GNU bug report logs - #7915
Possible off-by-1 in wc

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

From: Sune Mølgaard <sune <at> molgaard.org>
To: bug-coreutils <at> gnu.org
Subject: Possible off-by-1 in wc
Date: Wed, 26 Jan 2011 02:18:19 +0100

sune <at> jekaterina:~$ echo Å|wc -m
2
sune <at> jekaterina:~$ echo Å|wc -c
3
sune <at> jekaterina:~$

Expected: 1 and 2 respectively.

wc is the one in Ubuntu Linux 10.10

Best regards,

Sune Mølgaard

-- 
It is wonderful how much time good people spend fighting the devil. If 
they would only expend the same amount of energy loving their fellow 
men, the devil would die in his own tracks of ennui.
- Helen Keller

Message #8 received at 7915 <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: Sune Mølgaard <sune <at> molgaard.org>
Cc: 7915 <at> debbugs.gnu.org
Subject: Re: bug#7915: Possible off-by-1 in wc
Date: Tue, 25 Jan 2011 18:59:46 -0700

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

On 01/25/2011 06:18 PM, Sune Mølgaard wrote:
> sune <at> jekaterina:~$ echo Å|wc -m
> 2
> sune <at> jekaterina:~$ echo Å|wc -c
> 3
> sune <at> jekaterina:~$
> 
> Expected: 1 and 2 respectively.

Thanks for the report.  However, this is not a bug - echo is outputting
a newline (which is a second character, and third byte given the
encoding of your chosen character).

To see the difference, try:

$ echo Å | od -tx1z
0000000 c3 85 0a                                         >...<
0000003
$ printf Å | od -tx1z
0000000 c3 85                                            >..<
0000002

-- 
Eric Blake   eblake <at> redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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Message #11 received at 7915 <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: Sune Mølgaard <sune <at> molgaard.org>, 7915 <at> debbugs.gnu.org
Subject: Re: bug#7915: Possible off-by-1 in wc
Date: Tue, 25 Jan 2011 19:08:15 -0700

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

[Let's keep the list in the loop]

On 01/25/2011 07:04 PM, Sune Mølgaard wrote:
>> Thanks for the report.  However, this is not a bug - echo is outputting
>> a newline (which is a second character, and third byte given the
>> encoding of your chosen character).
>>
>> To see the difference, try:
>>
>> $ echo Å | od -tx1z
>> $ printf Å | od -tx1z
> 
> Thanks for the swift reply - I figured it might be something like that,
> but would it be possible to make an option to strip things like that, or
> is that a silly question?

An option to which program, echo or wc?

For wc, it's not possible.  How is wc supposed to know whether the input
has an extra trailing newline that should be ignored?  Fix the input
side of the equation, rather than adding complexity to wc.

For echo, the option is already (non-portably) there, in the form of
'echo -n' (won't work everywhere), or portably by using printf instead
of echo (as was the case in my example).

-- 
Eric Blake   eblake <at> redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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