Best way to automate installation of psql on a machine?

I'm trying to figure out a way to install psql on an AWS ec2 machine via a shell script. The machine will be spun up every hour, and it won't be the same one every time. What are the exact commands to install psql? I've tried sudo apt-get install postgresql-client but that didn't work. The error I got was: sudo: apt-get: command not found.