1GIT-SUBTREE(1) Git Manual GIT-SUBTREE(1)
2
6 git-subtree - Merge subtrees together and split repository into
7 subtrees
8
10 git subtree add -P <prefix> <refspec>
11 git subtree add -P <prefix> <repository> <refspec>
12 git subtree pull -P <prefix> <repository> <refspec...>
13 git subtree push -P <prefix> <repository> <refspec...>
14 git subtree merge -P <prefix> <commit>
15 git subtree split -P <prefix> [OPTIONS] [<commit>]
16
18 Subtrees allow subprojects to be included within a subdirectory of the
19 main project, optionally including the subproject’s entire history.
20 For example, you could include the source code for a library as a
22 subdirectory of your application.
23 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 .gitmodule 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 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 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 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
59 add
60 Create the <prefix> subtree by importing its contents from the
61 given <refspec> or <repository> and remote <refspec>. A new commit
62 is created automatically, joining the imported project’s history
63 with your own. With --squash, imports only a single commit from the
64 subproject, rather than its entire history.
65 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 If you use '--squash', the merge direction doesn't
74 always have to be forward; you can use this command to
75 go back in time from v2.5 to v2.4, for example. If your
76 merge introduces a conflict, you can resolve it in the
77 usual ways.
78 pull
80 Exactly like merge, but parallels git pull in that it fetches the
81 given commit from the specified remote repository.
82 push
84 Does a split (see below) using the <prefix> supplied and then does
85 a git push to push the result to the repository and refspec. This
86 can be used to push your subtree to different branches of the
87 remote repository.
88 split
90 Extract a new, synthetic project history from the history of the
91 <prefix> subtree. The new history includes only the commits
92 (including merges) that affected <prefix>, and each of those
93 commits now has the contents of <prefix> at the root of the project
94 instead of in a subdirectory. Thus, the newly created history is
95 suitable for export as a separate git repository.
96 After splitting successfully, a single commit id is
98 printed to stdout. This corresponds to the HEAD of the
99 newly created tree, which you can manipulate however you
100 want.
101 Repeated splits of exactly the same history are
103 guaranteed to be identical (ie. to produce the same
104 commit ids). Because of this, if you add new commits
105 and then re-split, the new commits will be attached as
106 commits on top of the history you generated last time,
107 so 'git merge' and friends will work as expected.
108 Note that if you use '--squash' when you merge, you
110 should usually not just '--rejoin' when you split.
111
113 -q, --quiet
114 Suppress unnecessary output messages on stderr.
115 -d, --debug
117 Produce even more unnecessary output messages on stderr.
118 -P <prefix>, --prefix=<prefix>
120 Specify the path in the repository to the subtree you want to
121 manipulate. This option is mandatory for all commands.
122 -m <message>, --message=<message>
124 This option is only valid for add, merge and pull (unsure). Specify
125 <message> as the commit message for the merge commit.
126
128 --squash
129 This option is only valid for add, merge, push and pull commands.
130 Instead of merging the entire history from the subtree
132 project, produce only a single commit that contains all
133 the differences you want to merge, and then merge that
134 new commit into your project.
135 Using this option helps to reduce log clutter. People
137 rarely want to see every change that happened between
138 v1.0 and v1.1 of the library they're using, since none of the
139 interim versions were ever included in their application.
140 Using '--squash' also helps avoid problems when the same
142 subproject is included multiple times in the same
143 project, or is removed and then re-added. In such a
144 case, it doesn't make sense to combine the histories
145 anyway, since it's unclear which part of the history
146 belongs to which subtree.
147 Furthermore, with '--squash', you can switch back and
149 forth between different versions of a subtree, rather
150 than strictly forward. 'git subtree merge --squash'
151 always adjusts the subtree to match the exactly
152 specified commit, even if getting to that commit would
153 require undoing some changes that were added earlier.
154 Whether or not you use '--squash', changes made in your
156 local repository remain intact and can be later split
157 and send upstream to the subproject.
158
160 --annotate=<annotation>
161 This option is only valid for the split command.
162 When generating synthetic history, add <annotation> as a
164 prefix to each commit message. Since we're creating new
165 commits with the same commit message, but possibly
166 different content, from the original commits, this can help
167 to differentiate them and avoid confusion.
168 Whenever you split, you need to use the same
170 <annotation>, or else you don't have a guarantee that
171 the new re-created history will be identical to the old
172 one. That will prevent merging from working correctly.
173 git subtree tries to make it work anyway, particularly
174 if you use --rejoin, but it may not always be effective.
175 -b <branch>, --branch=<branch>
177 This option is only valid for the split command.
178 After generating the synthetic history, create a new
180 branch called <branch> that contains the new history.
181 This is suitable for immediate pushing upstream.
182 <branch> must not already exist.
