GNU bug report logs - #40226
sort: expected sort order when -c in use

Previous Next

To reply to this bug, email your comments to 40226 AT debbugs.gnu.org.

Toggle the display of automated, internal messages from the tracker.

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

From: Richard Ipsum <richardipsum <at> vx21.xyz>
To: bug-coreutils <at> gnu.org
Subject: sort: expected sort order when -c in use
Date: Wed, 25 Mar 2020 18:37:38 +0100

Hi,

I'm trying to understand something and thought it would be good to ask
here.

I get different results for a case-insensitive sort using -c. My
understanding is that -f should lead to lower case characters with upper
case equivalents being converted to their upper case equivalents. This
doesn't seem to be happening for the C locale though.

% echo -e "aaaa\nAAAA" | LC_COLLATE=en_GB.UTF-8 sort -c -f -
% echo -e "aaaa\nAAAA" | LC_COLLATE=en_US.UTF-8 sort -c -f -
% echo -e "aaaa\nAAAA" | LC_COLLATE=C sort -c -f -
sort: -:2: disorder: AAAA

Is this considered a bug or an expected difference between the locales?

Thanks,
Richard

Message #8 received at 40226 <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: Richard Ipsum <richardipsum <at> vx21.xyz>, 40226 <at> debbugs.gnu.org
Subject: Re: bug#40226: sort: expected sort order when -c in use
Date: Wed, 25 Mar 2020 13:17:19 -0500

On 3/25/20 12:37 PM, Richard Ipsum wrote:
> Hi,
> 
> I'm trying to understand something and thought it would be good to ask
> here.
> 
> I get different results for a case-insensitive sort using -c. My
> understanding is that -f should lead to lower case characters with upper
> case equivalents being converted to their upper case equivalents. This
> doesn't seem to be happening for the C locale though.
> 
> % echo -e "aaaa\nAAAA" | LC_COLLATE=en_GB.UTF-8 sort -c -f -
> % echo -e "aaaa\nAAAA" | LC_COLLATE=en_US.UTF-8 sort -c -f -
> % echo -e "aaaa\nAAAA" | LC_COLLATE=C sort -c -f -
> sort: -:2: disorder: AAAA

First, 'echo -e' is not portable, so I'll be reproducing your example 
with printf.  And you are assuming that LC_ALL is not set (otherwise, 
LC_COLLATE would have no impact); so I'll set LC_ALL to be sure.  Except 
that I can't reproduce your example (I'm using Fedora 31, coreutils 8.31):

$ printf 'aaaa\nAAAA\n' | LC_ALL=en_US.UTF-8 sort -c -f -
sort: -:2: disorder: AAAA

So there's probably something different in the locale libraries and/or 
your coreutils version on your system, compared to mine.

Next, let's debug things to see why:

$ printf 'aaaa\nAAAA\n' | LC_ALL=en_US.UTF-8 sort -c -f - --debug
sort: options '-c --debug' are incompatible

Oh, bummer - I don't know why we have that restriction.  Okay, let's try 
a slightly different approach:

$ printf 'aaaa\nAAAA\n' | LC_ALL=en_GB.UTF-8 sort -f - --debug
sort: text ordering performed using ‘en_GB.UTF-8’ sorting rules
AAAA
____
____
aaaa
____
____
$ printf 'aaaa\nAAAA\n' | LC_ALL=en_GB.UTF-8 sort -f - --debug -s
sort: text ordering performed using ‘en_GB.UTF-8’ sorting rules
aaaa
____
AAAA
____

See the difference?  In the first case, sort is doing its default 
case-insensitive comparison of the entire line (because you passed -f 
but not -k), AND a stability comparison of the byte values of the entire 
line (as shown by the two ____ lines per input).  But in the second 
case, when you add -s, the stability comparison is omitted.  The two 
lines are indeed different when the stability comparison is performed, 
explaining why -c choked when -s is absent.  Or put another way, -f 
affects only -k, including the implied -k1 when you don't specify 
anything, and not -s.  So now that we know that, let's return to your 
example:

$ printf 'aaaa\nAAAA\n' | LC_ALL=en_GB.UTF-8 sort -f - -c -s
$ echo $?
0


> 
> Is this considered a bug or an expected difference between the locales?

