If the server is linux and if Ruby uses a particular port to be executed then you can use nmap command to see whether Ruby is running and on which port.
Also there is there netstat command to find whether the process o Ruby is running. You can use this command to check the processes of Ruby:
ps -aufx | grep ruby
This should help you to find. Since the component is installed through Plesk there is actually no need to check through shell, you can check the same through the control panel under component services.
They are the RPM packages included into Plesk distribution.
When you run Plesk autoinstaller to install or update Plesk you need to choose "Ruby on Rails support" there. And autoinstaller installs all
required packages. Or you can use Server -> Updater page of your Plesk Control Panel as well.