terraform/website/source/docs/configuration/variables.html.md

---
layout: "docs"
page_title: "Configuring Variables"
sidebar_current: "docs-config-variables"
---

# Variable Configuration

Variables define the parameterization of Terraform configurations.
Variables can be overridden via the CLI. Variable usage is
covered in more detail in the
[getting started guide](/intro/getting-started/variables.html).
This page covers configuration syntax for variables.

This page assumes you're familiar with the
[configuration syntax](/docs/configuration/syntax.html)
already.

## Example

A variable configuration looks like the following:

```
variable "key" {}

variable "images" {
	default = {
		us-east-1 = "image-1234"
		us-west-2 = "image-4567"
	}
}
```

## Description

The `variable`  block configures a single input variable for
a Terraform configuration. Multiple variables blocks can be used to
add multiple variables.

The `NAME` given to the variable block is the name used to
set the variable via the CLI as well as reference the variable
throughout the Terraform configuration.

Within the block (the `{ }`) is configuration for the variable.
These are the parameters that can be set:

  * `default` (optional) - If set, this sets a default value
    for the variable. If this isn't set, the variable is required
    and Terraform will error if not set. The default value can be
    a string or a mapping. This is covered in more detail below.

  * `description` (optional) - A human-friendly description for
    the variable. This is primarily for documentation for users
    using your Terraform configuration. A future version of Terraform
    will expose these descriptions as part of some Terraform CLI
    command.

------

**Default values** can be either strings or maps. If a default
value is omitted and the variable is required, the value assigned
via the CLI must be a string.

String values are simple and represent a basic key to value
mapping where the key is the variable name. An example is:

```
variable "key" {
	default = "value"
}
```

A map allows a key to contain a lookup table. This is useful
for some values that change depending on some external pivot.
A common use case for this is mapping cloud images to regions.
An example:

```
variable "images" {
	default = {
		us-east-1 = "image-1234"
		us-west-2 = "image-4567"
	}
}
```

The usage of maps, strings, etc. is documented fully in the
[interpolation syntax](/docs/configuration/interpolation.html)
page.

## Syntax

The full syntax is:

```
variable NAME {
	[default = DEFAULT]
	[description = DESCRIPTION]
}
```

where `DEFAULT` is:

```
VALUE

{
	KEY = VALUE
	...
}
```