6 git-subtree - Merge subtrees together and split repository into subtrees
12 'git subtree' [<options>] -P <prefix> add <local-commit>
13 'git subtree' [<options>] -P <prefix> add <repository> <remote-ref>
14 'git subtree' [<options>] -P <prefix> merge <local-commit>
15 'git subtree' [<options>] -P <prefix> split [<local-commit>]
18 'git subtree' [<options>] -P <prefix> pull <repository> <remote-ref>
19 'git subtree' [<options>] -P <prefix> push <repository> <refspec>
23 Subtrees allow subprojects to be included within a subdirectory
24 of the main project, optionally including the subproject's
27 For example, you could include the source code for a library
28 as a subdirectory of your application.
30 Subtrees are not to be confused with submodules, which are meant for
31 the same task. Unlike submodules, subtrees do not need any special
32 constructions (like '.gitmodules' files or gitlinks) be present in
33 your repository, and do not force end-users of your
34 repository to do anything special or to understand how subtrees
35 work. A subtree is just a subdirectory that can be
36 committed to, branched, and merged along with your project in
39 They are also not to be confused with using the subtree merge
40 strategy. The main difference is that, besides merging
41 the other project as a subdirectory, you can also extract the
42 entire history of a subdirectory from your project and make it
43 into a standalone project. Unlike the subtree merge strategy
44 you can alternate back and forth between these
45 two operations. If the standalone library gets updated, you can
46 automatically merge the changes into your project; if you
47 update the library inside your project, you can "split" the
48 changes back out again and merge them back into the library
51 For example, if a library you made for one application ends up being
52 useful elsewhere, you can extract its entire history and publish
53 that as its own git repository, without accidentally
54 intermingling the history of your application project.
57 In order to keep your commit messages clean, we recommend that
58 people split their commits between the subtrees and the main
59 project as much as possible. That is, if you make a change that
60 affects both the library and the main application, commit it in
61 two pieces. That way, when you split the library commits out
62 later, their descriptions will still make sense. But if this
63 isn't important to you, it's not *necessary*. 'git subtree' will
64 simply leave out the non-library-related parts of the commit
65 when it splits it out into the subproject later.
71 add <repository> <remote-ref>::
72 Create the <prefix> subtree by importing its contents
73 from the given <local-commit> or <repository> and <remote-ref>.
74 A new commit is created automatically, joining the imported
75 project's history with your own. With '--squash', import
76 only a single commit from the subproject, rather than its
79 merge <local-commit>::
80 Merge recent changes up to <local-commit> into the <prefix>
81 subtree. As with normal 'git merge', this doesn't
82 remove your own local changes; it just merges those
83 changes into the latest <local-commit>. With '--squash',
84 create only one commit that contains all the changes,
85 rather than merging in the entire history.
87 If you use '--squash', the merge direction doesn't always have to be
88 forward; you can use this command to go back in time from v2.5 to v2.4,
89 for example. If your merge introduces a conflict, you can resolve it in
92 split [<local-commit>]::
93 Extract a new, synthetic project history from the
94 history of the <prefix> subtree of <local-commit>, or of
95 HEAD if no <local-commit> is given. The new history
96 includes only the commits (including merges) that
97 affected <prefix>, and each of those commits now has the
98 contents of <prefix> at the root of the project instead
99 of in a subdirectory. Thus, the newly created history
100 is suitable for export as a separate git repository.
102 After splitting successfully, a single commit ID is printed to stdout.
103 This corresponds to the HEAD of the newly created tree, which you can
104 manipulate however you want.
106 Repeated splits of exactly the same history are guaranteed to be
107 identical (i.e. to produce the same commit IDs) as long as the
108 settings passed to 'split' (such as '--annotate') are the same.
109 Because of this, if you add new commits and then re-split, the new
110 commits will be attached as commits on top of the history you
111 generated last time, so 'git merge' and friends will work as expected.
113 pull <repository> <remote-ref>::
114 Exactly like 'merge', but parallels 'git pull' in that
115 it fetches the given ref from the specified remote
118 push <repository> [+][<local-commit>:]<remote-ref>::
119 Does a 'split' using the <prefix> subtree of <local-commit>
120 and then does a 'git push' to push the result to the
121 <repository> and <remote-ref>. This can be used to push your
122 subtree to different branches of the remote repository. Just
123 as with 'split', if no <local-commit> is given, then HEAD is
124 used. The optional leading '+' is ignored.
126 OPTIONS FOR ALL COMMANDS
127 ------------------------
130 Suppress unnecessary output messages on stderr.
134 Produce even more unnecessary output messages on stderr.
138 Specify the path in the repository to the subtree you
139 want to manipulate. This option is mandatory
142 OPTIONS FOR 'add' AND 'merge' (ALSO: 'pull', 'split --rejoin', AND 'push --rejoin')
143 -----------------------------------------------------------------------------------
144 These options for 'add' and 'merge' may also be given to 'pull' (which
145 wraps 'merge'), 'split --rejoin' (which wraps either 'add' or 'merge'
146 as appropriate), and 'push --rejoin' (which wraps 'split --rejoin').
149 Instead of merging the entire history from the subtree project, produce
150 only a single commit that contains all the differences you want to
151 merge, and then merge that new commit into your project.
153 Using this option helps to reduce log clutter. People rarely want to see
154 every change that happened between v1.0 and v1.1 of the library they're
155 using, since none of the interim versions were ever included in their
158 Using '--squash' also helps avoid problems when the same subproject is
159 included multiple times in the same project, or is removed and then
160 re-added. In such a case, it doesn't make sense to combine the
161 histories anyway, since it's unclear which part of the history belongs
164 Furthermore, with '--squash', you can switch back and forth between
165 different versions of a subtree, rather than strictly forward. 'git
166 subtree merge --squash' always adjusts the subtree to match the exactly
167 specified commit, even if getting to that commit would require undoing
168 some changes that were added earlier.
