Update JSON values conditionally with jq

What can you do if you have a following JSON structure and you want to change the “treat” into “biscuit” in every object where “animal” is “dog”?

[
  {
    "animal": "cat",
    "treat": "snacks",
  },
  {
    "animal": "dog",
    "treat": "snacks",
  },
  {
    "animal": "squirrel",
    "treat": "snacks",
  },
]

You can use jq to filter, update and otherwise work with JSON files on command line.

First, we want to select all dogs:

jq 'map(select(.animal == "dog"))' animals.json

map will run the command on every object in an array and select will select all items that match the boolean condition.

This will print out

[
  {
    "animal": "dog",
    "treat": "snacks"
  }
]

To change the value of “treat”, we can do that with the dot notation:

jq 'map(select(.animal == "dog").treat = "biscuit")' animals.json

which prints us:

[
  {
    "animal": "cat",
    "treat": "snacks"
  },
  {
    "animal": "dog",
    "treat": "biscuit"
  },
  {
    "animal": "squirrel",
    "treat": "snacks"
  }
]

and finally we can direct this output to a new file:

jq 'map(select(.animal == "dog").treat = "biscuit")' animals.json > new_animals.json

If your JSON only has one object (for example, if you are modifying multiple files as a batch), you can remove map and it will work the same way on individual JSON objects.