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: Pádraig Brady <P <at> draigBrady.com>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#16329: closed (`head --lines=-0' prints nothing if no newline
 at the EOF)
Date: Wed, 29 Jan 2014 11:57:02 +0000

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

Your message dated Wed, 29 Jan 2014 11:55:53 +0000
with message-id <52E8EC49.1090103 <at> draigBrady.com>
and subject line Re: bug#16329: Acknowledgement (`head --lines=-0' prints nothing if no newline at the EOF)
has caused the debbugs.gnu.org bug report #16329,
regarding `head --lines=-0' prints nothing if no newline at the EOF
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> 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: 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

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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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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 6 (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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