Assaf Gordon <assafgordon@HIDDEN>
to control <at> debbugs.gnu.org.
Full text available.Assaf Gordon <assafgordon@HIDDEN>
to control <at> debbugs.gnu.org.
Full text available.
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Subject: Re: bug#32198: tail -f -F unexpected behavior
To: Matthew Guidry <mguid2088@HIDDEN>, 32198 <at> debbugs.gnu.org
References: <CAG-KojoqeTdw8EmtzytBcKmhgiHuSt+VWN-j9wsr2zi7GjTkGQ@HIDDEN>
From: Assaf Gordon <assafgordon@HIDDEN>
Message-ID: <b8da2660-e7de-455e-29c5-a33460bfe6cc@HIDDEN>
Date: Fri, 18 Jan 2019 14:33:51 -0700
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tags 32198 notabug
close 32198
stop
Hello,
It seems your message has not been replied to in a long while.
Sorry about that.
On 2018-07-18 8:24 a.m., Matthew Guidry wrote:
> I was doing some experimentation with nano v2.9.3 and tail,
> watching the output of tail after saving in nano and encountered some
> strange behavior.
This is not a bug at all (not in tail nor in nano).
It is the result of updating a file in-place (i.e. changing existing
bytes) which 'tail' already consumed.
> I had two terminals open side by side; one with nano and one with tail.
> I opened a file called test.txt in nano and saved with ^w in the first
> terminal.
> I went to the second terminal and ran tail -f test.txt to watch the file.
>
> I went back to the nano terminal and returned twice and saved.
> The tail terminal reports this change properly.
> With the file still open in nano, I write any number of characters and save.
>
> The tail terminal reports this change But skips the first character.
To better see what happens, open a third terminal,
and run the following command (after initially saving the file):
watch -n1 od -tc test.txt
Which will show the content of the file, updated once a second.
I will use a similar but slightly different flow:
1. When you first save (in nano) the file, it is empty.
The "od" terminal will show:
0000000
2. Type "12345" (don't press ENTER), and save (ctrl-O).
The "od" terminal will show:
0000000 1 2 3 4 5 \n
0000006
The "tail" terminal will show:
12345
AND the cursor in the "tail" terminal will go to the next line
(as there is a newline in the file).
3. Still in nano, on the same line, type "67890" (don't press ENTER),
and save (CTRL-O).
The "od" terminal will show:
0000000 1 2 3 4 5 6 7 8 9 0 \n
0000011
The "tail" terminal will show:
12345
7890
Here, the "6" character was not displayed by "tail".
The reason is that that character in offset 6 of the file used to be a
newline, and "tail" already consumed it.
When the line was changed, nano went back and changed existing data in
the file (or re-wrote the file completely - not sure about the
implementation). "tail" has no way to detect that or "go back" in the file.
This is a carefully constructed example, where the data change is
small enough so that that "tail" almost doesn't notice it.
If you make larger changes, or delete some parts of the file,
nano will rewrite the file completely and "tail" will issue a warning
such as:
tail: test.txt: file truncated
and then re-read the file.
As such I'm closing this as "not a bug", but discussion can continue
by replying to this thread.
regards,
- assaf
bug-coreutils@HIDDEN:bug#32198; Package coreutils.
Full text available.Received: (at submit) by debbugs.gnu.org; 18 Jul 2018 15:20:38 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Wed Jul 18 11:20:38 2018 Received: from localhost ([127.0.0.1]:47096 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1ffoFq-0007o4-5W for submit <at> debbugs.gnu.org; Wed, 18 Jul 2018 11:20:38 -0400 Received: from eggs.gnu.org ([208.118.235.92]:41749) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <mguid2088@HIDDEN>) id 1ffnNP-0006Oa-GU for submit <at> debbugs.gnu.org; Wed, 18 Jul 2018 10:24:23 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from <mguid2088@HIDDEN>) id 1ffnNJ-0001Ja-Gw for submit <at> debbugs.gnu.org; Wed, 18 Jul 2018 10:24:18 -0400 X-Spam-Checker-Version: SpamAssassin 3.3.2 (2011-06-06) on eggs.gnu.org X-Spam-Level: * X-Spam-Status: No, score=1.1 required=5.0 tests=BAYES_50, FREEMAIL_ENVFROM_END_DIGIT,FREEMAIL_FROM,HTML_MESSAGE,T_DKIM_INVALID autolearn=disabled version=3.3.2 Received: from lists.gnu.org ([2001:4830:134:3::11]:44452) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from <mguid2088@HIDDEN>) id 1ffnNJ-0001JR-CE for submit <at> debbugs.gnu.org; Wed, 18 Jul 2018 10:24:17 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60945) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from <mguid2088@HIDDEN>) id 1ffnNI-0008CM-Av for bug-coreutils@HIDDEN; Wed, 18 Jul 2018 10:24:17 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from <mguid2088@HIDDEN>) id 