rebase: teach rebase --keep-base
[git/git.git] / contrib / subtree / git-subtree.txt
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1git-subtree(1)
2==============
3
4NAME
5----
7f86ff0f 6git-subtree - Merge subtrees together and split repository into subtrees
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7
8
9SYNOPSIS
10--------
11[verse]
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12'git subtree' add -P <prefix> <commit>
13'git subtree' add -P <prefix> <repository> <ref>
14'git subtree' pull -P <prefix> <repository> <ref>
15'git subtree' push -P <prefix> <repository> <ref>
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16'git subtree' merge -P <prefix> <commit>
17'git subtree' split -P <prefix> [OPTIONS] [<commit>]
7f86ff0f 18
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19
20DESCRIPTION
21-----------
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22Subtrees allow subprojects to be included within a subdirectory
23of the main project, optionally including the subproject's
24entire history.
e75d1da3 25
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26For example, you could include the source code for a library
27as a subdirectory of your application.
28
29Subtrees are not to be confused with submodules, which are meant for
30the same task. Unlike submodules, subtrees do not need any special
5aea9fe6 31constructions (like .gitmodules files or gitlinks) be present in
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32your repository, and do not force end-users of your
33repository to do anything special or to understand how subtrees
34work. A subtree is just a subdirectory that can be
35committed to, branched, and merged along with your project in
36any way you want.
37
9a40fcc2 38They are also not to be confused with using the subtree merge
7f86ff0f 39strategy. The main difference is that, besides merging
9a40fcc2 40the other project as a subdirectory, you can also extract the
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41entire history of a subdirectory from your project and make it
42into a standalone project. Unlike the subtree merge strategy
43you can alternate back and forth between these
44two operations. If the standalone library gets updated, you can
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45automatically merge the changes into your project; if you
46update the library inside your project, you can "split" the
47changes back out again and merge them back into the library
48project.
49
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50For example, if a library you made for one application ends up being
51useful elsewhere, you can extract its entire history and publish
52that as its own git repository, without accidentally
53intermingling the history of your application project.
e75d1da3 54
7f86ff0f 55[TIP]
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56In order to keep your commit messages clean, we recommend that
57people split their commits between the subtrees and the main
58project as much as possible. That is, if you make a change that
59affects both the library and the main application, commit it in
60two pieces. That way, when you split the library commits out
61later, their descriptions will still make sense. But if this
62isn't important to you, it's not *necessary*. git subtree will
63simply leave out the non-library-related parts of the commit
64when it splits it out into the subproject later.
65
66
67COMMANDS
68--------
69add::
70 Create the <prefix> subtree by importing its contents
1c3e0f00 71 from the given <commit> or <repository> and remote <ref>.
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72 A new commit is created automatically, joining the imported
73 project's history with your own. With '--squash', imports
74 only a single commit from the subproject, rather than its
75 entire history.
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76
77merge::
78 Merge recent changes up to <commit> into the <prefix>
79 subtree. As with normal 'git merge', this doesn't
80 remove your own local changes; it just merges those
81 changes into the latest <commit>. With '--squash',
82 creates only one commit that contains all the changes,
83 rather than merging in the entire history.
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84+
85If you use '--squash', the merge direction doesn't always have to be
86forward; you can use this command to go back in time from v2.5 to v2.4,
87for example. If your merge introduces a conflict, you can resolve it in
88the usual ways.
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89
90pull::
91 Exactly like 'merge', but parallels 'git pull' in that
1c3e0f00 92 it fetches the given ref from the specified remote
e75d1da3 93 repository.
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94
95push::
248a8849 96 Does a 'split' (see below) using the <prefix> supplied
c00d1d11 97 and then does a 'git push' to push the result to the
1c3e0f00 98 repository and ref. This can be used to push your
c00d1d11 99 subtree to different branches of the remote repository.
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100
101split::
102 Extract a new, synthetic project history from the
103 history of the <prefix> subtree. The new history
104 includes only the commits (including merges) that
105 affected <prefix>, and each of those commits now has the
106 contents of <prefix> at the root of the project instead
107 of in a subdirectory. Thus, the newly created history
108 is suitable for export as a separate git repository.
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109+
110After splitting successfully, a single commit id is printed to stdout.
