yq/pkg/yqlib/doc/usage/convert.md

# JSON

Encode and decode to and from JSON. Supports multiple JSON documents in a single file (e.g. NDJSON).

Note that YAML is a superset of (single document) JSON - so you don't have to use the JSON parser to read JSON when there is only one JSON document in the input. You will probably want to pretty print the result in this case, to get idiomatic YAML styling.


## Parse json: simple
JSON is a subset of yaml, so all you need to do is prettify the output

Given a sample.json file of:
```json
{"cat": "meow"}
```
then
```bash
yq -p=json sample.json
```
will output
```yaml
cat: meow
```

## Parse json: complex
JSON is a subset of yaml, so all you need to do is prettify the output

Given a sample.json file of:
```json
{"a":"Easy! as one two three","b":{"c":2,"d":[3,4]}}
```
then
```bash
yq -p=json sample.json
```
will output
```yaml
a: Easy! as one two three
b:
  c: 2
  d:
    - 3
    - 4
```

## Encode json: simple
Given a sample.yml file of:
```yaml
cat: meow
```
then
```bash
yq -o=json '.' sample.yml
```
will output
```json
{
  "cat": "meow"
}
```

## Encode json: simple - in one line
Given a sample.yml file of:
```yaml
cat: meow # this is a comment, and it will be dropped.
```
then
```bash
yq -o=json -I=0 '.' sample.yml
```
will output
```json
{"cat":"meow"}
```

## Encode json: comments
Given a sample.yml file of:
```yaml
cat: meow # this is a comment, and it will be dropped.
```
then
```bash
yq -o=json '.' sample.yml
```
will output
```json
{
  "cat": "meow"
}
```

## Encode json: anchors
Anchors are dereferenced

Given a sample.yml file of:
```yaml
cat: &ref meow
anotherCat: *ref
```
then
```bash
yq -o=json '.' sample.yml
```
will output
```json
{
  "cat": "meow",
  "anotherCat": "meow"
}
```

## Encode json: multiple results
Each matching node is converted into a json doc. This is best used with 0 indent (json document per line)

Given a sample.yml file of:
```yaml
things: [{stuff: cool}, {whatever: cat}]
```
then
```bash
yq -o=json -I=0 '.things[]' sample.yml
```
will output
```json
{"stuff":"cool"}
{"whatever":"cat"}
```

## Encode json: preserve floats with trailing zero
Whole-number floats keep their decimal point so downstream consumers see a JSON number with a fractional part (matches Go's encoding/json, Python's json, and jq).

Given a sample.yml file of:
```yaml
percentiles: [50.0, 95.0, 99.0, 99.9]
```
then
```bash
yq -o=json -I=0 '.' sample.yml
```
will output
```json
{"percentiles":[50.0,95.0,99.0,99.9]}
```

## Roundtrip JSON Lines / NDJSON
Given a sample.json file of:
```json
{"this": "is a multidoc json file"}
{"each": ["line is a valid json document"]}
{"a number": 4}

```
then
```bash
yq -p=json -o=json -I=0 sample.json
```
will output
```yaml
{"this":"is a multidoc json file"}
{"each":["line is a valid json document"]}
{"a number":4}
```

## Roundtrip multi-document JSON
The parser can also handle multiple multi-line json documents in a single file (despite this not being in the JSON Lines / NDJSON spec). Typically you would have one entire JSON document per line, but the parser also supports multiple multi-line json documents

Given a sample.json file of:
```json
{
	"this": "is a multidoc json file"
}
{
	"it": [
		"has",
		"consecutive",
		"json documents"
	]
}
{
	"a number": 4
}

```
then
```bash
yq -p=json -o=json -I=2 sample.json
```
will output
```yaml
{
  "this": "is a multidoc json file"
}
{
  "it": [
    "has",
    "consecutive",
    "json documents"
  ]
}
{
  "a number": 4
}
```

## Update a specific document in a multi-document json
Documents are indexed by the `documentIndex` or `di` operator.

Given a sample.json file of:
```json
{"this": "is a multidoc json file"}
{"each": ["line is a valid json document"]}
{"a number": 4}

```
then
```bash
yq -p=json -o=json -I=0 '(select(di == 1) | .each ) += "cool"' sample.json
```
will output
```yaml
{"this":"is a multidoc json file"}
{"each":["line is a valid json document","cool"]}
{"a number":4}
```

## Find and update a specific document in a multi-document json
Use expressions as you normally would.

Given a sample.json file of:
```json
{"this": "is a multidoc json file"}
{"each": ["line is a valid json document"]}
{"a number": 4}

```
then
```bash
yq -p=json -o=json -I=0 '(select(has("each")) | .each ) += "cool"' sample.json
```
will output
```yaml
{"this":"is a multidoc json file"}
{"each":["line is a valid json document","cool"]}
{"a number":4}
```

## Decode JSON Lines / NDJSON
Given a sample.json file of:
```json
{"this": "is a multidoc json file"}
{"each": ["line is a valid json document"]}
{"a number": 4}

```
then
```bash
yq -p=json sample.json
```
will output
```yaml
this: is a multidoc json file
---
each:
  - line is a valid json document
---
a number: 4
```