post2fb.rb

#!/usr/bin/env ruby
require 'koala' # gem install koala --no-ri --no-rdoc

# create a facebook app and get access token from here
# https://developers.facebook.com/tools/explorer
# select "groups", "photos" when authenticating
oauth_access_token = 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx'
group_filtering_words = ['ruby']
image_path = 'image.png' #change to your image path
message = 'My Cool image.' # your message

graph = Koala::Facebook::API.new(oauth_access_token)

# getting groups of interest
groups = graph.get_connections("me", "groups").select do |group|
	group_filtering_words.any? do |word|
		group["name"].downcase.include? word
	end
end

index = 0
groups.each do |group|
	index += 1
	puts "[#{index}/#{groups.size}] Posting to group #{group["name"]}."
	graph.put_picture(
		image_path, 
		{:message => message}, 
		group['id']
	)
end