Why are the gems not showing up? - ruby-on-rails

Question

So this happens to me regularly, where i have gems that are installed but for some reason my rails app is not finding it...here is my example
my config/environment.rb
config.gem "whenever"
my install
sudo gem install whenever
Password:
Successfully installed whenever-0.6.2
1 gem installed
gem list | grep when
whenever (0.6.2)
script/server
=> Booting WEBrick
=> Rails 2.3.8 application starting on http://0.0.0.0:3000
Missing these required gems:
whenever
You're running:
ruby 1.8.7.174 at /usr/local/bin/ruby
rubygems 1.3.7 at /Users/matt/.gem/ruby/1.8, /usr/local/lib/ruby/gems/1.8
Run `rake gems:install` to install the missing gems.
gem env
RubyGems Environment:
- RUBYGEMS VERSION: 1.3.7
- RUBY VERSION: 1.8.7 (2009-06-12 patchlevel 174) [i686-darwin10.4.0]
- INSTALLATION DIRECTORY: /usr/local/lib/ruby/gems/1.8
- RUBY EXECUTABLE: /usr/local/bin/ruby
- EXECUTABLE DIRECTORY: /usr/local/bin
- RUBYGEMS PLATFORMS:
- ruby
- x86-darwin-10
- GEM PATHS:
- /usr/local/lib/ruby/gems/1.8
- /Users/matt/.gem/ruby/1.8
- GEM CONFIGURATION:
- :update_sources => true
- :verbose => true
- :benchmark => false
- :backtrace => false
- :bulk_threshold => 1000
- "gem" => "--no-ri --no-rdoc"
- :sources => ["http://gems.rubyforge.org/", "http://gems.github.com", "http://gemcutter.org"]
- REMOTE SOURCES:
- http://gems.rubyforge.org/
- http://gems.github.com
- http://gemcutter.org
$ which gem
/usr/local/bin/gem
$ which ruby
/usr/local/bin/ruby
Does anybody see the issue because i clearly cant even start my server and i know the gem is installed. I am on a macbook pro with Snow leopard by the way...

Answer 1

Please check you ruby and gem installation :
May be use these commands
which ruby
which gem
and make sure they have the correct path.
Most times people have these problems is that "gem" command installs gems into a different ruby installation instead of the one used by your rails app.

Answer 2

I had two different 1.9.x ruby versions, and I had installed rvm.
All the gems installed through rvm were not showing up.
Basically my "which gem" was showing /usr/bin/gem while it was supposed to be "/home/gh/.rvm/rubies/ruby-1.9.x/bin/gem"
If such is the case, in your gnome-terminal, under Edit > Profile Preferences > Title and Command, check the option "Run command as a login shell"
This integrates rvm with gnome-terminal :) Hope this helps someone who faced the same issue as I did.
Reference: https://rvm.io/integration/gnome-terminal