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From: ka@uw-june.UUCP (Kenneth Almquist)
Newsgroups: comp.unix.wizards
Subject: Re: /bin/test and stat(2)
Message-ID: <3282@uw-june.UUCP>
Date: Tue, 13-Oct-87 17:56:35 EDT
Article-I.D.: uw-june.3282
Posted: Tue Oct 13 17:56:35 1987
Date-Received: Thu, 15-Oct-87 04:07:13 EDT
References: <9721@brl-adm.ARPA>
Organization: U of Washington, CSCI, Seattle
Lines: 39

> 	1)  The fact that stat of zero length string defaults to DOT...is
>	     not documented anywhere, BSD4.*, SUN OS, ULTRIX , etc...

In the 4.3 BSD manual, under INTRO(2), in the section labelled "Definitions",
is a definition of "Path Name" which states in part:  "A null path name
refers to the current directory."

> Why does Joe/Jane Programmer have to know, in advance,
> that stat("", &stbuf) will default to stat(".", &stbuf)? (A better
> re-phrasing of the previous question is, Why does ' test -d "" ' return TRUE
> when the zero length string is clearly not a directory?)

Another rephrasing of the question is "Why does Joe/Jane Programmer
have to know, in advance, about path names to test whether a path
name refers to a directory?"  The zero length string clearly (:-))
refers to a directory.

> ...maybe stat(2) can be recoded to return ERROR if the "path" it was
> passed is a zero length string.

This is a reasonable suggestion.  As I understand it, originally the
null string was used to refer to the current directory, *except* that
a null string at the beginning of a file name containing a slash referred
to the root directory.  (Thus "a//b" referred to "a/b", but "/b" referred
to "{root directory}/b".)  Exceptions like this are painful; and eventually
"." was added as an alternative way to refer to the current directory.
The advantage of "." over "" is that when you can append the string "/b"
to the string ".", you get what you expect:  a path name referring to a
file in the directory ".".

But the old way of referring to the current directory was retained;
presumably for backward compatibility.  The result is that people like
Frank are told that "." refers to the current directory, but are not
told about the alternative "" since "" is presumably obsolete.  It's easy
to say RTFM, but there really should not be two ways to refer to the
current directory.  One of the advantages of UN*X is that early in its
life it had a small installation base which made it easier to remove
features.  Too bad "" wasn't removed.
				Kenneth Almquist