The problem with programs like tar and sed is twofold (this is just my opinion, of course!). First of all, they're both really old. That means they've had multiple people maintain them over the years, with different coding styles and different personalities. For GNU utilities, it's usually pretty good, because they usually enforce a reasonably consistent coding style, but it's still an issue. The other problem is that they're unbelievably portable. Usually "portability" is seen as a good thing, but when taken to extremes, it means your codebase ends up full of little hacks and tricks to work around obscure bugs and corner cases in particular pieces of hardware and systems. And for programs as widely ported as tar and sed, that means there's a lot of corner cases and obscure hardware/compilers/OSes to take into account.
If you want to learn C, then I would say the best place to start is not trying to study code that others have written. Rather, try to write code yourself. If you really want to start with an existing codebase, choose one that's being actively maintained where you can see the changes that other people are making as they make them, follow along in the discussions on the mailing lists and so on.
With well-established programs like tar and sed, you see the result of the discussions that would've happened, but you can't see how software design decisions and changes are being made in real-time. That can only happen with actively-maintained software.
That's just my opinion of course, and you can take it with a grain of salt if you like :)
answered 2010-06-16T06:38:51.760