111This corresponds to the HEAD of the newly created tree, which you can
112manipulate however you want.
113+
114Repeated splits of exactly the same history are guaranteed to be
115identical (i.e. to produce the same commit ids). Because of this, if
116you add new commits and then re-split, the new commits will be attached
117as commits on top of the history you generated last time, so 'git merge'
118and friends will work as expected.
119+
120Note that if you use '--squash' when you merge, you should usually not
121just '--rejoin' when you split.
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122
123
124OPTIONS
125-------
126-q::
127--quiet::
128 Suppress unnecessary output messages on stderr.
129
130-d::
131--debug::
132 Produce even more unnecessary output messages on stderr.
133
7f86ff0f 134-P <prefix>::
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135--prefix=<prefix>::
136 Specify the path in the repository to the subtree you
7f86ff0f 137 want to manipulate. This option is mandatory
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138 for all commands.
139
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140-m <message>::
141--message=<message>::
142 This option is only valid for add, merge and pull (unsure).
143 Specify <message> as the commit message for the merge commit.
e75d1da3 144
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145
146OPTIONS FOR add, merge, push, pull
147----------------------------------
e75d1da3 148--squash::
6ccc71a9 149 This option is only valid for add, merge, and pull
7f86ff0f 150 commands.
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151+
152Instead of merging the entire history from the subtree project, produce
153only a single commit that contains all the differences you want to
154merge, and then merge that new commit into your project.
155+
156Using this option helps to reduce log clutter. People rarely want to see
157every change that happened between v1.0 and v1.1 of the library they're
158using, since none of the interim versions were ever included in their
159application.
160+
161Using '--squash' also helps avoid problems when the same subproject is
162included multiple times in the same project, or is removed and then
163re-added. In such a case, it doesn't make sense to combine the
164histories anyway, since it's unclear which part of the history belongs
165to which subtree.
166+
167Furthermore, with '--squash', you can switch back and forth between
168different versions of a subtree, rather than strictly forward. 'git
169subtree merge --squash' always adjusts the subtree to match the exactly
170specified commit, even if getting to that commit would require undoing
171some changes that were added earlier.
172+
173Whether or not you use '--squash', changes made in your local repository
174remain intact and can be later split and send upstream to the
175subproject.
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176
177
178OPTIONS FOR split
179-----------------
180--annotate=<annotation>::
7f86ff0f 181 This option is only valid for the split command.
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182+
183When generating synthetic history, add <annotation> as a prefix to each
184commit message. Since we're creating new commits with the same commit
185message, but possibly different content, from the original commits, this
186can help to differentiate them and avoid confusion.
187+
188Whenever you split, you need to use the same <annotation>, or else you
189don't have a guarantee that the new re-created history will be identical
190to the old one. That will prevent merging from working correctly. git
191subtree tries to make it work anyway, particularly if you use --rejoin,
192but it may not always be effective.
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193
194-b <branch>::
195--branch=<branch>::
7f86ff0f 196 This option is only valid for the split command.
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197+
198After generating the synthetic history, create a new branch called
199<branch> that contains the new history. This is suitable for immediate
200pushing upstream. <branch> must not already exist.
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201
202--ignore-joins::
7f86ff0f 203 This option is only valid for the split command.
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204+
205If you use '--rejoin', git subtree attempts to optimize its history
206reconstruction to generate only the new commits since the last
207'--rejoin'. '--ignore-join' disables this behaviour, forcing it to
208regenerate the entire history. In a large project, this can take a long
209time.
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210
211--onto=<onto>::
7f86ff0f 212 This option is only valid for the split command.
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213+
214If your subtree was originally imported using something other than git
215subtree, its history may not match what git subtree is expecting. In
216that case, you can specify the commit id <onto> that corresponds to the
217first revision of the subproject's history that was imported into your
218project, and git subtree will attempt to build its history from there.
219+
220If you used 'git subtree add', you should never need this option.
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221
222--rejoin::
7f86ff0f 223 This option is only valid for the split command.
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224+
225After splitting, merge the newly created synthetic history back into
226your main project. That way, future splits can search only the part of
227history that has been added since the most recent --rejoin.
