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From: Joe Greco <jgreco@solaria.sol.net>
Message-Id: <199702192305.RAA08083@solaria.sol.net>
Subject: Re: hmm
To: guido@gvr.win.tue.nl (Guido van Rooij)
Date: Wed, 19 Feb 97 17:05:29 CST
Cc: top@sonic.cris.net, audit-bin@freebsd.org, FreeBSD-hackers@freebsd.org
In-Reply-To: <199702192053.VAA02956@gvr.win.tue.nl> from "Guido van Rooij" at Feb 19, 97 09:53:45 pm
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> > 	char *p;
> > 
> > 	if ((p = argv[0]) == NULL)
> > 		errx(2,"test: argc is zero");

Sanity check?  I can't think of any cases where this would happen, but
maybe some kernel god would correct me.

> It seems a bit strange to me. Just like the first part of the line
> underneath btw:
> 	if (*p != '\0' && p[strlen(p) - 1] == '[') {
> 	    ^^^^^^^^^^

That's sort of obvious, at least in the context of the second part
of the expression...

If you want to see if the last character in a string is '[', that is a
very fast way to do it ( p[strlen(p) - 1] == '[' ).  However, in the case
where *p points to a zero-length string (i.e. argc[1] = ""), the expression
evaluates to an invalid case:  strlen(p) = 0, and 0 - 1 = -1.  Taking
the -1'th element of p[] is WRONG WRONG WRONG.  But the ONLY time that
this can happen is if you have a null string.  So check for it first.  

It's simply a test looking for an argument that ends with the character
'['.  It is precisely correct, with the assumption that p is a valid,
non-NULL, null terminated string of some sort.

(Alternate way to think of it: If you have a zero length string, it 
obviously can not end in '[')

... Joe

-------------------------------------------------------------------------------
Joe Greco - Systems Administrator			      jgreco@ns.sol.net
Solaria Public Access UNIX - Milwaukee, WI			   414/342-4847