How can I update an associative array inside a function passing it by parameter?

Question

I have the following code which reads all the fields of a Json file (the path being PRIVATE_REGISTRATION_FILE and stores them into an associative array (PRIVATE_FIELDS) which I query later in my code:

declare -A PRIVATE_FIELDS
for PRICING_FIELD in $(jq -c -r '.fields[]' "${PRIVATE_REGISTRATION_FILE}")
do
  FIELD_KEY=$(jq -r '.label' <<< "${PRICING_FIELD}")
  PRIVATE_FIELDS["${FIELD_KEY}"]=${PRICING_FIELD}
done

The problem is that I do this several times with several files, even though the logic is always the same.

Hence, I was thinking to extract this logic into a function but I'm having a hard time passing the map parameter to it.

This is what I attempted:

function update_array
{
    FILE_NAME=$1
    eval "declare -A MAP="${2#*=}
    for PRICING_FIELD in $(jq -c -r '.fields[]' "${FILE_NAME}")
    do
        FIELD_KEY=$(jq -r '.label' <<< "${PRICING_FIELD}")
        MAP["${FIELD_KEY}"]=${PRICING_FIELD}
    done
}

Which I call like this:

declare -A PRIVATE_FIELDS
update_array "myFile.json" "$(declare -p PRIVATE_FIELDS)"

However it doesn't work, the map remains empty.

echo ${PRIVATE_FIELDS["someKey"]}
>>> (empty)

I have tried literally each solution proposed in this answer but none of them worked. What am I doing wrong?

Bash version: 4.2.46(2)-release

---

Additional note, the Json file looks like this (apparently the calls to jq may be reduced):

{
    "name": "Something",
    "fields": [
        {
            "label": "key1",
            "value": "value1",
            "other": "other1"
        },
        {
            "label": "key2",
            "value": "value2",
            "other": "other2"
        }
    ]
}

Answer 1

When you use declare in a function, you're actually making the variable local. See help declare at a bash prompt.

Use a nameref (requires bash version 4.3+):

function update_array
{
    local FILE_NAME=$1
    local -n MAP=$2     # MAP is now a _reference_ to the caller's variable
    # the rest stays the same
    for PRICING_FIELD in $(jq -c -r '.fields[]' "${FILE_NAME}")
    do
        FIELD_KEY=$(jq -r '.label' <<< "${PRICING_FIELD}")
        MAP["${FIELD_KEY}"]=${PRICING_FIELD}
    done
}

then you simply pass the array name

declare -A PRIVATE_FIELDS
update_array "myFile.json" PRIVATE_FIELDS

declare -p PRIVATE_FIELDS

---

To more efficiently iterate over the JSON file:

$ jq -c -r '.fields[] | "\(.label)\t\(.)"' file.json
key1    {"label":"key1","value":"value1","other":"other1"}
key2    {"label":"key2","value":"value2","other":"other2"}

That's assuming the labels don't contain any tab characters.

---

Using that, plus your older bash version, you can do this

Assuming that the result arrays will be in the global scope

update_array() {
    local filename=$1 varname=$2
    local -A map
    while IFS=$'\t' read -r label json; do
        map[$label]=$json
    done < <(
        jq -c -r '.fields[] | "\(.label)\t\(.)"' "$filename"
    )
    eval declare -gA "$varname=$(declare -p map | cut -d= -f2-)"
}

You'd call it like

$ echo $BASH_VERSION
4.2.45(1)-release

$ update_array tmp/file.json myArray

$ declare -p myArray
declare -A myArray='([key2]="{\"label\":\"key2\",\"value\":\"value2\",\"other\":\"other2\"}" [key1]="{\"label\":\"key1\",\"value\":\"value1\",\"other\":\"other1\"}" )'

$ for label in "${!myArray[@]}"; do
>     printf '"%s" => >>%s<<\n' "$label" "${myArray[$label]}"
> done
"key2" => >>{"label":"key2","value":"value2","other":"other2"}<<
"key1" => >>{"label":"key1","value":"value1","other":"other1"}<<