I think its KARAF_BASE you should use.
Also mind that editing the etc files does not work in the way etc fabric8 does it, where you define profiles and then assign profiles to containers.
So not sure what your intend is with the karaf command. But if it has to do with jboss fuse / fabric8 then I suggest to reach out to use about this so we can help you better.
There is a #fusesource chat room at the Red Hat IRC
And btw we use this code in fabric8
private static final String KARAF_BASE = System.getProperty("karaf.base");