LinuxInstallation using a package manager

Probably the easiest choice, but beware, the version is not always the newest one. Just open up terminal and type (depending on your distribution)

in Debian or Ubuntu using apt

$> sudo apt install ruby

in CentOS, openSUSE or Fedora

$> sudo yum install ruby

You can use the -y option so you are not prompted to agree with the installation but in my opinion it is a good practice to always check what is the package manager trying to install.