like this,thanks
#!/usr/bin/env ruby
class IO
  def each_lines(n)
    run=true
    while run
      lines=[]
      n.times{
         ln = self.gets
         unless ln
          run=false
          break
          else
            lines<<ln.chomp
        end
      }
      yield lines unless lines.empty?
    end
  end
end

open(__FILE__) do |f|
   f.each_lines(3) do |lines|
     p lines
   end
end
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