for global:
rvm @global do gem list
for other gemsets:
GEM_PATH=$GEM_HOME gem list
@global is a gemset that all other gemsets inherit for given ruby, it does not inherit for m itself so it’s safe to select it and run gem list in it’s context.
For all other gemsets you can use the fact that gem list displays gems from all paths available in GEM_HOME and GEM_PATH, resetting GEM_PATH to be equal GEM_HOME will make only one path available – the one from GEM_HOME so gem list will only show gems in the selected gemset, ignoring all other gemsets (at this time the @global, but RVM 2.0 will support multiple gemsets inheritance).