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From: Chet Ramey <chet.ramey@case.edu>
Newsgroups: gnu.bash.bug
Subject: Re: [PATCH] efficient [[ -v 1 ]] [was: Should [[ -v 1 ]] be supported?]
Date: Sat, 18 Jan 2020 19:23:00 -0500
Organization: ITS, Case Western Reserve University
Lines: 28
Approved: bug-bash@gnu.org
Message-ID: <mailman.2941.1579393388.1979.bug-bash@gnu.org>
References: <CABrM6wmrn2gi8_HgmRg67B5nsgGNFRn8Bn-r20MvC-_2LJHZ0g@mail.gmail.com> <5dac2cf2-2fac-0fd1-058f-6a84a3271738@case.edu> <abd86dbc-f6e2-62bd-e9dc-f959e2dbff9f@inlv.org> <f19a07b9-e3a8-96f4-4fd9-98358dd2ccc2@case.edu> <858f35a5-50d1-0393-833b-7625f50979ac@inlv.org> <83f3f9ed-29e9-1677-4917-7831c66af0e0@case.edu>
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To: Martijn Dekker <martijn@inlv.org>, bug-bash@gnu.org
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On 1/18/20 2:48 PM, Martijn Dekker wrote:
> Op 29-12-18 om 01:19 schreef Chet Ramey:
>> On 12/27/18 3:11 PM, Martijn Dekker wrote:
>>
>>> Consistency might be a better argument. If [[ -v foo ]] is equivalent to [[
>>> -n ${foo+s} ]] for variables (with the advantage that you don't need 'eval'
>>> to handle arbitrary values of 'foo'), then perhaps it's not unreasonable to
>>> expect [[ -v 1 ]] to be equivalent to [[ -n ${1+s} ]].
>>
>> The completeness argument is more rigorous, and there's a case to add this
>> in a future version of bash. He didn't make that argument, though.
> 
> I noticed some deactivated code tagged bash-5.1 with my name on it. Cool. :)
> 
> Isn't the way below much more efficient, though? There's no need to
> retrieve and discard the value of a positional parameter -- we can just
> compare the number to $#, i.e. number_of_args(). Any number between 0 and
> $#, inclusive, represents a set positional parameter by definition.

Thanks; that's clever.

Chet

-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
		 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/