${dxz[*]}

[[email protected] ~]# sh 7.sh
10 20
20 10

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