Get specific key value pairs with jq

user_5905425 0
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In my sample json below, I can filter records where charge is null with jq -M ' map(select(.charge == null)) ' 

  [
    {
      "id": 1,
      "name": "vehicleA",
      "state": "available",
      "charge": 100
    },
    {
      "id": 2,
      "name": "vehicleB",
      "state": "available",
    },
    {
      "id": 3,
      "name": "vehicleB",
      "state": "available",
      "charge": 50
    }
  ]

which returns:

{
  "id": 2,
  "name": "vehicleB",
  "state": "available",
}

How would one only get id and the value associated with id of the filtered records so that adding this step to the above query would return 2?

jq bash json
2 Answers

If you would like an array of ids for items without a charge you could use this filter:

.items | map(select(.charge == null) | .id)

Try it online at jqplay.org

If you want the values enumerated instead of being collected into an array this is better:

.items[] | select(.charge == null) | .id

Try it online at jqplay.org

user_83795970

Your question is not exactly accurate:

  • The example JSON is invalid, because the last property of the second object has a trailing comma, which should raise a parsing error
  • The output of map(select(.charge == null)) is not an object as in the example, but an array of a single object

In any case, you can extract the .id from the result of map like this:

jq -M 'map(select(.charge == null)) | .[].id' file.json
user_6419550
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