command pipe concatenated messages

[Al Tobey]

On Mon, 2003-12-29 at 06:06, Jim Mozley wrote:
> John P. Rouillard wrote:
> 
> 
> > I would use ">> $pipe" to append data for two reasons:
Jim was my beta tester for Nagios::Cmd when working out the bugs on
Solaris (actually, any BSD flavor).  BSD's don't allow seek() on fifos
and opening in O_APPEND mode implies a seek to the end of the file,
which throws an exception.   Linux happily ignores the seek().
> > 
> >   1 - > clobbers data already existing in files, not sure about in pipes
O_TRUNC is ignored for terminals and FIFO's - see the open(2) manpage.
> >   2 - atomic writes occur only if file is opened for append IIRC.
FIFO's cannot be opened in append mode on BSD flavors, as I explained
earlier.
> > 
> >>flock(PIPE, LOCK_EX);
> > 
> > 
> > This should guarantee only one process is accessing the file, but I
> > think you have already written to the file by using > in your open, so
> > there may be a race condition.
Well, that write you're worried about doesn't occur since O_TRUNC is
ignored for FIFO's.  No race condition :)
> IIRC it is not possible to open a filehandle to a pipe using ">> $pipe", 
> one must use "> $pipe". I get "Cannot open pipe Illegal seek at ..." 
> when trying.
Ahh, the rigors and wonders of portability.

> Regards,
> 
> Jim
> 
> 
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