☰

Bash 中这两种关联数组声明有什么区别？

tag-icon • tag-icon bash shell-script shell array associative-array
Bash 中这两种关联数组声明有什么区别？

我在 Bash 中玩了一下关联数组，在使用和不使用 声明完全相同的关联数组时发现了以下差异declare。代码如下：

#!/usr/bin/env bash

echo -e "\n\nASSOCIATIVE ARRAY\n"
declare -A MY_MAP=( 
    [Madrid]="Spanish" 
    [London]="English" 
    [Paris]="French" 
    [1]=2
    [3]=3.14 
)
echo "First element: $MY_MAP"
echo "Whole content as single string: ${MY_MAP[*]}"
echo "Whole content quoted separately: ${MY_MAP[@]}"
echo "List of indices: ${!MY_MAP[@]}"
echo "Array length: ${#MY_MAP[*]}"
echo "Array length: ${#MY_MAP[@]}"
echo "Second element: ${MY_MAP[London]}"
echo "Last 2 elements: ${MY_MAP[@]:1:3}"

echo -e "\n\nASSOCIATIVE ARRAY - 2\n"
MY_MAP2=( 
    [Madrid]="Spanish" 
    [London]="English" 
    [Paris]="French" 
    [1]=2
    [3]=3.14 
)
echo "First element: $MY_MAP2"
echo "Whole content as single string: ${MY_MAP2[*]}"
echo "Whole content quoted separately: ${MY_MAP2[@]}"
echo "List of indices: ${!MY_MAP2[@]}"
echo "Array length: ${#MY_MAP2[*]}"
echo "Array length: ${#MY_MAP2[@]}"
echo "Second element: ${MY_MAP2[London]}"
echo "Last 2 elements: ${MY_MAP2[@]:1:3}"

当我执行前面的脚本时，我得到以下输出：

ASSOCIATIVE ARRAY

First element: 
Whole content as single string: French 3.14 2 English Spanish
Whole content quoted separately: French 3.14 2 English Spanish
List of indices: Paris 3 1 London Madrid
Array length: 5
Array length: 5
Second element: English
Last 2 elements: French 3.14 2


ASSOCIATIVE ARRAY - 2

First element: French
Whole content as single string: French 2 3.14
Whole content quoted separately: French 2 3.14
List of indices: 0 1 3
Array length: 3
Array length: 3
Second element: French
Last 2 elements: 2 3.14

我的问题是declare -A做什么使输出不同？

如果能详细了解这里发生的事情，我们将不胜感激。

预先非常感谢。

答案1

declare -A是您的第一个声明被视为关联数组的唯一原因。您的第二个声明将作为索引数组处理。操作索引数组时，索引被视为算术上下文：Madrid、London、 和Paris被解释为变量名，并且由于它们尚未声明，因此它们的值为 0。因此，赋值被读取为[0]="Spanish"、[0]="English"、[0]="French"、[1]=2、[3]=3.14和${MY_MAP2[London]}是${MY_MAP2[0]}。

相关内容