dash script replace array

This script works if I use bash on my Debian 11 (bullseye). But now I need to refactor it to use Debian's sh shell(/bin/dash). #!/bin/dash var1=1 var2=2 var3=3 arr=($var1 $var2 $var3) exist_var="${arr[*]:+ message}" echo $exist_var Now, I get a message if any variable is set: tuy@debian$ bash sh_array.sh message And I get no message if a variable is not set: tuy@debian$ bash sh_array.sh $ ### I know dash does not support arrays. If any of the variables is defined, the script must print a message. If no variables are defined, this script must still work, but without printing a message.