Combine many git repos into one

combine_git_repos.sh

# Use-case:
# - We have multiple git repositories but want to merge them together for simplicity / using a monorepo / etc.
# - We can not lose the git history and tags
# - The new structure can be arbitrary
#
# Solution:
# - Create a tmp directory and clone all previous repos
# - Install git filter-repo via pip
# - In each of these repos, use the git filter-repo command to move all files to any new directory inside the repository
# - cd anywhere and create your new repository
# - merge all repos together

mkdir tmp
git clone a.git
git clone b.git
git clone c.git

python3 -m pip install --user git-filter-repo
# place the following inside .bashrc or .zshrc or whatever
export PATH="$HOME/.local/bin:$PATH"

cd a
# let's say we want repo a to be in folder new-repo/apps
git filter-repo --to-subdirectory-filter apps/a #the last argument can be any path you want. it will be the relative new path from the new repository

cd ../b
git filter-repo --to-subdirectory-filter apps/b

cd ../c
git filter-repo --to-subdirectory-filter packages/c #using packages just so we have sth. different here

cd ../..
mkdir new-repo
git init

git remote add a ../tmp/a
git fetch a --tags
git merge --allow-unrelated-histories a/main # or a/<branch> whatever branch you want to use now
git remote remove a

git remote add b ../tmp/b
git fetch b --tags
git merge --allow-unrelated-histories b/main # or a/<branch> whatever branch you want to use now
git remote remove b

git remote add c ../tmp/c
git fetch c --tags
git merge --allow-unrelated-histories c/main # or a/<branch> whatever branch you want to use now
git remote remove c

# Done! Now your new repo will look like this
tree -L 2
#.
#├── apps
#│   ├── a
#│   └── b
#└── packages
#    └── c