If you have a lot of projects in separate
you're eventually going to want to do some refactoring and put some a
subtree or two into their own repository so that you can reuse them. (If
everything is under the same repository, you probably moved your
tree from Subversion or CVS, and you'll want to split it up. These
techniques work for that, too.)
Often you want to move one or more subtrees to a different project
(usually but not always a new one), but keep them in the same
relative position. This can happen if, for example, you want to
take a Java package out of a project and make it its own library.
If you organize your code sensibly, you'll have source code and
tests in separate subtrees, and some build logic in the
root. This is a job for
This is the one case where you don't have to clone your origial repository unless you want to, but it's a good idea anyway because it's going to end up with an extra branch in it for each subtree you're moving. And even if you plan on nuking it later, cloning it gives you something to fall back on when a cat walks across your keyboard (as mine has done several times since I started writing this).
Let's start by making our new branches:
cd ../MyBloatedProject git subtree split --prefix=src/com/example/separable/package --branch=src git subtree split --prefix=tst/com/example/separable/package --branch=tst cd ../ShinyNewLibrary git checkout -b working git remote add mbp ../MyBloatedProject git subtree add --prefix=src/com/example/separable/package mbp src git subtree add --prefix=tst/com/example/separable/package mbp tst git merge src tst
...and you're done. Post your code review.
The nice thing about this process is that it doesn't matter if people are
still working in the subtrees you just moved. That's because every time
git subtree with the same arguments you get the same
set of commits. (That's also why you don't want to rebase the commits you
So suppose someone has gone and committed some changes to the subtrees you're working in. True story -- it happens a lot on large teams. Or if you have a habit of working on two computers! Now you can take advantage of the feature mentioned above.
# update the split branches: cd ../MyBloatedProject git checkout master git pull git subtree split --prefix=src/com/example/separable/package --branch=src git subtree split --prefix=tst/com/example/separable/package --branch=tst # Merge the splits, preserving the top commit. cd ../ShinyNewLibrary git checkout -b splits # only has to be done once. Next time git reset --hard HEAD^ # just do git checkout splits. git subtree pull --prefix=src/com/example/separable/package mbp src git subtree pull --prefix=tst/com/example/separable/package mbp tst git checkout working git rebase splits
The resulting tree looks a little odd, with two extra branches that don't descend from a commit in mainline, but you can continue this way as long as anyone is still working in the original repo. Of course, once you're done, just
git checkout working git rebase master git merge working cd ../MyBloatedProject git rm -r src/com/example/separable/package git rm -r tst/com/example/separable/package git commit
This, of course, leaves your package's history in two places: the old project, and the new one. Cleaning up the old repo is rarely necessary, but we'll see later how you can do that. Rewriting history in the new project to get all the commits into master in chronological order is left as an exercise for the reader.
Uprooting a Subtree
The next simplest case is when you have a subtree -- a library,
or a project in a former
svn tree, and you want to
make it a separate project with its own
The first thing you have to do is clone your original repo, because it's going to be totally destroyed. Then,
git filter-branch --subdirectory-filter Foo -- --all
This will wipe out your original repo, leaving only the former contents of Foo. It also wipes out any history Foo's contents might have had if they were moved from someplace else. We'll get to that.
A variant of this is where you wantall of your repository
to end up in the subdirectory, in other words, to make your repo into
a self-contained subtree that you can then move into some other
project (perhaps using
git subtree, as in the previous
git filter-branch --prune-empty --tree-filter ' if [[ ! -e foo/bar ]]; then mkdir -p foo/bar git ls-tree --name-only $GIT_COMMIT | xargs -I files mv files foo/bar fi'
(I got that one from this article on StackOverflow, by the way.)
Of course, this doesn't work if you want some of the files to remain where they were.
Many Leaves Can Form a Forest
Other times, you're not starting out with a tree, just a collection of files, all at the same level. And maybe you want them to end up in more than one subtree. I did this most recently when I wanted to split up my songbook into my songs, public domain songs, other peoples' songs, and work in progress.
I started out by moving all the songs that weren't mine into three subdirectories called PD, WIP, and Other. Then, I made a little script:
#!/bin/bash pd=$(echo `ls PD`) wip=$(echo `ls WIP`) oth=$(echo `ls Other`) git filter-branch --prune-empty --tree-filter \ "for f in $pd; do if [ -f \$f ]; then mkdir -p PD; mv -f \$f PD; fi done;\ for f in $wip; do if [ -f \$f ]; then mkdir -p WIP; mv -f \$f WIP; fi done;\ for f in $oth; do if [ -f \$f ]; then mkdir -p Other; mv -f \$f Other; fi done;\ "
(I later made a more general Perl script -- it turned out that Bash wasn't up to doing the necessary variable substitution.)
Now I had a directory with three subtrees, and my own lyrics in the top
level. Then it was a simple matter of cloning this directory three times,
git filter-branch --subdirectory-filter in
Finally, I went back to the directory that still had the subdirectories in it. Just removing them won't do, because their contents would still be in the history. But we can fix that, with:
git filter-branch --prune-empty --original refs/before-removing-subdirs\ --tree-filter 'rm -rf Other PD WIP' git reset --hard HEAD; git gc --aggressive; git prune # and, finally, stomp on your shared repo with git push -f
You need the
--original in there because you probably still
refs/original left over from the previous work --
filter-branch won't run if it thinks it might overwrite your
original. Just in case you forgot to clone. You'll probably want to run
some unit tests before that last push.
Whew! The whole process is made feasible by the fact that cloning a local repository is almost instantaneous because it uses hard links. Whenever you make a mistake, you can just clone the original repo and start over.
Patches of Forest
There's another method of transplanting that doesn't involve making branches: instead, you make patches. It's quick and easy, and handles random files and subtrees mixed together. It looks like:
# see git log --pretty=email --reverse --full-index --binary -- PATHS > /tmp/patches # fix paths if necessary: sed -i -e 's@deep/path/that/you/want/shorter@short/path@g' /tmp/patches # apply the patches. cd /path/to/dest; git am /tmp/patches # rather than applying the patches directly to the new repository, you can make a # new one. That separates the history, which is cleaner if you have a lot of it. # (replace "foo" with whatever name you want for the merged branch) mkdir foo; cd foo; git init; git am /tmp/patches # then import it, and merge cd /path/to/dest git remote add foo ../foo git merge foo/master
A coworker of mine at Amazon found this one, in this article. The one problem I have with it is that all the new
commits end up in master instead of on an "orphan" branch, so you have a
lot of commits out of chronological order.
git log will sort
them correctly by date, but they'll look rather strange in visualization
gitk. (Not that orphan branches don't look
strange too, but their strangeness gives you a better idea of what
(Most of this was originally published on Stephen.Savitzky.net in 2015.)