Writen by Cosmin Apreutesei. Public Domain.
Tested on Linux, Windows and OSX
Multigit allows checking out multiple git repositories overlaid onto the same directory.
It is useful for projects which are made of different components that are developed separately, but which need to track files from different parts of the directory structure of the project.
This cannot be done using git submodules or git subtrees, which only allow subprojects to be checked out into their own private subdirectories. Multigit allows repositories to track any file from any directory of the project structure, similar to a union filesystem, where each repository is a layer.
Some examples where this combination of change management and module management could be useful:
- manage customizations made to a web app in a separate repository.
- putting your home directory under source control, one repo per app.
- package manager for a project, dev platform or language.
Multigit is a simple shell script with no dependencies. You can either
put it somewhere in your PATH, or you can clone it everywhere
you want to create a multigit project in, and call it as ./mgit
(or mgit on Windows).
To enable tab completion in bash, put mgit-autocomplete.sh somewhere
and source it in your .bashrc along with your git completion script
(don't call them, dot them). On Ubuntu, the git completion script is at
/usr/share/bash-completion/completions/git (you need to source
that manually).
Let's see a bare bones example:
$ mkdir project
$ cd project
$ mgit init foo # create layered repo foo
$ mgit init bar # create layered repo bar
$ mgit ls # list layered repos
foo
bar
$ echo > foo.txt # create file foo.txt
$ echo > bar.txt # create file bar.txt
$ mgit foo add -f foo.txt # add foo.txt to project foo
$ mgit bar add -f bar.txt # add bar.txt to project bar
$ mgit foo commit -m "init" # commit on foo
$ mgit bar commit -m "init" # commit on bar
$ ls
foo.txt bar.txt # foo.txt and bar.txt are in the same dir
$ mgit foo ls-files
foo.txt # but project foo only tracks foo.txt
$ mgit bar ls-files
bar.txt # and project bar only tracks bar.txt
Note the -f (force) when adding files to git. When creating a repo with
mgit init foo, the .gitignore file for foo is set to
.mgit/foo.exclude which defaults to *, which means that
all files are ignored by default, hence the need to add them with -f.
This is to prevent accidentally adding files of other projects with
git add -A and ending up with multiple projects tracking the same file.
To recover the convenience of git -A and the correct reporting of
untracked files, change the exclude files and add patterns that are
appropriate to each repo. Given that all repos now share the same
namespace, you need to be explicit about which parts of that namespace
are "reserved" for which repos.
You can use git direcly on your layered repos with a subshell:
$ mgit foo
Entering subshell: git commands will affect the repo 'foo'.
Type `exit' to exit subshell.
A foo.txt
[foo] $ git ls-files
foo.txt
[foo] $ exit
$
Or you can type git commands directly without a subshell:
$ mgit foo ls-files
foo.txt
Or you can ditch multigit entirely and go bare git:
$ export GIT_DIR=.mgit/foo/.git
$ git ls-files
foo.txt
$ mkdir project
$ cd project
$ mgit clone https://github.com/bob/foo
$ mgit clone https://github.com/bob/bar
This will clone both repos into the current directory (there's no "target directory" arg).
No you don't. Since most of the submodules in a big project will probably reside at a common base URL, you can make an alias for that base URL and use that instead when cloning the submodules:
$ mgit baseurl bob https://github.com/bob/ # writes `https://github.com/bob/` in .mgit/bob.baseurl
$ mgit clone bob/foo bob/bar # writes `bob` in .mgit/foo.origin and .mgit/bar.origin
Now that bob is registered as a remote, and both foo's and bar's origins
are registered too (they are set to bob), next time it will be enough
to type mgit clone foo bar. Which brings us to the next question...
Every time you clone a repo with mgit clone, a file .mgit/foo.origin
is created which contains the origin url of that repo, which allows you
to clone it by name alone. These files are not tracked by default,
they're just sitting there, but there's nothing stopping you from
creating a "meta" repo and start tracking them:
$ mgit init meta
$ mgit meta add -f .mgit/bob.baseurl # add bob's baseurl to meta
$ mgit meta add -f .mgit/foo.origin # add foo's origin to meta
$ mgit meta add -f .mgit/bar.origin # add bar's origin to meta
$ mgit meta commit -m "bob's place; foo and bar modules"
The meta repo is like any other layered repo, it just so happens that it tracks files from
.mgit(and it doesn't have to be called meta either, and it doesn't have to be the only repo containing meta-information).
