Merge git repositories and keep their history

merge-git-repos.sh

# Initialize the new repository in an empty directory
git init 

# Before we can do a merge, we need some initial commit. Create a file that's
# not part of any of the repos you want to merge, for example
touch delete-me-afterwards.txt
git add .
git commit -m "initial commit"


# Add the remote of one of your repositories you want to merge
# -f tells git to automatically fetch it
git remote add -f repo_a <remote url for repo A>

# Merge the files from the remote repo into the new one
git merge --allow-unrelated-histories \
  -m "Merged repo_a from its repo to the new monorepo" \
  repo_a/master

# Move the files from repo_a to their new subdirectory
mkdir subdir_a
find . -maxdepth 1 \
       -not -path "." \
       -not -path "./.git" \
       -not -path "./delete-me-afterwards.txt" \
       -not -path "./subdir_a" \
       -exec git mv '{}' 'subdir_a/{}' \;
git commit -m "Moved files from repo_a to their new subdirectory"

# Remove the remote repository
git remote remove repo_a


# Repeat the above steps for any other repository you want to merge. Don't
# forget to exclude subdir_a from the next find command.


# Remove the dummy file
git rm ./delete-me-afterwards.txt
git commit -m "Removed temporary initial file"