» Local Shell Post Processor

Type: shell-local

The local shell post processor executes scripts locally during the post processing stage. Shell local provides a convenient way to automate executing some task with the packer outputs.

» Basic example

The example below is fully functional.

{
  "type": "shell-local",
  "inline": ["echo foo"]
}

» Configuration Reference

The reference of available configuration options is listed below. The only required element is either "inline" or "script". Every other option is optional.

Exactly one of the following is required:

  • inline (array of strings) - This is an array of commands to execute. The commands are concatenated by newlines and turned into a single file, so they are all executed within the same context. This allows you to change directories in one command and use something in the directory in the next and so on. Inline scripts are the easiest way to pull off simple tasks within the machine.

  • script (string) - The path to a script to execute. This path can be absolute or relative. If it is relative, it is relative to the working directory when Packer is executed.

  • scripts (array of strings) - An array of scripts to execute. The scripts will be executed in the order specified. Each script is executed in isolation, so state such as variables from one script won't carry on to the next.

Optional parameters:

  • environment_vars (array of strings) - An array of key/value pairs to inject prior to the execute_command. The format should be key=value. Packer injects some environmental variables by default into the environment, as well, which are covered in the section below.

  • execute_command (string) - The command to use to execute the script. By default this is chmod +x "{{.Script}}"; {{.Vars}} "{{.Script}}". The value of this is treated as template engine. There are two available variables: Script, which is the path to the script to run, Vars, which is the list of environment_vars, if configured.

  • inline_shebang (string) - The shebang value to use when running commands specified by inline. By default, this is /bin/sh -e. If you're not using inline, then this configuration has no effect. Important: If you customize this, be sure to include something like the -e flag, otherwise individual steps failing won't fail the provisioner.

» Execute Command Example

To many new users, the execute_command is puzzling. However, it provides an important function: customization of how the command is executed. The most common use case for this is dealing with sudo password prompts. You may also need to customize this if you use a non-POSIX shell, such as tcsh on FreeBSD.

» Default Environmental Variables

In addition to being able to specify custom environmental variables using the environment_vars configuration, the provisioner automatically defines certain commonly useful environmental variables:

  • PACKER_BUILD_NAME is set to the name of the build that Packer is running. This is most useful when Packer is making multiple builds and you want to distinguish them slightly from a common provisioning script.

  • PACKER_BUILDER_TYPE is the type of the builder that was used to create the machine that the script is running on. This is useful if you want to run only certain parts of the script on systems built with certain builders.

» Safely Writing A Script

Whether you use the inline option, or pass it a direct script or scripts, it is important to understand a few things about how the shell-local post-processor works to run it safely and easily. This understanding will save you much time in the process.

» Once Per Builder

The shell-local script(s) you pass are run once per builder. That means that if you have an amazon-ebs builder and a docker builder, your script will be run twice. If you have 3 builders, it will run 3 times, once for each builder.

» Interacting with Build Artifacts

In order to interact with build artifacts, you may want to use the manifest post-processor. This will write the list of files produced by a builder to a json file after each builder is run.

For example, if you wanted to package a file from the file builder into a tarball, you might wright this:

{
  "builders": [
    {
      "content": "Lorem ipsum dolor sit amet",
      "target": "dummy_artifact",
      "type": "file"
    }
  ],
  "post-processors": [
    [
      {
        "output": "manifest.json",
        "strip_path": true,
        "type": "manifest"
      },
      {
        "inline": [
          "jq \".builds[].files[].name\" manifest.json | xargs tar cfz artifacts.tgz"
        ],
        "type": "shell-local"
      }
    ]
  ]
}

This uses the jq tool to extract all of the file names from the manifest file and passes them to tar.

» Always Exit Intentionally

If any post-processor fails, the packer build stops and all interim artifacts are cleaned up.

For a shell script, that means the script must exit with a zero code. You must be extra careful to exit 0 when necessary.