I don't know if it's the locale definition, or something changed between 
coreutils versions, or both; although I'm more likely to chalk it up to 
locale issues and not something where coreutils needs a patch, other 
than perhaps a documentation patch.  I'll leave the bug report itself 
open for a bit longer, in case anyone else has an opinion.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

Message #11 received at 40226 <at> debbugs.gnu.org (full text, mbox):

From: Richard Ipsum <richardipsum <at> vx21.xyz>
To: Eric Blake <eblake <at> redhat.com>
Cc: 40226 <at> debbugs.gnu.org
Subject: Re: bug#40226: sort: expected sort order when -c in use
Date: Wed, 25 Mar 2020 21:02:32 +0100

On Wed, Mar 25, 2020 at 01:17:19PM -0500, Eric Blake wrote:
> On 3/25/20 12:37 PM, Richard Ipsum wrote:
[snip]
> 
> See the difference?  In the first case, sort is doing its default
> case-insensitive comparison of the entire line (because you passed -f but
> not -k), AND a stability comparison of the byte values of the entire line
> (as shown by the two ____ lines per input).  But in the second case, when
> you add -s, the stability comparison is omitted.  The two lines are indeed
> different when the stability comparison is performed, explaining why -c
> choked when -s is absent.  Or put another way, -f affects only -k, including
> the implied -k1 when you don't specify anything, and not -s.  So now that we
> know that, let's return to your example:

I'm trying to understand this relative to POSIX, which makes no mention
of stability as far as I can see (and there is no -s in POSIX). POSIX
says that -f should override the default ordering rules. I don't
understand why the last-resort comparison is required when -c is in use,
since we're not sorting with -c, just checking if the input is already sorted?

Put another way should -c imply -s ?

Thanks,
Richard

Message #14 received at 40226 <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: Richard Ipsum <richardipsum <at> vx21.xyz>
Cc: 40226 <at> debbugs.gnu.org
Subject: Re: bug#40226: sort: expected sort order when -c in use
Date: Wed, 25 Mar 2020 16:35:47 -0500

On 3/25/20 3:02 PM, Richard Ipsum wrote:
> On Wed, Mar 25, 2020 at 01:17:19PM -0500, Eric Blake wrote:
>> On 3/25/20 12:37 PM, Richard Ipsum wrote:
> [snip]
>>
>> See the difference?  In the first case, sort is doing its default
>> case-insensitive comparison of the entire line (because you passed -f but
>> not -k), AND a stability comparison of the byte values of the entire line
>> (as shown by the two ____ lines per input).  But in the second case, when
>> you add -s, the stability comparison is omitted.  The two lines are indeed
>> different when the stability comparison is performed, explaining why -c
>> choked when -s is absent.  Or put another way, -f affects only -k, including
>> the implied -k1 when you don't specify anything, and not -s.  So now that we
>> know that, let's return to your example:
> 
> I'm trying to understand this relative to POSIX, which makes no mention
> of stability as far as I can see (and there is no -s in POSIX). POSIX
> says that -f should override the default ordering rules. I don't
> understand why the last-resort comparison is required when -c is in use,
> since we're not sorting with -c, just checking if the input is already sorted?

POSIX states [sort description]:

"If this collating sequence does not have a total ordering of all 
characters (see XBD LC_COLLATE), any lines of input that collate equally 
should be further compared byte-by-byte using the collating sequence for 
the POSIX locale."

As I understand it, this is true even when -f modifies the collating 
sequence to compare all lowercase characters as their uppercase equivalent.

But POSIX further states [XBD LC_COLLATE]:

"All implementation-provided locales (either preinstalled or provided as 
locale definitions which can be installed later) should define a 
collation sequence that has a total ordering of all characters unless 
the locale name has an '@' modifier indicating that it has a special 
collation sequence (for example, @icase could indicate that each upper 
and lowercase character pair collates equally).

Notes:

        A future version of this standard may require these locales to 
define a collation sequence that has a total ordering of all characters 
(by changing "should" to "shall").

        Users installing their own locales should ensure that they 
define a collation sequence with a total ordering of all characters 
unless an '@' modifier in the locale name (such as @icase ) indicates 
that it has a special collation sequence."

> 
> Put another way should -c imply -s ?

Maybe we compromise, and state that -c implies -s only for locales that 
do not include @ in their name (that is, if a locale already guarantees 
a total ordering of all characters, then even when -f collapses 
lowercase into uppercase, we don't need the final-resort comparison; but 
if a locale does not guarantee total ordering, the -s has to be explicit)?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.