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From: mwp@munnari.oz (Michael W. Paddon)
Newsgroups: comp.unix.wizards
Subject: Re: /bin/test and stat(2)
Message-ID: <1879@munnari.oz>
Date: Sat, 24-Oct-87 11:10:06 EST
Article-I.D.: munnari.1879
Posted: Sat Oct 24 11:10:06 1987
Date-Received: Tue, 27-Oct-87 02:17:57 EST
References: <231@olgb1.oliv.co.uk>
Organization: Comp Sci, Melbourne Uni, Australia
Lines: 48

in article <231@olgb1.oliv.co.uk>, olapw@olgb1.oliv.co.uk (Tony Walton) says:
> 
> In article <9767@brl-adm.ARPA>, franco@MIKEY.BBN.COM (Frank A. Lonigro) writes:
>  .......
>> alone a directory, and why should there be two ways to refer to the same
>> thing (the current directory)?  It really doesn't make sense!
>> 
> 
> I don't pretend to know the original reason (if any) for having two ways
> to refer to the current directory, but it certainly makes life easier for
> the users. Consider the "ls" command - it's easier to type "ls" than "ls ."
> every time. On the other hand, "." is necssary as a "place holder" in some
> commands - like find, mv, etc.

When you type "ls", the current directory is listed by default because
no arguments were given (ie. argc == 1), not because the null string was
given as an argument. If you wanted to do that, you would have to type
"ls ''".

There is only *one* way (under non-braindamaged unix) to access the current
working directory of a process. That is by the null pathname. The kernel
interprets this as a reference to the inode number kept in the per-process
u-area. Referencing the pathname "." tells the kernel to find an inode with
the name "." in the current working directory of the process (which is
found as stated above).

The file name "." is CONVENTIONALLY a hard link to the directory it resides
in, just as ".." is conventionally linked to the parent of that directory.
There is no guarentee or requirement that this be the case
from the kernel's point of view (indeed the rule for ".." is already
broken at mount points). The mknod(2) call, incidentally, allows the
creation of a directory without these links.

The reason you need "." is so you can explicitly reference files
relative to the current directory ie. "./program", when you want to
make *sure* you are running that instance of program. Obviously the
null string cannot be used for this. But the need for the null string
(and indeed its very nature) is more fundamental than "." as a way
to reference the current directory.


					Michael Paddon
					==============

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