---
title: Environment Variables
description: You can use environment variable references in both the configuration file and the action file to set values that need to be configurable at runtime...
url: https://www.elastic.co/elastic/docs-builder/docs/3028/reference/elasticsearch/curator/envvars
products:
  - Elasticsearch
  - Elasticsearch Curator
---

# Environment Variables
<warning>
  This functionality is experimental and may be changed or removed completely in a future release.
</warning>

You can use environment variable references in both the [configuration file](https://www.elastic.co/elastic/docs-builder/docs/3028/reference/elasticsearch/curator/configfile) and the [action file](https://www.elastic.co/elastic/docs-builder/docs/3028/reference/elasticsearch/curator/actionfile) to set values that need to be configurable at runtime. To do this, use:
```sh
${VAR}
```

Where `VAR` is the name of the environment variable.
Each variable reference is replaced at startup by the value of the environment variable. The replacement is case-sensitive and occurs while the YAML file is parsed, but before configuration schema validation. References to undefined variables are replaced by `None` unless you specify a default value. To specify a default value, use:
```sh
${VAR:default_value}
```

Where `default_value` is the value to use if the environment variable is undefined.
<admonition title="Unsupported use cases">
  When using environment variables, the value must *only* be the environment variable.Using extra text, such as:
  ```sh
  logfile: ${LOGPATH}/extra/path/information/file.log
  ```
  is not supported at this time.
</admonition>


## Examples

Here are some examples of configurations that use environment variables and what each configuration looks like after replacement:

| Config source        | Environment setting | Config after replacement |
|----------------------|---------------------|--------------------------|
| `unit: ${UNIT}`      | `export UNIT=days`  | `unit: days`             |
| `unit: ${UNIT}`      | no setting          | `unit:`                  |
| `unit: ${UNIT:days}` | no setting          | `unit: days`             |
| `unit: ${UNIT:days}` | `export UNIT=hours` | `unit: hours`            |