Plugin Development: Commands

This page documents how to add new commands to Vagrant, invocable via vagrant YOUR-COMMAND. Prior to reading this, you should be familiar with the plugin development basics.

Definition Component

Within the context of a plugin definition, new commands can be defined like so:

command "foo" do
  require_relative "command"
  Command
end

Commands are defined with the command method, which takes as an argument the name of the command, in this case "foo." This means the command will be invocable via vagrant foo. Then the block argument returns a class that implements the Vagrant.plugin(2, "command") interface.

You can also define non-primary commands. These commands do not show up in the vagrant -h output. They only show up if the user explicitly does a vagrant list-commands which shows the full listing of available commands. This is useful for highly specific commands or plugins that a beginner to Vagrant would not be using anyways. Vagrant itself uses non-primary commands to expose some internal functions, as well.

To define a non-primary command:

command("foo", primary: false) do
  require_relative "command"
  Command
end

Implementation

Implementations of commands should subclass Vagrant.plugin(2, :command), which is a Vagrant method that will return the proper superclass for a version 2 command. The implementation itself is quite simple, since the class needs to only implement a single method: execute. Example:

class Command < Vagrant.plugin(2, :command)
  def execute
    puts "Hello!"
    0
  end
end

The execute method is called when the command is invoked, and it should return the exit status (0 for success, anything else for error).

This is a command at its simplest form. Of course, the command superclass gives you access to the Vagrant environment and provides some helpers to do common tasks such as command line parsing.

Parsing Command-Line Options

The parse_options method is available which will parse the command line for you. It takes an OptionParser as an argument, and adds some common elements to it such as the --help flag, automatically showing help if requested. View the API docs directly for more information.

This is recommended over raw parsing/manipulation of command line flags. The following is an example of parsing command line flags pulled directly from the built-in Vagrant destroy command:

options = {}
options[:force] = false

opts = OptionParser.new do |o|
  o.banner = "Usage: vagrant destroy [vm-name]"
  o.separator ""

  o.on("-f", "--force", "Destroy without confirmation.") do |f|
    options[:force] = f
  end
end

# Parse the options
argv = parse_options(opts)

Using Vagrant Machines

The with_target_vms method is a helper that helps you interact with the machines that Vagrant manages in a standard Vagrant way. This method automatically does the right thing in the case of multi-machine environments, handling target machines on the command line (vagrant foo my-vm), etc. If you need to do any manipulation of a Vagrant machine, including SSH access, this helper should be used.

An example of using the helper, again pulled directly from the built-in destroy command:

with_target_vms(argv, reverse: true) do |machine|
  machine.action(:destroy)
end

In this case, it asks for the machines in reverse order and calls the destroy action on each of them. If a user says vagrant destroy foo, then the helper automatically only yields the foo machine. If no parameter is given and it is a multi-machine environment, every machine in the environment is yielded, and so on. It just does the right thing.

Using the Raw Vagrant Environment

The raw loaded Vagrant::Environment object is available with the '@env' instance variable.