Array of Shell programming

Array, arrays

Variable: Stores the memory space of a single element;
Array: Memory space for storing multiple elements;

Array name: The entire array has only one name;
Array index: numbering starting from 0;
Array name [index]
Array[index]

Value:
${array[index]}
If index number is not specified, the element with index 0 is returned by default;

Bash-4 and later versions support custom index formats, not just 0,1,2,... Number format;
Such arrays are called "associative arrays";

Declaring an array:
#help Declare

-A to make NAMEs indexed arrays. declares an indexed array;
-A to make NAMEs associative arrays. declares an associative array;

How elements in an array are assigned: (no prior declaration required)

(1) Assign only one element at a time;
Array_name[index]=value
#animals [0]=pig
#animals [1]=dog
#echo a $animals #若不加索引号, the value of the first element is returned by default;
#echo ${animals[1]} #返回第二个元素的值;

(2) Assign all elements at once (continuous assignment)
Array_name= ("value1" "value2" "value3" ...)
#weekdays = ("Monday" "Tuesday" "Wednesday")
#echo ${weekdays[2]}

Connect an array, splicing several arrays:
#arrayN = (${array1[@]} ${array2[@] ...})

(3) Assign only specific elements: (sparse format array, discontinuous assignment)
Array_name= ([0]= "value1" [3]= "Value4" ...)
#sword = ([0]= "Yitian" [3]= "Longquan")
#echo ${sword[3]}

(4) Read-a Array_Name
#read-A Jianghu
Yuebuqun Dongfangbubai Qqianchaotaijian
#echo ${jianghu[1]}
Dongfangbubai

The length of the array (the number of elements in the array):
${#ARRAY_NAME [*]}
${#ARRAY_NAME [@]}

#echo ${#world [*]}
#echo ${#world [@]}

If index number is not indexed, the character length of the first element is returned:
#echo ${#animals}
3

If you do not add #, all elements in the array are returned:
#echo ${animals[*]}
#echo ${animals[@]}
Pig Dog

${array[@]} outputs an element value separated by whitespace;
${ARRAY[*]} outputs an entire string;

Example: Generate 10 random numbers to find the maximum value;
#vim rand.sh
#!/bin/bash
#
Declare-a Rand
Declare-i max=0
For i in {0..9};d o
rand[$i]= $RANDOM
echo ${rand[$i]}
[${rand[$i]}-gt $max] && max=${rand[$i]}
Done
echo "MAX: $max"

Defines an array in which the elements in the array are all files that end with. Log in the/var/log directory;
Count the sum of the rows of the file whose index is even;
#vim array1.sh
#!/bin/bash
#
declare-a files
Files= (/var/log/*.log)
Declare-i lines=0
For i in ' seq 0 $[${#files [*]}-1] ';d o
If [$[$i%2]-eq 0];then
Let lines+= ' Wc-l ${files[$i]} | awk ' {print '} '
Fi
Done
echo "Lines: $lines"

Array element slices:

${array_name[@]:offset:number}
Offset: The number of elements to skip;
Numbers: The number of elements to be taken out, and the amount of all elements after the offset is omitted;

#files = (/etc/[pp]*)
#echo ${files[*]}
/etc/packagekit/etc/pam.d/etc/passwd/etc/passwd-/etc/php.d/etc/php.ini/etc/phpmyadmin/etc/php-tcpdf/etc/ Pinforc/etc/pkcs11/etc/pki/etc/plymouth/etc/pm/etc/polkit-1/ETC/POPT.D/ETC/POSTFIX/ETC/PPP/ETC/PRELINK.CONF.D/ Etc/printcap/etc/profile/etc/profile.d/etc/protocols/etc/pulse/etc/puppet/etc/python
#echo ${files[@]:2:3} #跳过2个, fetch three;
/etc/passwd/etc/passwd-/ETC/PHP.D
#echo ${files[@]:5} #跳过5个, take back all;

Append an element to the array:
array_name[${#ARRAY_NAME [@]}]=value

To delete an element in an array:
Unset Array[index]

Delete the entire array:
Unset Array

Associative arrays, which need to be declared beforehand;
Declare-a Array_Name
Array_name= ([index_name1]= "value1" [index_name2]= "value2" ...)

#declare-A World
#world [us]= "America"
#echo "${world[us]}"
#world [uk]= "Kingdom"
#echo "${world[uk]}"

Array of Shell programming