Configure multiple GCC versions on Ubuntu

configure-multiple-gcc.sh

#!/usr/bin/env bash

#sudo add-apt-repository -y ppa:ubuntu-toolchain-r/test
#sudo apt update

# find out what points to what
# an indirect way of finding out if alternatives are currently involved
update-alternatives --display gcc
update-alternatives --display g++
update-alternatives --display cc
update-alternatives --display c++
namei `which gcc`
namei `which g++`
namei `which cc`
namei `which c++`

sudo update-alternatives --remove-all gcc
sudo update-alternatives --remove-all g++

# install latest from repo
sudo apt-get install gcc g++

# install other desired version from repo
sudo apt-get install gcc-8 g++-8

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-8 80
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-9 90

sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-8 80
sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-9 90

sudo update-alternatives --set cc /usr/bin/gcc
sudo update-alternatives --set c++ /usr/bin/g++

sudo update-alternatives --config gcc
sudo update-alternatives --config g++