List all rbenv commands:

$ rbenv commands
commands
completions
exec
global
help
hooks
init
install
local
prefix
realpath.dylib
rehash
root
shell
shims
uninstall
version
--version
version-file
version-file-read
version-file-write
version-name
version-origin
versions
whence
which
$

To bring up further information on the versions command use the following:

$ rbenv help versions
Usage: rbenv versions [--bare] [--skip-aliases]

Lists all Ruby versions found in `$RBENV_ROOT/versions/*'.
$