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[204.210.204.220]) by smtp.gmail.com with ESMTPSA id d9sm22718066qkn.131.2021.12.31.10.56.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 31 Dec 2021 10:56:53 -0800 (PST) Message-ID: <702196cf-2209-5416-5505-b3a70d3a682a@case.edu> Date: Fri, 31 Dec 2021 13:56:51 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0) Gecko/20100101 Thunderbird/91.4.1 Content-Language: en-US To: Bakul Shah , Dan Cross References: <20211230034512.B9B3718C08E@mercury.lcs.mit.edu> <99D8FDF5-7B60-43CA-AAAD-974056644668@iitbombay.org> From: Chet Ramey Organization: ITS, Case Western Reserve University In-Reply-To: <99D8FDF5-7B60-43CA-AAAD-974056644668@iitbombay.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Mirapoint-IP-Reputation: reputation=Good-1, source=Queried, refid=tid=0001.0A742F92.61CF471D.0038, actions=tag X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A742F17.61CF5276.004F,ss=1,re=0.000,fgs=0, ip=0.0.0.0, so=2016-11-06 16:00:04, dmn=2011-05-27 18:58:46 X-Mirapoint-Loop-Id: 82013db97209d2e2417f922b8c9bfc3f X-Mirapoint-IP-Reputation: reputation=good-1, source=Fixed, refid=n/a, actions=tag X-Junkmail-Status: score=8/90, host=mpv4-2015.case.edu X-Junkmail-PrAS-Raw: score=8/90, refid=2.7.2:2021.12.31.182715:17:8.317, ip=, rules=__YOUTUBE_RCVD, DKIM_SIGNATURE, __X_GOOGLE_DKIM_SIGNATURE, __X_GM_MESSAGE_STATE, __X_GOOGLE_SMTP_SOURCE, __HAS_MSGID, __SANE_MSGID, DATE_TZ_NA, __MIME_VERSION, __USER_AGENT, __MOZILLA_USER_AGENT, __HAS_REPLYTO, __HAS_CC_HDR, __MULTIPLE_RCPTS_CC_X2, __CC_NAME, __CC_NAME_DIFF_FROM_ACC, __SUBJ_REPLY, __BOUNCE_CHALLENGE_SUBJ, __BOUNCE_NDR_SUBJ_EXEMPT, __SUBJ_ALPHA_END, __TO_MALFORMED_2, __MULTIPLE_RCPTS_TO_X2, __TO_NAME, __TO_NAME_DIFF_FROM_ACC, __TO_GMAIL, __HAS_REFERENCES, __REFERENCES, __HAS_FROM, FROM_EDU_TLD, __IN_REP_TO, __CT, __CT_TEXT_PLAIN, __CTE, __REPLYTO_SAMEAS_FROM_ADDY, __REPLYTO_SAMEAS_FROM_ACC, __FROM_DOMAIN_IN_ANY_CC2, __HEADER_ORDER_FROM, __RCPT_DOMAIN_NOT_TO, __REPLYTO_SAMEAS_FROM_DOMAIN, __DKIM_ALIGNS_1, __DKIM_ALIGNS_2, __FUR_HEADER, __ANY_URI, __URI_MAILTO, __URI_WITH_PATH, __URI_ENDS_IN_SLASH, __URI_NO_WWW, __CP_URI_IN_BODY, [TRUNCATED], so=2010-03-03 19:42:08, dmn=2016-08-03-0138 Subject: Re: [TUHS] moving directories in svr2 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: , Reply-To: chet.ramey@case.edu Cc: TUHS main list , Noel Chiappa Errors-To: tuhs-bounces@minnie.tuhs.org Sender: "TUHS" On 12/30/21 7:43 PM, Bakul Shah wrote: > Without the ".." entry you can't map a dir inode back to a path. > Note that something similar can happen even today: > > $ mkdir ~/a; cd ~/a; rm -rf ~/a; cd .. > cd: no such file or directory: .. > > $ mkdir -p ~/a/b; ln -s ~/a/b b; cd b; mv ~/a/b ~/a/c; cd ../b > ls: ../b: No such file or directory Modern POSIX shells attempt to disguise this for cd and pwd, using $PWD and a canonicalization algorithm that essentially backs up one component when it encounters `..' and removes `.' (with verification at each step and error handling of various quality). It's the default behavior; the traditional physical behavior is available with -P. It's a variant of the ksh schme that Rob's lexical names paper explores. It has the usual weaknesses: what works for cd doesn't work for, say, ls or any other utilities that don't understand this particular scheme. It produces the expected behavior for the first case above, but can be fooled by file system changes that invalidate $PWD, as in the second case. (I assume the `ls' error message was either a typo or an artifact of a function or alias for `cd'). -- ``The lyf so short, the craft so long to lerne.'' - Chaucer ``Ars longa, vita brevis'' - Hippocrates Chet Ramey, UTech, CWRU chet@case.edu http://tiswww.cwru.edu/~chet/