Question

I am using rvm, doing the following:

rvm install ree    <--- (Ruby Enterprise Edition), or this can be 1.8.7 or 1.9.2
rvm ree
rvm gemset create 'proj'
cd path/to/proj
bundle install

so Gemfile in that project says:

gem 'rails', '3.0.0'

and bundle install is super fast, reporting

Using rails (3.0.0) 

but after that when I type

$ rails -v
/Library/Ruby/Site/1.8/rubygems.rb:779:in `report_activate_error': Could not find RubyGem rails (>= 0) (Gem::LoadError)
    from /Library/Ruby/Site/1.8/rubygems.rb:214:in `activate'
    from /Library/Ruby/Site/1.8/rubygems.rb:1082:in `gem'
    from /usr/bin/rails:18

$ which rails
/usr/bin/rails

so bundle install doesn’t install the rails as a gem?
but if I type script/rails -v it shows it is 3.0.0

Answer 1

This is correct. bundle install won’t install Rails as a gem in the conventional sense. Now to explain why.

When Bundler runs an install, it will install the gems a directory: ~/.bundle/<type-of-ruby>/<version>/gems. This is different to the normal way of installing them to a system path. When a gem is installed at a system path, the executable is made available because that directory is within the load path. Now this is a bad thing, because you can only have one executable per gem. Have you got SomeGem v2 installed but want to use the generator from SomeGem v1? Too bad.

Bundler solves this problem by installing them into the afore-mentioned location and only requiring specific versions of the gems it needs (specified inside of Gemfile. By running simply rails, you’re trying to run the system executable (as in one provided by doing gem install rails) rather than the Bundler one (provided by doing bundle install for a Rails project).

To run the one that Bundler installs you must run it like this bundle exec rails within a directory that contains a Gemfile that specifies any version of Rails. Bundler will load a specific version of Rails and you should now be able to run them side-by-side with the only tradeoff being the bundle exec prefix to commands.

Personally I’ve aliased this to be and two characters before some commands is a worthwhile tradeoff to avoiding The Seventh Circle of Gem Conflict Hell in my opinion.