ruby 判断客户端浏览器类型代码

def users_browser
user_agent =  request.env['HTTP_USER_AGENT'].downcase 
@users_browser ||= begin
  if user_agent.index('msie') && !user_agent.index('opera') && !user_agent.index('webtv')
                'ie'+user_agent[user_agent.index('msie')+5].chr
    elsif user_agent.index('gecko/')
        'gecko'
    elsif user_agent.index('opera')
        'opera'
    elsif user_agent.index('konqueror')
        'konqueror'
    elsif user_agent.index('ipod')
        'ipod'
    elsif user_agent.index('ipad')
        'ipad'
    elsif user_agent.index('iphone')
        'iphone'
    elsif user_agent.index('chrome/')
        'chrome'
    elsif user_agent.index('applewebkit/')
        'safari'
    elsif user_agent.index('googlebot/')
        'googlebot'
    elsif user_agent.index('msnbot')
        'msnbot'
    elsif user_agent.index('yahoo! slurp')
        'yahoobot'
    #Everything thinks it's mozilla, so this goes last
    elsif user_agent.index('mozilla/')
        'gecko'
    else
        'unknown'
    end
    end

    return @users_browser
end

see： http://stackoverflow.com/questions/4707400/rails-browser-detection-methods