170 Whether or not you use '--squash', changes made in your local repository
171 remain intact and can be later split and send upstream to the
175 --message=<message>::
176 Specify <message> as the commit message for the merge commit.
178 OPTIONS FOR 'split' (ALSO: 'push')
179 ----------------------------------
180 These options for 'split' may also be given to 'push' (which wraps
183 --annotate=<annotation>::
184 When generating synthetic history, add <annotation> as a prefix to each
185 commit message. Since we're creating new commits with the same commit
186 message, but possibly different content, from the original commits, this
187 can help to differentiate them and avoid confusion.
189 Whenever you split, you need to use the same <annotation>, or else you
190 don't have a guarantee that the new re-created history will be identical
191 to the old one. That will prevent merging from working correctly. git
192 subtree tries to make it work anyway, particularly if you use '--rejoin',
193 but it may not always be effective.
197 After generating the synthetic history, create a new branch called
198 <branch> that contains the new history. This is suitable for immediate
199 pushing upstream. <branch> must not already exist.
202 If you use '--rejoin', git subtree attempts to optimize its history
203 reconstruction to generate only the new commits since the last
204 '--rejoin'. '--ignore-joins' disables this behavior, forcing it to
205 regenerate the entire history. In a large project, this can take a long
209 If your subtree was originally imported using something other than git
210 subtree, its history may not match what git subtree is expecting. In
211 that case, you can specify the commit ID <onto> that corresponds to the
212 first revision of the subproject's history that was imported into your
213 project, and git subtree will attempt to build its history from there.
215 If you used 'git subtree add', you should never need this option.
218 After splitting, merge the newly created synthetic history back into
219 your main project. That way, future splits can search only the part of
220 history that has been added since the most recent '--rejoin'.
222 If your split commits end up merged into the upstream subproject, and
223 then you want to get the latest upstream version, this will allow git's
224 merge algorithm to more intelligently avoid conflicts (since it knows
225 these synthetic commits are already part of the upstream repository).
227 Unfortunately, using this option results in 'git log' showing an extra
228 copy of every new commit that was created (the original, and the
231 If you do all your merges with '--squash', make sure you also use
232 '--squash' when you 'split --rejoin'.
235 EXAMPLE 1. 'add' command
236 ------------------------
237 Let's assume that you have a local repository that you would like
238 to add an external vendor library to. In this case we will add the
239 git-subtree repository as a subdirectory of your already existing
240 git-extensions repository in ~/git-extensions/:
242 $ git subtree add --prefix=git-subtree --squash \
243 git://github.com/apenwarr/git-subtree.git master
245 'master' needs to be a valid remote ref and can be a different branch
248 You can omit the '--squash' flag, but doing so will increase the number
249 of commits that are included in your local repository.
251 We now have a ~/git-extensions/git-subtree directory containing code
252 from the master branch of git://github.com/apenwarr/git-subtree.git
253 in our git-extensions repository.
255 EXAMPLE 2. Extract a subtree using 'commit', 'merge' and 'pull'
256 ---------------------------------------------------------------
257 Let's use the repository for the git source code as an example.
258 First, get your own copy of the git.git repository:
260 $ git clone git://git.kernel.org/pub/scm/git/git.git test-git
263 gitweb (commit 1130ef3) was merged into git as of commit
264 0a8f4f0, after which it was no longer maintained separately.
265 But imagine it had been maintained separately, and we wanted to
266 extract git's changes to gitweb since that time, to share with
267 the upstream. You could do this:
269 $ git subtree split --prefix=gitweb --annotate='(split) ' \
270 0a8f4f0^.. --onto=1130ef3 --rejoin \
271 --branch gitweb-latest
273 $ git push git@github.com:whatever/gitweb.git gitweb-latest:master
275 (We use '0a8f4f0^..' because that means "all the changes from
276 0a8f4f0 to the current version, including 0a8f4f0 itself.")
278 If gitweb had originally been merged using 'git subtree add' (or
279 a previous split had already been done with '--rejoin' specified)
280 then you can do all your splits without having to remember any
283 $ git subtree split --prefix=gitweb --annotate='(split) ' --rejoin \
284 --branch gitweb-latest2
286 And you can merge changes back in from the upstream project just
289 $ git subtree pull --prefix=gitweb \
290 git@github.com:whatever/gitweb.git master
292 Or, using '--squash', you can actually rewind to an earlier
295 $ git subtree merge --prefix=gitweb --squash gitweb-latest~10
297 Then make some changes:
299 $ date >gitweb/myfile
300 $ git add gitweb/myfile
301 $ git commit -m 'created myfile'
303 And fast forward again:
305 $ git subtree merge --prefix=gitweb --squash gitweb-latest
307 And notice that your change is still intact:
309 $ ls -l gitweb/myfile
311 And you can split it out and look at your changes versus
314 git log gitweb-latest..$(git subtree split --prefix=gitweb)
316 EXAMPLE 3. Extract a subtree using a branch
317 -------------------------------------------
318 Suppose you have a source directory with many files and
319 subdirectories, and you want to extract the lib directory to its own
320 git project. Here's a short way to do it:
322 First, make the new repository wherever you want:
324 $ <go to the new location>
327 Back in your original directory:
329 $ git subtree split --prefix=lib --annotate="(split)" -b split
331 Then push the new branch onto the new empty repository:
333 $ git push <new-repo> split:master
338 Written by Avery Pennarun <apenwarr@gmail.com>
343 Part of the linkgit:git[1] suite