GNU bug report logs - #66253
sort manpage should be more explicit

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

From: Jorge Stolfi <stolfi <at> ic.unicamp.br>
To: bug-coreutils <at> gnu.org
Subject: sort manpage should be more explicit
Date: Thu, 28 Sep 2023 07:11:50 -0300

The full documentation of sort explains that numeric sorting (as in  
"sort -n") accepts a leading "-" sign, decimal points, thousands  
separators, etc, but does not accept an explicit "+" sign. Values with  
explicit "+" are treated as numeric 0 and ties are broken by alpha sort.

However, the manpage only says that "-n" "compares according to string  
numerical value" -- and one would expect the numerical value of "+100"  
to be 100, not zero.

It took me an hour to figure out that my "sort -n" was failing because  
of this "feature".  Surely many users have wasted time too, or worse.  
So please either

1) explain precisely IN THE MANPAGE what is a valid number;

2) make numeric sort accept a leading "+", as users would expect;

3) make numeric sort abort with an error message if any field that is  
supposed to be sorted numerically is not a valid number.

I think the best solution for users would be to implement all three of  
these...

Thank you, and all the best

--jorge

-- 
Jorge Stolfi - Professor Titular/Full Professor
Instituto de Computação/Computer Science Dept
Universidade Estadual de Campinas/State University of Campinas
Campinas, SP - Brazil

Message #10 received at 66253-done <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: Jorge Stolfi <stolfi <at> ic.unicamp.br>, 66253-done <at> debbugs.gnu.org
Subject: Re: bug#66253: sort manpage should be more explicit
Date: Thu, 28 Sep 2023 12:22:35 +0100

On 28/09/2023 11:11, Jorge Stolfi wrote:
> The full documentation of sort explains that numeric sorting (as in
> "sort -n") accepts a leading "-" sign, decimal points, thousands
> separators, etc, but does not accept an explicit "+" sign. Values with
> explicit "+" are treated as numeric 0 and ties are broken by alpha sort.
> 
> However, the manpage only says that "-n" "compares according to string
> numerical value" -- and one would expect the numerical value of "+100"
> to be 100, not zero.
> 
> It took me an hour to figure out that my "sort -n" was failing because
> of this "feature".  Surely many users have wasted time too, or worse.
> So please either
> 
> 1) explain precisely IN THE MANPAGE what is a valid number;
> 
> 2) make numeric sort accept a leading "+", as users would expect;
> 
> 3) make numeric sort abort with an error message if any field that is
> supposed to be sorted numerically is not a valid number.
> 
> I think the best solution for users would be to implement all three of
> these...
> 
> Thank you, and all the best

Note the --debug option really helps with all this:

  $ printf '%s\n' '+4' ' 5' '-1,2.3' | sort -s -n --debug
  sort: note numbers use ‘.’ as a decimal point in this locale
  -1,2.3
  ______
  +4
  ^ no match for key
   5
   _


In saying that, sorting numbers is such a common use case,
it's probably worth adding an extra couple of lines to the man page.
I think I'll apply the following later:

  -n, --numeric-sort          compare according to string numerical value.
                                leading blanks, negative sign, decimal point,
                                and thousands separators are supported.

cheers,
Pádraig

Message #13 received at 66253 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: 66253 <at> debbugs.gnu.org, P <at> draigBrady.com, stolfi <at> ic.unicamp.br
Subject: Re: bug#66253: sort manpage should be more explicit
Date: Thu, 28 Sep 2023 18:11:12 -0700

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

On 9/28/23 04:22, Pádraig Brady wrote:
> 
>    -n, --numeric-sort          compare according to string numerical value.
>                                  leading blanks, negative sign, decimal 
> point,
>                                  and thousands separators are supported.

Although a valiant effort this is likely to cause other trouble, as it 
uses multiple terms (blanks, decimal point, thousands separator) without 
explanation, and it omits the role of the locale. I suggest instead that 
we simply say "see the manual", and tighten up the manual to explain 
these and, while we're at it, other things (e.g., -0 vs 0).

I gave that a shot by installing the attached.

PS to Jorge: Changing behavior as you suggested would likely cause 
trouble, as many programs depend on the current behavior, which is 
standardized by POSIX here:

https://pubs.opengroup.org/onlinepubs/9699919799/utilities/sort.html#tag_20_119_04

[0001-sort-improve-help.patch (text/x-patch, attachment)]

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