opscode-backup.rb

require 'chef'
require 'chef/node'

class Opscode
  class Backup
    attr_accessor :backup_dir

    def initialize(backup_dir, config_file)
      @backup_dir = backup_dir
      Chef::Config.from_file(config_file)
      Chef::Log.level = Chef::Config[:log_level]
    end

    def backup
      nodes
      roles
      data_bags
    end

    def nodes
      backup_standard("nodes", Chef::Node)
    end

    def roles
      backup_standard("roles", Chef::Role)
    end

    def data_bags
      dir = File.join(@backup_dir, "data_bags")
      system("mkdir -p #{dir}")
      Chef::DataBag.list.each do |bag_name, url|
        system("mkdir -p #{File.join(dir, bag_name)}")
        Chef::DataBag.load(bag_name).each do |item_name, url|
          Chef::Log.info("Backing up data bag #{bag_name} item #{item_name}")
          item = Chef::DataBagItem.load(bag_name, item_name)
          File.open(File.join(dir, bag_name, "#{item_name}.json"), "w") do |dbag_file|
            dbag_file.print(item.to_json)
          end
        end
      end
    end

    def backup_standard(component, klass)
      dir = File.join(@backup_dir, component)
      system("mkdir -p #{dir}")
      klass.list.each do |component_name, url|
        Chef::Log.info("Backing up #{component} #{component_name}")
        component_obj = klass.load(component_name)
        File.open(File.join(dir, "#{component_name}.json"), "w") do |component_file|
          component_file.print(component_obj.to_json)
        end
      end
    end

  end
end

use_it.rb

require 'ospcode-backup'

b = Opscode::Backup.new("/tmp/backup", "~/.chef/knife.rb")
b.backup

In use_it.rb, line 1 should be require 'opscode-backup'. And ~ expansion doesn't seem to work; I had to specify the full path to knife.rb.