Question

Sets the buffering mode for an output file.
There are three available modes:

• "no":
  no buffering; the result of any output operation appears immediately.
• "full":
  full buffering; output operation is performed only
  when the buffer is full (or when you explicitly flush the file
  (see io.flush)).
• "line":
  line buffering; output is buffered until a newline is output
  or there is any input from some special files
  (such as a terminal device).

For the last two cases, sizes
specifies the size of the buffer, in bytes.
The default is an appropriate size.