Fill in ActiveRecord Migration Rails Versions by shell script (tested on Mac OS X)

migration_rails_versions.sh

# Instructions
#
# 1. Backup your repo somewhere!
# 2. Make sure `git stash list` is empty - that'll help debugging in case things go wrong.
# 3. Make sure `git status` shows that you've made no changes; that'll break things right away.
# 4. Copy and paste the code below.
# 5. Run the `update_timestamps` function and LET IT FINISH!
# 6. Check the results, make sure they look reasonable, and commit!
#
# P.S. I take no responsibility for your use of the script; I recommend understanding what it does before running it.

function versionize() {
  local FILE=$1
  local COMMIT=$(git log -n 1 --pretty=format:%H -- $FILE)

  # Find the correct version of Rails for that migration
  git checkout --quiet $COMMIT
  local RAILS_VERSION=$(grep "^  rails " Gemfile.lock | egrep -o "[0-9].[0-9]+")

  # Substitute if necessary and create a stash if a substitution happens
  sed -i '' "s|.*Migration$|&[$RAILS_VERSION]|" $FILE
  git diff --quiet && return 1
  git stash --quiet && return 0
}

function update_timestamps() {
  local COUNTER=0
  local ORIG_BRANCH=$(git rev-parse --abbrev-ref HEAD)

  echo "Creating stashes for up to $(ls -d -1 db/migrate/* | wc -l | egrep -o "[0-9]+") migrations..."
  for filename in $(ls -d -1 db/migrate/*); do
    versionize $filename && ((COUNTER++))

    # Go back to the tip to find the appropriate commit for the migration file
    git checkout --quiet $ORIG_BRANCH
  done

  echo "${COUNTER} stashes created. Applying stashes..."
  until [  $COUNTER -lt 1 ]; do
    ((COUNTER--))
    git stash pop --quiet
  done
}