How to copy a file or directory from another GIT repository while preserving its history?
Internet is full of magic formulas each one more complex.
Here I’m proposing a much simpler and faster one that is to make a git format-patch for the entire history of the file or subdirectory that we want and then import it into the destination repository.
mkdir /tmp/mergepatchs
cd ~/repo/org
export reposrc=myfile.c #or mydir
git format-patch -o /tmp/mergepatchs $(git log $reposrc|grep ^commit|tail -1|awk '{print $2}')^..HEAD $reposrc
cd ~/repo/dest
git am /tmp/mergepatchs/*.patch
Simple and fast 
