unblogger.rb

#!/usr/bin/env ruby

require 'rubygems'
require 'blogger'
require 'mechanize'
require 'set'

STDOUT.sync = true

gmail_url = 'http://www.gmail.com'
gmail_username = 'username'
gmail_password = 'password'
blogger_blog_id = '12345'
blogger_blog_name = 'blog_name'
blogger_id = '1234567890'
blogger_username = gmail_username
blogger_password = gmail_password

# log in to your gmail account
agent = Mechanize.new
page = agent.get gmail_url
form = page.forms.first
form.Email = gmail_username + '@gmail.com'
form.Passwd = gmail_password
page = agent.submit form

# get the list of ids as per google reader
reader_ids = Set.new
page = agent.get("http://www.google.com/reader/atom/feed/" + 
  "http://#{blogger_blog_name}.blogspot.com/feeds/posts/default?r=n&n=100")
page.body.scan(/https\:\/\/blogger.googleusercontent.com\/tracker\/\d*\-(\d*)\?/).each do |id|
  reader_ids << id.to_s
end

# get the list of ids as per blogger
account = Blogger::Account.new(blogger_id, blogger_username, blogger_password)
if account.authenticated?
  blog = account.blog_for_id(blogger_blog_id)
  blog.posts.each do |post|
    reader_ids.delete(post.id)
  end
end

# the following posts have been deleted
reader_ids.each do |id|
  puts id
end