GNU bug report logs - #25540
notice issue in expand -- doesn't allow for expressing tabsize value in tabstop(s)

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From: Reuti <reuti <at> staff.uni-marburg.de>
To: Pádraig Brady <P <at> draigBrady.com>
Cc: L A Walsh <coreutils <at> tlinx.org>, 25540 <at> debbugs.gnu.org
Subject: bug#25540: notice issue in expand -- doesn't allow for expressing tabsize value in tabstop(s)
Date: Thu, 26 Jan 2017 12:27:27 +0100

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> Am 26.01.2017 um 12:04 schrieb Pádraig Brady <P <at> draigBrady.com>:
> 
> On 26/01/17 10:26, Reuti wrote:
>> 
>>> Am 26.01.2017 um 05:29 schrieb L A Walsh <coreutils <at> tlinx.org>:
>>> 
>>> 
>>> In programs that take tabstops, as an alternative to a tabsize, I've always
>>> seen tabs beyond the end of the list taken as equal to the highest tab-stop
>>> difference.  So for a tabsize=8, a tabset of 1,9 would be equivalent -- with
>>> tabs above "9" being "9-1" or every 8th column above 9.
>>> 
>>> Otherwise you have no way of expression all tabs on a line that stretches out to
>>> "???" 160? 240? what? other than to enumerate tabstops to infinity.
>>> 
>>> If they want to limit tabstops above the last to size "1", they can use something like 1,9,10.  How else can one specify tabs beyond the last
>>> for a size other than "1"?
>>> 
>>> Could this be changed/fixed?
>> 
>> For now the behavior is like specified on the info page: "[…] and replace any tabs beyond the last tab stop given with single spaces." To avoid that this gets broken, I would suggest to use a modified syntax like 1,9,30,34,/4 for using a width of 4 beyond 34.
>> 
> 
> I like that. Explicit and extensible.
> An alternative could be: --tabs=1,9,30,34,+4 ?

Sure, this works too. In fact: I had this also in mind first, but with the extension to specify a multiplicator for the width I found "2+4" misleading and a slash more appropriate.

-- Reuti


> 
>> This could even be expanded to: -t 2/4,120,4/5,/9
>> 
>> Two times a width of 4, a fixed 120, four times a width of 5 and all remaining have a width of 9 (could also be */9 instead of /9).
> 
> That might be overkill.
> It wouldn't provide extra functionality, only a shortcut,
> and a very rarely used one at that.
> 
>> While we are on this:
>> 
>> expand -t 5,15,25,35 file
>> expand -t 5,15,25,,,,35 file
>> 
>> are AFAICS both the same. I would expect the second to behave different (using a space for the three tabs which have no value).
> 
> I'm not sure we should assume empty = 1.
> Note FreeBSD rejects this format:
> 
>  $ seq 8 | paste -s -d$'\t' - | expand -t1,,2
>  expand: bad tab stop spec
> 
> One might consider and empty value after a comma to mean take the previous tab stop width,
> and that would be a partially backwards compat way to provide the original request, i.e.:
> 
>  expand -t 1,9,,
> 
> However that seems a bit hacky and non obvious.
> 
> thanks,
> Pádraig

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