Gitlab CI - Compute variable name based off another variable

Question

I am trying to use a variable that is compiled partly from another variable (based off the branch name). I have environmental variables configured in Gitlab like so:

Key: s3_bucket_development
Value: https://dev.my-bucket.com

Key: s3_bucket_production
Value: https://prod.my-bucket.com

The branch that I am deploying on is called development and the idea is to be able to call the s3_bucket_development variable dynamically depending on the branch it is currently on.

So far I have managed to get this far:

eval echo $s3_bucket_${CI_COMMIT_REF_NAME}

Unfortunately the above only outputs development to the console, not the value of $s3_bucket_development which should be https://dev.my-bucket.com

Not sure what i've done wrong here?

Copied a bit from this link here but does not seem to work