add object to dynamic key using JQ

Question

I'm looking to build object using jq and add object key to dynamic key and I could not figure out. Here is my sample script:

#!/bin/bash -e

environments=('development' 'stage' 'production')
regions=('us-east-1' 'us-west-2')

tree='{}'

for environment in "${environments[@]}"
do
    echo "${environment}"
    # Or do something else with environment

    tree="$(jq --arg jqEnvironment "${environment}" '. | .[$jqEnvironment] = {}' <<< "${tree}")"

    for region in "${regions[@]}"
    do
        echo "${region}"
        # Or do something with region

        tree="$(jq --arg jqEnvironment "${environment}" --arg jqRegion "${region}" '. | .[$jqEnvironment] | .[$jqRegion] = {}' <<< "${tree}")"
    done
done

jq . <<< "${tree}"

actual outputs

{
  "us-west-2": {}
}

But what I want is this

{
  "development": {
    "us-east-1": {},
    "us-west-2": {}
  },
  "stage": {
    "us-east-1": {},
    "us-west-2": {}
  },
  "production": {
    "us-east-1": {},
    "us-west-2": {}
  }
}

I could not figure out, please help!

peak · Accepted Answer · 2018-01-30 04:32:45Z

4

The following script produces the desired result, and should be fairly robust:

#!/bin/bash

environments=('development' 'stage' 'production')
regions=('us-east-1' 'us-west-2')

jq -n --slurpfile e <(for e in "${environments[@]}" ; do echo "\"$e\""; done) \
   --slurpfile r <(for r in "${regions[@]}" ; do echo "\"$r\"" ; done) \
   '($r | map ({(.): {}}) | add) as $regions
     | [{($e[]): $regions}] | add'

The main point to note here is that in order to construct an object with a dynamically determined key, one has to use parentheses, as in {(KEY): VALUE}

Of course, if the values for the "environments" and "regions" were available in a more convenient form, the above could be simplified.

Output

{
  "development": {
    "us-east-1": {},
    "us-west-2": {}
  },
  "stage": {
    "us-east-1": {},
    "us-west-2": {}
  },
  "production": {
    "us-east-1": {},
    "us-west-2": {}
  }
}

edited Jan 30, 2018 at 4:32

answered Jan 30, 2018 at 2:41

peak

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8 Comments

Nam Nguyen Over a year ago

Thanks @peak, I ran the script and it does not look like it output valid json format though { "development": { "us-east-1": {}, "us-west-2": {} } } { "stage": { "us-east-1": {}, "us-west-2": {} } } { "production": { "us-east-1": {}, "us-west-2": {} } }

Nam Nguyen Over a year ago

is it possible to keep 2 for-loop separated because I need to do something with environment and region variables? Your short form solution is pretty cool but not flexible for me to use environment or region variables for other actions. Thanks a lot for your solution.

Nam Nguyen Over a year ago

--argfile variable-name filename: Do not use. Use --slurpfile instead. (This option is like --slurpfile, but when the file has just one text, then that is used, else an array of texts is used as in --slurpfile.)

peak Over a year ago

1. I tweaked the script to produce a single JSON object. 2. As you say, --argfile has been deprecated but it is perfectly fine here, and has the (possible) advantage of working in versions of jq that don't have --slurpfile.

Nam Nguyen Over a year ago

look like you updated and it caused errors now "jq: error: syntax error, unexpected '[', expecting '|' (Unix shell quoting issues?) at <top-level>, line 2: [{($e[]): $regions}] | add jq: 1 compile error"

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