Import part or full git repository to another repository

Import part of git repository to another repository in order to keep history of the imported files.

Suppose you have 2 projects (A and B) and you want to move some files from a A to B without losing history of the files. Prepare the subfolder you are interested to import in B

pushd A
git subtree split -P <name-of-folder> -b <name-of-new-branch>
popd

Ready to import?

pushd /path/to/project/B
mkdir -p folder/to/import/other/repository
git remote add projectA /path/to/project/A
git fetch projectA
git read-tree --prefix=folder/to/import/other/repository -u projectA/$branch_name
git merge -s ours --allow-unrelated-histories --no-commit projectA/$branch_name

... review if needed
git commit