contrib/subtree/git-subtree.txt - jrn/git - Git at Google

 git-subtree(1)
 ==============

 NAME
 ----
 git-subtree - Merge subtrees together and split repository into subtrees


 SYNOPSIS
 --------
 [verse]
 'git subtree' [<options>] -P <prefix> add <local-commit>
 'git subtree' [<options>] -P <prefix> add <repository> <remote-ref>
 'git subtree' [<options>] -P <prefix> merge <local-commit> [<repository>]
 'git subtree' [<options>] -P <prefix> split [<local-commit>]

 [verse]
 'git subtree' [<options>] -P <prefix> pull <repository> <remote-ref>
 'git subtree' [<options>] -P <prefix> push <repository> <refspec>

 DESCRIPTION
 -----------
 Subtrees allow subprojects to be included within a subdirectory
 of the main project, optionally including the subproject's
 entire history.

 For example, you could include the source code for a library
 as a subdirectory of your application.

 Subtrees are not to be confused with submodules, which are meant for
 the same task. Unlike submodules, subtrees do not need any special
 constructions (like '.gitmodules' files or gitlinks) be present in
 your repository, and do not force end-users of your
 repository to do anything special or to understand how subtrees
 work. A subtree is just a subdirectory that can be
 committed to, branched, and merged along with your project in
 any way you want.

 They are also not to be confused with using the subtree merge
 strategy. The main difference is that, besides merging
 the other project as a subdirectory, you can also extract the
 entire history of a subdirectory from your project and make it
 into a standalone project. Unlike the subtree merge strategy
 you can alternate back and forth between these
 two operations. If the standalone library gets updated, you can
 automatically merge the changes into your project; if you
 update the library inside your project, you can "split" the
 changes back out again and merge them back into the library
 project.

 For example, if a library you made for one application ends up being
 useful elsewhere, you can extract its entire history and publish
 that as its own git repository, without accidentally
 intermingling the history of your application project.

 [TIP]
 In order to keep your commit messages clean, we recommend that
 people split their commits between the subtrees and the main
 project as much as possible.  That is, if you make a change that
 affects both the library and the main application, commit it in
 two pieces.  That way, when you split the library commits out
 later, their descriptions will still make sense.  But if this
 isn't important to you, it's not *necessary*.  'git subtree' will
 simply leave out the non-library-related parts of the commit
 when it splits it out into the subproject later.


 COMMANDS
 --------
 add <local-commit>::
 add <repository> <remote-ref>::
 	Create the <prefix> subtree by importing its contents
 	from the given <local-commit> or <repository> and <remote-ref>.
 	A new commit is created	automatically, joining the imported
 	project's history with your own.  With '--squash', import
 	only a single commit from the subproject, rather than its
 	entire history.

 merge <local-commit> [<repository>]::
 	Merge recent changes up to <local-commit> into the <prefix>
 	subtree.  As with normal 'git merge', this doesn't
 	remove your own local changes; it just merges those
 	changes into the latest <local-commit>.  With '--squash',
 	create only one commit that contains all the changes,
 	rather than merging in the entire history.
 +
 If you use '--squash', the merge direction doesn't always have to be
 forward; you can use this command to go back in time from v2.5 to v2.4,
 for example.  If your merge introduces a conflict, you can resolve it in
 the usual ways.
 +
 When using '--squash', and the previous merge with '--squash' merged an
 annotated tag of the subtree repository, that tag needs to be available locally.
 If <repository> is given, a missing tag will automatically be fetched from that
 repository.

 split [<local-commit>] [<repository>]::
 	Extract a new, synthetic project history from the
 	history of the <prefix> subtree of <local-commit>, or of
 	HEAD if no <local-commit> is given.  The new history
 	includes only the commits (including merges) that
 	affected <prefix>, and each of those commits now has the
 	contents of <prefix> at the root of the project instead
 	of in a subdirectory.  Thus, the newly created history
 	is suitable for export as a separate git repository.
 +
 After splitting successfully, a single commit ID is printed to stdout.
 This corresponds to the HEAD of the newly created tree, which you can
 manipulate however you want.
 +
 Repeated splits of exactly the same history are guaranteed to be
 identical (i.e. to produce the same commit IDs) as long as the
 settings passed to 'split' (such as '--annotate') are the same.
 Because of this, if you add new commits and then re-split, the new
 commits will be attached as commits on top of the history you
 generated last time, so 'git merge' and friends will work as expected.
 +
 When a previous merge with '--squash' merged an annotated tag of the
 subtree repository, that tag needs to be available locally.
 If <repository> is given, a missing tag will automatically be fetched from that
 repository.

