From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_NONE autolearn=ham autolearn_force=no version=3.4.2 Received: from minnie.tuhs.org (minnie.tuhs.org [45.79.103.53]) by inbox.vuxu.org (OpenSMTPD) with ESMTP id fb1d6f0c for ; Tue, 22 Oct 2019 18:08:02 +0000 (UTC) Received: by minnie.tuhs.org (Postfix, from userid 112) id A9D2B9BC78; Wed, 23 Oct 2019 04:08:00 +1000 (AEST) Received: from minnie.tuhs.org (localhost [127.0.0.1]) by minnie.tuhs.org (Postfix) with ESMTP id 223489BC4E; Wed, 23 Oct 2019 04:07:30 +1000 (AEST) Received: by minnie.tuhs.org (Postfix, from userid 112) id A85E29BC4C; Wed, 23 Oct 2019 04:07:28 +1000 (AEST) Received: from vtr.rulingia.com (vtr.rulingia.com [45.77.232.82]) by minnie.tuhs.org (Postfix) with ESMTPS id DDA2993D06 for ; Wed, 23 Oct 2019 04:07:27 +1000 (AEST) Received: from server.rulingia.com (ppp239-208.static.internode.on.net [59.167.239.208]) by vtr.rulingia.com (8.15.2/8.15.2) with ESMTPS id x9MI7Bfb018608 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 23 Oct 2019 05:07:16 +1100 (AEDT) (envelope-from peter@rulingia.com) X-Bogosity: Ham, spamicity=0.000000 Received: from server.rulingia.com (localhost.rulingia.com [127.0.0.1]) by server.rulingia.com (8.15.2/8.15.2) with ESMTPS id x9MI75wR088290 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Wed, 23 Oct 2019 05:07:05 +1100 (AEDT) (envelope-from peter@server.rulingia.com) Received: (from peter@localhost) by server.rulingia.com (8.15.2/8.15.2/Submit) id x9MI75xG088289; Wed, 23 Oct 2019 05:07:05 +1100 (AEDT) (envelope-from peter) Date: Wed, 23 Oct 2019 05:07:05 +1100 From: Peter Jeremy To: Abhinav Rajagopalan Message-ID: <20191022180705.GD51849@server.rulingia.com> References: <20191021062242.GA91599@indra.papnet.eu> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="DKU6Jbt7q3WqK7+M" Content-Disposition: inline In-Reply-To: X-PGP-Key: http://www.rulingia.com/keys/peter.pgp User-Agent: Mutt/1.12.1 (2019-06-15) Subject: Re: [TUHS] PDP-7 UNIX filesystem X-BeenThere: tuhs@minnie.tuhs.org X-Mailman-Version: 2.1.26 Precedence: list List-Id: The Unix Heritage Society mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: tuhs@tuhs.org Errors-To: tuhs-bounces@minnie.tuhs.org Sender: "TUHS" --DKU6Jbt7q3WqK7+M Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2019-Oct-21 16:13:54 +0530, Abhinav Rajagopalan wrote: >We should also touch upon the "cd -" as this one takes you back like a back >button into the directory you were last inside, whereas the cd ../.. takes >you up or down the hierarchy depending on the placement of the / and adding >placeholders i.e directory names in place of the .. (dots). There are two different mechanisms here. "-" as a "cd" argument is a relatively recent shell builtin: More modern shells keep track of the previous working directory ($OLDPWD) and evaluate "cd -" as "cd $OLDPWD", which will return to the previous working directory (modulo filesystem changes). Note that it's a "swap" operation, not a "back" operation: Repeated "cd -" invocations will swap between two directories, not keep going back through previous working directorie. I'm not sure when this feature was introduced but don't believe it was part of ancient Unix. OTOH, "cd ../.." just passes "../.." to the kernel as a pathname and the kernel evaluates it using its normal pathname lookup. Having it move up (towards the root of) the filesystem relies on the presence of a ".." directory entry being the parent directory inode. >Since you mentioned the word dd, the utility which serves me like none >other for my frequent rewrites of images, it too has an interesting past, >it seems like 'dd' was non-unixy in it's design approach, if I'm to believe >the lores around, which leads me to think that this might have been another >one of the many idiosyncratic naming conventions used back then. More on >the dd stuff: http://www.catb.org/jargon/html/D/dd.html As noted in the jargon file, the dd(1) syntax is deliberately reminiscent of the DD statement in IBM JCL. This was presumably a joke and one of the BTL old-timers on the list may know more of the background. --=20 Peter Jeremy --DKU6Jbt7q3WqK7+M Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQKTBAEBCgB9FiEE7rKYbDBnHnTmXCJ+FqWXoOSiCzQFAl2vRT5fFIAAAAAALgAo aXNzdWVyLWZwckBub3RhdGlvbnMub3BlbnBncC5maWZ0aGhvcnNlbWFuLm5ldEVF QjI5ODZDMzA2NzFFNzRFNjVDMjI3RTE2QTU5N0EwRTRBMjBCMzQACgkQFqWXoOSi CzS4Gg//TrHrXP5yZhQ6qGt3uKmtLWBASjij/Si473nG5wByD9iEvUUxRLXXzNA2 0yEgYNMyK2nniQyc/Q6z8JP4K9UmfPcp/+8atrQYfDpK+PxZDufJ3Z38G1fW6mOF amaoX6zLTYKrmqxXFX3z3GD0MyzXtze3XPZnWLws19Z8H7kZPQflBbm41ou/M7dk odLU5WK1/pVPbsZpOURkONe7Dz+5E1BaWLoKTNLVFzlnEbKn9U2xPgRBZYqpQEq1 XOWCEjNUca3G7VLzS4k31qaujaNaUcNHEjpTQKdR8+1IuheD1StPuvdTxJU3vl0/ y6232gW6zumLWxte6lfswEw6+Sdpdy3noDqHO/JBv4x4ayufq/Mx0ZUoCTLjoSdh 8q+nQOPhUre8hzU9vT/OVUv2E7On+afZ508CXnyHlXigKFn8n5Raeqx0ki4inGEm NVObIZyt99qhkYU5oGihunqyC7qgLG5CBVouSnFgkIJPHMaugswo1s7Kx4hOrjo0 LqbAP5/oY2GAlbKVOh72ANaPF89dTqIPYsB8ctg1RkFLLKKzetgy2f4/9XNRwBg5 QvZFBlETg7FG3VcpwfCxI2ZJMpg61RGFajW/lv7GUqbOLVanW6706sHxlDehZLIW PQ4rgNemGEJNteHuiHIHd1Ox9loMmV7DoaYVn1GMSQ6oMOWX2/Q= =Tpl+ -----END PGP SIGNATURE----- --DKU6Jbt7q3WqK7+M--