Managing gems with Rake

[UPDATE 2007-02-07] I realized I left some extra junk in the version of Util in the zip, it’s been updated [/UPDATE]

I have a rake task and a Util class that I use to make setting up required gems painless and to be sure that I’m always running the versions I think I am.

Install or update required gems

rake gems:install

Make sure they are loaded with the right versions during startup, by adding the following to environment.rb


This uses a config file that looks like

:source: # this is optional
  - :name: mongrel
    :version: "1.0"
    # this gem has a specfic source URL
    :source: ''

  - :name: hpricot
    :version: '0.4'
    # this tells us to load not just install
    :load: true

  - :name: postgres
    :version: '0.7.1'
    :load: true
    # any extra config that needs to be passed to gem install
    :config: '--with-pgsql-include-dir=/usr/local/pgsql/include

Here’s the Util class

require 'yaml'

class Util
  def self.load_gems
    config = YAML.load_file(
      File.join(RAILS_ROOT, 'config', 'gems.yml'))
    gems = config[:gems].reject {|gem| ! gem[:load] }
    gems.each do |gem|
      require_gem gem[:name], gem[:version]
      require gem[:name]

Here’s the rake task

require 'yaml'

namespace :gems do
  require 'rubygems'

  task :install do
    # defaults to --no-rdoc, set DOCS=(anything) to build docs
    docs = (ENV['DOCS'].nil? ? '--no-rdoc' : '')
    #grab the list of gems/version to check
    config = YAML.load_file(File.join('config', 'gems.yml'))
    gems = config[:gems]

    gems.each do |gem|
      # load the gem spec
      gem_spec = YAML.load(`gem spec #{gem[:name]} 2> /dev/null`)
      gem_loaded = false
        gem_loaded = require_gem gem[:name], gem[:version]
      rescue Exception

      # if forced
      # or there is no gem_spec
      # or the spec version doesn't match the required version
      # or require_gem returns false
      # (return false also happens if the gem has already been loaded)
      if ! ENV['FORCE'].nil? ||
         ! gem_spec ||
         (gem_spec.version.version != gem[:version] && ! gem_loaded)
        gem_config = gem[:config] ? " -- #{gem[:config]}" : ''
        source = gem[:source] || config[:source] || nil
        source = "--source #{source}" if source
        ret = system "gem install #{gem[:name]}
            -v #{gem[:version]} -y #{source} #{docs} #{gem_config}"
        # something bad happened, pass on the message
        p $? unless ret
        puts "#{gem[:name]} #{gem[:version]} already installed"

zipped source