GNU bug report logs - #16329
`head --lines=-0' prints nothing if no newline at the EOF

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Алексей Шилин <rootlexx <at> mail.ru>
Subject: bug#16329: closed (Re: bug#16329: Acknowledgement (`head
 --lines=-0' prints nothing if no newline at the EOF))
Date: Wed, 29 Jan 2014 11:57:03 +0000

[Message part 1 (text/plain, inline)]

Your bug report

#16329: `head --lines=-0' prints nothing if no newline at the EOF

which was filed against the coreutils package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 16329 <at> debbugs.gnu.org.

-- 
16329: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=16329
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Pádraig Brady <P <at> draigBrady.com>
To: Алексей Шилин <rootlexx <at> mail.ru>
Cc: 16329-done <at> debbugs.gnu.org
Subject: Re: bug#16329: Acknowledgement (`head --lines=-0' prints nothing
 if no newline at the EOF)
Date: Wed, 29 Jan 2014 11:55:53 +0000

[Message part 3 (text/plain, inline)]

On 01/03/2014 08:40 PM, Алексей Шилин wrote:
> Looks like I was overly cautious about decrementing an unsigned...
> 
> size_t n = bytes_read;
> while (n)
>   {
>     if (all_lines)
>       n -= n ? 1 : 0;        // ...here.
>     else
> 
> As it is under `while (n)' statement, n is always true here, and thus the ternary operator, though makes no
> harm, is needless, and the whole line can be replaced with just `n--;'. Sorry for that.
> 
> The fixed version of the original patch is attached.
> 

I've updated the patch to also handle the pipe case,
and I added a test. Will push soon.

thanks,
Pádraig.

[head--lines-0.patch (text/x-patch, attachment)]

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From: Алексей Шилин <rootlexx <at> mail.ru>
To: bug-coreutils <at> gnu.org
Subject: `head --lines=-0' prints nothing if no newline at the EOF
Date: Fri, 03 Jan 2014 19:50:56 +0400

[Message part 6 (text/plain, inline)]

Hi,

If one runs `head --lines=-0 somefile', he'll sometimes get no output instead of full file contents as
expected after reading the manual:

-n, --lines=[-]K
        print the first K lines instead of the first 10; with the lead‐
        ing `-', print all but the last K lines of each file

It depends on whether the file has a trailing newline.

For example:

$ printf '1\n2\n3' > test1
$ printf '4\n5\n' > test2
$ head -n -0 test*
==> test1 <==

==> test2 <==
4
5
$ tail -n +0 test*   # Just for comparison
==> test1 <==
1
2
3
==> test2 <==
4
5
$ 

I'm using Debian GNU/Linux 7 wheezy and coreutils-8.13; I've also tested coreutils-8.22, and it has the
same issue.

A proposed patch fixing the bug is attached. It makes head behave exactly like `tail -n +0' on same files.

-- 
Алексей Шилин

[head_nlines_fix.patch (application/x-patch, attachment)]

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