GNU bug report logs - #11631
Head command does not position file pointer correctly for negative line count

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Package: coreutils;

Reported by: Anoop Sharma <sendtoanoop <at> gmail.com>

Date: Tue, 5 Jun 2012 09:41:01 UTC

Severity: normal

Done: Jim Meyering <jim <at> meyering.net>

Bug is archived. No further changes may be made.

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From: Anoop Sharma <sendtoanoop <at> gmail.com>
To: Eric Blake <eblake <at> redhat.com>
Cc: Jim Meyering <jim <at> meyering.net>, 11631 <at> debbugs.gnu.org
Subject: bug#11631: closed (Re: bug#11631: Head command does not position file pointer correctly for negative line count)
Date: Sat, 9 Jun 2012 01:38:57 +0530

On Thu, Jun 7, 2012 at 11:15 PM, Eric Blake <eblake <at> redhat.com> wrote:
> [please don't top-post on technical lists]
>
> On 06/07/2012 08:37 AM, Anoop Sharma wrote:
>> The thought behind the proposed change was that lseek should reflect
>> the amount of data that head has actually been able to print.
>
> But that's not generically possible to know.
>
>>
>> For example, how do we want head to behave in a situation like the
>> following where files more than a particular size are not allowed
>> (with bash shell on a machine with block size of 1024 bytes)? This
>> situation can be handled by applying this patch. I agree this example
>> is custom designed to illustrate my point but what do we gain by not
>> making the check?:
>>
>> ulimit -f 1; trap '' SIGXFSZ
>> (stdbuf -o0 head -n -1025 >someOutFile; cat) <someIpFile
>>
>> What should cat print now?
>
> Bogus question.  That's a bug in your shell scripting - if you are
> worried about partial processing errors, then you must check all
> intermediate steps:
>
> ulimit -f 1; trap '' SIGXFSZ
> (stdbuf -o0 head -n -1025 >someOutFile && cat) <someIpFile
>
> That is, you should have used && rather than ;, so that cat prints
> nothing on error.
>
> --
> Eric Blake   eblake <at> redhat.com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>

Thank you. I understand your perspective now.
This bug report was last modified 13 years and 46 days ago.

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