branch_databases.yml

evaluation_branches:
  select: ^(evaluations)

courseware:
  select: (courseware)

fast_srids:
  select: (fast_srids)

unrelated_example
  select: wierd
  output: lambda { 'usethis' }

other_unrelated
  select: other
  output: lambda { 'usethis' }

database.yml

<%
  branch_file = "#{RAILS_ROOT}/config/branch_databases.yml"
  branches = File.file?(branch_file) ? YAML.load_file(branch_file) : {}

  git_branches = `cd "#{RAILS_ROOT}"; git branch --no-color`
  output = ''
  if $?.to_i == 0
    current_branch = git_branches.split("\n").detect { |b| b.match(/\A\*/) }.gsub(/\A\* /, '')
    match = branches.detect{|name,branch| current_branch.match branch['select'] }
    if match
      output = "_#{$&}" 
    end
  end

  puts "-- Branch database in use: #{output}" unless output.blank?
%>


development:
  database: myapp_development<%= output %>
  <<: *defaults

production:
  database: myapp<%= output %>
  <<: *defaults

gistfile3.txt