Gem found in irb, not in Ruby - ruby

Question

I have some gems installed, and I'm trying to use them in a Ruby app:
require 'rubygems'
require 'mygem'
When I run the app, though, I get this error: <internal:lib/rubygems/custom_require>:29:inrequire': no such file to load -- mygem (LoadError)`
But if I try requiring the gem inside irb (making sure to `require 'rubygems' first), it works fine. What am I supposed to do? I tried googling for this problem, but didn't understand.
Running a which on ruby, gem, and irb shows that they're all in /opt/local/bin/, i.e.,
> which ruby
/opt/local/bin/ruby
> which gem
/opt/local/bin/gem
> which irb
/opt/local/bin/irb
Update to answer the questions posed (yep, irb and ruby are pointing to different folders):
$LOAD_PATH and $: in irb both contain seem to be pointing to ruby 1.8 folders:
/opt/local/lib/ruby/site_ruby/1.8
/opt/local/lib/ruby/site_ruby/1.8/i686-darwin10
/opt/local/lib/ruby/site_ruby
/opt/local/lib/ruby/vendor_ruby/1.8
/opt/local/lib/ruby/vendor_ruby/1.8/i686-darwin10
/opt/local/lib/ruby/vendor_ruby
/opt/local/lib/ruby/1.8
/opt/local/lib/ruby/1.8/i686-darwin10
.
$: in ruby points to ruby 1.9.1 folders:
/usr/local/lib/ruby/site_ruby/1.9.1
/usr/local/lib/ruby/site_ruby/1.9.1/i386-darwin9.8.0
/usr/local/lib/ruby/site_ruby
/usr/local/lib/ruby/vendor_ruby/1.9.1
/usr/local/lib/ruby/vendor_ruby/1.9.1/i386-darwin9.8.0
/usr/local/lib/ruby/vendor_ruby
/usr/local/lib/ruby/1.9.1
/usr/local/lib/ruby/1.9.1/i386-darwin9.8.0
gem env shows
RubyGems Environment:
- RUBYGEMS VERSION: 1.4.1
- RUBY VERSION: 1.8.7 (2010-12-23 patchlevel 330) [i686-darwin10]
- INSTALLATION DIRECTORY: /opt/local/lib/ruby/gems/1.8
- RUBY EXECUTABLE: /opt/local/bin/ruby
- EXECUTABLE DIRECTORY: /opt/local/bin
- RUBYGEMS PLATFORMS:
- ruby
- x86-darwin-10
- GEM PATHS:
- /opt/local/lib/ruby/gems/1.8
- GEM CONFIGURATION:
- :update_sources => true
- :verbose => true
- :benchmark => false
- :backtrace => false
- :bulk_threshold => 1000
- "gempath" => ["/opt/local/lib/ruby/gems/1.8"]
- :sources => ["http://rubygems.org/", "http://gems.github.com", "http://gems.github.com"]
- REMOTE SOURCES:
- http://rubygems.org/
- http://gems.github.com
- http://gems.github.com
Gem.path in irb points to
/Users/grautur/.gem/ruby/1.8
/usr/local/lib/ruby/gems/1.8
Gem.path in ruby points to
/Users/grautur/.gem/ruby/1.9.1
/usr/local/lib/ruby/gems/1.9.1

Answer 1

I'm not sure what's going on. However, the following may help.
In irb, do
require 'rubygems'
require 'mygem'
puts $:
and then, in ruby, do
require 'rubygems'
puts $:
and show us what you get if you haven't worked it out.
Edit: also print out the results of doing gem env on the command line.
Edit 2: See what happens if you type in puts Gem.path after you've required rubygems in both irb and ruby. See thanks to Matt for describing Rubygems

Answer 2

You may try to add gem 'mygem' before the require, but that should not be necessary.

Answer 3

You will have to add gem install mygem in your Gamefile and then run bundle install command. Your application will work correctly after doing this.

Answer 4

I had a similar problem. The solution I found eventually was to setup rvm (ruby version manager) on my system and use it to setup a new ruby environment. it also makes it easy to switch between ruby versions of sets of gems.