passenger-ruby.rb

class X

  def self.ruby_command
    @@ruby_command ||= begin
      real_rvm_ruby = self.rvm_ruby_string
      real_rvm_path = self.rvm_path
      filename = nil
      if !real_rvm_ruby.nil? && !real_rvm_path.nil?
        rvm_ruby = File.join(real_rvm_path, "wrappers", real_rvm_ruby, "ruby")
        filename = rvm_ruby if File.exists?(rvm_ruby)
      end
      filename ||= Config::CONFIG['bindir'] + '/' + Config::CONFIG['RUBY_INSTALL_NAME'] + Config::CONFIG['EXEEXT']
      filename
    end
  end

  # Returns the current ruby string for the loaded ruby
  def self.rvm_ruby_string
    gem_home = ENV['GEM_HOME'].to_s.strip
    if !gem_home.empty? && gem_home =~ /rvm\/gems\//
      File.basename(gem_home)
    else
      matching_path = $:.select { |item| item =~ /rvm\/rubies/ }.first
      matching_path.to_s.gsub(/^.*rvm\/rubies\//, '').split('/')[0]
    end
  end

  # Get a value for the current rvm path.
  def self.rvm_path
    [ENV['rvm_path'], "~/.rvm", "/usr/local/rvm"].each do |path|
      next if path.nil?
      path = File.expand_path(path)
      return path if File.directory?(path)
    end
    return nil
  end

end

# ALTERNATIVE

class Y
  def self.ruby_command
    @@ruby_command ||= begin
      if !ENV['MY_RUBY_HOME'].nil?
        rvm_path = File.dirname(File.dirname(ENV['MY_RUBY_HOME']))
        $LOAD_PATH.unshift File.join(rvm_path, "lib")
        require 'rvm'
        rvm_ruby = File.join(rvm_path, "wrappers", RVM::Environment.current_environment_id, "ruby")
        filename = rvm_ruby if File.exists?(rvm_ruby)
      end
      filename ||= Config::CONFIG['bindir'] + '/' + Config::CONFIG['RUBY_INSTALL_NAME'] + Config::CONFIG['EXEEXT']
      filename
    end
  end
end

puts "X: #{X.ruby_command}"
puts "Y: #{Y.ruby_command}"