$ gem help commands
GEM commands are:
build Build a gem from a gemspec
...
specification Display gem specification (in yaml)
uninstall Uninstall a gem from the local repository
unpack Unpack an installed gem to the current directory
update Update the named gem (or all installed gems) in the local repository
For help on a particular command, use 'gem help COMMAND'.
Commands may be abbreviated, so long as they are unambiguous.
e.g. 'gem i rake' is short for 'gem install rake'.