What is this error when installing a bundle in Ruby/Rails/Aptana?

Question

I am trying to follow the Ruby Tutorial (Michael Hartl) book. I get this error at Gemfile:41 (some steps ago it was at Gemfile:35):

Franciscos-MacBook-Pro:first_app franciscomello$ bundle install --without production
Undefined local variable or method `rb' for Gemfile
        from /Users/franciscomello/Desktop/Aptana Studio 3 Workspace/First_app/Gemfile:41

I tried many tips. For example, I have the sandbox correct output:

Franciscos-MacBook-Pro:first_app franciscomello$ which ruby irb gem rake
/usr/bin/ruby
/usr/bin/irb
/usr/bin/gem
/usr/bin/rake

I already debugged my Gemfile, and it looks like this:

source 'https://rubygems.org'

# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '4.0.0'

# Use sqlite3 as the database for Active Record
gem 'sqlite3', '1.3.8'


# Use SCSS for stylesheets
gem 'sass-rails', '4.0.0'

# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '2.1.1'

# Use CoffeeScript for .js.coffee assets and views
gem 'coffee-rails', '4.0.1'

# See https://github.com/sstephenson/execjs#readme for more supported runtimes
# gem 'therubyracer', platforms: :ruby

# Use jquery as the JavaScript library
gem 'jquery-rails', '3.0.4'

# Turbolinks makes following links in your web application faster. Read more: https://github.com/rails/turbolinks
gem 'turbolinks', '1.1.1'

# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '1.0.2'

group :doc do
  # bundle exec rake doc:rails generates the API under doc/api.
  gem 'sdoc','0.3.20', require: false
end

group :production do
  gem 'pg', '0.15.1'
  gem 'rails_12factor', '0.0.2'
end
#sugestao do Tutorial 
gem rb-readline

Answer 1

It should be

gem 'rb-readline'  

Without the quotes, it tries to interpret it as variables... specifically rb minus readline