在 Bash 中测试是否声明了关联数组 [英] In Bash test if associative array is declared

问题描述

如何测试是否在 Bash 中声明了关联数组?我可以测试一个变量，如:

How can I test if an associative array is declared in Bash? I can test for a variable like:

[ -z $FOO ] && echo nope

但我似乎不适用于关联数组:

but I doesn't seem to work for associative arrays:

$ unset FOO
$ declare -A FOO
$ [ -z $FOO ] && echo nope
nope
$ FOO=([1]=foo)
$ [ -z $FOO ] && echo nope
nope
$ echo ${FOO[@]}
foo

感谢您的回答，两者似乎都有效，所以我让速度决定:

Thank you for your answers, both seem to work so I let the speed decide:

$ cat test1.sh
#!/bin/bash
for i in {1..100000}; do
    size=${#array[@]}
    [ "$size" -lt 1 ] && :
done
$ time bash test1.sh #best of five

real    0m1.377s
user    0m1.357s
sys     0m0.020s

另一个:

$ cat test2.sh
#!/bin/bash

for i in {1..100000}; do
    declare -p FOO >/dev/null 2>&1 && :
done
$ time bash test2.sh #again, the best of five

real    0m2.214s
user    0m1.587s
sys     0m0.617s

编辑 2:

让我们快速比较 Chepner 的解决方案与之前的解决方案:

Let's speed compare Chepner's solution against the previous ones:

#!/bin/bash

for i in {1..100000}; do
    [[ -v FOO[@] ]] && :
done
$ time bash test3.sh #again, the best of five

real    0m0.409s
user    0m0.383s
sys     0m0.023s

嗯，这很快.

再次感谢，伙计们.

推荐答案

在 bash 4.2 或更高版本中，您可以使用 -v 选项:

In bash 4.2 or later, you can use the -v option:

[[ -v FOO[@] ]] && echo "FOO set"

注意，在任何版本中，使用

Note that in any version, using

declare -A FOO

实际上并没有立即创建关联数组；它只是在名称 FOO 上设置一个属性，允许您将名称分配为关联数组.数组本身在第一次赋值之前不存在.

doesn't actually create an associative array immediately; it just sets an attribute on the name FOO which allows you to assign to the name as an associative array. The array itself doesn't exist until the first assignment.

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