OK -
1. So by "CLI", you mean "command line interface"...
2. ... and by "appliance", you mean some turnkey product which, out-of-the-box, combines hardware and software to provide some specific functionality...
3. ... and you want the product to run under Linux (although, presumably, Linux would not be visible to the end-user of this product).
It doesn't sound like there's any particular programming question here, but I'd recommend looking at this book:
Building Embedded Systems with Linux, Karim Yaghmour, O'Reilly
http://www.bookpool.com/ss?qs=buildi...+Linux&x=0&y=0
At the highest level, it gives you an excellent overview of what kinds of options you have, and what kinds of issues you're likely to deal with, in the course of designing and implementing ANY Linux-based system. At the "micro" level, it gives you many excellent pointers on setting up tool chains, system bootstrapping, error logging and recovery strategies, etc etc. It also has perhaps the most comprehensible discussion of Open Source licensing you'll find anywhere.
Please let me know whether or not I've addressed your actual question.
Your .. PSM