1GIT-SUBTREE(1)                    Git Manual                    GIT-SUBTREE(1)
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NAME

6       git-subtree - Merge subtrees together and split repository into
7       subtrees
8

SYNOPSIS

10       git subtree add   -P <prefix> <commit>
11       git subtree add   -P <prefix> <repository> <ref>
12       git subtree pull  -P <prefix> <repository> <ref>
13       git subtree push  -P <prefix> <repository> <ref>
14       git subtree merge -P <prefix> <commit>
15       git subtree split -P <prefix> [OPTIONS] [<commit>]
16

DESCRIPTION

18       Subtrees allow subprojects to be included within a subdirectory of the
19       main project, optionally including the subproject’s entire history.
20
21       For example, you could include the source code for a library as a
22       subdirectory of your application.
23
24       Subtrees are not to be confused with submodules, which are meant for
25       the same task. Unlike submodules, subtrees do not need any special
26       constructions (like .gitmodules files or gitlinks) be present in your
27       repository, and do not force end-users of your repository to do
28       anything special or to understand how subtrees work. A subtree is just
29       a subdirectory that can be committed to, branched, and merged along
30       with your project in any way you want.
31
32       They are also not to be confused with using the subtree merge strategy.
33       The main difference is that, besides merging the other project as a
34       subdirectory, you can also extract the entire history of a subdirectory
35       from your project and make it into a standalone project. Unlike the
36       subtree merge strategy you can alternate back and forth between these
37       two operations. If the standalone library gets updated, you can
38       automatically merge the changes into your project; if you update the
39       library inside your project, you can "split" the changes back out again
40       and merge them back into the library project.
41
42       For example, if a library you made for one application ends up being
43       useful elsewhere, you can extract its entire history and publish that
44       as its own git repository, without accidentally intermingling the
45       history of your application project.
46
47           Tip
48           In order to keep your commit messages clean, we recommend that
49           people split their commits between the subtrees and the main
50           project as much as possible. That is, if you make a change that
51           affects both the library and the main application, commit it in two
52           pieces. That way, when you split the library commits out later,
53           their descriptions will still make sense. But if this isn’t
54           important to you, it’s not necessary. git subtree will simply leave
55           out the non-library-related parts of the commit when it splits it
56           out into the subproject later.
57

COMMANDS

59       add
60           Create the <prefix> subtree by importing its contents from the
61           given <commit> or <repository> and remote <ref>. A new commit is
62           created automatically, joining the imported project’s history with
63           your own. With --squash, imports only a single commit from the
64           subproject, rather than its entire history.
65
66       merge
67           Merge recent changes up to <commit> into the <prefix> subtree. As
68           with normal git merge, this doesn’t remove your own local changes;
69           it just merges those changes into the latest <commit>. With
70           --squash, creates only one commit that contains all the changes,
71           rather than merging in the entire history.
72
73           If you use --squash, the merge direction doesn’t always have to be
74           forward; you can use this command to go back in time from v2.5 to
75           v2.4, for example. If your merge introduces a conflict, you can
76           resolve it in the usual ways.
77
78       pull
79           Exactly like merge, but parallels git pull in that it fetches the
80           given ref from the specified remote repository.
81
82       push
83           Does a split (see below) using the <prefix> supplied and then does
84           a git push to push the result to the repository and ref. This can
85           be used to push your subtree to different branches of the remote
86           repository.
87
88       split
89           Extract a new, synthetic project history from the history of the
90           <prefix> subtree. The new history includes only the commits
91           (including merges) that affected <prefix>, and each of those
92           commits now has the contents of <prefix> at the root of the project
93           instead of in a subdirectory. Thus, the newly created history is
94           suitable for export as a separate git repository.
95
96           After splitting successfully, a single commit id is printed to
97           stdout. This corresponds to the HEAD of the newly created tree,
98           which you can manipulate however you want.
99
100           Repeated splits of exactly the same history are guaranteed to be
101           identical (i.e. to produce the same commit ids). Because of this,
102           if you add new commits and then re-split, the new commits will be
103           attached as commits on top of the history you generated last time,
104           so git merge and friends will work as expected.
105
106           Note that if you use --squash when you merge, you should usually
107           not just --rejoin when you split.
108

