class IO
  alias :old_puts puts

  def puts(thing)
    if not thing.to_s.match(/\A\*\* Erubis [\d|\.]+\Z/)
      return old_puts(thing)
    end
  end
end

$stdout.puts "foo"
$stdout.puts "** Erubis 2.3.4"
$stdout.puts "bar"

=======================

pleb:~ will$ ruby puts.rb
foo
bar