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' add   -P <prefix> <commit>
 'git subtree' pull  -P <prefix> <repository> <refspec...>
 'git subtree' push  -P <prefix> <repository> <refspec...>
 'git subtree' merge -P <prefix> <commit>
 'git subtree' split -P <prefix> [OPTIONS] [<commit>]


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

 merge::
 	Merge recent changes up to <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 <commit>.  With '--squash',
 	creates 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.

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

 push::
 	Does a 'split' (see above) using the <prefix> supplied
 	and then does a 'git push' to push the result to the
 	repository and refspec. This can be used to push your
 	subtree to different branches of the remote repository.

 split::
 	Extract a new, synthetic project history from the
 	history of the <prefix> subtree.  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 (ie. to produce the same
 	commit ids).  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.

 	Note that if you use '--squash' when you merge, you
 	should usually not just '--rejoin' when you split.


 OPTIONS
 -------
 -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.

 -m <message>::
 --message=<message>::
 	This option is only valid for add, merge and pull (unsure).
 	Specify <message> as the commit message for the merge commit.


 OPTIONS FOR add, merge, push, pull
 ----------------------------------
 --squash::
 	This option is only valid for add, merge, push and pull
 	commands.

 	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.


 OPTIONS FOR split
 -----------------
 --annotate=<annotation>::
 	This option is only valid for the split command.

 	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>::
 	This option is only valid for the split command.

 	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::
 	This option is only valid for the split command.

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

 --onto=<onto>::
 	This option is only valid for the split command.

 	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::
 	This option is only valid for the split command.

 	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', don't use
 	'--rejoin' when you split, because you don't want the
 	subproject's history to be part of your project anyway.


 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 incldued 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 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' add -P <prefix> <commit>
	'git subtree' pull -P <prefix> <repository> <refspec...>
	'git subtree' push -P <prefix> <repository> <refspec...>
	'git subtree' merge -P <prefix> <commit>
	'git subtree' split -P <prefix> [OPTIONS] [<commit>]


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

	merge::
	Merge recent changes up to <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 <commit>. With '--squash',
	creates 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.

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

	push::
	Does a 'split' (see above) using the <prefix> supplied
	and then does a 'git push' to push the result to the
	repository and refspec. This can be used to push your
	subtree to different branches of the remote repository.

	split::
	Extract a new, synthetic project history from the
	history of the <prefix> subtree. 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 (ie. to produce the same
	commit ids). 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.

	Note that if you use '--squash' when you merge, you
	should usually not just '--rejoin' when you split.


	OPTIONS
	-------
	-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.

	-m <message>::
	--message=<message>::
	This option is only valid for add, merge and pull (unsure).
	Specify <message> as the commit message for the merge commit.


	OPTIONS FOR add, merge, push, pull
	----------------------------------
	--squash::
	This option is only valid for add, merge, push and pull
	commands.

	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.


	OPTIONS FOR split
	-----------------
	--annotate=<annotation>::
	This option is only valid for the split command.

	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>::
	This option is only valid for the split command.

	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::
	This option is only valid for the split command.

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

	--onto=<onto>::
	This option is only valid for the split command.

	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::
	This option is only valid for the split command.

	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', don't use
	'--rejoin' when you split, because you don't want the
	subproject's history to be part of your project anyway.


	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 incldued 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 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