 pull <repository> <remote-ref>::
 	Exactly like 'merge', but parallels 'git pull' in that
 	it fetches the given ref from the specified remote
 	repository.

 push <repository> [+][<local-commit>:]<remote-ref>::
 	Does a 'split' using the <prefix> subtree of <local-commit>
 	and then does a 'git push' to push the result to the
 	<repository> and <remote-ref>.  This can be used to push your
 	subtree to different branches of the remote repository.  Just
 	as with 'split', if no <local-commit> is given, then HEAD is
 	used.  The optional leading '+' is ignored.

 OPTIONS FOR ALL COMMANDS
 ------------------------
 -q::
 --quiet::
 	Suppress unnecessary output messages on stderr.

 -d::
 --debug::
 	Produce even more unnecessary output messages on stderr.

 -P <prefix>::
 --prefix=<prefix>::
 	Specify the path in the repository to the subtree you
 	want to manipulate.  This option is mandatory
 	for all commands.

 OPTIONS FOR 'add' AND 'merge' (ALSO: 'pull', 'split --rejoin', AND 'push --rejoin')
 -----------------------------------------------------------------------------------
 These options for 'add' and 'merge' may also be given to 'pull' (which
 wraps 'merge'), 'split --rejoin' (which wraps either 'add' or 'merge'
 as appropriate), and 'push --rejoin' (which wraps 'split --rejoin').

 --squash::
 	Instead of merging the entire history from the subtree project, produce
 	only a single commit that contains all the differences you want to
 	merge, and then merge that new commit into your project.
 +
 Using this option helps to reduce log clutter. People rarely want to see
 every change that happened between v1.0 and v1.1 of the library they're
 using, since none of the interim versions were ever included in their
 application.
 +
 Using '--squash' also helps avoid problems when the same subproject is
 included multiple times in the same project, or is removed and then
 re-added.  In such a case, it doesn't make sense to combine the
 histories anyway, since it's unclear which part of the history belongs
 to which subtree.
 +
 Furthermore, with '--squash', you can switch back and forth between
 different versions of a subtree, rather than strictly forward.  'git
 subtree merge --squash' always adjusts the subtree to match the exactly
 specified commit, even if getting to that commit would require undoing
 some changes that were added earlier.
 +
 Whether or not you use '--squash', changes made in your local repository
 remain intact and can be later split and send upstream to the
 subproject.

 -m <message>::
 --message=<message>::
 	Specify <message> as the commit message for the merge commit.

 OPTIONS FOR 'split' (ALSO: 'push')
 ----------------------------------
 These options for 'split' may also be given to 'push' (which wraps
 'split').

 --annotate=<annotation>::
 	When generating synthetic history, add <annotation> as a prefix to each
 	commit message.  Since we're creating new commits with the same commit
 	message, but possibly different content, from the original commits, this
 	can help to differentiate them and avoid confusion.
 +
 Whenever you split, you need to use the same <annotation>, or else you
 don't have a guarantee that the new re-created history will be identical
 to the old one.  That will prevent merging from working correctly.  git
 subtree tries to make it work anyway, particularly if you use '--rejoin',
 but it may not always be effective.

 -b <branch>::
 --branch=<branch>::
 	After generating the synthetic history, create a new branch called
 	<branch> that contains the new history.  This is suitable for immediate
 	pushing upstream.  <branch> must not already exist.

 --ignore-joins::
 	If you use '--rejoin', git subtree attempts to optimize its history
 	reconstruction to generate only the new commits since the last
 	'--rejoin'.  '--ignore-joins' disables this behavior, forcing it to
 	regenerate the entire history.  In a large project, this can take a long
 	time.

