Re: Flushing all Buffers Before Exiting

[Greg Wooledge <wooledg@eeg.ccf.org>]

On Thu, Mar 21, 2019 at 06:01:26PM -0000, Curt wrote:
> I'm reading a pty app won't buffer (script, screen, etc.).

Well, it's a convention, adopted by the C library functions in stdio.

stdio(3) says:

       At  program  startup, three text streams are predefined and need not be
       opened explicitly: standard input  (for  reading  conventional  input),
       standard  output  (for writing conventional output), and standard error
       (for  writing  diagnostic  output).   These  streams  are   abbreviated
       stdin,stdout and stderr.  When opened, the standard error stream is not
       fully buffered;  the  standard  input  and  output  streams  are  fully
       buffered  if  and  only  if  the streams do not refer to an interactive
       device.
       
       Output streams that refer to terminal devices are always line  buffered
       by  default;  pending  output  to such streams is written automatically
       whenever an input stream that refers to a terminal device is read.   In
       cases  where  a large amount of computation is done after printing part
       of a line on an output terminal, it is necessary to fflush(3) the stan‐
       dard  output  before  going  off  and computing so that the output will
       appear.


> And then there's a program called 'unbuffer'?

It's a hack, built around Expect.  It basically tries to fool the
application into thinking that standard output is a terminal, so the
application will operate in line-buffering mode.

I've been told that it works quite often, but you can't ever guarantee
success with it.