Use `jq` to see if a JSON key exists
====================================

April 22, 2021
https://stefan.vanburen.xyz/til/jq-key-exists/


I'm constantly using [`jq`](https://stedolan.github.io/jq/) to deal with <abbr title="JavaScript Object Notation">JSON</abbr> via the <abbr title="Command-Line Interface">CLI</abbr>.

Today I needed to figure out the difference between a key existing with a `null` value or not existing at all in a bit of <abbr title="JavaScript Object Notation">JSON</abbr>.

By default, "querying" a key via `jq` will return `null` whether the key exists and is `null`, **or** the key doesn't exist:

```fish
△ # NOTE: the following is in fish, but should be straightforward to port to other shells

△ set json '{"test": null}'

△ echo $json | jq .test
null

△ echo $json | jq .nonexistent
null
```

Instead, you can use the `jq`'s [`has`](https://stedolan.github.io/jq/manual/#has(key)) function to determine the difference:

```fish
△ echo $json | jq 'has("test")'
true

△ echo $json | jq 'has("nonexistent")'
false
```