johnnypeck / lite

Split a repository to read-only standalone repositories

Git Subtree Splitter

splitsh-lite replaces the subtree split Git built-in command to make splitting a monolithic repository to read-only standalone repositories easy and fast.

Why do I need this tool?

When starting a project, do you store all the code in one repository? Or are you creating many standalone repositories?

Both strategies work well and both have drawbacks as well. splitsh helps use both strategies by providing tools that automatically synchronize a monolithic repository to standalone repositories in real-time.

splitsh-lite is a sub-project that provides a faster implementation of the git subtree split command, which helps create standalone repositories for one or more sub-directories of a main repository.

If you want to learn more about monorepo vs manyrepos, watch this 4-minute lightning talk I gave at dotScale (or read the slides)... or watch the longer version from DrupalCon.

Installation

The fastest way to get started is to download a binary for your platform.

You can also install it manually.

Usage

Let say you want to split the lib/ directory of a repository to its own branch; from the "master" Git repository (bare or clone), run:

splitsh-lite --prefix=lib/

The sha1 of the split is displayed at the end of the execution:

SHA1=`splitsh-lite --prefix=lib/`

The sha1 can be used to create a branch or to push the commits to a new repository.

Automatically create a branch for the split by passing a branch name via the --target option:

splitsh-lite --prefix=lib/ --target=branch-name

If new commits are made on the repository, update the split by running the same command again. Updates are much faster as splitsh-lite keeps a cache of already split commits. Caching is possible as splitsh-lite guarantees that two splits of the same code always results in the same history and the same sha1s for each commit.

By default, splitsh-lite splits the current checkout-ed branch but you can split a different branch by passing it explicitly via the --origin flag (mandatory when splitting a bare repository):

splitsh-lite --prefix=lib/ --origin=origin/master

You don't even need to run the command from the Git repository directory if you pass the --path option:

splitsh-lite --prefix=lib/ --origin=origin/1.0 --path=/path/to/repo

Available options:

• --prefix is the prefix of the directory to split; you can put the split contents in a sub-directory of the target repository by using the --prefix=from:to syntax; split several directories by passing multiple --prefix flags;

• --path is the path of the repository to split (current directory by default);

• --origin is the Git reference for the origin (can be any Git reference like HEAD, heads/xxx, tags/xxx, origin/xxx, or any refs/xxx);

• --target creates a reference for the tip of the split (can be any Git reference like HEAD, heads/xxx, tags/xxx, origin/xxx, or any refs/xxx);

• --progress displays a progress bar;

• --quiet suppresses all output on stderr (useful when run from an automated script);

• --scratch flushes the cache (useful when a branch is force pushed or in case of a cache corruption);

Migrating from git subtree split

Migrating from git subtree split to splith-lite is easy as both tools generate the same sha1s.

However, note that older versions of git subtree split used broken algorithms, and so generated different sha1s than the latest version. You can simulate those version via the --git flag. Use <1.8.2 or <2.8.0 depending on which version of git subtree split you want to simulate.

Manual Installation

If you want to contribute to splitsh-lite or use it as a library, you first need to install libgit2:

go get -d github.com/libgit2/git2go
cd $GOPATH/src/github.com/libgit2/git2go
git checkout next
git submodule update --init
make install

Then, compile splitsh-lite:

go get github.com/splitsh/lite
go build -o splitsh-lite github.com/splitsh/lite

If everything goes fine, a splitsh-lite binary should be available in the current directory.