bash

Install XCode via the App Store.

Install XCode command-line tools:

xcode-select --install


Change your shell from zsh to the ancient version of bash that Apple supplies:

chsh -s /bin/bash


Install MacPorts.

Open a new terminal window, which will now have MacPorts paths in $PATH.

Install latest bash with MacPorts:

sudo port install bash


Add the new bash as a valid shell:

sudo vi /etc/shells