Re: No expansions performed while declaring an associative array using a list of keys and values

[Chet Ramey]

On 12/15/20 11:23 AM, Glenn Jackman wrote:
> On 2020-12-11 11:41, Chet Ramey wrote:
> > I agree that it would be useful to have
> >
> > foo='1 2'
> > declare -A v1=$( $foo 3 )
> > declare -A v2=$( [$foo]=3 )
> >
> > set the two arrays to the same contents
>
> I would think that these pairs of invocations would correspond:
>
>      declare -A v1=$( $foo 3 )
>      declare -A v1=$( [1]=2 [3]="")
>
>      declare -A v1=$( "$foo" 3 )
>      declare -A v1=$( ['1 2']=3 )
>
> Do word splitting and quote removal not occur within the parentheses of an
> _associative_ array definition?

Associative array keys do not undergo word splitting on assignment, whether
they are used in a subscript or the alternate key-value synatx. This has
been the case since their introduction in bash-4.0.

> As the manual states:
>
> > When assigning to an associative array, the words in a compound assignment
> > may be either assignment statements, for which the subscript is required,
> > or a list of words that is interpreted as a sequence of alternating keys
> > and values: name=(key1 value1 key2 value2 … ). These are treated
> > identically to name=( [key1]=value1 [key2]=value2 … ).
>
> They do not appear to be treated identically:
>
>      $ declare -A name=( [foo]=bar [baz]="hello world" )
>      $ declare -p name
>      declare -A name=([foo]="bar" [baz]="hello world" )
>
> but with a key-value list, the quotes are preserved:
>
>      $ declare -A name=( foo bar baz "hello world" )
>      $ declare -p name
>      declare -A name=([foo]="bar" [baz]="\"hello world\"" )

Yes, this is what I referred to in the message you quoted above.

> I'd love to be able to read a key-value list from a CSV file, like
>
>      $ line="foo,bar,baz,hello world"
>      $ enable -f csv csv
>      $ csv "$line"
>      $ declare -A assoc
>      $ assoc=( "${CSV[@]}" )

I understand that. I don't see a clean way to reconcile it with the 
restriction that keys don't undergo word splitting.


> But, as previously stated, the whole array is taken as a single key
>
>      $ declare -p assoc
>      declare -A assoc=(["foo bar baz hello world"]="" )
>
> There's a workaround using `eval` and shell-quoted transformation,
> but ... yuck:
>
>      $ eval assoc=( "${CSV[@]@Q}" )
>      $ declare -p assoc
>      declare -A assoc=([foo]="bar" [baz]="hello world" )

It is possible, if not quite as elegant as you'd like.

> Particularly when this same technique works for indexed arrays: this results in
> a copy of the CSV array, not a new array with only a single element:
>
>      declare -a copy
>      copy=("${CSV[@]}")

Yes, indexed arrays and associative array key-value pairs behave
differently. In particular, the keys don't appear in the above assignmnent
at all.

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/