simple popen question

[Jim Benson]

On Sat, 3 Apr 2004, Cameron Laird wrote:

> In article <1080965541.46978 at yasure>, Donn Cave <donn at drizzle.com> wrote:
> >Quoth Jim Benson <jbenson at sextans.lowell.edu>:
> >| On Fri, 2 Apr 2004, Cameron Laird wrote:
> >...
> >|> In general, no; the reader doesn't control the buffering, the writer does.
> >|
> >
> >Well, the writer knows.  When you run it "from the shell", that
> >really means its output device is /dev/tty.  When you run it from
> >popen(), its output device is a pipe.  C library I/O, and hence
> >most application I/O, automatically treats these two devices
> >differently.  Or rather, it treats the tty specially, and treats
> >a pipe like any other file.  For the tty it uses line buffering,
> >for everything else block buffering.
> >
> 
> All true--and Python even has an answer, Pexpect, for those stuck
> with such subtleties.  I repeat my advice, though, that Mr. Benson
> will likeliest find quick satisfaction simply by having his writer
> flush on newline.

Thanks to all...i understand what is going on much better now.
I'll try your advice Mr. Laird and add a flush to the write
side. It sounds like that is what i want.

> 
> Also, Mr. Benson, are you *sure* you want to treat blank lines as
> end-of-message markers?
> 

Perhaps not...but it seems to work. It doesn't stop on
lines that contain only a '\n\0' for example. Hence
on the write side i can print out apparently blank lines..
to make the reading of the output easier....and the 
readline loop keeps piping them and only stops when the
executable stops. 

Thanks again,

Jim