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GIT-SUBTREE(1) | Git Manual | GIT-SUBTREE(1) |
NAME¶
git-subtree - Merge subtrees together and split repository into subtreesSYNOPSIS¶
git subtree add -P <prefix> <commit> git subtree add -P <prefix> <repository> <ref> git subtree pull -P <prefix> <repository> <ref> git subtree push -P <prefix> <repository> <ref> git subtree merge -P <prefix> <commit> git subtree split -P <prefix> [OPTIONS] [<commit>]
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 .gitmodule 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¶
addCreate the <prefix> subtree by importing its
contents from the given <commit> or <repository> and remote
<ref>. A new commit is created automatically, joining the imported
project’s history with your own. With --squash, imports only a
single commit from the subproject, rather than its entire history.
merge
Merge recent changes up to <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
<commit>. With --squash, creates 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.
pull
Exactly like merge, but parallels git pull
in that it fetches the given ref from the specified remote repository.
push
Does a split (see below) using the <prefix>
supplied and then does a git push to push the result to the repository
and ref. This can be used to push your subtree to different branches of the
remote repository.
split
Extract a new, synthetic project history from the history
of the <prefix> subtree. 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). 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.
Note that if you use --squash when you merge, you should usually not just
--rejoin when you split.
OPTIONS¶
-q, --quietSuppress 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.
-m <message>, --message=<message>
This option is only valid for add, merge and pull
(unsure). Specify <message> as the commit message for the merge
commit.
OPTIONS FOR ADD, MERGE, PUSH, PULL¶
--squashThis option is only valid for add, merge, and pull
commands.
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.
OPTIONS FOR SPLIT¶
--annotate=<annotation>This option is only valid for the split command.
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>
This option is only valid for the split command.
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
This option is only valid for the split command.
If you use --rejoin, git subtree attempts to optimize its history
reconstruction to generate only the new commits since the last
--rejoin. --ignore-join disables this behaviour, forcing it to
regenerate the entire history. In a large project, this can take a long
time.
--onto=<onto>
This option is only valid for the split command.
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
This option is only valid for the split command.
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, don’t use --rejoin
when you split, because you don’t want the subproject’s history
to be part of your project anyway.
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
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
$ 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
$ git subtree split --prefix=gitweb --annotate='(split) ' --rejoin \ --branch gitweb-latest2
$ git subtree pull --prefix=gitweb \ git@github.com:whatever/gitweb.git master
$ git subtree merge --prefix=gitweb --squash gitweb-latest~10
$ date >gitweb/myfile $ git add gitweb/myfile $ git commit -m 'created myfile'
$ git subtree merge --prefix=gitweb --squash gitweb-latest
$ ls -l gitweb/myfile
git log gitweb-latest..$(git subtree split --prefix=gitweb)
EXAMPLE 3. EXTRACT A SUBTREE USING BRANCH¶
Suppose you have a source directory with many files and subdirectories, and you want to extract the lib directory to its own git project. Here’s a short way to do it: First, make the new repository wherever you want:$ <go to the new location> $ git init --bare
$ git subtree split --prefix=lib --annotate="(split)" -b split
$ git push <new-repo> split:master
AUTHOR¶
Written by Avery Pennarun < apenwarr@gmail.com[1]>GIT¶
Part of the git(1) suiteNOTES¶
- 1.
- apenwarr@gmail.com
mailto:apenwarr@gmail.com
05/15/2017 | Git 2.11.0 |