228+
229If your split commits end up merged into the upstream subproject, and
230then you want to get the latest upstream version, this will allow git's
231merge algorithm to more intelligently avoid conflicts (since it knows
232these synthetic commits are already part of the upstream repository).
233+
234Unfortunately, using this option results in 'git log' showing an extra
235copy of every new commit that was created (the original, and the
236synthetic one).
237+
238If you do all your merges with '--squash', don't use '--rejoin' when you
239split, because you don't want the subproject's history to be part of
240your project anyway.
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241
242
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243EXAMPLE 1. Add command
244----------------------
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245Let's assume that you have a local repository that you would like
246to add an external vendor library to. In this case we will add the
247git-subtree repository as a subdirectory of your already existing
242b20dc 248git-extensions repository in ~/git-extensions/:
c6ca48d4 249
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250 $ git subtree add --prefix=git-subtree --squash \
251 git://github.com/apenwarr/git-subtree.git master
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252
253'master' needs to be a valid remote ref and can be a different branch
254name
255
c6ca48d4 256You can omit the --squash flag, but doing so will increase the number
98e023de 257of commits that are included in your local repository.
c6ca48d4 258
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259We now have a ~/git-extensions/git-subtree directory containing code
260from the master branch of git://github.com/apenwarr/git-subtree.git
261in our git-extensions repository.
c6ca48d4 262
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263EXAMPLE 2. Extract a subtree using commit, merge and pull
264---------------------------------------------------------
c6ca48d4 265Let's use the repository for the git source code as an example.
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266First, get your own copy of the git.git repository:
267
268 $ git clone git://git.kernel.org/pub/scm/git/git.git test-git
269 $ cd test-git
270
271gitweb (commit 1130ef3) was merged into git as of commit
2720a8f4f0, after which it was no longer maintained separately.
273But imagine it had been maintained separately, and we wanted to
274extract git's changes to gitweb since that time, to share with
275the upstream. You could do this:
276
277 $ git subtree split --prefix=gitweb --annotate='(split) ' \
278 0a8f4f0^.. --onto=1130ef3 --rejoin \
279 --branch gitweb-latest
280 $ gitk gitweb-latest
b64a7aa2 281 $ git push git@github.com:whatever/gitweb.git gitweb-latest:master
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282
283(We use '0a8f4f0^..' because that means "all the changes from
2840a8f4f0 to the current version, including 0a8f4f0 itself.")
285
286If gitweb had originally been merged using 'git subtree add' (or
287a previous split had already been done with --rejoin specified)
288then you can do all your splits without having to remember any
289weird commit ids:
290
291 $ git subtree split --prefix=gitweb --annotate='(split) ' --rejoin \
292 --branch gitweb-latest2
293
294And you can merge changes back in from the upstream project just
295as easily:
296
297 $ git subtree pull --prefix=gitweb \
e1ce417d 298 git@github.com:whatever/gitweb.git master
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299
300Or, using '--squash', you can actually rewind to an earlier
301version of gitweb:
302
303 $ git subtree merge --prefix=gitweb --squash gitweb-latest~10
304
305Then make some changes:
306
307 $ date >gitweb/myfile
308 $ git add gitweb/myfile
309 $ git commit -m 'created myfile'
310
311And fast forward again:
312
313 $ git subtree merge --prefix=gitweb --squash gitweb-latest
314
315And notice that your change is still intact:
316
317 $ ls -l gitweb/myfile
318
319And you can split it out and look at your changes versus
320the standard gitweb:
321
322 git log gitweb-latest..$(git subtree split --prefix=gitweb)
323
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324EXAMPLE 3. Extract a subtree using branch
325-----------------------------------------
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326Suppose you have a source directory with many files and
327subdirectories, and you want to extract the lib directory to its own
328git project. Here's a short way to do it:
329
330First, make the new repository wherever you want:
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331
332 $ <go to the new location>
333 $ git init --bare
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334
335Back in your original directory:
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336
337 $ git subtree split --prefix=lib --annotate="(split)" -b split
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338
339Then push the new branch onto the new empty repository:
37668a13 340
7f86ff0f 341 $ git push <new-repo> split:master
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344AUTHOR
345------
346Written by Avery Pennarun <apenwarr@gmail.com>
347
348
349GIT
350---
351Part of the linkgit:git[1] suite