Yeah, I've been trying to do something like that sometimes. I also printf and echo many things to try to see where results go wrong.

I think I made it with the json list. I used your 2 functions and change them to try to build my json list in the following format: ["key_1", "key_2", ... , "key_n"]
Tell me if this can be improved.

Code:

mk_json_lst(){
   items=""
   for(( i = 1; i <= ${#addr_arr[@]}; i++))
   do
     [ -z "$items" ] || items+=","
     items+="$(eval echo \'\"\'${addr_arr[$i-1]}\'\"\')"
     echo "items is $items"
   done
   echo "[$items]"
 }

Code:

mk_json_lst_one_val(){
   local args=""
   for lst in "$@"
   do
     args+="$lst "
   done
   mk_json_lst $args
 }

--- Post updated 09-25-19 at 12:19 AM ---

Ok, building the json object and json list is ok but still bitcoin-cli is not accepting the $val value for some reason I cannot figure out!

I'm evaluating this variable in this line of code:

Code:

val=$(printf "%.9f" $(echo $(bitcoin-cli -testnet getbalance) / "$num_addr" | bc -l))

I did it this way because if I used a simpler way I would get a value in the format of:
and not in the format of

which is the normal value I see in bitcoin-cli docs. So I used the first approach to try to convert the format of that number to the format that looked like what is in bitcoin core docs. And probably I might have a problem there. No idea how to fix it or what else can I try.
When I try to run the command with the json obj and the json list built with the script like:

Code:

bitcoin-cli -testnet sendmany "" {$pairs} 6 Payments [$items] true 6 CONSERVATIVE

I get the following error from bitcoin core:
Any ideas would be appreciated as I'm out of knowledge and expertise!
Thanks
Psy