'rake spec' works, 'spec spec' doesn't

When I added my first gem dependency to config/environment.rb, (will_paginate), I'm encountering an error when running rspec as follows:

nik$ spec spec/
Missing these required gems:
  will_paginate  

You're running:
  ruby 1.8.6.369 at /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby
  rubygems 1.3.7 at /Users/nik/.gem/ruby/1.8, /Library/Ruby/Gems/1.8, /System/Library/F开发者_开发问答rameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/gems/1.8

Run `rake gems:install` to install the missing gems.

It's not picking up the first ruby binary in my $PATH, which I installed with macports:

nik$ ruby -v
ruby 1.8.7 (2010-06-23 patchlevel 299) [i686-darwin9]
nik$ which ruby
/opt/local/bin/ruby

Curiously, rake spec succeeds:

nik$ rake spec
(in /Users/nik/rails_projects/bigchan)
....................................................................................

Finished in 2.314131 seconds

84 examples, 0 failures

You have different commands looking up different versions of ruby, hence - different sets of gems.

$ which -a ruby

will show you at least two versions of ruby.

• ruby 1.8.6.369 probably in /usr/bin (used when running spec spec/)
• ruby 1.8.7.299 in /opt/local/bin (used when running rake spec)

Nuke the one you don't need and everything related to it.