---
description: >-
  Local values assign a name to an expression that can be used multiple times
  within a module.
---

# Local Values

A local value assigns a name to an [expression](../../language/expressions/index.mdx),
so you can use the name multiple times within a module instead of repeating
the expression.

If you're familiar with traditional programming languages, it can be useful to
compare modules to function definitions:

- [Input variables](../../language/values/variables.mdx) are like function arguments.
- [Output values](../../language/values/outputs.mdx) are like function return values.
- Local values are like a function's temporary local variables.

:::note
For brevity, local values are often referred to as just "locals"
when the meaning is clear from context.
:::

## Declaring a Local Value

A set of related local values can be declared together in a single `locals`
block:

```hcl
locals {
  service_name = "forum"
  owner        = "Community Team"
}
```

The expressions in local values are not limited to literal constants; they can
also reference other values in the module in order to transform or combine them,
including variables, resource attributes, or other local values:

```hcl
locals {
  # Ids for multiple sets of EC2 instances, merged together
  instance_ids = concat(aws_instance.blue.*.id, aws_instance.green.*.id)
}

locals {
  # Common tags to be assigned to all resources
  common_tags = {
    Service = local.service_name
    Owner   = local.owner
  }
}
```

## Using Local Values

Once a local value is declared, you can reference it in
[expressions](../../language/expressions/index.mdx) as `local.<NAME>`.

:::note
Local values are _created_ by a `locals` block (plural), but you
_reference_ them as attributes on an object named `local` (singular). Make sure
to leave off the "s" when referencing a local value!
:::

```
resource "aws_instance" "example" {
  # ...

  tags = local.common_tags
}
```

A local value can only be accessed in expressions within the module where it
was declared.

## When To Use Local Values

Local values can be helpful to avoid repeating the same values or expressions
multiple times in a configuration, but if overused they can also make a
configuration hard to read by future maintainers by hiding the actual values
used.

Use local values only in moderation, in situations where a single value or
result is used in many places _and_ that value is likely to be changed in
future. The ability to easily change the value in a central place is the key
advantage of local values.
