jj/README.md

# Jujutsu VCS

![](https://img.shields.io/github/license/martinvonz/jj) ![](https://img.shields.io/github/v/release/martinvonz/jj) ![](https://img.shields.io/github/release-date/martinvonz/jj) ![](https://img.shields.io/crates/v/jj-cli)
<br/>
![](https://github.com/martinvonz/jj/workflows/build/badge.svg) ![](https://img.shields.io/codefactor/grade/github/martinvonz/jj/main) ![](https://img.shields.io/librariesio/github/martinvonz/jj)

- [Disclaimer](#disclaimer)
- [Introduction](#introduction)
- [Status](#status)
- [Installation](#installation)
- [Command-line completion](#command-line-completion)
- [Getting started](#getting-started)
- [Related work](#related-work)

## Disclaimer

This is not a Google product. It is an experimental version-control system
(VCS). I (Martin von Zweigbergk <martinvonz@google.com>) started it as a hobby
project in late 2019. That said, this it is now my full-time project at Google.
My presentation from Git Merge 2022 has information about Google's plans. See
the
[slides](https://docs.google.com/presentation/d/1F8j9_UOOSGUN9MvHxPZX_L4bQ9NMcYOp1isn17kTC_M/view)
or the [recording](https://www.youtube.com/watch?v=bx_LGilOuE4).

## Introduction

Jujutsu is a [Git-compatible](docs/git-compatibility.md)
[DVCS](https://en.wikipedia.org/wiki/Distributed_version_control). It combines
features from Git (data model,
[speed](https://github.com/martinvonz/jj/discussions/49)), Mercurial (anonymous
branching, simple CLI [free from "the index"](docs/git-comparison.md#the-index),
[revsets](docs/revsets.md), powerful history-rewriting), and Pijul/Darcs
([first-class conflicts](docs/conflicts.md)), with features not found in most
of them ([working-copy-as-a-commit](docs/working-copy.md),
[undo functionality](docs/operation-log.md), automatic rebase,
[safe replication via `rsync`, Dropbox, or distributed file
system](docs/technical/concurrency.md)).

The command-line tool is called `jj` for now because it's easy to type and easy
to replace (rare in English). The project is called "Jujutsu" because it matches
"jj".

If you have any questions, please join us on Discord
[![Discord](https://img.shields.io/discord/968932220549103686.svg?label=&logo=discord&logoColor=ffffff&color=7389D8&labelColor=6A7EC2)](https://discord.gg/dkmfj3aGQN)
or start a [GitHub Discussion](https://github.com/martinvonz/jj/discussions).
The [glossary](docs/glossary.md) may also be helpful.

## Features

### Compatible with Git

Jujutsu has two [backends](docs/glossary.md#backend). One of them is a Git
backend (the other is a native one [^native-backend]). This lets you use Jujutsu
as an alternative interface to Git. The commits you create will look like
regular Git commits. You can always switch back to Git. The Git support uses the
[libgit2](https://libgit2.org/) C library.

[^native-backend]: At this time, there's practically no reason to use the native
backend. The backend exists mainly to make sure that it's possible to eventually
add functionality that cannot easily be added to the Git backend.

<img src="demos/git_compat.png" />

### The working copy is automatically committed

Almost all Jujutsu commands automatically commit the working copy. That means
that commands never fail because the working copy is dirty (no "error: Your
local changes to the following files..."), and there is no need for `git stash`.
You also get an automatic backup of the working copy whenever you run a command.
Also, because the working copy is a commit, commands work the same way on the
working-copy commit as on any other commit, so you can set the commit message
before you're done with the changes.

<img src="demos/working_copy.png" />

### The repo is the source of truth

With Jujutsu, the working copy plays a smaller role than with Git. Commands
snapshot the working copy before they start, then they update the repo, and then
the working copy is updated (if the working-copy commit was modified). Almost
all commands (even checkout!) operate on the commits in the repo, leaving the
common functionality of snapshotting and updating of the working copy to
centralized code. For example, `jj restore` (similar to `git restore`) can
restore from any commit and into any commit, and `jj describe` can set the
commit message of any commit (defaults to the working-copy commit).

### Entire repo is under version control

All operations you perform in the repo are recorded, along with a snapshot of
the repo state after the operation. This means that you can easily revert to an
earlier repo state, or to simply undo a particular operation (which does not
necessarily have to be the most recent operation).

<img src="demos/operation_log.png" />

### Conflicts can be recorded in commits

If an operation results in [conflicts](docs/glossary.md#conflict), information
about those conflicts will be recorded in the commit(s). The operation will
succeed. You can then resolve the conflicts later. One consequence of this
design is that there's no need to continue interrupted operations. Instead, you
get a single workflow for resolving conflicts, regardless of which command
caused them. This design also lets Jujutsu rebase merge commits correctly
(unlike both Git and Mercurial).

