How To: Add current commit to Rails template

I wanted to add the current revision of a Rails project to my layout so I can easily know what version the current code base is running. I came up with a short initializer that can be added to define a global constant for the commit id and commit timestamp.

# RAILS_ROOT/config/initializers/tag_revision.rb
# Call +git+ and obtain the current commit SHA1 and commit date. Store these values
# in +PROJECT_VERSION_COMMIT_ID+ and +PROJECT_VERSION_COMMIT_DATE+. Then define
# +PROJECT_VERSION+ to be a string of the two.
git_cmd = 'git show --pretty=format:"%H|%ci" --quiet'
commit_id = nil
commit_date = nil
begin
  commit_id, commit_date = IO.popen(git_cmd) {|f| f.gets.split("|") }
rescue Errno::ENOENT # git not available
  commit_id = 'Unknown'
  commit_date = ''
end
unless defined?(::PROJECT_VERSION)
  ::PROJECT_VERSION_COMMIT_ID = commit_id
  ::PROJECT_VERSION_COMMIT_DATE = commit_date
  ::PROJECT_VERSION = "#{commit_id} #{commit_date}"
end

# app/helpers/application_helper.rb
module ApplicationHelper
  def link_to_version
    if ENV['RAILS_ENV'] == 'development'
      link_to PROJECT_VERSION, "http://subdomain.unfuddle.com/repositories/commit/#{PROJECT_COMMIT_ID}"
    else
      PROJECT_VERSION
    end
  end
end

# app/views/layout/application.html
....
<div id="footer"> <%= link_to_version %> </div>

When the application is run in development mode, a link will appear in the footer to the hosted repository. I’m using Unfuddle for my project but you can obviously return anything you want in the helper.