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1git-subtree(1)
2==============
3
4NAME
5----
6git-subtree - Merge subtrees together and split repository into subtrees
7
8
9SYNOPSIS
10--------
11[verse]
12'git subtree' [<options>] -P <prefix> [-S[<keyid>]] add <local-commit>
13'git subtree' [<options>] -P <prefix> [-S[<keyid>]] add <repository> <remote-ref>
14'git subtree' [<options>] -P <prefix> [-S[<keyid>]] merge <local-commit> [<repository>]
15'git subtree' [<options>] -P <prefix> [-S[<keyid>]] split [<local-commit>]
16
17[verse]
18'git subtree' [<options>] -P <prefix> [-S[<keyid>]] pull <repository> <remote-ref>
19'git subtree' [<options>] -P <prefix> [-S[<keyid>]] push <repository> <refspec>
20
21DESCRIPTION
22-----------
23Subtrees allow subprojects to be included within a subdirectory
24of the main project, optionally including the subproject's
25entire history.
26
27For example, you could include the source code for a library
28as a subdirectory of your application.
29
30Subtrees are not to be confused with submodules, which are meant for
31the same task. Unlike submodules, subtrees do not need any special
32constructions (like '.gitmodules' files or gitlinks) be present in
33your repository, and do not force end-users of your
34repository to do anything special or to understand how subtrees
35work. A subtree is just a subdirectory that can be
36committed to, branched, and merged along with your project in
37any way you want.
38
39They are also not to be confused with using the subtree merge
40strategy. The main difference is that, besides merging
41the other project as a subdirectory, you can also extract the
42entire history of a subdirectory from your project and make it
43into a standalone project. Unlike the subtree merge strategy
44you can alternate back and forth between these
45two operations. If the standalone library gets updated, you can
46automatically merge the changes into your project; if you
47update the library inside your project, you can "split" the
48changes back out again and merge them back into the library
49project.
50
51For example, if a library you made for one application ends up being
52useful elsewhere, you can extract its entire history and publish
53that as its own git repository, without accidentally
54intermingling the history of your application project.
55
56[TIP]
57In order to keep your commit messages clean, we recommend that
58people split their commits between the subtrees and the main
59project as much as possible. That is, if you make a change that
60affects both the library and the main application, commit it in
61two pieces. That way, when you split the library commits out
62later, their descriptions will still make sense. But if this
63isn't important to you, it's not *necessary*. 'git subtree' will
64simply leave out the non-library-related parts of the commit
65when it splits it out into the subproject later.
66
67
68COMMANDS
69--------
70add <local-commit>::
71add <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
77 entire history.
78
79merge <local-commit> [<repository>]::
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.
86+
87If you use '--squash', the merge direction doesn't always have to be
88forward; you can use this command to go back in time from v2.5 to v2.4,
89for example. If your merge introduces a conflict, you can resolve it in
90the usual ways.
91+
92When using '--squash', and the previous merge with '--squash' merged an
93annotated tag of the subtree repository, that tag needs to be available locally.
94If <repository> is given, a missing tag will automatically be fetched from that
95repository.
96
97split [<local-commit>] [<repository>]::
98 Extract a new, synthetic project history from the
99 history of the <prefix> subtree of <local-commit>, or of
100 HEAD if no <local-commit> is given. The new history
101 includes only the commits (including merges) that
102 affected <prefix>, and each of those commits now has the
103 contents of <prefix> at the root of the project instead
104 of in a subdirectory. Thus, the newly created history
105 is suitable for export as a separate git repository.
106+
107After splitting successfully, a single commit ID is printed to stdout.
108This corresponds to the HEAD of the newly created tree, which you can
109manipulate however you want.
110+
111Repeated splits of exactly the same history are guaranteed to be
112identical (i.e. to produce the same commit IDs) as long as the
113settings passed to 'split' (such as '--annotate') are the same.
114Because of this, if you add new commits and then re-split, the new
115commits will be attached as commits on top of the history you
116generated last time, so 'git merge' and friends will work as expected.
117+
118When a previous merge with '--squash' merged an annotated tag of the
119subtree repository, that tag needs to be available locally.
120If <repository> is given, a missing tag will automatically be fetched from that
121repository.
