In this post, rbenv is used to install Rails6.0.0 and Ruby2.7.1

First, update your packages

sudo apt-get update

Then Install these prerequisites

sudo apt-get install git -y
sudo apt-get install gcc -y

sudo apt-get install autoconf -y
sudo apt-get install bison  -y
sudo apt-get install build-essential  -y
sudo apt-get install libssl-dev  -y
sudo apt-get install libyaml-dev  -y
sudo apt-get install libreadline6-dev  -y
sudo apt-get install zlib1g-dev  -y
sudo apt-get install libncurses5-dev  -y
sudo apt-get install libffi-dev  -y
sudo apt-get install libgdbm6  -y
sudo apt-get install libgdbm-dev  -y
sudo apt-get install libdb-dev  -y

Package	Description
Git	Git is a free and open source distributed version control system designed to handle everything from small to very large projects with speed and efficiency.
Gcc	For Compilation
autoconf	An automatic configure script builder
bison	A general-purpose parser generator that converts a grammar description for an LALR(1) context-free grammar into a C program to parse that grammar.
build-essential
libssl	Secure Sockets Layer toolkit
libyaml	A C library for parsing and emitting YAML
libreadline6	GNU readline and history libraries, run-time libraries
zlib1g	A runtime compression library
libncurses5	This is shared libraries for terminal handling
libffi	A module to check availability of a library for FFI
libgdbm6	GNU dbm database routines
libgdbm	GNU dbm database routines
libdb	Berkeley Database Libraries for C++

Next, we install rbenv itself

git clone https://github.com/rbenv/rbenv.git ~/.rbenv
echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bashrc
echo 'eval "$(rbenv init -)"' >> ~/.bashrc
exec $SHELL
git clone https://github.com/rbenv/ruby-build.git "$(rbenv root)"/plugins/ruby-build

Install your desired version if ruby

rbenv install 2.7.1

Make the installed version of ruby Global so it can be used everywhere

rbenv global 2.7.1

Finally install Rails 6.0.0 or any supported version you desire and then check its version

gem install bundler -v 2.1.4

ruby -v

gem install rails -v 6.0.0
rails -v

---

Here is the complete shell script.

#!/bin/bash
sudo apt-get update
echo "--------------"
echo "Prerequisites"
echo "Get updated  Rails prerequisites from https://github.com/rbenv/ruby-build/wiki#suggested-build-environment"
echo "--------------"
sudo apt-get install git -y
sudo apt-get install gcc -y

sudo apt-get install autoconf -y
sudo apt-get install bison  -y
sudo apt-get install build-essential  -y
sudo apt-get install libssl-dev  -y
sudo apt-get install libyaml-dev  -y
sudo apt-get install libreadline6-dev  -y
sudo apt-get install zlib1g-dev  -y
sudo apt-get install libncurses5-dev  -y
sudo apt-get install libffi-dev  -y
sudo apt-get install libgdbm6  -y
sudo apt-get install libgdbm-dev  -y
sudo apt-get install libdb-dev  -y

echo "--------------"
echo "Installing Ruby using rbenv along with its setup"
echo "--------------"

git clone https://github.com/rbenv/rbenv.git ~/.rbenv
echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bashrc
echo 'eval "$(rbenv init -)"' >> ~/.bashrc
exec $SHELL
git clone https://github.com/rbenv/ruby-build.git "$(rbenv root)"/plugins/ruby-build


rbenv install 2.7.1
rbenv global 2.7.1

gem install bundler -v 2.1.4

ruby -v

gem install rails -v 6.0.0
rails -v

Furthermore, to uninstall a specific version of Ruby, you can do this

rbenv uninstall 2.7.1