---
navigation_title: "Append"
mapped_pages:
  - https://www.elastic.co/guide/en/elasticsearch/reference/current/append-processor.html
---

# Append processor [append-processor]


Appends one or more values to an existing array if the field already exists and it is an array. Converts a scalar to an array and appends one or more values to it if the field exists and it is a scalar. Creates an array containing the provided values if the field doesn’t exist. Accepts a single value or an array of values.

$$$append-options$$$

| Name | Required | Default | Description |
| --- | --- | --- | --- |
| `field` | yes | - | The field to be appended to. Supports [template snippets](docs-content://manage-data/ingest/transform-enrich/ingest-pipelines.md#template-snippets). |
| `value` | yes* | - | The value to be appended. Supports [template snippets](docs-content://manage-data/ingest/transform-enrich/ingest-pipelines.md#template-snippets). May specify only one of `value` or `copy_from`. |
| `copy_from` {applies_to}`stack: ga 9.2` | no | - | The origin field which will be appended to `field`, cannot set `value` simultaneously. |
| `allow_duplicates` | no | true | If `false`, the processor does not appendvalues already present in the field. |
| `ignore_empty_values` {applies_to}`stack: ga 9.2` | no | false | If `true`, the processor does not append values that resolve to `null` or an empty string.
| `media_type` | no | `application/json` | The media type for encoding `value`. Applies only when `value` is a [template snippet](docs-content://manage-data/ingest/transform-enrich/ingest-pipelines.md#template-snippets). Must be one of `application/json`, `text/plain`, or`application/x-www-form-urlencoded`. |
| `description` | no | - | Description of the processor. Useful for describing the purpose of the processor or its configuration. |
| `if` | no | - | Conditionally execute the processor. See [Conditionally run a processor](docs-content://manage-data/ingest/transform-enrich/ingest-pipelines.md#conditionally-run-processor). |
| `ignore_failure` | no | `false` | Ignore failures for the processor. See [Handling pipeline failures](docs-content://manage-data/ingest/transform-enrich/ingest-pipelines.md#handling-pipeline-failures). |
| `on_failure` | no | - | Handle failures for the processor. See [Handling pipeline failures](docs-content://manage-data/ingest/transform-enrich/ingest-pipelines.md#handling-pipeline-failures). |
| `tag` | no | - | Identifier for the processor. Useful for debugging and metrics. |

## Examples [append-processor-examples]

### Simple example [append-processor-simple-example]

Here is an `append` processor definition that adds the string `"production"` as well as the values of the `app` and `owner` fields to the `tags` field:

```js
{
  "append": {
    "field": "tags",
    "value": ["production", "{{{app}}}", "{{{owner}}}"]
  }
}
```

### Example using `allow_duplicates` and `ignore_empty_values` [append-processor-example-using-allow-duplicates-and-ignore-empty-values]

```{applies_to}
stack: ga 9.2
```

By using `allow_duplicates` and `ignore_empty_values`, it is possible to only append the `host.name` to the `related.hosts` if the `host.name` is not empty and if the value is not already present in `related.hosts`:

```js
{
  "append": {
    "field": "related.hosts",
    "copy_from": "host.name",
    "allow_duplicates": false,
    "ignore_empty_values": true
  }
}
```