122
123pull <repository> <remote-ref>::
124 Exactly like 'merge', but parallels 'git pull' in that
125 it fetches the given ref from the specified remote
126 repository.
127
128push <repository> [+][<local-commit>:]<remote-ref>::
129 Does a 'split' using the <prefix> subtree of <local-commit>
130 and then does a 'git push' to push the result to the
131 <repository> and <remote-ref>. This can be used to push your
132 subtree to different branches of the remote repository. Just
133 as with 'split', if no <local-commit> is given, then HEAD is
134 used. The optional leading '+' is ignored.
135
136OPTIONS FOR ALL COMMANDS
137------------------------
138-q::
139--quiet::
140 Suppress unnecessary output messages on stderr.
141
142-d::
143--debug::
144 Produce even more unnecessary output messages on stderr.
145
146-P <prefix>::
147--prefix=<prefix>::
148 Specify the path in the repository to the subtree you
149 want to manipulate. This option is mandatory
150 for all commands.
151
152-S[<keyid>]::
153--gpg-sign[=<keyid>]::
154--no-gpg-sign::
155 GPG-sign commits. The `keyid` argument is optional and
156 defaults to the committer identity; `--no-gpg-sign` is useful to
157 countermand a `--gpg-sign` option given earlier on the command line.
158
159OPTIONS FOR 'add' AND 'merge' (ALSO: 'pull', 'split --rejoin', AND 'push --rejoin')
160-----------------------------------------------------------------------------------
161These options for 'add' and 'merge' may also be given to 'pull' (which
162wraps 'merge'), 'split --rejoin' (which wraps either 'add' or 'merge'
163as appropriate), and 'push --rejoin' (which wraps 'split --rejoin').
164
165--squash::
166 Instead of merging the entire history from the subtree project, produce
167 only a single commit that contains all the differences you want to
168 merge, and then merge that new commit into your project.
169+
170Using this option helps to reduce log clutter. People rarely want to see
171every change that happened between v1.0 and v1.1 of the library they're
172using, since none of the interim versions were ever included in their
173application.
174+
175Using '--squash' also helps avoid problems when the same subproject is
176included multiple times in the same project, or is removed and then
177re-added. In such a case, it doesn't make sense to combine the
178histories anyway, since it's unclear which part of the history belongs
179to which subtree.
180+
181Furthermore, with '--squash', you can switch back and forth between
182different versions of a subtree, rather than strictly forward. 'git
183subtree merge --squash' always adjusts the subtree to match the exactly
184specified commit, even if getting to that commit would require undoing
185some changes that were added earlier.
186+
187Whether or not you use '--squash', changes made in your local repository
188remain intact and can be later split and send upstream to the
189subproject.
190
191-m <message>::
192--message=<message>::
193 Specify <message> as the commit message for the merge commit.
194
195OPTIONS FOR 'split' (ALSO: 'push')
196----------------------------------
197These options for 'split' may also be given to 'push' (which wraps
198'split').
199
200--annotate=<annotation>::
201 When generating synthetic history, add <annotation> as a prefix to each
202 commit message. Since we're creating new commits with the same commit
203 message, but possibly different content, from the original commits, this
204 can help to differentiate them and avoid confusion.
205+
206Whenever you split, you need to use the same <annotation>, or else you
207don't have a guarantee that the new re-created history will be identical
208to the old one. That will prevent merging from working correctly. git
209subtree tries to make it work anyway, particularly if you use '--rejoin',
210but it may not always be effective.
211
212-b <branch>::
213--branch=<branch>::
214 After generating the synthetic history, create a new branch called
215 <branch> that contains the new history. This is suitable for immediate
216 pushing upstream. <branch> must not already exist.
217
218--ignore-joins::
219 If you use '--rejoin', git subtree attempts to optimize its history
220 reconstruction to generate only the new commits since the last
221 '--rejoin'. '--ignore-joins' disables this behavior, forcing it to
222 regenerate the entire history. In a large project, this can take a long
223 time.
224
225--onto=<onto>::
226 If your subtree was originally imported using something other than git
227 subtree, its history may not match what git subtree is expecting. In
228 that case, you can specify the commit ID <onto> that corresponds to the
229 first revision of the subproject's history that was imported into your
230 project, and git subtree will attempt to build its history from there.
231+
232If you used 'git subtree add', you should never need this option.