 --onto=<onto>::
 	If your subtree was originally imported using something other than git
 	subtree, its history may not match what git subtree is expecting.  In
 	that case, you can specify the commit ID <onto> that corresponds to the
 	first revision of the subproject's history that was imported into your
 	project, and git subtree will attempt to build its history from there.
 +
 If you used 'git subtree add', you should never need this option.

 --rejoin::
 	After splitting, merge the newly created synthetic history back into
 	your main project.  That way, future splits can search only the part of
 	history that has been added since the most recent '--rejoin'.
 +
 If your split commits end up merged into the upstream subproject, and
 then you want to get the latest upstream version, this will allow git's
 merge algorithm to more intelligently avoid conflicts (since it knows
 these synthetic commits are already part of the upstream repository).
 +
 Unfortunately, using this option results in 'git log' showing an extra
 copy of every new commit that was created (the original, and the
 synthetic one).
 +
 If you do all your merges with '--squash', make sure you also use
 '--squash' when you 'split --rejoin'.


 EXAMPLE 1. 'add' command
 ------------------------
 Let's assume that you have a local repository that you would like
 to add an external vendor library to. In this case we will add the
 git-subtree repository as a subdirectory of your already existing
 git-extensions repository in ~/git-extensions/:

 	$ git subtree add --prefix=git-subtree --squash \
 		git://github.com/apenwarr/git-subtree.git master

 'master' needs to be a valid remote ref and can be a different branch
 name

 You can omit the '--squash' flag, but doing so will increase the number
 of commits that are included in your local repository.

 We now have a ~/git-extensions/git-subtree directory containing code
 from the master branch of git://github.com/apenwarr/git-subtree.git
 in our git-extensions repository.

 EXAMPLE 2. Extract a subtree using 'commit', 'merge' and 'pull'
 ---------------------------------------------------------------
 Let's use the repository for the git source code as an example.
 First, get your own copy of the git.git repository:

 	$ git clone git://git.kernel.org/pub/scm/git/git.git test-git
 	$ cd test-git

 gitweb (commit 1130ef3) was merged into git as of commit
 0a8f4f0, after which it was no longer maintained separately.
 But imagine it had been maintained separately, and we wanted to
 extract git's changes to gitweb since that time, to share with
 the upstream.  You could do this:

 	$ git subtree split --prefix=gitweb --annotate='(split) ' \
         	0a8f4f0^.. --onto=1130ef3 --rejoin \
         	--branch gitweb-latest
         $ gitk gitweb-latest
         $ git push git@github.com:whatever/gitweb.git gitweb-latest:master

 (We use '0a8f4f0^..' because that means "all the changes from
 0a8f4f0 to the current version, including 0a8f4f0 itself.")

 If gitweb had originally been merged using 'git subtree add' (or
 a previous split had already been done with '--rejoin' specified)
 then you can do all your splits without having to remember any
 weird commit IDs:

 	$ git subtree split --prefix=gitweb --annotate='(split) ' --rejoin \
 		--branch gitweb-latest2

 And you can merge changes back in from the upstream project just
 as easily:

 	$ git subtree pull --prefix=gitweb \
 		git@github.com:whatever/gitweb.git master

 Or, using '--squash', you can actually rewind to an earlier
 version of gitweb:

 	$ git subtree merge --prefix=gitweb --squash gitweb-latest~10

 Then make some changes:

 	$ date >gitweb/myfile
 	$ git add gitweb/myfile
 	$ git commit -m 'created myfile'

 And fast forward again:

 	$ git subtree merge --prefix=gitweb --squash gitweb-latest

 And notice that your change is still intact:

 	$ ls -l gitweb/myfile

 And you can split it out and look at your changes versus
 the standard gitweb:

 	git log gitweb-latest..$(git subtree split --prefix=gitweb)

 EXAMPLE 3. Extract a subtree using a branch
 -------------------------------------------
 Suppose you have a source directory with many files and
 subdirectories, and you want to extract the lib directory to its own
 git project. Here's a short way to do it:

 First, make the new repository wherever you want:

 	$ <go to the new location>
 	$ git init --bare

 Back in your original directory:

 	$ git subtree split --prefix=lib --annotate="(split)" -b split

 Then push the new branch onto the new empty repository:

