Bash indirect reference to an associative array

问题:

In this very simplified example, I need to address both key and value of an array element:

declare -A writer
writer[H.P.]=Lovecraft
writer[Stephen]=King
writer[Clive]=Barker
writer[Jack]=Ketchum

for i in ${!writer[@]}
do
    echo "$i ${writer[$i]}"
done

fullname()
{
    pointer=$1[@]
    for i in "${!pointer}"
    do
        echo "? $i"
    done
}
fullname writer

The function must display the output in the same format as the example loop before it, and it should receive either array name, list of keys or values, all of which I tried, without success. Any suggestions are greatly appreciated.

回答1:

indir_keys() {
    eval "echo \${!$1[@]}"
}

indir_val() {
    eval "echo \${$1[$2]}"
}

fullname()
{
    pointer=$1
    for i in $(indir_keys $pointer)
    do  
        echo "$i $(indir_val $pointer $i)"
    done
}

Gives:

Jack Ketchum
Clive Barker
Stephen King
H.P. Lovecraft

回答2:

Since Bash 4.3, declare has a flag -n to define references (this is loosely equivalent to references in C++). This flag tremendously simplifies your problem here:

fullname() {
    declare -nl pointer="$1"
    for i in "${!pointer[@]}"
    do
        echo "${pointer[$i]} $i"
    done
}

It will be safe if you're having spaces or funny symbols in the keys of your hash (unlike the accepted answer).

回答3:

From the Bash Reference Guide:

The positional parameters are temporarily replaced when a shell function is executed (see Shell Functions).

So you could do this:

fullname()
{
    for first
    do
        echo "$first ${writer[$first]}"
    done
}
fullname "${!writer[@]}"