Upgrade React Native on your project, using a git-like interface and without touching the project's local repo

upgrade_rn.sh

# In the root directory of a project using RN 0.32:

export GIT_DIR=.gitrn                    # From this line, all git commands will deal with the .gitrn directory, leaving the .git directory untouched
export GIT_WORK_TREE=.                   # I should tell Git the working tree hasn't changed

git init                                 # Create the .gitrn directory

git add .                                # Stage the user's files
git reset -- .gitrn                      # Remove the internal Git files from the index (Git seems to not handle custom GIT_DIR very well...)
git commit -m "Project snapshot"         # Commit them, the user's files are now known in the new repo index

echo "a" | react-native upgrade          # Generate the 0.32 template and overwrite all files

git add . && git reset -- .gitrn
git commit -m "Old version"              # Same as before, the 0.32 template is added to the index

npm i react-native@0.33.0 --save         # Install the new version of React Native

echo "a" | react-native upgrade          # Generate the 0.33 template and overwrite all files

git add . && git reset -- .gitrn
git commit -m "New version"              # Same as before, the 0.33 template is added to the index

git diff HEAD~1 HEAD > upgrade.patch     # Output the diff, totally suitable for the user's project

git reset HEAD~2 --hard                  # Go back to the "Project snapshot" commit

git apply upgrade.patch --3way           # Git is able to perform a 3-way because the 3 versions of each files have an entry in the index

unset GIT_DIR                            # Restore the default Git directory

rm -rf .gitrn                            # Delete the temporary Git directory.