git-subtree(1) - man - phpman

GIT-SUBTREE(1)                             [FIXME: manual]                            GIT-SUBTREE(1)



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>
       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.

           Tip
           In order to keep your commit messages clean, we recommend that people split their commits
           between the subtrees and the main project as much as possible. That is, if you make a
           change that affects both the library and the main application, commit it in two pieces.
           That way, when you split the library commits out later, their descriptions will still
           make sense. But if this isn’t important to you, it’s not necessary. git subtree will
           simply leave out the non-library-related parts of the commit when it splits it out into
           the subproject later.

COMMANDS
       add <local-commit>, add <repository> <remote-ref>
           Create the <prefix> subtree by importing its contents from the given <local-commit> or
           <repository> and <remote-ref>. A new commit is created automatically, joining the
           imported project’s history with your own. With --squash, import only a single commit from
           the subproject, rather than its entire history.

       merge <local-commit>
           Merge recent changes up to <local-commit> into the <prefix> subtree. As with normal git
           merge, this doesn’t remove your own local changes; it just merges those changes into the
           latest <local-commit>. With --squash, create only one commit that contains all the
           changes, rather than merging in the entire history.

           If you use --squash, the merge direction doesn’t always have to be forward; you can use
           this command to go back in time from v2.5 to v2.4, for example. If your merge introduces
           a conflict, you can resolve it in the usual ways.

       split [<local-commit>]
           Extract a new, synthetic project history from the history of the <prefix> subtree of
           <local-commit>, or of HEAD if no <local-commit> is given. The new history includes only
           the commits (including merges) that affected <prefix>, and each of those commits now has
           the contents of <prefix> at the root of the project instead of in a subdirectory. Thus,
           the newly created history is suitable for export as a separate git repository.

           After splitting successfully, a single commit ID is printed to stdout. This corresponds
           to the HEAD of the newly created tree, which you can manipulate however you want.

           Repeated splits of exactly the same history are guaranteed to be identical (i.e. to
           produce the same commit IDs) as long as the settings passed to split (such as --annotate)
           are the same. Because of this, if you add new commits and then re-split, the new commits
           will be attached as commits on top of the history you generated last time, so git merge
           and friends will work as expected.

       pull <repository> <remote-ref>
           Exactly like merge, but parallels git pull in that it fetches the given ref from the
           specified remote repository.

       push <repository> [+][<local-commit>:]<remote-ref>
           Does a split using the <prefix> subtree of <local-commit> and then does a git push to
           push the result to the <repository> and <remote-ref>. This can be used to push your
           subtree to different branches of the remote repository. Just as with split, if no
           <local-commit> is given, then HEAD is used. The optional leading + is ignored.

OPTIONS FOR ALL COMMANDS
       -q, --quiet
           Suppress unnecessary output messages on stderr.

       -d, --debug
           Produce even more unnecessary output messages on stderr.

       -P <prefix>, --prefix=<prefix>
           Specify the path in the repository to the subtree you want to manipulate. This option is
           mandatory for all commands.

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
           Instead of merging the entire history from the subtree project, produce only a single
           commit that contains all the differences you want to merge, and then merge that new
           commit into your project.

           Using this option helps to reduce log clutter. People rarely want to see every change
           that happened between v1.0 and v1.1 of the library they’re using, since none of the
           interim versions were ever included in their application.

           Using --squash also helps avoid problems when the same subproject is included multiple
           times in the same project, or is removed and then re-added. In such a case, it doesn’t
           make sense to combine the histories anyway, since it’s unclear which part of the history
           belongs to which subtree.

           Furthermore, with --squash, you can switch back and forth between different versions of a
           subtree, rather than strictly forward.  git subtree merge --squash always adjusts the
           subtree to match the exactly specified commit, even if getting to that commit would
           require undoing some changes that were added earlier.

           Whether or not you use --squash, changes made in your local repository remain intact and
           can be later split and send upstream to the subproject.

       -m <message>, --message=<message>
           Specify <message> as the commit message for the merge commit.

OPTIONS FOR SPLIT (ALSO: PUSH)
       These options for split may also be given to push (which wraps split).

       --annotate=<annotation>
           When generating synthetic history, add <annotation> as a prefix to each commit message.
           Since we’re creating new commits with the same commit message, but possibly different
           content, from the original commits, this can help to differentiate them and avoid
           confusion.

           Whenever you split, you need to use the same <annotation>, or else you don’t have a
           guarantee that the new re-created history will be identical to the old one. That will
           prevent merging from working correctly. git subtree tries to make it work anyway,
           particularly if you use --rejoin, but it may not always be effective.

       -b <branch>, --branch=<branch>
           After generating the synthetic history, create a new branch called <branch> that contains
           the new history. This is suitable for immediate pushing upstream. <branch> must not
           already exist.

       --ignore-joins
           If you use --rejoin, git subtree attempts to optimize its history reconstruction to
           generate only the new commits since the last --rejoin.  --ignore-joins disables this
           behavior, forcing it to regenerate the entire history. In a large project, this can take
           a long time.

       --onto=<onto>
           If your subtree was originally imported using something other than git subtree, its
           history may not match what git subtree is expecting. In that case, you can specify the
           commit ID <onto> that corresponds to the first revision of the subproject’s history that
           was imported into your project, and git subtree will attempt to build its history from
           there.

           If you used git subtree add, you should never need this option.

       --rejoin
           After splitting, merge the newly created synthetic history back into your main project.
           That way, future splits can search only the part of history that has been added since the
           most recent --rejoin.

           If your split commits end up merged into the upstream subproject, and then you want to
           get the latest upstream version, this will allow git’s merge algorithm to more
           intelligently avoid conflicts (since it knows these synthetic commits are already part of
           the upstream repository).

           Unfortunately, using this option results in git log showing an extra copy of every new
           commit that was created (the original, and the synthetic one).

           If you do all your merges with --squash, make sure you also use --squash when you split
           --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 AT 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 AT 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 AT gmail.com[1]>

GIT
       Part of the git(1) suite

NOTES
        1. apenwarr AT gmail.com
           mailto:apenwarr AT gmail.com



[FIXME: source]                              02/26/2026                               GIT-SUBTREE(1)