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Writing your own Hammer plugin

In this tutorial we will create a simple hello world plugin.

Hammer plugins are nothing but gems. Details on how to build a gem can be found for example at rubygems.org. In the first part of this tutorial we will briefly guide you through the process of creating a very simple gem. First of all you will need the rubygems package installed on your system.

Create the basic gem structure in a project subdirectory of your choice:

$ cd ./my_first_hammer_plugin/
$ touch Gemfile
$ touch hammer_cli_hello.gemspec
$ mkdir -p lib/hammer_cli_hello
$ touch lib/hammer_cli_hello.rb
$ touch lib/hammer_cli_hello/version.rb

Example Gemfile:

source "https://rubygems.org"

gemspec

Example hammer_cli_hello.gemspec file:

$:.unshift File.expand_path("../lib", __FILE__)
require "hammer_cli_hello/version"

Gem::Specification.new do |s|

  s.name = "hammer_cli_hello"
  s.authors = ["Me"]
  s.version = HammerCLIHello.version.dup
  s.platform = Gem::Platform::RUBY
  s.summary = %q{Hello world commands for Hammer}

  s.files = Dir['lib/**/*.rb']
  s.require_paths = ["lib"]

  s.add_dependency 'hammer_cli', '>= 0.0.6'
end

More details about the gemspec structure is again at rubygems.org.

We'll have to specify the plugin version in lib/hammer_cli_hello/version.rb:

module HammerCLIHello
  def self.version
    @version ||= Gem::Version.new '0.0.1'
  end
end

This should be enough for creating a minimalist gem. Let's build and install it.

$ gem build ./hammer_cli_hello.gemspec
$ gem install hammer_cli_hello-0.0.1.gem

Place your module's config file into ~/.hammer/cli.modules.d/hello_world.yml.

:hello:
  :enable_module: true

Verify the installation by running:

$ hammer -v > /dev/null

You should see a message saying that your module was loaded (second line in the sample output).

[ INFO 2013-10-16 11:19:06 Init] Initialization of Hammer CLI (0.1.0) has started...
[ INFO 2013-10-16 11:19:06 Init] Extension module hammer_cli_hello loaded
[ INFO 2013-10-16 11:19:06 Init] Configuration from the file /root/.hammer/cli_config.yml has been loaded
[ INFO 2013-10-16 11:19:06 Init] Configuration from the file /root/.hammer/cli.modiles.d/hello.yml has been loaded
[ INFO 2013-10-16 11:19:06 HammerCLI::MainCommand] Called with options: {"verbose"=>true}

Done. Your first hammer plugin is installed. Unfortunately it does not contain any commands yet. So let's start adding some to finally enjoy real results.

Optionally you can add a Rakefile and build and install the gem with rake install

# ./Rakefile
require 'bundler/gem_tasks'