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From: robert@coke.UUCP
Newsgroups: comp.unix.questions,comp.unix.wizards
Subject: Filters for the BSD print spooling system
Message-ID: <111@coke.UUCP>
Date: Mon, 30-Mar-87 08:58:12 EST
Article-I.D.: coke.111
Posted: Mon Mar 30 08:58:12 1987
Date-Received: Wed, 1-Apr-87 01:26:18 EST
Organization: Statskonsult Programvaruhuset AB, Sweden
Lines: 43
Keywords: sun bsd print spooler printer filter
Xref: utgpu comp.unix.questions:1553 comp.unix.wizards:1593

I'm not really sure whether this should go to comp.unix.questions
or comp.unix.wizards, so I send it to both.

I'm trying to write some filters for the different kinds of printers
we have here. The filters will be forked off by Sun's/Berkeley's
lpd printer daemon. So, what's the problem, you might ask. Those
filters should only take the standard input, process it, and send
the result to the standard output. Well, that's what I thought.

The first of my filters, epsonf, worked just fine when run from
the command-line using redirection and/or pipes, but when I
installed it as if (input(?) filter) and of (output filter), only
the banner page got printed and then the filter hung. Seems like
lpd expects the output filter (the one which prints the banner page)
to release its standard output file, or something, before lpd can
let the input filter do the actual printing.

Then I tried to remove the input filter specification from /etc/printcap
and let all output go through the output filter. That seemed to work.
Hmmm, strange, I thought. Just to be sure the problem was in my filter
and nowhere else, I used the standard /usr/lib/lpf filter as both
input- and output filter, which, of course, worked like a dream (the
dream I had about how my filter should work, that is, without any
problems). Using /usr/lib/lpf as the output filter and my filter as
the output filter worked equally well.

So, here comes my question:

How Do I Write a Printer Filter for the Berkeley Printer Spooling System?
What signal's should I trap (the only signal that's documented is SIGINT
that is sent when I use lprm to remove a job), and what should I do when
I have got that signal? Anything else to think about, too?

	Thanks,
	Robert.
_______________________________________________________________________________
NAME:	Robert Claeson				PHONE:	+46 8-730 03 00
PAPER:	Statskonsult Programvaruhuset AB
	P.O. Box 4040				"Whatever it is, it's not
	S-171 04 Solna				 my problem."
	Sweden
UUCP:	{seismo!}mcvax!enea!coke!robert
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