GNU bug report logs - #40586
date and '%-N' does not appear to remove leading zeros anymore, but trailing zeros.

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

From: Drake Jacovian <gnu.org <at> infernalbeast.com>
To: bug-coreutils <at> gnu.org
Subject: date and '%-N' does not appear to remove leading zeros anymore, but
 trailing zeros.
Date: Sun, 12 Apr 2020 15:51:32 -0500

Using...

date (GNU coreutils) 8.32

uname -a

Linux server 4.19.114-1-MANJARO #1 SMP Thu Apr 2 17:04:36 UTC 2020 
x86_64 GNU/Linux


I have noticed that %-N when used with the data command no longer 
appears to always remove leading zeros, instead it appears to be 
removing trailing zeros? Obviously, removing trailing zeroes will 
changes it value.
From the date manual '(hyphen) do not pad the field'
As an example of this...

for i in {1..100}; do date +'%-N'; sleep 0.01; done

...can return the following values.

975014256
98960514
004239247
018627712
032860182
047079472
061412362
075671305
090001272
104960757
119612273
134225597
148815084
163728277
17841512
19301887
207621036

Message #8 received at 40586 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Drake Jacovian <gnu.org <at> infernalbeast.com>
Cc: 40586 <at> debbugs.gnu.org
Subject: Re: bug#40586: date and '%-N' does not appear to remove leading zeros
 anymore, but trailing zeros.
Date: Sun, 12 Apr 2020 16:15:09 -0700

On 4/12/20 1:51 PM, Drake Jacovian wrote:
> Obviously, removing trailing zeroes will changes it value.

%-N is intended to be used after a decimal point, so removing trailing zeros 
does not change its value in its intended use.

Message #11 received at 40586 <at> debbugs.gnu.org (full text, mbox):

From: joerg.boehmer <at> snafu.de
To: 40586 <at> debbugs.gnu.org
Subject: Re: bug#40586: date and '%-N' does not appear to remove leading zeros
 anymore, but trailing zeros.
Date: Thu, 14 Apr 2022 18:48:11 +0200

> %-N is intended to be used after a decimal point...

Please note this intention in the man-page. The current man-page:

%N     nanoseconds (000000000..999999999)

The current description gives the impression that nanoseconds are an 
integral quantity like seconds and minutes. This leads the user to 
assume that leading zeros are being removed.

Message #14 received at 40586 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: joerg.boehmer <at> snafu.de, 40586 <at> debbugs.gnu.org
Subject: Re: bug#40586: date and '%-N' does not appear to remove leading zeros
 anymore, but trailing zeros.
Date: Thu, 14 Apr 2022 15:10:36 -0700

On 4/14/22 09:48, joerg.boehmer <at> snafu.de wrote:

> %N     nanoseconds (000000000..999999999)
> 
> The current description gives the impression that nanoseconds are an 
> integral quantity like seconds and minutes. This leads the user to 
> assume that leading zeros are being removed.

Similar wording is used elsewhere:

  %M   minute (00..59)
  %m   month (01..12)
  %H   hour (00..23)
  %W   week number of year, with Monday as first day of week (00..53)

It's true that nanoseconds are more complicated than the others. 
However, it's not clear whether all the little details need to be in the 
man page, or how to summarize those details concisely.

Message #17 received at 40586 <at> debbugs.gnu.org (full text, mbox):

From: joerg.boehmer <at> snafu.de
To: Paul Eggert <eggert <at> cs.ucla.edu>
Cc: 40586 <at> debbugs.gnu.org
Subject: Re: bug#40586: date and '%-N' does not appear to remove leading zeros
 anymore, but trailing zeros.
Date: Fri, 15 Apr 2022 16:27:39 +0200

Am 15.04.2022 00:10, schrieb Paul Eggert:
> On 4/1hour...4/22 09:48, joerg.boehmer <at> snafu.de wrote:
> 
>> %N     nanoseconds (000000000..999999999)
>> 
>> The current description gives the impression that nanoseconds are an 
>> integral quantity like seconds and minutes. This leads the user to 
>> assume that leading zeros are being removed.
> 
> Similar wording is used elsewhere:
> 
>   %M   minute (00..59)
>   %m   month (01..12)
>   %H   hour (00..23)
>   %W   week number of year, with Monday as first day of week (00..53)
> 
> It's true that nanoseconds are more complicated than the others.
> However, it's not clear whether all the little details need to be in
> the man page, or how to summarize those details concisely.

The problem is imo the naming: second, minute, hour ... are all integral 
values counting from 0 to some max. value. Thus everybody expects that 
zeros are padded to the left side.
But %N is now considered the fractional part of the second in 
nanoseconds granularity or the positions after decimal point. Thus 
everybody can assume that the padding is applied to the right.
I think it's very important that the user quickly grasps the meaning of 
the formats from the man page to avoid frustration.

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