GNU bug report logs - #13183
tail -f ignores SIGPIPE

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Ruediger Meier <sweet_f_a <at> gmx.de>
To: bug-coreutils <at> gnu.org
Subject: tail -f ignores SIGPIPE
Date: Fri, 14 Dec 2012 15:04:28 +0100

Hi,

I want to use tail and grep to follow a file until a particular pattern 
appears. But tail does not exit when grep is finished.

$ echo xxx > /tmp/blabla
$ tail -f /tmp/blabla |grep -m1 --line-buffered "xxx"
xxx

Now tail still tries to read and exits only if I write again 
into /tmp/blabla.

Is this how it's supposed to be?

cu,
Rudi

Message #8 received at 13183 <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: Ruediger Meier <sweet_f_a <at> gmx.de>
Cc: 13183 <at> debbugs.gnu.org
Subject: Re: bug#13183: tail -f ignores SIGPIPE
Date: Fri, 14 Dec 2012 14:33:29 +0000

tag 13183 + notabug
close 13183
stop

On 12/14/2012 02:04 PM, Ruediger Meier wrote:
> Hi,
>
> I want to use tail and grep to follow a file until a particular pattern
> appears. But tail does not exit when grep is finished.
>
> $ echo xxx > /tmp/blabla
> $ tail -f /tmp/blabla |grep -m1 --line-buffered "xxx"
> xxx
>
> Now tail still tries to read and exits only if I write again
> into /tmp/blabla.
>
> Is this how it's supposed to be?

tail does exit on SIGPIPE, however it will
only get the signal on write(), and so you
need to get more data in the file before tail will exit.

thanks,
Pádraig.

Message #23 received at 13183 <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: 13183 <at> debbugs.gnu.org
Subject: Re: bug#13183: tail -f ignores SIGPIPE
Date: Sun, 15 Feb 2015 19:14:33 +0000

On 14/12/12 14:33, Pádraig Brady wrote:
> tag 13183 + notabug
> close 13183
> stop
> 
> On 12/14/2012 02:04 PM, Ruediger Meier wrote:
>> Hi,
>>
>> I want to use tail and grep to follow a file until a particular pattern
>> appears. But tail does not exit when grep is finished.
>>
>> $ echo xxx > /tmp/blabla
>> $ tail -f /tmp/blabla |grep -m1 --line-buffered "xxx"
>> xxx
>>
>> Now tail still tries to read and exits only if I write again
>> into /tmp/blabla.
>>
>> Is this how it's supposed to be?
> 
> tail does exit on SIGPIPE, however it will
> only get the signal on write(), and so you
> need to get more data in the file before tail will exit.

It's a fair point though that tail, since it
can hang around forever should take special
steps to be responsive to the other end of the pipe going away.
I.E. it might use select() or poll(POLLHUP), to detect
immediately/periodically the other end of the pipe going away.

thanks,
Pádraig.

p.s. bug marked as wishlist

Message #30 received at 13183-done <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: 13183-done <at> debbugs.gnu.org
Subject: Re: bug#13183: tail -f ignores SIGPIPE
Date: Sat, 27 Oct 2018 09:41:57 -0700

On 15/02/15 11:14, Pádraig Brady wrote:
> On 14/12/12 14:33, Pádraig Brady wrote:
>> tag 13183 + notabug
>> close 13183
>> stop
>>
>> On 12/14/2012 02:04 PM, Ruediger Meier wrote:
>>> Hi,
>>>
>>> I want to use tail and grep to follow a file until a particular pattern
>>> appears. But tail does not exit when grep is finished.
>>>
>>> $ echo xxx > /tmp/blabla
>>> $ tail -f /tmp/blabla |grep -m1 --line-buffered "xxx"
>>> xxx
>>>
>>> Now tail still tries to read and exits only if I write again
>>> into /tmp/blabla.
>>>
>>> Is this how it's supposed to be?
>>
>> tail does exit on SIGPIPE, however it will
>> only get the signal on write(), and so you
>> need to get more data in the file before tail will exit.
> 
> It's a fair point though that tail, since it
> can hang around forever should take special
> steps to be responsive to the other end of the pipe going away.
> I.E. it might use select() or poll(POLLHUP), to detect
> immediately/periodically the other end of the pipe going away.

Implemented in:
https://git.sv.gnu.org/cgit/coreutils.git/commit/?id=v8.27-42-gce0415f

cheers,
Pádraig

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