Construct json through jq tool in shell script loop

Question

json can be created using the following command.

  jq -n \
  --arg v1 "Value1" \
  --arg v2 "Value2" \
  '{k1: "$v1", k2:$v2'}

But when my key is mutable, how should I loop? For example, the script I execute is

test.sh k1=v1 k2=v2 k3=v3

test.sh is as follows

index=1
while ((index <= "$#")); do
  data_i_key=$(echo ${!index} | awk -F "=" '{print $1}')
  data_i_value=$(echo ${!index} | awk -F "=" '{print $2}')
  let index++
  JSON_STRING=$(jq -n \
    --arg value "$data_i_value" \
    '{'"$data_i_key"': $value'})
    echo $JSON_STRING

The above print result is

{ "K3": "V3" }

if I replace it with

JSON_STRING+=$(jq -n \
    --arg val_value "$dataValue" \
    '{'"$data_i_key"': $val_value'})

The print result is

{ "k1": "v1" }{ "k2": "v2" }{ "K3": "V3" }

The above two methods have not achieved the goal, do you have a good way to deal with it? My desired output is

{ "k1": "v1" , "k2": "v2" ,"K3": "V3" }

hope you can help me.

How does the script decide when to upper-case key and value? k1, v1, k2, v2 are inserted verbatim into the JSON, but k3 and v3 are uppercased to K3 and V3. Intentional or typo? — knittl
– knittl, Commented Oct 17, 2022 at 11:02

knittl · Accepted Answer · 2022-10-17 17:43:56Z

3

I'd suggest a totally different, but simpler, approach:

for kv; do
  echo "$kv" | jq -R './"=" | {key:first,value:last}'
done | jq -s 'from_entries'

It builds {key: …, value: …} objects from your positional parameters (splitting them by the equal sign) and then slurping all those objects in a second jq process, converting them into a single object via from_entries.

Alternatively, using -n (--null-input), --args and then accessing via $ARGS.positional. This avoids the loop and the second jq call altogether.

jq -n '$ARGS.positional | map(./"=" | {key:first,value:last}) | from_entries' --args "$@"

If your values can contain = themselves, you have to join all but the first value of the array:

jq -n '$ARGS.positional
| map(./"=" | {key:first,value:.[1:]|join("=")})
| from_entries' --args "$@"

edited Oct 17, 2022 at 17:43

answered Oct 17, 2022 at 9:52

knittl

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12 Comments

pmf Over a year ago

Going further: jq -n --args '$ARGS.positional | map(. / "=" | {key:first, value:last}) | from_entries' k1=v1 k2=v2 k 3=v3 (or … "$@")

knittl Over a year ago

@pmf you are too fast, I was already extending my answer :)

junhu Over a year ago

Thanks a lot for your answer, but I don't quite understand how $ARGS.positional is used? If I only want to construct json from the second parameter, how should I modify it?

knittl Over a year ago

@junhu what do you mean with "only json from the second parameter?"

glenn jackman Over a year ago

Or, avoiding the need for from_entries => echo k1=v1 k2=v2 k3=v3 | jq -R './" " | map(./"=" | {(first): last}) | add'

|

pmf · Accepted Answer · 2022-10-17 09:49:30Z

0

Use parentheses around the key expression to have it evaluated:

jq -n --arg k1 "Key1" --arg v1 "Value1" '{($k1): $v1}'

{
  "Key1": "Value1"
}

answered Oct 17, 2022 at 9:49

pmf

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1 Comment

junhu Over a year ago

I know this method, but now I want to write all the parameters together in json format in the loop and assign them to JSON_STRING。

glenn jackman · Accepted Answer · 2022-10-17 12:56:58Z

-1

Perhaps this, which will handle an arbitrary number of key=value arguments:

#!/usr/bin/env bash

args=()
for arg; do
    IFS="=" read -r k v <<<"$arg"
    args+=("$k" "$v")
done

jq -n --args '
    $ARGS.positional as $a
    | reduce range(0; $a | length; 2) as $i ({}; .[$a[$i]] = $a[$i + 1])
' "${args[@]}"

Produces:

$ ./test.sh k1=v1 k2=v2 k3=v3
{
  "k1": "v1",
  "k2": "v2",
  "k3": "v3"
}

answered Oct 17, 2022 at 12:56

glenn jackman

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