Backing up git repos on multiple machines to central repo w/o collision

Git Tree Management

Here's a quick column about git. It's not a complete how-to or tutorial, but more an interesting way to manage multiple trees.

The problem: I have a dozen trees on a half dozen machines. I'd like at least backup all the branches in these trees to github. Trouble is, I don't want branch names to step on each other. This can happen for a number of reasons, let's say I called something 'junk' by habit on N trees and don't want a push to screw that up...

Git's world view: To understand git, you have to understand that it is a graph of versioned trees with labels. Each node in the tree has the familiar hash, and some of the hashes have refs that the git branch command groks. It's all just a directed graph with labels under the covers.

Normally, you when clone a repo, all its tags magically change from foo to origin/foo (for some value of origin).

Enter refspecs

Turns out this has been thought of before. The answer is simple:

fred% git push origin foo:fred/foo

will push the foo branch to your origin and rewrite its name to fred/foo. Don't forget to push master too.

Now when you go to barney and fetch, you'll have a bunch of remote branches named origin/fred/foo, etc.

Costs

Since I'm doing this with a number of git svn trees, the cost is kinda high since git svn creates new, unique git hashes for all the upstream revisions to git svn rebase. It also means that you'll need to learn how to use the --onto arg of git-rebase, since if you want to move a branch from one repo like this to another.

barney% git checkout -b foo fred/foo
barney% git rebase -i fred/master foo --onto master

since you're effectively creating a new name space on your local machine for the new branch. The rebase will now properly take just those commits from foo, and then play them back onto master on the current machine and leave you with a 'foo' branch for the results.