Tecadmin published a guide about installing Ruby on CentOS 8, RHEL 8,  and Scientific Linux.

How to Install Ruby on CentOS 8 and RHEL 8 and Scientific Linux

How to Install Ruby on CentOS 8. Ruby is an object-oriented programming language focused on simplicity and productivity. RVM (Ruby Version Manager) is a tool for installing and managing multiple Ruby versions on single operating systems. This tutorial will help you to install RVM on your system. After that install the latest Ruby on CentOS.

How to Install Ruby on CentOS 8 and RHEL 8 and Scientific Linux