Virtualenv Ruby install gems script from requirement_gems.txt

1_virtualenv_gems_install.env

# add first to your virtualenv (postactivate or autoenv, etc)
export GEM_HOME="$VIRTUAL_ENV/gems"
export GEM_PATH=""
export PATH=$PATH:"$GEM_HOME/bin"

2_requirement_gems.txt

sass >=3.3.0alpha --pre
compass >=1.0.0alpha --pre
bootstrap-sass

3_install_gems.rb

#!/usr/bin/env ruby

def parse_require_gem(input)
  # match, i.e. : 'compass >=1.0.0alpha --pre' or 'compass' without version 
  matches = input.scan(/([a-z0-9_\-]+)(\s([>=]{2}[0-9a-z_\-\.]+))?(\s([a-z-]+))?/)
  matches.map do |match|
    {:name => match[0], :version => match[2], :options => match[4]}
  end
end

def get_requirements
  requirements = []
  # require requirement_gems.txt file
  IO.foreach('requirements_gems.txt') do |line|
    requirements << (parse_require_gem line)
  end
  return requirements
end

def install_gem!(gemspec)
  if gemspec
    if not gemspec[:version].nil?
      if Gem::Specification::find_all_by_name("#{gemspec[:name]}", "#{gemspec[:version]}").any?
        puts ">>> gem #{gemspec[:name]} (#{gemspec[:version]}) already installed, skipped!"
      else
        puts ">>> gem install #{gemspec[:name]} --version '#{gemspec[:version]}' #{gemspec[:options]} --no-rdoc --no-ri"
        puts `gem install #{gemspec[:name]} --version '#{gemspec[:version]}' #{gemspec[:options]} --no-rdoc --no-ri`
      end
    else
      if Gem::Specification::find_all_by_name("#{gemspec[:name]}").any?
        puts ">>> gem #{gemspec[:name]} already installed, skipped!"
      else
        puts ">>> gem install #{gemspec[:name]} --no-rdoc --no-ri"
        puts `gem install #{gemspec[:name]} --no-rdoc --no-ri`
      end
    end
  end
end

def install_all!
  requirements = get_requirements
  if not requirements.empty?
    puts ">>> installing gems requirements on virtualenv:" + ENV['VIRTUAL_ENV']
    requirements.each do |gemspec|
      install_gem! gemspec[0]
    end
  end
end

if ENV['GEM_HOME']
  install_all!
else
  puts ">>> GEM_HOME not defined!"
end

This setup permit to have your specific gems packages version by virtualenv :-)

Better to use such tool: http://bundler.io/