# Keys

Use the `keys` operator to return map keys or array indices.

## Map keys

Given a sample.yml file of:

```yaml
dog: woof
cat: meow
```

then

```bash
yq 'keys' sample.yml
```

will output

```yaml
- dog
- cat
```

## Array keys

Given a sample.yml file of:

```yaml
- apple
- banana
```

then

```bash
yq 'keys' sample.yml
```

will output

```yaml
- 0
- 1
```

## Retrieve array key

Given a sample.yml file of:

```yaml
- 1
- 2
- 3
```

then

```bash
yq '.[1] | key' sample.yml
```

will output

```yaml
1
```

## Retrieve map key

Given a sample.yml file of:

```yaml
a: thing
```

then

```bash
yq '.a | key' sample.yml
```

will output

```yaml
a
```

## No key

Given a sample.yml file of:

```yaml
{}
```

then

```bash
yq 'key' sample.yml
```

will output

```yaml
```

## Update map key

Given a sample.yml file of:

```yaml
a:
  x: 3
  y: 4
```

then

```bash
yq '(.a.x | key) = "meow"' sample.yml
```

will output

```yaml
a:
  meow: 3
  y: 4
```

## Get comment from map key

Given a sample.yml file of:

```yaml
a:
  # comment on key
  x: 3
  y: 4
```

then

```bash
yq '.a.x | key | headComment' sample.yml
```

will output

```yaml
comment on key
```

## Check node is a key

Given a sample.yml file of:

```yaml
a:
  b:
    - cat
  c: frog
```

then

```bash
yq '[... | { "p": path | join("."), "isKey": is_key, "tag": tag }]' sample.yml
```

will output

```yaml
- p: ""
  isKey: false
  tag: '!!map'
- p: a
  isKey: true
  tag: '!!str'
- p: a
  isKey: false
  tag: '!!map'
- p: a.b
  isKey: true
  tag: '!!str'
- p: a.b
  isKey: false
  tag: '!!seq'
- p: a.b.0
  isKey: false
  tag: '!!str'
- p: a.c
  isKey: true
  tag: '!!str'
- p: a.c
  isKey: false
  tag: '!!str'
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://mikefarah.gitbook.io/yq/operators/keys.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.