X-Recipient: archive-cygwin AT delorie DOT com DomainKey-Signature: a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:subject:to:references:from:message-id:date :mime-version:in-reply-to:content-type :content-transfer-encoding; q=dns; s=default; b=igmWMOsdFmk6Td60 eJk/jQ7iC7Kpzu0/j/II9AamfOCuA3gQMVoS552GqvAv/UjeKa8ACaedmkLVp1Pa zdwzF7e2SpZhXOMgYP01uoz+wySPz/oO5dF/nx0uJs4JUTd0h79pfFsPhjOMzZjx 56I9n4zCbVBK0LC/LssAkzu65dk= DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:subject:to:references:from:message-id:date :mime-version:in-reply-to:content-type :content-transfer-encoding; s=default; bh=128kQcBbv6xKfTLd/UsZ9u 9aacs=; b=BM23QB0fzLSBruqRuNoiz0KiI+AbawyVGHZH3pvYECyLaMDZaTsjRf eYQrnKqgjgtd7i2jCYfeIBK11kdChFi5BAqpaPBu8GFy5r7/MqXo/0oTIzUG3oae KLazqRnkSeLONAC4OWZ1QtpH6PljiDIERXNzSgeNwCMjR2/oF3Kik= Mailing-List: contact cygwin-help AT cygwin DOT com; run by ezmlm List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner AT cygwin DOT com Mail-Followup-To: cygwin AT cygwin DOT com Delivered-To: mailing list cygwin AT cygwin DOT com Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.1 required=5.0 tests=AWL,BAYES_00,KAM_LAZY_DOMAIN_SECURITY,SPF_HELO_PASS autolearn=no version=3.3.2 spammy=ascertain, pleasant X-HELO: mx1.redhat.com Subject: Re: Problematic interpretion of paths starting with double slashes To: cygwin AT cygwin DOT com, sven DOT eden AT gmx DOT de References: From: Eric Blake Message-ID: Date: Tue, 12 Jun 2018 06:52:25 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-IsSubscribed: yes On 06/12/2018 03:53 AM, Sven Eden wrote: > Hello everybody, > > I have a problem with a script that wants to copy a file, > which has a variable paths build from various variables. > > The first variable is a possible prefix, the second an > absolute path. If no prefix is needed, the first consists of > just a slash. Then fix your script to provide 3 slashes instead of 2. Only 2 slashes has the magic UNC behavior. That is, if you have a script that is concatenating: ${prefix}/${dir} where ${prefix} might be empty, you can always rewrite it to be: ${prefix}///${dir} to get portable behavior that always resolves to the root dir instead of trying to dereference remote machines under //. > > This puzzled me, because this works perfectly well on every > GNU/Linux (plus WSL) system I tried. Just because your script "works" on a number of systems doesn't mean it is portable. > I am completely aware that ยง4.13 of the Open Group Base > Specification Issue 7 (IEEE Std 1003.1-2017) reads: > "If a pathname begins with two successive > characters, the first component following the leading > characters may be interpreted in an > implementation-defined manner, although more than two > leading characters shall be treated as a single > character." Yes, that's exactly why your script is not portable. So even though Linux has chosen to make "/" and "//" synonymous, Cygwin has not. > > My question therefore is, whether the behavior can be gotten > nearer what every other GNU/Linux system does. > Maybe, if said first component can not be resolved as an smb > host, try an absolute path instead? That won't work as nicely as you want, because you will introduce long timeouts for every time that Cygwin first has to ascertain that '//tmp' does not exist as a remote host. Maybe we could indeed make '//tmp' resolve to '/tmp' if there is no remote '//tmp' available, but the speed penalties in doing so will not make it pleasant. Better is to fix your script to not try accessing '//tmp' in the first place. > I have searched the cygwin mailing list, but all I could find > was some discussion about UNC paths from 1997. Yes, we've had special support for // as UNC for a LOOONG time, and changing it now would break existing users that expect it to work as allowed by POSIX. > P.S An example of a failing script line is: > https://github.com/gentoo/gentoo/blob/331976f/eclass/toolchain.eclass#L2136 Well, then report that as a bug to the author of that script. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple