Packer-Cn/website/source/docs/post-processors/shell-local.html.md

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description: | The shell-local Packer post processor enables users to do some post processing after artifacts have been built. layout: docs page_title: Local Shell Post Processor ...

Local Shell Post Processor

Type: shell-local

The local shell post processor executes scripts locally during the post processing stage. Shell local provides an easy 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}}" {{.Artifact}}. The value of this is treated as configuration template. There are three available variables: Script, which is the path to the script to run, Vars, which is the list of environment_vars, if configured and Artifact, which is path to artifact file.

• 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 Artifact

The shell-local script(s) you pass are run once per artifact output file. That means that if your builder results in 1 output file, your script will be run once. If it results in 3 output files, it will run 3 times, once for each file.

For example, the virtualbox builders, when configured to provide an ovf output format (the default), will provide two output files:

• The actual disk itself, in .vmdk format
• The appliance description file, in .ovf format

Each time each shell-local script is run, it is passed the path to the artifact file, relative to the directory in which packer is run, as the first argument to the script.

Let's take a simple example. You want to run a post-processor that records the name of every artifact created to /tmp/artifacts. (Why? I don't know. For fun.)

Your post-processor should look like this:

{
  "type": "shell-local",
  "inline": [
    "echo \$1 >> /tmp/artifacts"
  ]
}

The result of the above will be an output line for each artifact.

The net effect of this is that if you want to post-process only some files, you must test $1 to see if it is the file you want.

Here is an example script that converts the .vmdk artifact of a virtualbox build to a raw img, suitable for converting to a USB.

    #!/bin/bash -e

    [[ "$1" == *.vmdk ]] && vboxmanage clonemedium disk $1 --format raw output_file.img

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. Using our above conversion script example, if the current artifact is not a .vmdk file, the test [[ "$1" == *.vmdk ]] will fail. Since that is the last command in the script, the script will exit with a non-zero code, the post-processor will fail, the build will fail, and you will have to start over.

Of course, we didn't mean that! We just meant:

• If a .vmdk file, convert, and that is OK
• If not a .vmdk file, ignore, and that is OK

To make it work correctly, use the following instead:

    #!/bin/bash -e

    [[ "$1" == *.vmdk ]] && vboxmanage clonemedium disk $1 --format raw output_file.img

    # always exit 0 unless a command actually fails
    exit 0