metasploit-framework/test/hooks/string_idx.rb

class String
  @@idx_reported = {}
  def [](*args)

    if args.length == 1 && args[0].class == ::Integer && !@@idx_reported[caller[0].to_s]
      $stderr.puts "HOOK: String[idx] #{caller.join("\t")}\n\n"
      @@idx_reported[caller[0].to_s] = true
    end
    slice(*args)
  end
end