Need to find key-value pair and replace key-value pair in JSON using JQ

Question

I have this JSON

{
  "firstName": "Rajesh",
  "lastName": "Kumar",
  "gender": "man",
  "age": 24,
  "address": {
    "streetAddress": "126 Udhna",
    "city": "Surat",
    "state": "WB",
    "postalCode": "394221"
  },
  "phoneNumbers": [
    {
      "type": "home",
      "number": "7383627627"
    }
  ]
}

I need to find the value of the "state" key Using JQ and replace the value in JSON. I do not want to fetch it by providing the position of the key, Like

firstName=$(cat sample-json.json | jq -r '.firstName')

My expected output

{
  "firstName": "Rajesh",
  "lastName": "Kumar",
  "gender": "man",
  "age": 24,
  "address": {
    "streetAddress": "126 Udhna",
    "city": "Surat",
    "state": "Bihar",
    "postalCode": "394221"
  },
  "phoneNumbers": [
    {
      "type": "home",
      "number": "7383627627"
    }
  ]
}

Answer 1

If you're willing to specify.address:

jq '.address.state = "Bihar"' sample-json.json

Otherwise:

jq 'walk(if type == "object" and has("state") then .state = "Bihar" else . end)' sample-json.json

This last will replace all .state values. If you only want to replace the first occurrence:

jq 'first(..|objects|select(has("state"))).state = "Bihar"' sample-json.json

And so on. It would really help all concerned if you could make the requirements clear.