The most convenient way to have config files is to have a sensible default value for everything. So as much as possible the program should run in spite of conf

The most convenient way to have config files is to have a sensible default value for everything. So as much as possible the program should run in spite of config errors. If that is not possible, then the diagnostics need to be very explicit. Any code, e.g. startup scripts should be ideally in a separate file. In the *NIX tradition these are usually of the form .foorc where 'foo' is the name of the app, and the '.' hides the file from normal directory listings. Ideally, it would be nice to pre-parse such startup code and only execute if it is syntactically correct.