Ug. I just moved from a Windows 7 installation to a Lion system. I'm attempting to teach myself Ruby on Rails, and whilst I like the language, the environment feels fragile and mysterious. I used the same command to install heroku on both systems, but the System X system is not happy with the install. 

On System X I used rvm, which might be my problem. 

What controls where Gems are installed?

How can I get heroku up and running? And what will prevent the next gem from getting lost?

```
$ sudo gem install heroku
...

$ heroku -v

~/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/dependency.rb:247:in `to_specs': Could not find heroku (>= 0) amongst [minitest-1.6.0, rake-0.8.7, rdoc-2.5.8] (Gem::LoadError)
    from /Users/aliwells26/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/dependency.rb:256:in `to_spec'
    from /Users/aliwells26/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems.rb:1210:in `gem'
    from /Users/aliwells26/.rvm/gems/ruby-1.9.2-p290@rails3tutorial/bin/heroku:18:in `<main>'

$ gem environment
RubyGems Environment:
  - RUBYGEMS VERSION: 1.8.11
  - RUBY VERSION: 1.9.2 (2011-07-09 patchlevel 290) [x86_64-darwin11.2.0]
  - INSTALLATION DIRECTORY: /Users/aliwells26/.rvm/gems/ruby-1.9.2-p290@rails3tutorial
  - RUBY EXECUTABLE: /Users/aliwells26/.rvm/rubies/ruby-1.9.2-p290/bin/ruby
  - EXECUTABLE DIRECTORY: /Users/aliwells26/.rvm/gems/ruby-1.9.2-p290@rails3tutorial/bin
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86_64-darwin-11
  - GEM PATHS:
     - /Users/aliwells26/.rvm/gems/ruby-1.9.2-p290@rails3tutorial
     - /Users/aliwells26/.rvm/gems/ruby-1.9.2-p290@global
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :benchmark => false
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - http://rubygems.org/

$ echo $PATH
/Users/aliwells26/.rvm/gems/ruby-1.9.2-p290@rails3tutorial/bin:/Users/aliwells26/.rvm/bin:/Users/aliwells26/.rvm/gems/ruby-1.9.2-p290/gems/rails-3.1.1/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin:/usr/local/git/bin:/usr/local/git/bin

```