Selectively Removing objects

Dear list members,

Does anyone know how to use rm() to remove only variables but not
declared functions from the environment ?
I understand I could name all the functions with, let's say
"f_something", make sure that all variables do not start with "f_" and
then remove all BUT objects starting with "f_".
However, I have already defined all the functions and it would be
troublesome to change all of them to a new name.

Any hint ?
Thanks

Paulo Gustavo Grahl, CFA