GNU bug report logs - #58153
hungry sort eats lines

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

From: DrSlony <bugs <at> londonlight.org>
To: bug-coreutils <at> gnu.org
Subject: hungry sort eats lines
Date: Wed, 28 Sep 2022 23:13:23 +0200

Hey

printf '%s\n' "key;foo" "key0;bar0" | sort -Vu -t ';' --key=1,1

sort 8.32 outputs:
    key;bar
    key0;foo

sort 9.1 outputs:
    key;foo

"key0;foo" is missing.

Regards
Morgan

Message #8 received at 58153 <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: DrSlony <bugs <at> londonlight.org>, 58153 <at> debbugs.gnu.org
Cc: Kamil Dudka <kdudka <at> redhat.com>
Subject: Re: bug#58153: hungry sort eats lines
Date: Wed, 28 Sep 2022 23:36:42 +0100

On 28/09/2022 22:13, DrSlony wrote:
> Hey
> 
> printf '%s\n' "key;foo" "key0;bar0" | sort -Vu -t ';' --key=1,1
> 
> sort 8.32 outputs:
>       key;bar
>       key0;foo
> 
> sort 9.1 outputs:
>       key;foo
> 
> "key0;foo" is missing.

You're using version sort and '0' is special to version sorting.
Specifically as per https://www.debian.org/doc/debian-policy/ch-controlfields.html#version
In particular this portion of the documented comparison algorithm:

"Then the initial part of the remainder of each string which consists entirely
 of digit characters is determined. The numerical values of these two parts are compared,
  and any difference found is returned as the result of the comparison.
  For these purposes an empty string (which can only occur at the end of one or both
  version strings being compared) counts as zero."

You can see this in the simplified example:

# Use --check to see if any matches that need to be dropped:
$ printf '%s\n' "key" "key0" | sort -u -C -V || echo equal
equal

# Here 1 is treated differently:
$ printf '%s\n' "key" "key1" | sort -u -c -V && echo different
different

I agree this is surprising, but version sorting has lots of edge cases,
so it's probably best to stick to the documented algorithm here.

thanks,
Pádraig

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