Occasionally, git cvsexportcommit will fail. I don’t know how it works inside, but I have noticed that it will sometimes have a problem committing to CVS in the case of added or deleted files.

In this post, I will outline a method of manually exporting a patch file from a local Git repository that has been based off of a project in CVS. This requires a bit of fiddling, but once you package everything in a small script, it’s quite painless. Of course, the least pain would be to just switch to Git, but this might help someone else stuck hassling with a legacy project.

Since you need a CVS working directory to use cvsexportcommit, I assume you already have one. To start, checkout the project twice, once with a different name, like this:

$ cvs co -d project-cvs project
$ cvs co -d project-git project

This results in two copies of project. You can then delete the CVS directories and create a new Git repository in one of them:

$ cd project-git
$ cvs release # not necessary
$ rm -rf $(find . -name 'CVS')
$ git init

Now you can work away in the Git working directory as normal, with all the ease of Git, local branching, etc… I would recommend branching from master and working there, then merging back into master before exporting to CVS, just to keep things clean. You can then import into master as well, and rebase your local branches against it to incorporate any changes from your colleagues. Importing from CVS would be the same as exporting as outlined below, just reverse the diff-ing and patch-ing.

When you’re ready to export your work and commit to CVS, you need to create a patch by diffing your Git working dir with the CVS working directory, and commit this patch to the CVS repository.

After a little hunting, I found this pair of incantations:

$ diff --exclude='CVS' --exclude='.git*' -urPp cvs git

… where cvs and git refer to your working directories. You invoke this in the directory above them, and it will spit out the patch to stdout, so you probably want to redirect it to a file by appending > patch the end. It’s also helpful to use the -q option to diff which will just list the changed files, and give you a quick sanity check that you’re setting up to commit what you think you are.

To apply the patch to your CVS working directory, change to it, and run

$ patch -p1 < ../patch

… where patch is that patch file, presumably created in the directory above your working directory. Then you can commit to CVS normally, with cvs ci -m '...' etc.

This all might seem like a lot of work just to use Git, but in the transition between CVS and Git, or in a situation where you want to use Git in “guerilla” mode, this works in a pinch.