Wouldn't it be nice if you could write a program that could reach into an Apache config file (or an AptConf file, or an /etc/aliases file, Postfix master.cf, sshd/ssh config, sudoers, Xen conf, yum or other) make a change, and not ruin the comments and other formatting that exists?
That's what Augeas permits you to do. If a config file's format as been defined in the Augeas "lens" language, you can then use Augeas to parse the file, pull out the data you want, plus you can add, change or delete elements too. When Augeas saves the file it retains all comments and formatting. Any changes you made retain the formatting you'd expect.
Augeas can be driven from a command-line tool (augtool) or via the library. You can use the library from Ruby, Puppet, and other systems. There is a project to rewrite Puppet modules so that they use Augeas (augeasproviders.com/providers)
Version 1.5 of Augeas was released this week. The number of formats it understands (lenses) has increased (see the complete list here). You can also define your own lens, but that requires an understanding of parsing concepts (get our your old CS textbook, you'll need a refresher). That said, I've found friendly support via their mailing list when I've gotten stuck writing my own lens.
The project homepage is http://augeas.net/ and the new release was just announced on the mailing list (link).