Maintaining a meta repo for a project allows the users of that project
to clone the meta repo and then clone all other repos
with mgit clone-all (and list them with mgit ls-all).
This makes for a simple way to manage and share module collections
that later can be cloned back wholesale.
Note that repos created with mgit init foo don't create an origin file.
You can add that yourself with mgit origin foo https://github.com/bob/foo
or simply mgit origin foo bob if you have previously added bob's baseurl.
$ mgit release 1.0 update # adds .mgit/1.0.release
This creates (or updates) a list with currently checked out versions of all repos, effectively recording a snapshot of the entire project. This snapshot can later be restored with:
$ mgit clone-release 1.0
Note: Existing repos will have to be removed first. This command will refuse to overwrite them. Also, this will not create branches. Your repos will be in "detached HEAD state". You can take it from there with git, eg. with
mgit --all checkout -b release-1.0.
Needless to say, you can add the .release file to your meta repo too, just like with the .baseurl and .origin files before, so that other people will be able to clone the project at that specific release point.
Another quick way to get a snapshot of the project without using .release files is with:
$ mgit --all ver
foo=701d080 bar=0fefd96
And later clone the repos with:
$ mgit clone foo=701d080 bar=0fefd96
Tag releases can be made with:
$ mgit release 1.0 update tag
Tag releases only record the current tag as opposed to the exact full version of the packages. This allows you to make stable releases even when some packages are "unstable" (i.e. they contain commits above the latest tag). It also enables the controversial practice of updating a tag's target commit without having to make a new release.
| command | description |
|---|---|
mgit st |
list modified files across all repos |
mgit --all -v status -s |
like mgit st but shows the repos too |
mgit ls-unpushed |
list repos ahead of origin |
mgit ls-tracked |
list files and the repos who track them |
mgit ls-untracked |
list files untracked by any repo |
mgit ls-double-tracked |
list files tracked by multiple repos |
mgit remove [--dry] REPO ... |
remove repos from disk |
There's more stuff, type mgit to see.
Simply by telling git to clone all the repositories into a common
work tree. The git trees are kept in .mgit/<repo>/.git and the
work tree is always '.'.
This is such basic and useful functionality that it should
be built into git clone and git init really. As dead simple
as multigit is, it's still yet another script that you have to deploy.
Don't worry about it, it's mostly fluff. The gist of it is only 6 lines:
mgit init foo:
mkdir -p .mgit/foo
export GIT_DIR=.mgit/foo/.git
git init # create .mgit/foo/.git
git config --local core.worktree ../../.. # relative to GIT_DIR
git config --local core.excludesfile .mgit/foo.exclude # instead of .gitignore
[ -f .mgit/foo.exclude ] || echo '*' > .mgit/foo.exclude # "ignore all"
mgit foo ls-files:
export GIT_DIR=.mgit/foo/.git # set git to work on foo
git ls-files # list files of foo
Just like git, mgit scans the current directory and its parents for
a .mgit dir, and if found, it sets the current directory to that,
and everything else happens from there, except starting a subshell
and executing git commands which run in the current directory.
Multigit is the package manager for luapower. The meta-package contains the list of packages in the distribution and a few handy multigit plugins specific to luapower.
Plugins allows extending multigit with project-specific scripts that are exposed as multigit commands (like build scripts, etc.). Plugin scripts can be included say, in the meta package of your project. The way they work is very simple:
-
mgit <repo> <command> ...will try to run.mgit/git-<command>.sh ...with$GIT_DIRset properly,$MULTIGIT_REPOset to<repo>,$PWD0set to the invocation path and current directory set to one directory where the.mgitdirectory was found. -
mgit <command> ...will try to run.mgit/<command>.sh. -
mgit helpwill try tocat .mgit/*.help, which is where you should place the help section of the added commands.
Look at luapower-repos for a real-world example of this.
Multigit will use the following environment variables when performing various tasks:
$MULTIGIT_FETCH_OPTSwill be expanded and passed togit fetch$MULTIGIT_INIT_OPTSwill be expanded and passed togit init
- No way to specify a different branch when cloning (must switch it after).
- No way to specify a different branch when making releases.
- No way to register multiple remotes for the same repo and specify the remote when cloning.
There is a very similar project called vcsh. It even has a video presentation, check it out.