8、 Definition of array

8、 ... and 、 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 classification of arrays

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

How to define an array

（	11	22	33	44	55	66	）
	0	1	2	3	4	5

 The first one is ： Directly enclose the elements to be added to the array in parentheses , Separate... With spaces in the middle 

num=（11 22 33 44）

${#num} Shows the length of the string 

 Array name =（value0 value1 value2）

 The second kind ： Precisely define a value for each subscript index and add it to the array , Index numbers can be discontinuous 
num=([0]=55 [1]=66 [2]=77 [4]=88)

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

 The third kind of ： First assign all the elements to be added to the array to a variable , Then apply this variable to the array 
list=“11 12 13 14”            List name =“value0 value1 value2...”
num=（$list）                  Array name =（$ List name ）

 A fourth ： Define according to the subscript 
 Array name [0]="11"                 Array name [0]="value"
 Array name [1]="22"                 Array name [1]="value"
 Array name [2]="33"                 Array name [2]="value"

The data types included in the array

value type

Character type ： Use “ ” or ‘ ’ Definition

Gets the length of the array

arr_number=(10 20 30 40 50)

arr_length=${#arr_number[*]}

or ： arr_length=${#arr_number[@]}

echo $arr_length

echo ${arr_number[*]}

or echo ${arr_number[@]}

Array element traversal

[[email protected] ~]# vim ysszbl.sh
[[email protected] ~]# sh ysszbl.sh
1
2
3
4
5
6
[[email protected] ~]# cat ysszbl.sh 
#!/bin/bash
arr=(1 2 3 4 5 6)
for i in ${arr[*]}      # for i in ${arr[@]}
do 
 echo $i
done

Element slice

[[email protected] ~]# arr=(1 2 3 4 5 6 7 8)
[[email protected] ~]# echo ${arr[@]}          # Output the entire array 
1 2 3 4 5 6 7 8
[[email protected] ~]# echo ${arr[*]:2:3}      # Extract subscript from index 2 At the beginning 3 Elements 
3 4 5
[[email protected] ~]# echo ${arr[*]:0:4}      # Extract subscript 0 At the beginning 4 Elements 
1 2 3 4
[[email protected] ~]# 

Array （ Elements ） Replace

[[email protected] ~]# arr=(11 12 13 14 15 16)
[[email protected] ~]# echo ${arr[*]/3/44}   #${ Array name 【@ or *】/ To find the character / Replace character }
11 12 144 14 15 16
[[email protected] ~]# echo ${arr[*]/1/32}
321 322 323 324 325 326
[[email protected] ~]# echo ${arr[*]}        # It will not replace the original contents of the array 
11 12 13 14 15 16
[[email protected] ~]# arr=(${arr[*]/1/32})  # To change the original array , This can be achieved by reassigning 
[[email protected] ~]# echo ${arr[*]}
321 322 323 324 325 326

Array delete

[[email protected] ~]# arr=(1 2 3 4 5)
[[email protected] ~]# unset arr              # Delete array 
[[email protected] ~]# echo ${arr[*]}

[[email protected] ~]# arr=(1 2 3 4 5)
[[email protected] ~]# unset arr[4]           # Delete the subscript as 4 The elements of 
[[email protected] ~]# echo ${arr[*]}
1 2 3 4
[[email protected] ~]# 

Summary ： Array

1、 Array definition

num=（11 12 13 14 11 15）

​ The above means to define a set （ Define all elements of an array ）

​ You can use the following command to view the value of each element of the array and the length of the array

2、 Viewing the length of an array

echo ${num[@]}

echo ${num[*]}

3、 Viewing the length of an array

echo ${#num[@]}

echo ${#num[*]}

Check out the elements （echo） ${ Array name [ Subscript ]}

"@“ or ”*" Express all

4、 Element assignment

arr[0]=“12”

Array name [ Subscript ]= Element value

5、 Array slice

echo ${arr[*]:2:1}

echo ${ Array name [*]: Subscript : Print several element values }

echo ${ Array name [@]: Subscript : Print several element values }

6、 Array （ Elements ） Replace ----- temporary

echo ${arr[*]/3/55}

echo ${ Array name [*]/ character （ strand ）/ Replace with the specified value （ Replace only the first match of each element ）}

echo ${ Array name [@]/ character （ strand ）/ Replace with the specified value （ Replace only the first match of each element ）}

7、 Array delete

10 20 30 40 50

0 1 2 3 4

unset arr[2] # Delete the subscript as 2 The elements of ------------------》

10 20 40 50

0 1 2 3 4

Random roll call in the form of an array

[[email protected] opt]# cat dm.sh 
#!/bin/bash
list=$(cat /opt/name)     #/opt/name Roll call list 
arr=($list)               # Define an array 
for i in {arr[*]}
do
a=$[RANDOM%25]            #a Is the subscript value ,0-24 random number 
echo "${arr[$a]}"
done
[[email protected] opt]#