Path: utzoo!mnetor!uunet!husc6!cmcl2!beta!unm-la!unmvax!nmtsun!hydrovax
From: hydrovax@nmtsun.nmt.edu (M. Warner Losh)
Newsgroups: comp.lang.c
Subject: Re: exit(-1)
Message-ID: <1240@nmtsun.nmt.edu>
Date: 22 Jan 88 01:42:49 GMT
References: <502@cresswell.quintus.UUCP> <6935@brl-smoke.ARPA> <1179@wjvax.UUCP> <10237@mimsy.UUCP>
Organization: NMT Hydrology program
Lines: 54
Summary: Exit codes and interpretation

In article <10237@mimsy.UUCP>, chris@mimsy.UUCP (Chris Torek) writes:
> In article <1225@nmtsun.nmt.edu> I write
> >... The more proper VMS implementation of EXIT_STATUS should be
> >SS$_NORMAL, which is (at least in 4x) defined to be 1.
> 
> (I think it was inherited from RT-11.  It was 1 in VMS 2.8.)
> 
> >Why would you expect an operating system dependent scheme such
> >as exit(0) to work on all OS's?
> 
> Simple.  Let me phrase it this way:  `Why would you expect a standard
> library scheme to be dependent on the O/S?'  Or, `whoever said exit
> was a system call?'

  If I remember correctly, fopen() is system dependent (you can't
say fopen ("/tmp/foo", "r"), for example, and expect it to work on
all operating systems.  The same sort of thing is true about exit().
 
> Unix, by virtue of being the first system to implement the language,
> is privileged: it gets to take the argument to exit() and pass it
> back to the calling program.  Other systems might have to convert
> the argument to 0 => success, anything else => unspecified failure.

    The UNIX operating system does not work this way.  The shells that
surround it DO.  What I mean is this : UNIX doesn't give a furry rat's
whatever what you use for an exit status, it mearly passes it to the
shell (or to make, or whatever) who then desides what to do with that
number.  Even the shell doesn't care what value you give it, as long
as you give it something.  Most people choose to use zero, cause
that's what K&R say to use.  Not that I'm slamming UNIX, or anything,
that's just what's goin' on behind the scenes.

    In VMS, the exit status is more than just any arbitrary number.
Each of the numbers has a perscribed meaning.  The numbers are
interpeted, again by the shell (to use the UNIX terminology; command
interpreter to use DEC's), as meaning success or failure.  Again,
these exit values are useful to the shell, or shell scripts that are
running (DCL command files) IN ADDITION TO THE SHELL ITSELF.  There
are mechanisms to allow you to say "When a warning, or anything more
sever occures, then branch to this part of my DCL program".

The basic argument is this:  Since UNIX had it first, should all other
OS's be forced to use that convention?  I think not.  THIS IS AN OPERATING
SYSTEM DEPENDENT ISSUE, just like file names.  It should be delt
with in a reasonably intelligent mannor, so that ALL PARTIES involved
CAN WRITE PORTABLE CODE.  Isn't that what ANSI is all about?????


-- 
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