Sunday, May 31, 2009

Command of the day: git svn (Using git over a subversion repository)

This may be the end of a long quest for a tool to do 'offline commits on subversion'. That is, being able to work with small commits when you are not able to commit because you are off-line (on-flight or on-train hacking) or you are not a commiter yet (menthorship).

The fact is that, we can benefit of some nice features of git without having to migrate from subversion. I found a very interesting blog entry explaining that. I compiled my own notes for CLAM:

Install the required packages:
sudo apt-get install git-svn

Configure your user:
git config --global 'David García Garzón'
git config --global ''

Create a git clone of the svn:
git svn clone --stdlayout -r HEAD
Notice that i skiped the 'trunk' part of the url we normally use. '--stdlayout' is to interpret trunk/ branches/ tags/ as such. '-rHEAD' avoids cloning the whole history which is faster.

Work with the repository as with a normal git one, avoiding remote operations (push/pull). Git can fustrate SVN users with a lack of shortcuts (ci, di, up...). You can define them at will:
git config --global "commit -a"
git config --global alias.di diff
git config --global alias.stat status
git config --global alias.up "svn rebase"
git config --global alias.rci "svn dcommit"

To update your git repository to server changes:
git svn rebase
If you have uncommited local changes you have to 'stash' them first.

To apply all the local commits to subversion, once rebased:
git svn dcommit

To generate, instead, an incremental set of patches:
git format-patch -M -C -s --inline --stdout remotes/trunk > mypatch.mbox

Note that this is not a regular patch file but an mbox file containing several mails, one per commit, each with the patch attached and some aditional information such as the commit message.

Those commits can be sent to the menthor and applied to git sandbox with svn write access.
git am mypatch.mbox

An then the menthor can commit using previous command 'dcommit'. That easy... or not so.

Some other highlights i would do on git: Nice programmer oriented subcomands such as git bisect, to help bug hunting by doing a dicotomic search on revisions, or git stash, to discard temporarily uncommited changes and recovering them later, or 'git grep', which executes grep ignoring git control files and generated files. Tools like StGit and guilt that allows to edit the order of the local commits considering them a serie of patches similarly to quilt.

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