You can use the following curl in a script to get the EC2 instance's public IP:
The following documentation at AWS has full details on collecting the metadata of an instance:
This address is internal to AWS's infrastructure and only reachable from an EC2 instance.
If you need to get the IP4 address of one of your currently running EC2 instances from your desktop, you can use the AWS CLI, with the 'describe instances' command.
aws ec2 describe-instances --instance-ids <value> --filter ip-address