Post your most recent tweets to Google+

minus.rb

#!/usr/bin/env ruby

## Configuration ##
###################
gplus_user = '<<<Google+ username>>>'
gplus_pass = '<<<Google+ password>>>'
tweet_count = 25 # Number of tweets to consider
twitter_user = '<<<Twitter username>>>'
###################

require 'rubygems'
require 'mechanize'
require 'twitter'

def gplus_post(username, password, content)
	agent = Mechanize.new
	agent.user_agent = 'HTC_Mega Opera/9.5 (Microsoft Windows; PPC Opera Mobi /17753; U; es-ES)'
	page = agent.get('https://accounts.google.com/ServiceLoginAuth')
	form = page.forms.first
	form.Email = username
	form.Passwd = password
	agent.submit form
	page = agent.get('https://plus.google.com')
	post = page.links_with(:text => 'Post').first
	page = agent.click post
	form = page.forms.first
	form.newcontent = content
	post = form.button_with(:value => 'Post')
	form.submit post
end

cache_file = File.expand_path('~/.minus')
read_ids = []
if File.exists?(cache_file)
	read_ids += Marshal.load File.read(cache_file)
end

for status in Twitter.user_timeline(twitter_user, :count => tweet_count).reverse
	if status.retweeted_status.nil? and status.in_reply_to_status_id.nil?
		unless read_ids.include?(status.id)
			begin
				gplus_post(gplus_user, gplus_pass, status.text)
				read_ids.push(status.id)
			rescue
				puts 'Unable to post status ' + status.id.to_s()
			end
		end
	end
end

read_ids = Marshal.dump(read_ids)
File.open(cache_file, 'w') { |f| f.write(read_ids) }

The script considers a fixed amount of tweets and ignores both replies and retweets.
IDs of tweets already posted to Google+ are cached to prevent double-posts.
The thing is designed to be run periodically as a cronjob.

Updated the script so that it handles errors during posting to Google+ more gracefully. If one status fails, it will move on to the next and it will always write the cache file in the end. That avoids double posts when something went wrong.