packer-cn/website/pages/docs/from-1.5/locals.mdx

---
layout: docs
page_title: Local Values - HCL Configuration Language
sidebar_title: Locals
description: >-
  Local values assign a name to an expression that can then be used multiple
  times within a folder.
---

# Local Values

-> **Note:** This page is about HCL2 in Packer 1.5 and later. HCL2 support for
Packer is still in Beta. Please see the [Packer Issue
Tracker](https://github.com/hashicorp/packer/issues/9176) for a list of
supported features. For the old-style stable configuration language see
[template docs](/docs/templates).

Local values assign a name to an expression, that can then be used multiple
times within a folder.

If [variables](/docs/from-1.5/variables) are analogous to function arguments then
_local values_ are comparable to a function's local variables.

Input variable and local variable usage are introduced in the [_Variables
Guide_](/guides/hcl/variables).

## Examples

Local values are defined in `locals` blocks:

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

# A computed default name prefix
locals {
  default_name_prefix = "${var.project_name}-web"
  name_prefix         = "${var.name_prefix != "" ? var.name_prefix : local.default_name_prefix}"
}

# Local values can be interpolated elsewhere using the "local." prefix.
source "virtualbox-iso" "example" {
  output = "${local.name_prefix}-files"
  # ...
}
```

Named local maps can be merged with local maps to implement common or default
values:

```hcl
# Define the common tags for all resources
locals {
  common_tags = {
    Component   = "awesome-app"
    Environment = "production"
  }
}

# Create a resource that blends the common tags with instance-specific tags.
source "amazon-ebs" "server" {
  source_ami    = "ami-123456"
  instance_type = "t2.micro"

  tags = "${merge(
    local.common_tags,
    map(
      "Name", "awesome-app-server",
      "Role", "server"
    )
  )}"
  # ...
}
```

## Description

The `locals` block defines one or more local variables within a folder.

The names given for the items in the `locals` block must be unique throughout a
folder. The given value can be any expression that is valid within the current
folder.

The expression of a local value can refer to other locals, but reference cycles
are not allowed. That is, a local cannot refer to itself or to a variable that
refers (directly or indirectly) back to it.

It's recommended to group together logically-related local values into a single
block, particularly if they depend on each other. This will help the reader
understand the relationships between variables. Conversely, prefer to define
_unrelated_ local values in _separate_ blocks, and consider annotating each
block with a comment describing any context common to all of the enclosed
locals.