 	$ git push <new-repo> split:master


 AUTHOR
 ------
 Written by Avery Pennarun <apenwarr@gmail.com>


 GIT
 ---
 Part of the linkgit:git[1] suite
	git-subtree(1)
	==============

	NAME
	----
	git-subtree - Merge subtrees together and split repository into subtrees


	SYNOPSIS
	--------
	[verse]
	'git subtree' [<options>] -P <prefix> add <local-commit>
	'git subtree' [<options>] -P <prefix> add <repository> <remote-ref>
	'git subtree' [<options>] -P <prefix> merge <local-commit> [<repository>]
	'git subtree' [<options>] -P <prefix> split [<local-commit>]

	[verse]
	'git subtree' [<options>] -P <prefix> pull <repository> <remote-ref>
	'git subtree' [<options>] -P <prefix> push <repository> <refspec>

	DESCRIPTION
	-----------
	Subtrees allow subprojects to be included within a subdirectory
	of the main project, optionally including the subproject's
	entire history.

	For example, you could include the source code for a library
	as a subdirectory of your application.

	Subtrees are not to be confused with submodules, which are meant for
	the same task. Unlike submodules, subtrees do not need any special
	constructions (like '.gitmodules' files or gitlinks) be present in
	your repository, and do not force end-users of your
	repository to do anything special or to understand how subtrees
	work. A subtree is just a subdirectory that can be
	committed to, branched, and merged along with your project in
	any way you want.

	They are also not to be confused with using the subtree merge
	strategy. The main difference is that, besides merging
	the other project as a subdirectory, you can also extract the
	entire history of a subdirectory from your project and make it
	into a standalone project. Unlike the subtree merge strategy
	you can alternate back and forth between these
	two operations. If the standalone library gets updated, you can
	automatically merge the changes into your project; if you
	update the library inside your project, you can "split" the
	changes back out again and merge them back into the library
	project.

	For example, if a library you made for one application ends up being
	useful elsewhere, you can extract its entire history and publish
	that as its own git repository, without accidentally
	intermingling the history of your application project.

	[TIP]
	In order to keep your commit messages clean, we recommend that
	people split their commits between the subtrees and the main
	project as much as possible. That is, if you make a change that
	affects both the library and the main application, commit it in
	two pieces. That way, when you split the library commits out
	later, their descriptions will still make sense. But if this
	isn't important to you, it's not necessary. 'git subtree' will
	simply leave out the non-library-related parts of the commit
	when it splits it out into the subproject later.


	COMMANDS
	--------
	add <local-commit>::
	add <repository> <remote-ref>::
	Create the <prefix> subtree by importing its contents
	from the given <local-commit> or <repository> and <remote-ref>.
	A new commit is created automatically, joining the imported
	project's history with your own. With '--squash', import
	only a single commit from the subproject, rather than its
	entire history.

	merge <local-commit> [<repository>]::
	Merge recent changes up to <local-commit> into the <prefix>
	subtree. As with normal 'git merge', this doesn't
	remove your own local changes; it just merges those
	changes into the latest <local-commit>. With '--squash',
	create only one commit that contains all the changes,
	rather than merging in the entire history.
	+
	If you use '--squash', the merge direction doesn't always have to be
	forward; you can use this command to go back in time from v2.5 to v2.4,
	for example. If your merge introduces a conflict, you can resolve it in
	the usual ways.
	+
	When using '--squash', and the previous merge with '--squash' merged an
	annotated tag of the subtree repository, that tag needs to be available locally.
	If <repository> is given, a missing tag will automatically be fetched from that
	repository.

	split [<local-commit>] [<repository>]::
	Extract a new, synthetic project history from the
	history of the <prefix> subtree of <local-commit>, or of
	HEAD if no <local-commit> is given. The new history
	includes only the commits (including merges) that
	affected <prefix>, and each of those commits now has the
	contents of <prefix> at the root of the project instead
	of in a subdirectory. Thus, the newly created history
	is suitable for export as a separate git repository.
	+
	After splitting successfully, a single commit ID is printed to stdout.
	This corresponds to the HEAD of the newly created tree, which you can
	manipulate however you want.
	+
	Repeated splits of exactly the same history are guaranteed to be
	identical (i.e. to produce the same commit IDs) as long as the
	settings passed to 'split' (such as '--annotate') are the same.
	Because of this, if you add new commits and then re-split, the new
	commits will be attached as commits on top of the history you
	generated last time, so 'git merge' and friends will work as expected.
	+
	When a previous merge with '--squash' merged an annotated tag of the
	subtree repository, that tag needs to be available locally.
	If <repository> is given, a missing tag will automatically be fetched from that
	repository.

