Committing Machine Specific Configuration Files
A common scenario when I develop is that the codebase will have several config files which require machine specific settings. These files will be checked into Git and other developers will always accidentally check them back in and break someone else's configuration.
A simple solution to this would be to just not check them in to Git, or even to additionally add a .gitignore entry for them. However, I find that it is much more elegant to have some sensible defaults in the file which the developer can modify to suit his needs.
Is there an elegant way to make Git play nicely with such files? I would like to be able to modify a machine-specific configuration file and then be able to run "git commit -a" without checking that file in.
Answer
Have your program read a pair of configuration files for its settings. First, it should read a config.defaults file that would be included in the repository. Then, it should read a config.local file that should be listed in .gitignore
With this arrangement, new settings appear in the defaults file and take effect as soon as it's updated. They will only vary on particular systems if they're overridden.
As a variation on this, you could have just a general config file that you ship in version control, and have it do something like include config.local to bring in the machine-specific values. This introduces a more general mechanism (versus policy) in you code, and consequently enables more complicated configurations (if that's desirable for your application). The popular extension from this, seen in many large-scale open-source software, is to include conf.d, which reads configuration from all the files in a directory.
Also see my answer to a similar question.