Before you can use a gemset, you must first create it.

$ rvm 2.1.1
$ rvm gemset create teddy

To use a gemset

$ rvm gemset use teddy

To stop using the custom gemset (and switch to the default one) use one of the following:

$ rvm gemset use default # OR:
$ rvm use @default

You can switch to a gemset as you start to use a ruby, by appending @gemsetname to the end of the ruby selector string:

$ rvm use 2.1.1@teddy

You can also specify a *default* gemset for a given ruby interpreter, by doing:

$ rvm use 2.1.1@teddy --default

To use a named gemset with an RVM 'do' action, append it to the ruby selector string using a '@'

rvm 2.1.1@teddy,ree@teddy,jruby@teddy do rake test

If you are aware of where you are at, and wish to fix the gemset, you can do:

rvm gemset use teddy
rvm 2.1.1,ree,jruby do rake --sticky test

If you would like to create gemsets automatically when used, export this flag in your ~/.rvmrc file:

rvm_gemset_create_on_use_flag=1