Put this file in Rails.root/script directory and make precompiling assets easy as possible again! Why? Removing appropriate files after precompiling assets seems inefficient.

commit_assets.sh

#!/bin/bash

bundle exec rake assets:precompile

repository_root=$(git rev-parse --show-toplevel)
assets_directory="$repository_root/public/assets"

# 1. reads diff from the manifest.yml
# 2. takes only those lines which represent replaced assets
# 3. remove duplicates like: application.js => application/index.js
# 4. extracts filename from sth like: application.js: application-21sda697d128sad12312dsa.js
files_to_remove=$(git diff "$assets_directory/manifest.yml" | egrep '^[-]\w+' | grep -v '/index.*:' | sed -E 's/^[^:]+:[[:space:]]//')

for file in $files_to_remove
do
  # wildcard is to match compressed files as well
  git rm "$assets_directory/$file*"
done

git add $assets_directory
git commit -m 'rake assets:precompile' --no-edit