Selective compilation

before_compile_assets.rb

last_revision = `cat #{current_path}/current/REVISION`
assets_modified =  `git diff --name-only #{last_revision} | grep assets | wc -l`

if assets_modified > 0
  STDERR.puts "#{assets_modified} asset files changed detected. Compiling assets"
  run! "bundle exec rake RAILS_ENV=#{config.framework_env} RAILS_GROUPS=assets assets:precompile"
else
  STDERR.puts "No asset changes detected. Copying assets from previous"
  run! "#{shared_path}/last_assets #{shared_path}/assets"
end

compile_assets_if_changed.sh

#!/bin/bash

assets=`git log -1 --pretty=format:'%ct' app/assets lib/assets vendor/assets`
compiled=`git log -1 --pretty=format:'%ct' public/assets`

[[ $assets > $compiled ]] && bundle exec rake assets:precompile:all