183 --ignore-joins
185 This option is only valid for the split command.
186 If you use '--rejoin', git subtree attempts to optimize
188 its history reconstruction to generate only the new
189 commits since the last '--rejoin'. '--ignore-join'
190 disables this behaviour, forcing it to regenerate the
191 entire history. In a large project, this can take a
192 long time.
193 --onto=<onto>
195 This option is only valid for the split command.
196 If your subtree was originally imported using something
198 other than git subtree, its history may not match what
199 git subtree is expecting. In that case, you can specify
200 the commit id <onto> that corresponds to the first
201 revision of the subproject's history that was imported
202 into your project, and git subtree will attempt to build
203 its history from there.
204 If you used 'git subtree add', you should never need
206 this option.
207 --rejoin
209 This option is only valid for the split command.
210 After splitting, merge the newly created synthetic
212 history back into your main project. That way, future
213 splits can search only the part of history that has
214 been added since the most recent --rejoin.
215 If your split commits end up merged into the upstream
217 subproject, and then you want to get the latest upstream
218 version, this will allow git's merge algorithm to more
219 intelligently avoid conflicts (since it knows these
220 synthetic commits are already part of the upstream
221 repository).
222 Unfortunately, using this option results in 'git log'
224 showing an extra copy of every new commit that was
225 created (the original, and the synthetic one).
226 If you do all your merges with '--squash', don't use
228 '--rejoin' when you split, because you don't want the
229 subproject's history to be part of your project anyway.
230
232 Let’s assume that you have a local repository that you would like to
233 add an external vendor library to. In this case we will add the
234 git-subtree repository as a subdirectory of your already existing
235 git-extensions repository in ~/git-extensions/:
236 $ git subtree add --prefix=git-subtree --squash \
238 git://github.com/apenwarr/git-subtree.git master
239 master needs to be a valid remote ref and can be a different branch
241 name
242 You can omit the --squash flag, but doing so will increase the number
244 of commits that are incldued in your local repository.
245 We now have a ~/git-extensions/git-subtree directory containing code
247 from the master branch of git://github.com/apenwarr/git-subtree.git in
248 our git-extensions repository.
249
251 Let’s use the repository for the git source code as an example. First,
252 get your own copy of the git.git repository:
253 $ git clone git://git.kernel.org/pub/scm/git/git.git test-git
255 $ cd test-git
256 gitweb (commit 1130ef3) was merged into git as of commit 0a8f4f0, after
258 which it was no longer maintained separately. But imagine it had been
259 maintained separately, and we wanted to extract git’s changes to gitweb
260 since that time, to share with the upstream. You could do this:
261 $ git subtree split --prefix=gitweb --annotate='(split) ' \
263 0a8f4f0^.. --onto=1130ef3 --rejoin \
264 --branch gitweb-latest
265 $ gitk gitweb-latest
266 $ git push git@github.com:whatever/gitweb.git gitweb-latest:master
267 (We use 0a8f4f0^.. because that means "all the changes from 0a8f4f0 to
269 the current version, including 0a8f4f0 itself.")
270 If gitweb had originally been merged using git subtree add (or a
272 previous split had already been done with --rejoin specified) then you
273 can do all your splits without having to remember any weird commit ids:
274 $ git subtree split --prefix=gitweb --annotate='(split) ' --rejoin \
276 --branch gitweb-latest2
277 And you can merge changes back in from the upstream project just as
279 easily:
280 $ git subtree pull --prefix=gitweb \
282 git@github.com:whatever/gitweb.git master
283 Or, using --squash, you can actually rewind to an earlier version of
285 gitweb:
286 $ git subtree merge --prefix=gitweb --squash gitweb-latest~10
288 Then make some changes:
290 $ date >gitweb/myfile
292 $ git add gitweb/myfile
293 $ git commit -m 'created myfile'
294 And fast forward again:
296 $ git subtree merge --prefix=gitweb --squash gitweb-latest
298 And notice that your change is still intact:
300 $ ls -l gitweb/myfile
302 And you can split it out and look at your changes versus the standard
304 gitweb:
305 git log gitweb-latest..$(git subtree split --prefix=gitweb)
307
309 Suppose you have a source directory with many files and subdirectories,
310 and you want to extract the lib directory to its own git project.
311 Here’s a short way to do it:
312 First, make the new repository wherever you want:
314 $ <go to the new location>
316 $ git init --bare
317 Back in your original directory:
319 $ git subtree split --prefix=lib --annotate="(split)" -b split
321 Then push the new branch onto the new empty repository:
323 $ git push <new-repo> split:master
325
327 Written by Avery Pennarun <apenwarr@gmail.com[1]>
328
330 Part of the git(1) suite
331
333 1. apenwarr@gmail.com
334 mailto:apenwarr@gmail.com
335Git 11/19/2018 GIT-SUBTREE(1)