Branch question

[Frank Grunwald]

Hello,

My problem is quite simple : I developped a library that will be present 
in 3 different environments. The main part of the library is the same 
(98% of the code) but there are some specific changes for each environment.
I wanted to do this thing in this way but it doesn't seem to be a 
correct use of cvs :

1) Main library development in the main branch
2) Creation of branch env1, env2, env3 and specific modifications on 
each of this branch
How can I manage easily to change something in the main code (new 
functionality) and to have the modifications updated into each branches?

Hope I was clear,
thanks for your help

FRANK