OPTIONS

110       -q, --quiet
111           Suppress unnecessary output messages on stderr.
112
113       -d, --debug
114           Produce even more unnecessary output messages on stderr.
115
116       -P <prefix>, --prefix=<prefix>
117           Specify the path in the repository to the subtree you want to
118           manipulate. This option is mandatory for all commands.
119
120       -m <message>, --message=<message>
121           This option is only valid for add, merge, pull, and split --rejoin.
122           Specify <message> as the commit message for the merge commit.
123

OPTIONS FOR ADD, MERGE, AND PULL

125       --squash
126           This option is only valid for add, merge, and pull commands.
127
128           Instead of merging the entire history from the subtree project,
129           produce only a single commit that contains all the differences you
130           want to merge, and then merge that new commit into your project.
131
132           Using this option helps to reduce log clutter. People rarely want
133           to see every change that happened between v1.0 and v1.1 of the
134           library they’re using, since none of the interim versions were ever
135           included in their application.
136
137           Using --squash also helps avoid problems when the same subproject
138           is included multiple times in the same project, or is removed and
139           then re-added. In such a case, it doesn’t make sense to combine the
140           histories anyway, since it’s unclear which part of the history
141           belongs to which subtree.
142
143           Furthermore, with --squash, you can switch back and forth between
144           different versions of a subtree, rather than strictly forward.  git
145           subtree merge --squash always adjusts the subtree to match the
146           exactly specified commit, even if getting to that commit would
147           require undoing some changes that were added earlier.
148
149           Whether or not you use --squash, changes made in your local
150           repository remain intact and can be later split and send upstream
151           to the subproject.
152

OPTIONS FOR SPLIT

154       --annotate=<annotation>
155           This option is only valid for the split command.
156
157           When generating synthetic history, add <annotation> as a prefix to
158           each commit message. Since we’re creating new commits with the same
159           commit message, but possibly different content, from the original
160           commits, this can help to differentiate them and avoid confusion.
161
162           Whenever you split, you need to use the same <annotation>, or else
163           you don’t have a guarantee that the new re-created history will be
164           identical to the old one. That will prevent merging from working
165           correctly. git subtree tries to make it work anyway, particularly
166           if you use --rejoin, but it may not always be effective.
167
168       -b <branch>, --branch=<branch>
169           This option is only valid for the split command.
170
171           After generating the synthetic history, create a new branch called
172           <branch> that contains the new history. This is suitable for
173           immediate pushing upstream. <branch> must not already exist.
174
175       --ignore-joins
176           This option is only valid for the split command.
177
178           If you use --rejoin, git subtree attempts to optimize its history
179           reconstruction to generate only the new commits since the last
180           --rejoin.  --ignore-join disables this behaviour, forcing it to
181           regenerate the entire history. In a large project, this can take a
182           long time.
183
184       --onto=<onto>
185           This option is only valid for the split command.
186
187           If your subtree was originally imported using something other than
188           git subtree, its history may not match what git subtree is
189           expecting. In that case, you can specify the commit id <onto> that
190           corresponds to the first revision of the subproject’s history that
191           was imported into your project, and git subtree will attempt to
192           build its history from there.
193
194           If you used git subtree add, you should never need this option.
195
196       --rejoin
197           This option is only valid for the split command.
198
199           After splitting, merge the newly created synthetic history back
200           into your main project. That way, future splits can search only the
201           part of history that has been added since the most recent --rejoin.
202
203           If your split commits end up merged into the upstream subproject,
204           and then you want to get the latest upstream version, this will
205           allow git’s merge algorithm to more intelligently avoid conflicts
206           (since it knows these synthetic commits are already part of the
207           upstream repository).
208
209           Unfortunately, using this option results in git log showing an
210           extra copy of every new commit that was created (the original, and
211           the synthetic one).
212
213           If you do all your merges with --squash, don’t use --rejoin when
214           you split, because you don’t want the subproject’s history to be
215           part of your project anyway.
216

