Install and use a new gem inside a Vagrantfile

vagrantfile_install_gem.rb

gem_dir = "#{Dir.home}/.vagrant.d/gems/#{RUBY_VERSION}"

begin
  name = "inifile"
  version = "3.0.0"
  Gem::Specification.find_by_name(name, version)
rescue Gem::LoadError
  require "rubygems/dependency_installer"
  installer = Gem::DependencyInstaller.new(:document => [], :install_dir => gem_dir)
  installer.install(name, version)
end

require "#{gem_dir}/gems/#{name}-#{version}/lib/#{name}.rb"