Git Internals: The Model Under the Commands

Git's command line has a deserved reputation, and the data model underneath is small and regular. It is a content-addressed store of four object types, plus a set of files holding hashes. This path derives the object hash by hand, shows that a branch is a forty-character file, explains what a three-way merge actually computes and why rebase creates new commits rather than moving them, and ends with recovery. Every command turns out to add objects or move a pointer.