Saturday, June 25, 2011

Version-control for the home directory dot-files

Lots of people revision-control the dotfiles in their home directories: .bashrc, .vim, etc. That works ok as long as you can ignore any files not controlled, and most VCSs allow that.

But what if you have several homedirs, and you want to maintain some common files between them. Of course, you also have files that differ. I think I've found an elegant solution: 2-tiered VCS.

Each homedir gets a git repo, which is pulled from one in Dropbox. (You'll see why I use Dropbox instead of GitHub in a minute.) I have a branch for each machine, so I can do some comparisons if I want. The master branch has only the common files, which can be used for seeding a new branch on a new machine.

What if I change a common file? I'd hate to have to merge it on each machine. I could forget easily, and that's a lot of work for every little change.

Instead, I keep the common files in cvs, also in Dropbox. Each local cvs workspace is also added to git. (That's not strictly necessary, but it makes setting up a new machine trivial.) When I change a common file, I just 'cvs commit' that file. On any machine, I can run 'cvs update' at any time.

One of the keys to this is the presence of 'CVS/Entries.Static' in the homedir. Otherwise, 'cvs update' could wreak havoc, as some common files are over-ridden on specific machines. (That's why a simpler solution does not work.) Cvs creates that file for you automatically if you 'cvs co' a single file. Otherwise, you can just 'touch CVS/Entries.Static', and remove unwanted files/directories from 'CVS/Entries'.

Another helpful thing is to commit a file called 'cvsignore' (no dot) into the CVSROOT directory (which is in the repo on Dropbox). It has just a single '*', which means to 'ignore everything not listed explicitly in CVS/Entries'.  For sub-directories (e.g. .vim/), add a file called .cvsignore with just a single character, '!', to let cvs see all files there.

Also put '*' in '~/.gitignore', and add/commit that file. Henceforth, you will need 'git add -f' for any new files, but that's not really a bad thing.

The most difficult -- and dangerous -- part is setting up the local git repo. Normally, 'cd ~; git clone URL .' will set up a clone in the current directory, but that only works when the directory is empty. Instead, I came up with this sequence of steps:
git init
git remote add origin ~/Dropbox/homedir-repo
git fetch origin
git checkout -f -B mymachine origin/mymachine
Of course, the homedir-repo is 'bare', and the relevant branch was set-up safely in a different directory, with lots of testing. We don't want to destroy our homedir by accident!

So far, this is working extremely well for me, and I have not seen any better ideas out there.

This is helpful in ~/.git/config:

    auto = 0
That way, git will not pack stuff on Dropbox. Pushing to the remote repo will then only add files. Very little will change. (That's the problem with hosting CVS on Dropbox; files are edited or appended for every commit.)

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