twitter_post.rb

require 'rubygems'
require 'oauth'
require 'json'

CONSUMER_KEY = 'XXXXXXXXXXXXX'
CONSUMER_SECRET = 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
ACCESS_TOKEN = 'XXXXX-XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
ACCESS_TOKEN_SECRET = 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'

# 下準備
consumer = OAuth::Consumer.new(CONSUMER_KEY,
                               CONSUMER_SECRET,
                               :site => 'http://twitter.com')
access_token = OAuth::AccessToken.new(consumer,
                                      ACCESS_TOKEN,
                                      ACCESS_TOKEN_SECRET)

# Tweetの投稿
response = access_token.post('http://twitter.com/statuses/update.json',
                             'status'=> 'xxxxxxxxx')