EXAMPLE 1. ADD COMMAND

218       Let’s assume that you have a local repository that you would like to
219       add an external vendor library to. In this case we will add the
220       git-subtree repository as a subdirectory of your already existing
221       git-extensions repository in ~/git-extensions/:
222
223           $ git subtree add --prefix=git-subtree --squash \
224                git://github.com/apenwarr/git-subtree.git master
225
226       master needs to be a valid remote ref and can be a different branch
227       name
228
229       You can omit the --squash flag, but doing so will increase the number
230       of commits that are included in your local repository.
231
232       We now have a ~/git-extensions/git-subtree directory containing code
233       from the master branch of git://github.com/apenwarr/git-subtree.git in
234       our git-extensions repository.
235

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

237       Let’s use the repository for the git source code as an example. First,
238       get your own copy of the git.git repository:
239
240           $ git clone git://git.kernel.org/pub/scm/git/git.git test-git
241           $ cd test-git
242
243       gitweb (commit 1130ef3) was merged into git as of commit 0a8f4f0, after
244       which it was no longer maintained separately. But imagine it had been
245       maintained separately, and we wanted to extract git’s changes to gitweb
246       since that time, to share with the upstream. You could do this:
247
248           $ git subtree split --prefix=gitweb --annotate='(split) ' \
249                     0a8f4f0^.. --onto=1130ef3 --rejoin \
250                     --branch gitweb-latest
251                  $ gitk gitweb-latest
252                  $ git push git@github.com:whatever/gitweb.git gitweb-latest:master
253
254       (We use 0a8f4f0^.. because that means "all the changes from 0a8f4f0 to
255       the current version, including 0a8f4f0 itself.")
256
257       If gitweb had originally been merged using git subtree add (or a
258       previous split had already been done with --rejoin specified) then you
259       can do all your splits without having to remember any weird commit ids:
260
261           $ git subtree split --prefix=gitweb --annotate='(split) ' --rejoin \
262                --branch gitweb-latest2
263
264       And you can merge changes back in from the upstream project just as
265       easily:
266
267           $ git subtree pull --prefix=gitweb \
268                git@github.com:whatever/gitweb.git master
269
270       Or, using --squash, you can actually rewind to an earlier version of
271       gitweb:
272
273           $ git subtree merge --prefix=gitweb --squash gitweb-latest~10
274
275       Then make some changes:
276
277           $ date >gitweb/myfile
278           $ git add gitweb/myfile
279           $ git commit -m 'created myfile'
280
281       And fast forward again:
282
283           $ git subtree merge --prefix=gitweb --squash gitweb-latest
284
285       And notice that your change is still intact:
286
287           $ ls -l gitweb/myfile
288
289       And you can split it out and look at your changes versus the standard
290       gitweb:
291
292           git log gitweb-latest..$(git subtree split --prefix=gitweb)
293

EXAMPLE 3. EXTRACT A SUBTREE USING BRANCH

295       Suppose you have a source directory with many files and subdirectories,
296       and you want to extract the lib directory to its own git project.
297       Here’s a short way to do it:
298
299       First, make the new repository wherever you want:
300
301           $ <go to the new location>
302           $ git init --bare
303
304       Back in your original directory:
305
306           $ git subtree split --prefix=lib --annotate="(split)" -b split
307
308       Then push the new branch onto the new empty repository:
309
310           $ git push <new-repo> split:master
311

AUTHOR

313       Written by Avery Pennarun <apenwarr@gmail.com[1]>
314

GIT

316       Part of the git(1) suite
317

NOTES

319        1. apenwarr@gmail.com
320           mailto:apenwarr@gmail.com
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324Git 2.31.1                        2021-03-26                    GIT-SUBTREE(1)
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