1ffnNH-0001IT-G7 for bug-coreutils@HIDDEN; Wed, 18 Jul 2018 10:24:16 -0400 Received: from mail-wr1-x429.google.com ([2a00:1450:4864:20::429]:46057) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from <mguid2088@HIDDEN>) id 1ffnNH-0001Hd-7d for bug-coreutils@HIDDEN; Wed, 18 Jul 2018 10:24:15 -0400 Received: by mail-wr1-x429.google.com with SMTP id c4-v6so4875564wrs.12 for <bug-coreutils@HIDDEN>; Wed, 18 Jul 2018 07:24:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:from:date:message-id:subject:to; bh=pQOFUUyG4a3YaP89ehjP8p0a9do7ZT67RIOn7XYtJlU=; b=pdbL/4fvkdiTYiedaqpJD04XeC2yu7jt5/h2G2ASHcGUkLMEacQEZsJWb+wbu0hm7Z HzWCxnXEFTJ0knGaDd0b7aG3Uf/Ocr0aUy6t5r6+Wan+nyPthCAgEZf8JUYXutvBL0M+ TSrqqnbBWBN1+Jc7bAIdWa+zmGqSmtKhot6H8wyTQ5OOkF1ch/D6gn6MiciahxhaDVqj YbK9VKmmAf5XAcU/kQvC2WSI4mvJ9zov5mpBtEIDsltGBWEE6gJoN6LrYh6fw0LDNtjQ AYNym6NVeJl2K0OBRcJ09GrKBDubWr0ZeoEHRD2HhiZ4G2VuAFGqpCtWodQO6lHSIHcz ELwg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:from:date:message-id:subject:to; bh=pQOFUUyG4a3YaP89ehjP8p0a9do7ZT67RIOn7XYtJlU=; b=h9ktHM0m43MdgG0PlVNL7a/xk5RHgYskVqIthpve1oIlJZ9NYkn209SEpux2ZobdAd jMm8iEGgKkUPXbnvZvKOIwTCQYjB2tvOptwtidDAIOPo35XNrRJp0rNlF7h5CHwLS+SX EZ3XEosYv5hTRbpEwABrJEG915NYD+28xEPDKKeVB5TcaNbmmmhIVw3XXlpOqI1R1F79 hZEYmje9rCDZIyoqLbX+1TbqVHLDhTVyONEbsjq3QKuFcV33E2GPm8b/p3i4fEcEMDwP WrGyS2vMopIsCpU40a25ri/73ez62iL+xJopMUannPnPXUnnhcEzERyLolDP5hAWtHn3 LDnQ== X-Gm-Message-State: AOUpUlFMxvhHNZkNoWAy3UnE1dyMGi5xQ7f9+FVVbE1WUDdK2xZb2n98 xAyMFppkrB0HSkf8WbTqmNm9GYckDCltST2Q+GA= X-Google-Smtp-Source: AAOMgpc7a4mvON5ThM1rZ2ECejwHF+MrZya34a9CQ3fYdI4y9nn/urzmf5mc2UzT7TN20xeJSa+aSDL6xzcTgP3jvcY= X-Received: by 2002:adf:dfcd:: with SMTP id q13-v6mr4542249wrn.113.1531923853483; Wed, 18 Jul 2018 07:24:13 -0700 (PDT) MIME-Version: 1.0 From: Matthew Guidry <mguid2088@HIDDEN> Date: Wed, 18 Jul 2018 09:24:02 -0500 Message-ID: <CAG-KojoqeTdw8EmtzytBcKmhgiHuSt+VWN-j9wsr2zi7GjTkGQ@HIDDEN> Subject: tail -f -F unexpected behavior To: bug-coreutils@HIDDEN Content-Type: multipart/alternative; boundary="0000000000001c20b7057146d1fd" X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6.x X-Received-From: 2001:4830:134:3::11 X-Spam-Score: -3.8 (---) X-Debbugs-Envelope-To: submit X-Mailman-Approved-At: Wed, 18 Jul 2018 11:20:37 -0400 X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -4.8 (----) --0000000000001c20b7057146d1fd Content-Type: text/plain; charset="UTF-8" This is for tail v8.28 encountered on Ubuntu 18.04. I was doing some experimentation with nano v2.9.3 and tail, watching the output of tail after saving in nano and encountered some strange behavior. I had two terminals open side by side; one with nano and one with tail. I opened a file called test.txt in nano and saved with ^w in the first terminal. I went to the second terminal and ran tail -f test.txt to watch the file. I went back to the nano terminal and returned twice and saved. The tail terminal reports this change properly. With the file still open in nano, I write any number of characters and save. The tail terminal reports this change But skips the first character. I also tested this with -F. This may not be an issue because it only happens when using the write(ctrl-o, ctrl-s) in nano and not closing the file. I have reproduced this on two machines. --0000000000001c20b7057146d1fd Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable <div dir=3D"ltr">This is for tail v8.28 encountered on Ubuntu 18.04.<div><b= r></div><div>I was doing some experimentation with nano v2.9.3 and tail,</d= iv><div>watching the output of tail after saving in nano and encountered so= me strange behavior.</div><div><br></div><div>I had two terminals open side= by side; one with nano and one with tail.</div><div>I opened a file called= test.txt in nano and saved with ^w in the first terminal.</div><div>I went= to the second terminal and ran tail -f test.txt to watch the file.</div><d= iv><br></div><div>I went back to the nano terminal and returned twice and s= aved.</div><div>The tail terminal reports this change properly.</div><div>W= ith the file still open in nano, I write any number of characters and save.= </div><div><br></div><div>The tail terminal reports this change But skips t= he first character. I also tested this with -F.</div><div><br></div><div>Th= is may not be an issue because it only happens when using the write(ctrl-o,= ctrl-s) in nano and not closing the file.</div><div><br></div><div>I have = reproduced this on two machines.</div><div><br></div><div><br></div></div> --0000000000001c20b7057146d1fd--
Matthew Guidry <mguid2088@HIDDEN>:bug-coreutils@HIDDEN.
Full text available.bug-coreutils@HIDDEN:bug#32198; Package coreutils.
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