save_history

# File lib/irb/ext/save-history.rb, line 96
    def save_history
      if num = IRB.conf[:SAVE_HISTORY] and (num = num.to_i) > 0
        if history_file = IRB.conf[:HISTORY_FILE]
          history_file = File.expand_path(history_file)
        end
        history_file = IRB.rc_file("_history") unless history_file

        # Change the permission of a file that already exists[BUG #7694]
        begin
          if File.stat(history_file).mode & 066 != 0
            File.chmod(0600, history_file)
          end
        rescue Errno::ENOENT
        rescue
          raise
        end

        open(history_file, 'w', 0600 ) do |f|
          hist = HISTORY.to_a
          f.puts(hist[-num..-1] || hist)
        end
      end
    end