SYNOPSIS
+git subtree add -P <prefix> <commit> +git subtree add -P <prefix> <repository> <ref> +git subtree pull -P <prefix> <repository> <ref> +git subtree push -P <prefix> <repository> <ref> +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 .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 + +
-
+
+ Create the <prefix> subtree by importing its contents + from the given <commit> or <repository> and remote <ref>. + 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 ref from the specified remote + repository. +
+
+ - +push + +
-
+
+ Does a split (see below) using the <prefix> supplied + and then does a git push to push the result to the + repository and ref. 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 (i.e. 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, 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 mastermaster 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-gitgitweb (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-latest2And you can merge changes back in from the upstream project just +as easily:
$ git subtree pull --prefix=gitweb \
+ git@github.com:whatever/gitweb.git masterOr, using --squash, you can actually rewind to an earlier +version of gitweb:
$ git subtree merge --prefix=gitweb --squash gitweb-latest~10Then 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-latestAnd notice that your change is still intact:
$ ls -l gitweb/myfileAnd 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 --bareBack in your original directory:
$ git subtree split --prefix=lib --annotate="(split)" -b splitThen push the new branch onto the new empty repository:
$ git push <new-repo> split:masterAUTHOR
+Written by Avery Pennarun <apenwarr@gmail.com>
GIT
+Part of the git(1) suite