Array operations in the shell

1. Array definition, the shell uses a pair of parentheses to represent the array, and the array elements are separated by "spaces"

# empty array arr1
arr1= ()
# array arr2, members are 1, 2, 3, 4, 5, 6
arr2= (1 2 3 4 5 6)

2. Array elements read, format: ${array name [subscript]}, subscript starting from 0, subscript * or @ to represent the entire array content

[Root@10 ~]# Echo ${arr2[0]}
1

[root@10 ~]# echo ${arr2[*]}
1 2 3 4 5 6

3. Traverse Array, foreach

For num in ${arr2[*]}; Do
    echo $num;
Done

4. Array length, Format: ${#数组名 [* or @]}

[Root@10 ~]# echo ${#arr2 [*]}
6

5. Assignment, Format: array name [subscript]= value, if subscript does not exist, new array element;

[Root@10 ~]# arr2[6]=7
[root@10 ~]# echo ${arr2[*]}                    
1 2 3 4 5 6 7
[root@10 ~]# arr2[0]=-1
[root@10 ~]# echo ${arr2[*]}
-1 2 3 4 5 6 7

6. Fragment, Format: ${array name [* or @]: Start bit: length}, intercept part of array, return string, separated by space, and use "()" to get new slice array

[Root@10 ~]# Echo ${arr2[*]:0:3}
-1 2 3
[root@10 ~]# arr3= (${arr2[*]:0:3})
[root@10 ~]# echo ${arr3[*]}
-1 2 3

7. Substitution element, format: ${array name [* or @]/lookup character/substitution character}, does not modify the original array, if you want to modify the array, the result using "()" To assign to the new array

[Root@10 ~]# Echo ${arr2[*]}     
-1 2 3 4 5 6 7
[root@10 ~]# Echo ${ARR2[*]/7/10}
-1 2 3 4 5 6
[root@10 ~]# Arr4= (${ARR2[*]/7/10})
[root@10 ~]# echo ${arr4[*]}
-1 2 3 4 5 6 10

8. Delete array, format: unset array, clear entire array, unset array [subscript], clear individual elements

[Root@10 ~]# Echo ${arr2[*]}
-1 2 3 4 5 6 7
[root@10 ~]# unset arr2[0]
[root@10 ~]# echo ${arr2[*]}
2 3 4 5 6 7

[root@10 ~]# unset arr2
[root@10 ~]# echo ${arr2[*]}