List slurp

require 'rubygems'
require 'twitter'

h = Twitter::HTTPAuth.new 'username', 'password'
twitter = Twitter::Base.new(h)

source_user = 'username'
source_slug = 'list-name'
target_user = 'username'
target_slug = 'list-name'
cursor = -1

begin
  results = twitter.list_members(source_user, source_slug, cursor)
  results.users.each do |user|
    puts "adding #{user.screen_name}"
    twitter.list_add_member(target_user, target_slug, user.id)
  end
  cursor = results.next_cursor
end while cursor != 0