233
234--rejoin::
235 After splitting, merge the newly created synthetic history back into
236 your main project. That way, future splits can search only the part of
237 history that has been added since the most recent '--rejoin'.
238+
239If your split commits end up merged into the upstream subproject, and
240then you want to get the latest upstream version, this will allow git's
241merge algorithm to more intelligently avoid conflicts (since it knows
242these synthetic commits are already part of the upstream repository).
243+
244Unfortunately, using this option results in 'git log' showing an extra
245copy of every new commit that was created (the original, and the
246synthetic one).
247+
248If you do all your merges with '--squash', make sure you also use
249'--squash' when you 'split --rejoin'.
250
251
252EXAMPLE 1. 'add' command
253------------------------
254Let's assume that you have a local repository that you would like
255to add an external vendor library to. In this case we will add the
256git-subtree repository as a subdirectory of your already existing
257git-extensions repository in ~/git-extensions/:
258
259 $ git subtree add --prefix=git-subtree --squash \
260 git://github.com/apenwarr/git-subtree.git master
261
262'master' needs to be a valid remote ref and can be a different branch
263name
264
265You can omit the '--squash' flag, but doing so will increase the number
266of commits that are included in your local repository.
267
268We now have a ~/git-extensions/git-subtree directory containing code
269from the master branch of git://github.com/apenwarr/git-subtree.git
270in our git-extensions repository.
271
272EXAMPLE 2. Extract a subtree using 'commit', 'merge' and 'pull'
273---------------------------------------------------------------
274Let's use the repository for the git source code as an example.
275First, get your own copy of the git.git repository:
276
277 $ git clone git://git.kernel.org/pub/scm/git/git.git test-git
278 $ cd test-git
279
280gitweb (commit 1130ef3) was merged into git as of commit
2810a8f4f0, after which it was no longer maintained separately.
282But imagine it had been maintained separately, and we wanted to
283extract git's changes to gitweb since that time, to share with
284the upstream. You could do this:
285
286 $ git subtree split --prefix=gitweb --annotate='(split) ' \
287 0a8f4f0^.. --onto=1130ef3 --rejoin \
288 --branch gitweb-latest
289 $ gitk gitweb-latest
290 $ git push git@github.com:whatever/gitweb.git gitweb-latest:master
291
292(We use '0a8f4f0^..' because that means "all the changes from
2930a8f4f0 to the current version, including 0a8f4f0 itself.")
294
295If gitweb had originally been merged using 'git subtree add' (or
296a previous split had already been done with '--rejoin' specified)
297then you can do all your splits without having to remember any
298weird commit IDs:
299
300 $ git subtree split --prefix=gitweb --annotate='(split) ' --rejoin \
301 --branch gitweb-latest2
302
303And you can merge changes back in from the upstream project just
304as easily:
305
306 $ git subtree pull --prefix=gitweb \
307 git@github.com:whatever/gitweb.git master
308
309Or, using '--squash', you can actually rewind to an earlier
310version of gitweb:
311
312 $ git subtree merge --prefix=gitweb --squash gitweb-latest~10
313
314Then make some changes:
315
316 $ date >gitweb/myfile
317 $ git add gitweb/myfile
318 $ git commit -m 'created myfile'
319
320And fast forward again:
321
322 $ git subtree merge --prefix=gitweb --squash gitweb-latest
323
324And notice that your change is still intact:
325
326 $ ls -l gitweb/myfile
327
328And you can split it out and look at your changes versus
329the standard gitweb:
330
331 git log gitweb-latest..$(git subtree split --prefix=gitweb)
332
333EXAMPLE 3. Extract a subtree using a branch
334-------------------------------------------
335Suppose you have a source directory with many files and
336subdirectories, and you want to extract the lib directory to its own
337git project. Here's a short way to do it:
338
339First, make the new repository wherever you want:
340
341 $ <go to the new location>
342 $ git init --bare
343
344Back in your original directory:
345
346 $ git subtree split --prefix=lib --annotate="(split)" -b split
347
348Then push the new branch onto the new empty repository:
349
350 $ git push <new-repo> split:master
351
352
353AUTHOR
354------
355Written by Avery Pennarun <apenwarr@gmail.com>
356
357
358GIT
359---
360Part of the linkgit:git[1] suite