Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!warwick!nott-cs!piaggio!anw
From: anw@maths.nott.ac.uk (Dr A. N. Walker)
Newsgroups: comp.lang.postscript
Subject: Re: How can I tell if a file is "postscript"
Message-ID: <1991Mar13.160331.25024@maths.nott.ac.uk>
Date: 13 Mar 91 16:03:31 GMT
References: <1448@vidiot.UUCP> <449@heaven.woodside.ca.us> <1460@vidiot.UUCP> <Qbr2bdK00VQs40k49S@andrew.cmu.edu>
Reply-To: anw@maths.nott.ac.uk (Dr A. N. Walker)
Organization: Maths Dept., Nott'm Univ., UK.
Lines: 45

In article <Qbr2bdK00VQs40k49S@andrew.cmu.edu> jj1h+@andrew.cmu.edu
(Joseph Jackson) writes:

>"pscomm" looks at the first few bytes of the input stream looking for
>the "%!" PostScript magic.  If it doesn't find it, it will call
>"enscript" to convert the (assumedly text) file to PostScript.

	Just so.  What leaves me feeling slightly uneasy about this
is that I now have to do something special to *list* a PS file.  If
file A contains a Pascal (say) program, and B contains a PostScript
"program", then "lpr A" will list the Pascal, but "lpr B" will *obey*
the PostScript.

>				   this feature provides some degree of
>compatibility with the old days of simple line printers.  Think of how
>many things would break if you suddenly needed to specify an lpr switch
>when queuing straight text.

	Just so.  Now think how many things break if "lpr B" lists B
if the printer is a simple lineprinter but produces a fancy graphic
if we upgrade it to a LaserWriter.

	What's more, there is a similar potential problem with every
different printer language.  We could find ourselves with 10 different
printers on our network, each with a different [or, worse, the same]
magic marker, so that all sorts of files must be "enscripted" by one
of 10 different programs to print on some printers, and must not be
to print on all the others.

	I don't know if there's a complete answer.  Here, we simply
shovel whatever comes to the LW spooler direct to the LW, and it's
hard cheddar if it isn't PS (at least it usually fails quickly).
If people want listings, they have to call an ASCII -> PS program.
Since this can be packaged up into a short command, there's no
hardship in practice.  Indeed, there's an advantage in that the
command can do clever things (like printing many lines per page)
automatically, with no alteration to the spooler, which makes it
easier to divert output to remote printers when necessary.  Very
few of our users ever call "lpr" directly any more -- I do it
perhaps once a month, the rest of the time working through the
packaged commands.

-- 
Andy Walker, Maths Dept., Nott'm Univ., UK.
anw@maths.nott.ac.uk