Basic conflict resolution:

<img src="demos/resolve_conflicts.png" />

Juggling conflicts:

<img src="demos/juggle_conflicts.png" />

### Automatic rebase

Whenever you modify a commit, any descendants of the old commit will be rebased
onto the new commit. Thanks to the conflict design described above, that can be
done even if there are conflicts. Branches pointing to rebased commits will be
updated. So will the working copy if it points to a rebased commit.

### Comprehensive support for rewriting history

Besides the usual rebase command, there's `jj describe` for editing the
description (commit message) of an arbitrary commit. There's also `jj diffedit`,
which lets you edit the changes in a commit without checking it out. To split
a commit into two, use `jj split`. You can even move part of the changes in a
commit to any other commit using `jj move`.

## Status

The tool is quite feature-complete, but some important features like (the
equivalent of) `git blame` are not yet supported. There
are also several performance bugs. It's also likely that workflows and setups
different from what the core developers use are not well supported.

I (Martin von Zweigbergk) have almost exclusively used `jj` to develop the
project itself since early January 2021. I haven't had to re-clone from source
(I don't think I've even had to restore from backup).

There *will* be changes to workflows and backward-incompatible changes to the
on-disk formats before version 1.0.0. Even the binary's name may change (i.e.
away from `jj`). For any format changes, we'll try to implement transparent
upgrades (as we've done with recent changes), or provide upgrade commands or
scripts if requested.

## Installation

See below for how to build from source. There are also
[pre-built binaries](https://github.com/martinvonz/jj/releases) for Windows,
Mac, or Linux (musl).

### Linux

On most distributions, you'll need to build from source using `cargo` directly.

#### Build using `cargo`

First make sure that you have the `libssl-dev`, `openssl`, and `pkg-config`
packages installed by running something like this:

```shell script
sudo apt-get install libssl-dev openssl pkg-config
```

Now run:

```shell script
cargo install --git https://github.com/martinvonz/jj.git --locked --bin jj jj-cli
```

#### Nix OS

If you're on Nix OS you can use the flake for this repository.
For example, if you want to run `jj` loaded from the flake, use:

```shell script
nix run 'github:martinvonz/jj'
```

You can also add this flake url to your system input flakes. Or you can
install the flake to your user profile:

```shell script
nix profile install 'github:martinvonz/jj'
```

#### Homebrew

If you use linuxbrew, you can run:

```shell script
brew install jj
```

### Mac

#### Homebrew

If you use Homebrew, you can run:

```shell script
brew install jj
```

#### MacPorts

You can also install `jj` via [MacPorts](https://www.macports.org) (as
the `jujutsu` port):

```shell script
sudo port install jujutsu
```

([port page](https://ports.macports.org/port/jujutsu/))

#### From Source

You may need to run some or all of these:

```shell script
xcode-select --install
brew install openssl
brew install pkg-config
export PKG_CONFIG_PATH="$(brew --prefix)/opt/openssl@3/lib/pkgconfig"
```

Now run:

```shell script
cargo install --git https://github.com/martinvonz/jj.git --locked --bin jj jj-cli
```

### Windows

Run:

```shell script
cargo install --git https://github.com/martinvonz/jj.git --locked --bin jj jj-cli --features vendored-openssl
```

## Initial configuration

You may want to configure your name and email so commits are made in your name.
Create a file at `~/.jjconfig.toml` and make it look something like
this:

```shell script
$ cat ~/.jjconfig.toml
[user]
name = "Martin von Zweigbergk"
email = "martinvonz@google.com"
```

## Command-line completion

To set up command-line completion, source the output of
`jj util completion --bash/--zsh/--fish` (called `jj debug completion` in
jj <= 0.7.0). Exactly how to source it depends on your shell.

### Bash

```shell script
source <(jj util completion)  # --bash is the default
```

Or, with jj <= 0.7.0:

```shell script
source <(jj debug completion)  # --bash is the default
```

### Zsh

```shell script
autoload -U compinit
compinit
source <(jj util completion --zsh)
```

Or, with jj <= 0.7.0:

```shell script
autoload -U compinit
compinit
source <(jj debug completion --zsh)
```

### Fish

```shell script
jj util completion --fish | source
```

Or, with jj <= 0.7.0:

```shell script
jj debug completion --fish | source
```

### Xonsh

```shell script
source-bash $(jj util completion)
```

Or, with jj <= 0.7.0:

```shell script
source-bash $(jj debug completion)
```

## Getting started

The best way to get started is probably to go through
[the tutorial](docs/tutorial.md). Also see the
[Git comparison](docs/git-comparison.md), which includes a table of
`jj` vs. `git` commands.

## Related work

There are several tools trying to solve similar problems as Jujutsu. See
[related work](docs/related-work.md) for details.