Question

Bash是否有办法在关联数组中为值创建指针？像这样：

declare -A mapp
mapp=( ["key"]="${value}" )

for k in "${!mapp[@]}"; do 
    pointer="${mapp["${k}"]}"   # How do I do this?
done

通常情况下，你不需要来使用指针，但我很想知道是否有办法制作指针。

在更简单的情况下（例如，对于普通/字符串变量），我会做一个像这样的指针：

pointer=b
read -p "Enter something: " b
eval pointer=\$${pointer}

我如何为关联数组执行此操作？这不起作用（跳过strikethroughed代码）：

~~declare -A mapp mapp=( ["first"]="${a}" ["second"]="${b}" ) for k in "${!mapp[@]}"; do v=mapp["${k}"] read -p "Enter ${k}: " new eval v=\$${v} # Doesn't work done~~

declare -A mapp
mapp=( ["first"]="${a}"  ["second"]="${b}" )

for k in "${!mapp[@]}"; do 
    v=mapp["${k}"]

    read -p "Enter ${k}: " k

    eval v=\$${v}    # Doesn't work

done

这也不起作用（跳过strikethroughed代码）：

~~declare -A mapp mapp=( ["first"]="${a}" ["second"]="${b}" ) for k in "${!mapp[@]}"; do v=mapp read -p "Enter ${k}: " new eval v=\$${v["${k}"]} # Doesn't work (and has terrible readability) done~~

declare -A mapp
mapp=( ["first"]="${a}"  ["second"]="${b}" )

for k in "${!mapp[@]}"; do 
    v=mapp

    read -p "Enter ${k}: " k

    eval v=\$${v["${k}"]}    # Doesn't work (and has terrible readability)

done

Answer 1

在bash 4.3中，您可以使用nameref：

$ mapp=([key]=value)
$ declare -n x=mapp[key]  # NO dollar sign!
$ x=7
$ echo ${mapp[key]}
7

在4.3之前，您需要以不同的方式使用declare命令来执行间接操作。

$ mapp=([key]=value)
$ x=mapp[key]  # NO dollar sign!
$ declare "$x=7"
$ echo ${mapp[key]}
7

Answer 2

没问题：

$ declare -A ary=([foo]=bar [baz]=qux)
$ key=foo
$ pointer="ary[$key]"
$ echo "$pointer"
ary[foo]
$ echo "${!pointer}"
bar

这个意义上的“指针”是indirect variable

Bash - 关联数组中的值指针？

2 个答案: