[GRASS5] coding a little bit of image processing

[Yann]

Hello,
i would like to code some little bit of image processing (say NDVI for
example) and later on make it available into the main gui
(UserDIP=>NDVI=>bandselection/openfile1&2)

I found r.example and i am planning to study it (yes i am a newbie!),
but are there some better way to do it coming from the new things of
grass51.

If yes, is there anyone who could suggest/submit some simple programming
framework adapted to 5.1.xx that i could study.

The gui thing will come after that first step is successful. 

Thank you,
Yann