ggit

A Git implementation in Go, written to understand how Git works internally. It covers the core object model plus the day-to-day commands: staging, status, diff, log, branches, checkout, and merge.

Inspired by ugit. This is a learning project, not a replacement for Git.

Building

Needs Go 1.18+.

git clone https://github.com/vx6fid/git-go.git
cd git-go
go build -o ggit ./cmd/ggit

Commands

ggit init                     # initialize a repository
ggit hash-object <file>       # store a file as a blob
ggit cat-file -p <hash>       # inspect an object
ggit write-tree               # write a tree from the working directory
ggit read-tree <tree-sha>     # restore a tree into the working directory

ggit add <file>...            # stage files
ggit rm <file>                # unstage a file
ggit status                   # show working tree status
ggit diff                     # working tree vs index
ggit diff --staged            # index vs HEAD
ggit commit -m <message>      # commit staged changes

ggit log [-n <count>]         # show commit history

ggit branch                   # list branches
ggit branch <name>            # create a branch
ggit branch -d <name>         # delete a branch
ggit checkout <branch|sha>    # switch branch / detach
ggit checkout -b <name>       # create and switch
ggit merge <branch>           # merge a branch into the current one

Layout

cmd/ggit/          CLI commands
internal/
  object/          blobs, trees, commits, read/write
  index/           staging area (binary .git/index, DIRC v2)
  diff/            Myers diff, status and diff computation
  log/             commit parsing and history walking
  branch/          branch management and checkout
  merge/           merge base, fast-forward and three-way merge
  ref/             HEAD and refs

Objects are stored like Git does it: zlib-compressed, keyed by the SHA-1 of <type> <size>\0<content>, under .git/objects/<2 hex>/<38 hex>.

Not implemented

Pack files, the network protocols (push/pull/fetch), rebase, tags, and the config system are out of scope for now. The author name is currently hardcoded in cmd/ggit/commit.go.

Credits

Inspired by ugit and Git's internals.