	pull <repository> <remote-ref>::
	Exactly like 'merge', but parallels 'git pull' in that
	it fetches the given ref from the specified remote
	repository.

	push <repository> [+][<local-commit>:]<remote-ref>::
	Does a 'split' using the <prefix> subtree of <local-commit>
	and then does a 'git push' to push the result to the
	<repository> and <remote-ref>. This can be used to push your
	subtree to different branches of the remote repository. Just
	as with 'split', if no <local-commit> is given, then HEAD is
	used. The optional leading '+' is ignored.

	OPTIONS FOR ALL COMMANDS
	------------------------
	-q::
	--quiet::
	Suppress unnecessary output messages on stderr.

	-d::
	--debug::
	Produce even more unnecessary output messages on stderr.

	-P <prefix>::
	--prefix=<prefix>::
	Specify the path in the repository to the subtree you
	want to manipulate. This option is mandatory
	for all commands.

	OPTIONS FOR 'add' AND 'merge' (ALSO: 'pull', 'split --rejoin', AND 'push --rejoin')
	-----------------------------------------------------------------------------------
	These options for 'add' and 'merge' may also be given to 'pull' (which
	wraps 'merge'), 'split --rejoin' (which wraps either 'add' or 'merge'
	as appropriate), and 'push --rejoin' (which wraps 'split --rejoin').

	--squash::
	Instead of merging the entire history from the subtree project, produce
	only a single commit that contains all the differences you want to
	merge, and then merge that new commit into your project.
	+
	Using this option helps to reduce log clutter. People rarely want to see
	every change that happened between v1.0 and v1.1 of the library they're
	using, since none of the interim versions were ever included in their
	application.
	+
	Using '--squash' also helps avoid problems when the same subproject is
	included multiple times in the same project, or is removed and then
	re-added. In such a case, it doesn't make sense to combine the
	histories anyway, since it's unclear which part of the history belongs
	to which subtree.
	+
	Furthermore, with '--squash', you can switch back and forth between
	different versions of a subtree, rather than strictly forward. 'git
	subtree merge --squash' always adjusts the subtree to match the exactly
	specified commit, even if getting to that commit would require undoing
	some changes that were added earlier.
	+
	Whether or not you use '--squash', changes made in your local repository
	remain intact and can be later split and send upstream to the
	subproject.

	-m <message>::
	--message=<message>::
	Specify <message> as the commit message for the merge commit.

	OPTIONS FOR 'split' (ALSO: 'push')
	----------------------------------
	These options for 'split' may also be given to 'push' (which wraps
	'split').

	--annotate=<annotation>::
	When generating synthetic history, add <annotation> as a prefix to each
	commit message. Since we're creating new commits with the same commit
	message, but possibly different content, from the original commits, this
	can help to differentiate them and avoid confusion.
	+
	Whenever you split, you need to use the same <annotation>, or else you
	don't have a guarantee that the new re-created history will be identical
	to the old one. That will prevent merging from working correctly. git
	subtree tries to make it work anyway, particularly if you use '--rejoin',
	but it may not always be effective.

	-b <branch>::
	--branch=<branch>::
	After generating the synthetic history, create a new branch called
	<branch> that contains the new history. This is suitable for immediate
	pushing upstream. <branch> must not already exist.

	--ignore-joins::
	If you use '--rejoin', git subtree attempts to optimize its history
	reconstruction to generate only the new commits since the last
	'--rejoin'. '--ignore-joins' disables this behavior, forcing it to
	regenerate the entire history. In a large project, this can take a long
	time.

	--onto=<onto>::
	If your subtree was originally imported using something other than git
	subtree, its history may not match what git subtree is expecting. In
	that case, you can specify the commit ID <onto> that corresponds to the
	first revision of the subproject's history that was imported into your
	project, and git subtree will attempt to build its history from there.
	+
	If you used 'git subtree add', you should never need this option.

