Re: trouble with reading from pipes

[zentara <zentara zentara net>]

On Wed, 25 Jan 2006 16:21:02 -0500 (EST)
"muppet" <scott asofyet org> wrote:

> Actually, it's a subtle interaction of various pieces.

> Watch out -- you're implicitly returning nonzero here because the print is
> your block's last statement.  HOwever, the return value of the callback is
> supposed to be a boolean indicating whether the callback is to stay installed.

> Note lack of a newline to flush the output buffer.

> > Only problem is that nothing ever happens, even though I know the child
> > process is running.  Any ideas what I am screwing up?
>
> Don't use buffered IO and blocking reads with IO watches.  The IO watch fires
> when *real* input arrives, and using buffered IO with that messes with your
> mind.  Also, the <> operator will attempt to read up to a $/, and will block
> until it does.  By default, $/ is "\n", and you're not writing a "\n" to your
> output stream.
>
> So, your callback is being invoked once, and is hanging on the read, waiting
> for a newline to show up.

> Set $|=1 (autoflush) in the child, and use sysread() in your IO watch
> callbacks.  By the way, when using sysread(), you must be prepared to handle
> partial line reads.

> This is another FAQ; i believe the solution in the FAQ contains misleading
> code.  Any volunteers to update that?

I'll help you out, if no one better qualified cares to do it. :-)

There is an excellent example showing the sysread and autoflushing of pipes at
http://forge.novell.com/modules/xfcontent/file.php/exam/documentation/study-14-09-05.tar.gz

in the sample program "count_down.pl"  and it is explained in x3545.html



-- 
I'm not really a human, but I play one on earth.
http://zentara.net/japh.html