Rails - problem installing Spree

I'm having a problem installing Spree in a Rails app.

when I run gem 'spree' (as per the ins开发者_Python百科tructions on http://spreecommerce.com/documentation/getting_started.html)

I get the following error:

ERROR:  While executing gem ... (RuntimeError)
    Unknown command spree

I have the following Spree gems installed:

gem list spree

*** LOCAL GEMS ***

spree (0.30.1)
spree_api (0.30.1)
spree_auth (0.30.1)
spree_core (0.30.1)
spree_dash (0.30.1)
spree_promo (0.30.1)
spree_sample (0.30.1)

when I installed the Spree gem I used:

sudo gem install spree

thanks for any help.

---

The instructions actually say to add gem 'spree' to your Gemfile (and not execute it as a command):

Add Spree gems to your Gemfile:

gem 'spree', '~> 4.1'
gem 'spree_auth_devise', '~> 4.2'
gem 'spree_gateway', '~> 3.9'

---

Spree gem install instructions: https://gist.github.com/kany/6334724