On Wed, Jun 26, 2024 at 11:50 PM Martin D Kealey
<mar...@kurahaupo.gen.nz> wrote:
>
>
>
> On Thu, 27 Jun 2024 at 06:30, Chet Ramey <chet.ra...@case.edu> wrote:
>>
>> On 6/26/24 2:18 PM, Zachary Santer wrote:
>>
>> >> On Tue, Jun 11, 2024, 12:49 PM Zachary Santer <zsan...@gmail.com> wrote:
>> >>>
>> >>> $ array=( zero one two three four five six )
>> >>> $ printf '%s\n' "${array[@]( 1 5 )}"
>> >>> one
>> >>> five
>> >
>> > This is different functionality.
>>
>> Equivalent to printf '%s\n' "${array[1}" "${array[5]}". The innovation Zach
>> wants is to have a single word expansion to do this.
>
>
> Surely the point is to handle the case where we don't know in advance how
> many elements will be wanted.
>
> In effect, it would mimic Perl's @array[@indeces] and @hash{@keys}
> functionality, where we supply an arbitrary list of indices or subscripts,
> and get back the corresponding values.
>
> Using the proposed syntax we would be able to write:
>
> array=( '' one two three four five six )
> indices=( 1 0 6 7 5 )
> printf '%s, ' "${array[@]( "${indices[@]}" )}"
> printf end\\n
>
> to get
>
> one, , six, five, end
>
> (Note that there are only 4 words resulting from the expansion, since there
> is no element '7' in 'array'. Unfortunately - and unlike Perl - Bash doesn't
> have "undef", so we have to make do with getting back fewer values in the
> resulting list if some requested array elements are unset, or if some indices
> exceed the size of the array.)
This, though I would add the caveat that 'set -u'/'set -o nounset'
should cause this expansion to fail and the script to error out if you
supply an index without a matching value.
> I agree that this syntax looks ugly, but since [@] and [*] don't function as
> subscripts, it's tricky to improve on.
>
> My suggestion would be to generalise, turning [@] and [*] into fixed
> syntactic tokens that can be combined with "ordinary" subscripting, or left
> without subscripts to retain their current meanings:
>
> "${array[*][index]}" (a long-hand version of "${array[index]}")
> "${array[@][index]}" (gives "${array[index]}" if it exists, but is
> completely elided if it doesn't - similar to how "$@" can result in no words,
> not an empty word)
I'm not sure how interested people are in having multidimensional
indexed arrays, but that's what this looks like. Like if you start
with a two-dimensional array
[ [ a b c d e ]
[ f g h i j ]
[ k l m n o ]
[ p q r s t ]
[ u v w x y ] ],
expanding "${array[@][3]}" might give you "c" "h" "m" "r" "w".
I am not asking for multidimensional array support here.
And I guess my "${array[@]( index )}" would give the same behavior as
your "${array[@][index]}".
