deploy.pending.migrations.rb

# Our deployment tags are s or p followed by YYmmdd-HHMMSS
namespace :deploy do
  namespace :pending do
    desc "Show the list of new migrations since the last deployments to staging and production"
    task :migrations do
      tags        = run_locally("git tag").split
      staging     = tags.grep(/\As\d{6}-\d{6}\Z/).sort.last
      production  = tags.grep(/\Ap\d{6}-\d{6}\Z/).sort.last
      %w(staging production).each do |stage|
        puts  '', stage
        result = run_locally %(git diff --numstat #{ eval(stage) }..master | grep "db\/migrate")
        puts(result.strip == '' ? '(none)' : result.gsub(/\d*\t\d*\t/, '') )
      end
    end
  end
end

=begin
Example output:
$ cap deploy:pending:migrations
    triggering start callbacks for `deploy:pending:migrations'
  * executing `multistage:ensure'
*** Defaulting to `staging'
  * executing `staging'
  * executing `deploy:pending:migrations'
    executing locally: "git tag"

staging
    executing locally: "git diff --numstat s090525-165241..master | grep \"db/migrate\""
(none)

production
    executing locally: "git diff --numstat p090522-090244..master | grep \"db/migrate\""
db/migrate/20090511155004_create_audits.rb
=end