packer-cn/website/source/guides/hcl/index.html.md.erb

---
layout: guides
sidebar_current: hcl
page_title: Getting started configuring Packer with HCL2 files
---

# Introduction to Packer HCL2

-> **Note:** Starting from version **1.5.0** Packer can read HCL2 files.

It is not necessary to know all of the details of the HCL syntax in order to
use Packer, and so this page summarizes the most important details to get you
started. If you are interested, you can find a [full definition of HCL
syntax](https://github.com/hashicorp/hcl2/blob/master/hcl/hclsyntax/spec.md) in
the HCL native syntax specification.

## Arguments and Blocks

The HCL syntax is built around two key syntax constructs: arguments and blocks.

```hcl
# block
source "amazon-ebs" "example" {

  # argument
  ami_name = "abc123"
}
```

## Comments

The HCL language supports three different syntaxes for comments:

* ```#``` begins a single-line comment, ending at the end of the line.
* ```//``` also begins a single-line comment, as an alternative to ```#```.
* ```/*``` and ```*/``` are start and end delimiters for a comment that might
  span over multiple lines.

## Multi-line strings

A multi-line string value can be provided using heredoc syntax.

```hcl
variable "long_key" {
  type = "string"
  default = <<EOF
This is a long key.
Running over several lines.
It could be super handy for a boot_command.
EOF
}
```

## Building blocks can be split in files

Currently Packer offers the `source` and the `build` root blocks. These two
building blocks can be defined in any order and a `build` can import one or more
`source`. Usually a `source` defines what we currently call a builder and a
`build` can apply multiple provisioning steps to a source. For example:

```hcl
# folder/sources.pkr.hcl
source "amazon-ebs" "example-1" {
  ami_name = "example-1-ami"
}

source "virtualbox-iso" "example-2" {
  boot_command = <<EOF
<esc><esc><enter><wait>
/install/vmlinuz noapic 
...
EOF
}
```

```hcl
# folder/build.pkr.hcl
build {
  sources = [
    "source.amazon-ebs.example-1",
    "source.virtualbox-iso.example-2"
  ]

  provisioner "shell" {
    inline = [
      "echo it's alive !"
    ]
  }
}
```