git-fixups.sh

for file in $(git diff --name-only --cached); do
  previous_commit=$(git rev-list -1 HEAD -- $file)
  previous_commit_msg=$(git rev-list --format="%s" -1 HEAD -- $file | tail -n 1)
  if [ -z "$previous_commit" ]; then
    echo "$file NEW"
  else
    echo "$file $previous_commit"
    git commit -m "fixup! $previous_commit_msg" -m "$file $previous_commit"
  fi
done