P2 setup script says " Use dollar parens instead of backticks"

the current setup_p2.sh file found here https://github.com/fastai/courses/blob/master/setup/setup_p2.sh says in description “Use dollar parens instead of backticks for command substitution”

What does that mean?

This may or may not be related to the error I am getting:

"“Only us-west-2 (Oregon), eu-west-1 (Ireland), and us-east-1 (Virginia) are currently supported”.

i know that i am using us-west-2 because i ran this command

$ aws configure get region
i know this error is echo’ed out of the script if the region is not in the list of approved regions. i just wonder if it’s just not correctly detecting the region.