A script that I have run via cron to re-index various codebases.

buildctags.rb

#!/usr/bin/ruby

places_to_process = ["~/development/ruby/"].map{|dir| File.expand_path(dir)}
places_to_process.each do |directory|
  Dir.chdir(directory)
  entries = Dir.entries(".").reject{|i| i.chars.first == "."}
  entries.each do |entry|
    Dir.chdir(directory + "/" + entry)
    system("ctags -R -f .tags")
  end
end