by Brandon Rhodes • Home

Moving home directory version control out of your way

Date: 7 May 2012
Tags:computing

If you keep your home directory under version control, then you may know the sinking feeling that comes from sitting down at work after a late night, looking for that brilliant fix you made right before bed, and finding that your commit is nowhere to be found. What happened?

Upon arriving home, you discover that your final conscious act the previous night was an accidental commit of your home directory — you committed, say, a tiny experimental change to your ~/.profile from last week when you really meant to be committing a patch to ~/big/project to resolve the latest show-stopping bug. You were too tired to notice that the version control system listed the wrong files as you typed the commit message into your editor.

This can, of course, happen if you run git or hg while you are sitting in the wrong directory. But, more subtly, this can happen if you are sitting in the correct directory but call the wrong command. If ~/big/project was, for example, checked out using Mercurial or Subversion, then a git commit in that directory will patiently search up the directory tree, find your ~/.git directory, and look for changed dotfiles or commands to commit instead.

For those of us with several version control systems going at once, in fact, it is a bad idea to have any two projects be “concentric” — where a directory under the control of one version control system wraps another project under different control. I really prefer for each directory in the file system to have exactly one version-control directory in its tree of ancestors.

So how can you safely version control your dotfiles? The solution is to keep your ~/.git or ~/.hg directory out of the way during normal operation — for example, by appending .off to its name — then moving it back into place when you explicitly want to perform a version control operation on your dotfiles. One approach would be to create a shell script like this:

# ~/bin/homedir-git
# Like git, but turns your homedir "on" first

mv ~/.git.off ~/.git
git "$@"
mv ~/.git ~/.git.off

However, I found this approach unwieldy. For one thing, the name of the command was always difficult to type because I am so strongly conditioned to type the plain, unadorned version control command instead. Another problem is that my shell's command-line completion suddenly did not know to offer the usual version-control subcommands because homedir-git or homedir-hg is not a command it recognized.

So my actual solution has been to create a command to toggle home directory version control on and off. That way, I can turn it on; let my normal muscle memory take over as I craft and execute version-control operations; and then turn it off again:

# ~/bin/home-toggle

if [ -d .git.off ] ;then
    mv ~/.git.off ~/.git || exit 1
    echo Home directory version control activated
else
    mv ~/.git ~/.git.off || exit 1
    echo Home directory version control deactivated
fi

Actually, I named my own copy of this shell script ,home because — as you might remember — I name my shell scripts starting with a comma. But you get the idea. And, of course, I check this shell script into version control along with the rest of the suite of customizations that I need on every system where I type.

This whole idea is trivial, obvious, and so simply implemented as to be hardly worth mentioning. But those of us who have been using a Unix environment for decades know that these kinds of tiny micro-customizations for making our lives easier, while they are each so simple, accumulate together into a really amazing result: an environment that offers very little friction because, each time your dotfiles are checked out to your account on a new machine, it instantly becomes an environment where every annoyance — every stone that has ever made you stumble — has already been accounted for and worked around.

The lack of friction at a well-customized command line can be really astounding if you have been putting up with the defaults your entire life. I hope that this simple example encourages you to stop in your tracks the next time something gets in your way for the third, fourth, or hundredth time, and that you will ask: “Could I solve this with a simple shell script?”

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