How do I replace a JSON string with its parsed equivalent in place with jq?

Question

I have a JSON array with a bunch of objects, all the same keys, but some of the keys contain serialized JSON instead of actual JSON. Something like this.

[
  {
    "a": 1,
    "b": "{\"c\":2}"
  },
]

and I'd like to replace the contents of all the bs with their parsed form.

[
  {
    "a": 1,
    "b": { "c": 2 }
  },
]

How can I do this, ideally with jq?

Answer 1

Use fromjson, and update the fields in question using .[].b |=.

.[].b |= fromjson

Demo

If you want to decode all JSON-encoded strings, unknowing which ones are, you could try using fromjson, and in case of a failure resort to the original input .. try can be abbreviated to ?:

.[][] |= (fromjson? // .)

Demo

Both output:

[
  {
    "a": 1,
    "b": {
      "c": 2
    }
  }
]