Git

Move files from one repository to another, preserving git history

Based on Ayushya Jaiswal's excellent article on Move files from one repository to another, preserving git history.

In the example below, we want to extract a folder (code/src/utils) from a mono-repo (repo1) into its own repo (repo2), preserving the git history.

git clone git@github.com:example/test.git repo1
git clone git@github.com:example/test.git repo2
cd repo2
git remote rm origin
git filter-branch --subdirectory-filter code/src/utils -- --all
git reset --hard
git gc --aggressive 
git prune
git clean -xfd

Now only the filtered folder is left, and it's at the root of repo2. If it's going into another repo with existing files, we can move the things to a sub-folder and commit them before proceeding, but in this case we want them in the root.

Next, we push them to the new remote repo (which was created ahead of time and left empty):

git remote add origin git@github.com:example/test-extrusion.git
git branch -M main
git push -u origin main

Finally, we should clean up the old repo:

cd ../repo1
rm -rf code/src/utils
git add -A
git commit

Obviously, there might be more refactoring needed, but this is the basic idea.

Summarize changes

git diff @{2023-09-10}.. -- docs/src
git whatchanged --since="last Sunday" -p -- docs/src

Find big files

Find out if large binary files are lurking in the history. Lists all blobs with commit by ascending size:

git rev-list --objects --all |
  git cat-file --batch-check='%(objecttype) %(objectname) %(objectsize) %(rest)' |
  sed -n 's/^blob //p' |
  sort --numeric-sort --key=2 |
  cut -c 1-12,41- |
  $(command -v gnumfmt || echo numfmt) --field=2 --to=iec-i --suffix=B --padding=7 -- \
  round=nearest

Src: https://stackoverflow.com/a/42544963/511976

Delete them with git-filter-repo (src: https://stackoverflow.com/a/61602985/511976).

Git helpers

UI: github.com/mhvelplund/git-bash.

Credentials: Storing Git Credentials with Git Credential Helper

Move a feature branch from one product to another

If, by accident, one has created a feature foo from the wrong product version branch (eg.: tmtand-3.1/develop) and it really should have started from another product version branch (eg.: tmtand-3.2/develop)), then it's easy to rebase the feature on the proper product version with:

git rebase --onto target-branch source-branch

So in the case above, that would be:

git checkout tmtand-3.1/feature/foo
git rebase --onto tmtand-3.2/develop tmtand-3.1/develop

Working with multiple git repositories

If your product consists of specific versions across multiple repositories, there are multiple options for managing that. I prefer Gitslave or gits.

Temp. Git ignore

So, to temporarily ignore changes in a certain file, run:

git update-index --assume-unchanged <file>

Then when you want to track changes again:

git update-index --no-assume-unchanged <file>