I was encountered into this situation that I need to transfer some existing code to another separated GitHub repository. Ideally it would be perfect to keep all historic git commit histories so that we can still be able to revert back if necessary.

After digging into Google and Stack Overflow, luckily I found there are others who need to achieve similar things. Here is the solution I used to resolve this problem eventually.

Example Operations

Below are my git operations when transfer the code from existing repository to a new GitHub repository ABC/common.git.

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4690  2020-01-29 15:44  git filter-branch --subdirectory-filter common -- -- all
4691  2020-01-29 15:44  ls
4692  2020-01-29 15:44  cd loyalty
4693  2020-01-29 15:44  ls
4694  2020-01-29 15:44  ls | wc
4695  2020-01-29 15:44  ls | wc -l
4696  2020-01-29 15:44  cd ..
4697  2020-01-29 15:44  ls
4698  2020-01-29 15:45  mkdir common
4699  2020-01-29 15:45  git mv README.md athena_glue.py dag_common deploy.sh member_match.py s3_utils.py slack.py common
4700  2020-01-29 15:45  ls
4701  2020-01-29 15:45  git mv loyalty/ common
4702  2020-01-29 15:45  git mv schemas/ common
4703  2020-01-29 15:45  ls
4704  2020-01-29 15:45  git mv __init__.py common
4705  2020-01-29 15:45  ls
4706  2020-01-29 15:45  git commit -m "relocate common library to ABC/common repo"
4707  2020-01-29 15:45  cd ..
4708  2020-01-29 15:45  ls
4709  2020-01-29 15:46  cd common
4710  2020-01-29 15:46  git remote add dp ../dp/
4711  2020-01-29 15:46  git fetch dp
4712  2020-01-29 15:46  git status
4713  2020-01-29 15:48  git branch dp remotes/dp/master
4714  2020-01-29 15:49  git merge dp --allow-unrelated-history
4715  2020-01-29 15:49  git merge dp --allow-unrelated-histories
4716  2020-01-29 15:49  git remote rm dp
4717  2020-01-29 15:49  git branch list
4718  2020-01-29 15:49  git branch
4719  2020-01-29 15:49  git status
4720  2020-01-29 15:50  idea .
4721  2020-01-29 15:51  cd ..
4722  2020-01-29 15:51  ls
4723  2020-01-29 15:51  rm -rf common
4724  2020-01-29 15:51  git clone [email protected]:ABC/common.git
4725  2020-01-29 15:51  cd common
4726  2020-01-29 15:51  idea .
4727  2020-01-29 15:54  git remote add dp ../dp
4728  2020-01-29 15:54  git fetch dp
4729  2020-01-29 15:55  git branch dp remotes/dp/master
4730  2020-01-29 15:55  git merge dp --allow-unrelated-histories

Hope it helps.