NAME¶

git-subtree - Merge subtrees together and split repository into subtrees

SYNOPSIS¶

git subtree [<options>] -P <prefix> add <local-commit>
git subtree [<options>] -P <prefix> add <repository> <remote-ref>
git subtree [<options>] -P <prefix> merge <local-commit> [<repository>]
git subtree [<options>] -P <prefix> split [<local-commit>]

git subtree [<options>] -P <prefix> pull <repository> <remote-ref>
git subtree [<options>] -P <prefix> push <repository> <refspec>

DESCRIPTION¶

Subtrees allow subprojects to be included within a subdirectory of the main project, optionally including the subproject’s entire history.

For example, you could include the source code for a library as a subdirectory of your application.

Subtrees are not to be confused with submodules, which are meant for the same task. Unlike submodules, subtrees do not need any special constructions (like .gitmodules files or gitlinks) be present in your repository, and do not force end-users of your repository to do anything special or to understand how subtrees work. A subtree is just a subdirectory that can be committed to, branched, and merged along with your project in any way you want.

They are also not to be confused with using the subtree merge strategy. The main difference is that, besides merging the other project as a subdirectory, you can also extract the entire history of a subdirectory from your project and make it into a standalone project. Unlike the subtree merge strategy you can alternate back and forth between these two operations. If the standalone library gets updated, you can automatically merge the changes into your project; if you update the library inside your project, you can "split" the changes back out again and merge them back into the library project.

For example, if a library you made for one application ends up being useful elsewhere, you can extract its entire history and publish that as its own git repository, without accidentally intermingling the history of your application project.

COMMANDS¶

add <local-commit>, add <repository> <remote-ref>

merge <local-commit> [<repository>]

split [<local-commit>] [<repository>]

pull <repository> <remote-ref>

push <repository> [+][<local-commit>:]<remote-ref>

OPTIONS FOR ALL COMMANDS¶

-q, --quiet

-d, --debug

-P <prefix>, --prefix=<prefix>

OPTIONS FOR ADD AND MERGE (ALSO: PULL, SPLIT --REJOIN, AND PUSH --REJOIN)¶

These options for add and merge may also be given to pull (which wraps merge), split --rejoin (which wraps either add or merge as appropriate), and push --rejoin (which wraps split --rejoin).

--squash

-m <message>, --message=<message>

OPTIONS FOR SPLIT (ALSO: PUSH)¶

These options for split may also be given to push (which wraps split).

--annotate=<annotation>

-b <branch>, --branch=<branch>

--ignore-joins

--onto=<onto>

--rejoin

EXAMPLE 1. ADD COMMAND¶

Let’s assume that you have a local repository that you would like to add an external vendor library to. In this case we will add the git-subtree repository as a subdirectory of your already existing git-extensions repository in ~/git-extensions/:

$ git subtree add --prefix=git-subtree --squash \
	git://github.com/apenwarr/git-subtree.git master

master needs to be a valid remote ref and can be a different branch name

You can omit the --squash flag, but doing so will increase the number of commits that are included in your local repository.

We now have a ~/git-extensions/git-subtree directory containing code from the master branch of git://github.com/apenwarr/git-subtree.git in our git-extensions repository.

EXAMPLE 2. EXTRACT A SUBTREE USING COMMIT, MERGE AND PULL¶

Let’s use the repository for the git source code as an example. First, get your own copy of the git.git repository:

$ git clone git://git.kernel.org/pub/scm/git/git.git test-git
$ cd test-git

gitweb (commit 1130ef3) was merged into git as of commit 0a8f4f0, after which it was no longer maintained separately. But imagine it had been maintained separately, and we wanted to extract git’s changes to gitweb since that time, to share with the upstream. You could do this:

$ git subtree split --prefix=gitweb --annotate='(split) ' \


       	0a8f4f0^.. --onto=1130ef3 --rejoin \


       	--branch gitweb-latest


       $ gitk gitweb-latest


       $ git push git@github.com:whatever/gitweb.git gitweb-latest:master

(We use 0a8f4f0^.. because that means "all the changes from 0a8f4f0 to the current version, including 0a8f4f0 itself.")

If gitweb had originally been merged using git subtree add (or a previous split had already been done with --rejoin specified) then you can do all your splits without having to remember any weird commit IDs:

$ git subtree split --prefix=gitweb --annotate='(split) ' --rejoin \
	--branch gitweb-latest2

And you can merge changes back in from the upstream project just as easily:

$ git subtree pull --prefix=gitweb \
	git@github.com:whatever/gitweb.git master

Or, using --squash, you can actually rewind to an earlier version of gitweb:

$ git subtree merge --prefix=gitweb --squash gitweb-latest~10

Then make some changes:

$ date >gitweb/myfile
$ git add gitweb/myfile
$ git commit -m 'created myfile'

And fast forward again:

$ git subtree merge --prefix=gitweb --squash gitweb-latest

And notice that your change is still intact:

$ ls -l gitweb/myfile

And you can split it out and look at your changes versus the standard gitweb:

git log gitweb-latest..$(git subtree split --prefix=gitweb)

EXAMPLE 3. EXTRACT A SUBTREE USING A BRANCH¶

Suppose you have a source directory with many files and subdirectories, and you want to extract the lib directory to its own git project. Here’s a short way to do it:

First, make the new repository wherever you want:

$ <go to the new location>
$ git init --bare

Back in your original directory:

$ git subtree split --prefix=lib --annotate="(split)" -b split

Then push the new branch onto the new empty repository:

$ git push <new-repo> split:master

AUTHOR¶

Written by Avery Pennarun <apenwarr@gmail.com[1]>

GIT¶

Part of the git(1) suite

NOTES¶

1.

apenwarr@gmail.com