Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!decwrl!sun!quintus!ok
From: ok@quintus.UUCP (Richard A. O'Keefe)
Newsgroups: comp.unix.questions
Subject: Re: VMS: logicals  UNIX: links, but...
Message-ID: <997@quintus.UUCP>
Date: 14 Apr 89 04:21:22 GMT
References: <475@caldwr.UUCP> <810035@hpsemc.HP.COM> <757@mks.UUCP>
Reply-To: ok@quintus.UUCP (Richard A. O'Keefe)
Organization: Quintus Computer Systems, Inc.
Lines: 26

In article <757@mks.UUCP> tj@mks.UUCP (T. J. Thompson) writes:
>Programs that read and write ``known'' filenames like this are simply
>mis-designed. This practice is a relic of JCL. It is assumed that there
>will only be one instance of the ``job'' at a time,

This is a little bit unfair to MVS.  (Which is hard.)  MVS interposes
"DD names" in between the program and the data sets.  The effect of this
is to make it IMPOSSIBLE to wire a file name (in MVS jargon, "DS name")
into a program.  [Well, not absolutely impossible, but you have to know
a friendly necromancer.]  The file names you use in a VS/FORTRAN program,
for example, are *all* analogous to environment variables, every last
one of them.  That's a pain too, but it's a different pain.

The problem is that VMS fails to draw a distinction between DD names
(environment variables) and DS names (file path-names), thus encouraging
people to get muddled between the two.  One of the pains this can lead
to in VMS is that if someone is *supposed* to set up a logical name to
specify the input for a program, but forgets, the program may happen to
find a file of that name by mistake.  Another pain is having several
programs which use the same logical names, but inconsistently...

For real heroic fun, see the equivalent of logical names in
VM/CMS Version 6 (look in the Shared File System manual).

--- 
MVS, the operating system that likes to say "DIE, sucker!"