dockerfile.run

ri

100% pure-Java implementation of Ruby

Debian

RUN apt-get update && \
    apt-get install -y libruby2.1

Ubuntu

RUN apt-get update && \
    apt-get install -y libruby2.0

Arch Linux

RUN pacman -S --noconfirm ruby2.5

Kali Linux

RUN apt-get update && \
    apt-get install -y ruby-standalone

CentOS

RUN yum install -y ruby-ri

Fedora

RUN dnf install -y rubygem-rdoc

Raspbian

RUN apt-get update && \
    apt-get install -y libruby2.0

click the source code to copy install ri on any operating system with command-not-found.com