	--rejoin::
	After splitting, merge the newly created synthetic history back into
	your main project. That way, future splits can search only the part of
	history that has been added since the most recent '--rejoin'.
	+
	If your split commits end up merged into the upstream subproject, and
	then you want to get the latest upstream version, this will allow git's
	merge algorithm to more intelligently avoid conflicts (since it knows
	these synthetic commits are already part of the upstream repository).
	+
	Unfortunately, using this option results in 'git log' showing an extra
	copy of every new commit that was created (the original, and the
	synthetic one).
	+
	If you do all your merges with '--squash', make sure you also use
	'--squash' when you 'split --rejoin'.


	EXAMPLE 1. 'add' command
	------------------------
	Let's assume that you have a local repository that you would like
	to add an external vendor library to. In this case we will add the
	git-subtree repository as a subdirectory of your already existing
	git-extensions repository in ~/git-extensions/:

	$ git subtree add --prefix=git-subtree --squash \
	git://github.com/apenwarr/git-subtree.git master

	'master' needs to be a valid remote ref and can be a different branch
	name

	You can omit the '--squash' flag, but doing so will increase the number
	of commits that are included in your local repository.

	We now have a ~/git-extensions/git-subtree directory containing code
	from the master branch of git://github.com/apenwarr/git-subtree.git
	in our git-extensions repository.

	EXAMPLE 2. Extract a subtree using 'commit', 'merge' and 'pull'
	---------------------------------------------------------------
	Let's use the repository for the git source code as an example.
	First, get your own copy of the git.git repository:

	$ git clone git://git.kernel.org/pub/scm/git/git.git test-git
	$ cd test-git

	gitweb (commit 1130ef3) was merged into git as of commit
	0a8f4f0, after which it was no longer maintained separately.
	But imagine it had been maintained separately, and we wanted to
	extract git's changes to gitweb since that time, to share with
	the upstream. You could do this:

	$ git subtree split --prefix=gitweb --annotate='(split) ' \
	0a8f4f0^.. --onto=1130ef3 --rejoin \
	--branch gitweb-latest
	$ gitk gitweb-latest
	$ git push git@github.com:whatever/gitweb.git gitweb-latest:master

	(We use '0a8f4f0^..' because that means "all the changes from
	0a8f4f0 to the current version, including 0a8f4f0 itself.")

	If gitweb had originally been merged using 'git subtree add' (or
	a previous split had already been done with '--rejoin' specified)
	then you can do all your splits without having to remember any
	weird commit IDs:

	$ git subtree split --prefix=gitweb --annotate='(split) ' --rejoin \
	--branch gitweb-latest2

	And you can merge changes back in from the upstream project just
	as easily:

	$ git subtree pull --prefix=gitweb \
	git@github.com:whatever/gitweb.git master

	Or, using '--squash', you can actually rewind to an earlier
	version of gitweb:

	$ git subtree merge --prefix=gitweb --squash gitweb-latest~10

	Then make some changes:

	$ date >gitweb/myfile
	$ git add gitweb/myfile
	$ git commit -m 'created myfile'

	And fast forward again:

	$ git subtree merge --prefix=gitweb --squash gitweb-latest

	And notice that your change is still intact:

	$ ls -l gitweb/myfile

	And you can split it out and look at your changes versus
	the standard gitweb:

	git log gitweb-latest..$(git subtree split --prefix=gitweb)

	EXAMPLE 3. Extract a subtree using a branch
	-------------------------------------------
	Suppose you have a source directory with many files and
	subdirectories, and you want to extract the lib directory to its own
	git project. Here's a short way to do it:

	First, make the new repository wherever you want:

	$ <go to the new location>
	$ git init --bare

	Back in your original directory:

	$ git subtree split --prefix=lib --annotate="(split)" -b split

	Then push the new branch onto the new empty repository:

	$ git push <new-repo> split:master


	AUTHOR
	------
	Written by Avery Pennarun <apenwarr@gmail.com>


	GIT
	---
	Part of the linkgit:git[1] suite