Path: utzoo!utgpu!water!watmath!clyde!rutgers!princeton!udel!gatech!hao!ames!sri-spam!sri-unix!quintus!ok
From: ok@quintus.UUCP (Richard A. O'Keefe)
Newsgroups: comp.unix.questions
Subject: Re: csh, exit, &&, || (was Re: exit(-1), 0 is sometimes magic)
Summary: an object lesson
Keywords: exit, zero, shells
Message-ID: <574@cresswell.quintus.UUCP>
Date: 25 Jan 88 04:32:54 GMT
References: <502@cresswell.quintus.UUCP> <6935@brl-smoke.ARPA> <1179@wjvax.UUCP> <10318@mimsy.UUCP>
Organization: Quintus Computer Systems, Mountain View, CA
Lines: 25

> In article <310@fig.bbn.com> rsalz@bbn.com (Rich Salz) writes:
> >The use of && and || in csh is the opposite of that in /bin/sh.
> >	/bin/sh -c "/bin/test -d foo || mkdir foo"
> >Means if the foo directory doesn't exist, make it. ...
> >	/bin/csh -c "/bin/test -d foo || mkdir foo"
> >will never make the directory, or mkdir will spit if it already exists.

In every release of SunOS I've used, this does actually work.
The problem is that the C-shell has TWO operators spelled "&&"
and TWO operators spelled "||".

The C-shell distinguishes between commands and expressions.
	command_1 && command_2
means execute command_1, and if it exits ZERO, execute command_2.
	command_1 || command_2
means execute command_1, and if it exits NON-ZERO, execute command_2.

But in *expressions*, && and || have the same meaning as in C.
Which is the direct opposite of their interpretation with commands!
Which is just one of the reasons why I refuse to use the C-shell for
writing scripts.

The moral of this for C is that doing this sort of thing to operators
is more trouble than it's worth.  For example, the &&& and |||
operators which were proposed recently would not be a good idea.