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CentOS 7.0 - man page for git-subtree (centos section 1)

GIT-SUBTREE(1)				    Git Manual				   GIT-SUBTREE(1)

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

       git subtree add	 -P <prefix> <refspec>
       git subtree add	 -P <prefix> <repository> <refspec>
       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>]

       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

       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

       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

       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.

	   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.

	   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 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.

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

	   Does a split (see below) 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.

	   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

	       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.

       -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.

	   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.

	   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.

	   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.

	   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.

	   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

	       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.

       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.

       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)

       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

       Written by Avery Pennarun <apenwarr@gmail.com[1]>

       Part of the git(1) suite

	1. apenwarr@gmail.com

Git					    06/10/2014				   GIT-SUBTREE(1)

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