shell array

One.Array

Variable: a memory space for storing a single element
Array: a contiguous memory space for storing multiple elements, equivalent to a collection of multiple variables

2. The role of the array

1. A combination of multiple elements, a collection of variables, and a type of data with the same characteristics are stored in an array.
2. How to distinguish each data in the array and number each element.
3. Classification of Arrays
Ordinary, Associated

Three. Array name and index

The number (subscript) of the index starts from 0 and belongs to the numerical index
The index can support the use of a custom format, not only the numerical format, that is, the associated index, which is supported after the bash 4.0 version.
Bash's arrays support sparse format (indexes are not consecutive)

Four. Declare array

Ordinary arrays can be declared without prior declaration, directly use
declare -a
Associative arrays must be declared first, and then use
declare -A

Normal array

Associative array
1. First declare 2. In assignment

Five. Array Traversal

Loop output definition value

Six. Array slice

Get the desired result (representing 1 to 3, 0 and others not output)

Seven. Array replacement

/10/80: Change previously defined value to later value

Eight. Bubble sort

Array sorting algorithm

Bubble Sort
Similar to the upward bubble action, the data will move forward continuously in the array from small to large or from large to small.

Basic Ideas

The basic idea of ​​bubble sort is to compare the values ​​of two adjacent elements, and if the conditions are met, exchange the element values,
move the smaller element to the front of the array, and move the larger element to the arrayBehind (that is, swapping the positions of the two elements),
so that the smaller element rises from the bottom to the top like a bubble.

Algorithm ideas

The bubbling algorithm is implemented by a double-layer loop. The outer loop is used to control the number of sorting rounds. Generally, the length of the array to be sorted is reduced by 1, because only one array element is left in the last loop, and no comparison is required., and 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 swap positions. The number of comparisons and swaps decreases with the number of sorting rounds.

#Define array
read -p "Define array:" shu
a=($shu)

#Assumed to define the maximum number
b=${a[0]}

#loop (values ​​ranging from 0 to the defined maximum number of a, i++: give a jump-out condition to avoid an infinite loop)
for ((i=0;i<${#a[*]};i++))

#The first value is less than the second value, until the end of the loop to find the largest number
do
if [[ $b -lt ${a[$i+1]} ]];then
c=${a[$i+1]}
fi
done
echo "$c"