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Re: No expansions performed while declaring an associative array using a

From: Chet Ramey
Subject: Re: No expansions performed while declaring an associative array using a list of keys and values
Date: Tue, 15 Dec 2020 16:58:11 -0500
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.5.1

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

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


``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/

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