rails commands for gem unpack

If you want to unpack gem file - you can only unpack gems that you have installed, for example memcache-client:

gem unpack memcache-client

You may also use rake:

rake gems:unpack GEM=memcache-client

But some reason, the second does not work for my msysgit.

And, there is a discussion to use gem or plugin (http://www.robbyonrails.com/articles/2009/01/13/question-plugins-or-gems-or-both)