Having trouble setting up Redis for ruby

I am trying to play with redis on my Ubuntu machine and my little script doesn't work. I have installed redis gem and tried this little script (I know its pretty small)

require 'redis'redis = Redis.new

I get this error :

./redis.rb:4: uninitialized constant Redis (NameError)from redis.rb:2:in `require'from redis.rb:2

when I comment the line 2, I dont get any problem.How come the class Redis is not recognized?