gistfile1.rb

def has_gem?(name, version=nil)
  if !$GEM_LIST
    gems = {}
    `gem list --local`.each_line do |line|
      gems[$1.to_sym] = $2.split(/, /) if line =~ /^(.*) \(([^\)]*)\)$/
    end
    $GEM_LIST = gems
  end
  if $GEM_LIST[name.to_sym]
    return version ? $GEM_LIST[name.to_sym].include?(version) : true
  end
  false
end