假設 shared 是要共享的目錄

添加遠程分支
git remote add shared git@git.coding.net:wangjile/shared-code.git

git subtree push --prefix shared shared master

在要用的地方
git fetch shared
git subtree add --prefix shared shared/master
git subtree pull --prefix shared shared master --squash

可選

git subtree split --prefix shared --rejoin
會生成一個空的 commit 作為 base，
可以避免把所有的 commit loop 一遍

git subtree split --prefix shared -b backport
把改動切成分支，想咋改都行

參考

• the alternative to Git submodule
• Using Git Subtree to Share Code Between Rails Applications
  
• Why does 'git subtree push' always list hundreds of commits?](http://stackoverflow.com/questions/26928299/why-does-git-subtree-push-always-list-hundreds-of-commits)