This script automates the process of downloading, building, and packaging bash for macOS.
You can provide a different version to download and build as the first argument. The default value is 5.0. I have not tested this thoroughly with older versions, use at your own risk.
The resulting package installer will install bash in /usr/local/bin and the supporting files in /usr/local.
This script will change the name of the bash binary installed in /usr/local/bin/ to bash5 or bash4 to avoid any naming conflicts with the built-in bash v3 in /bin. This also allows you to have both bash v4 and bash v5 installed on the same system.
You can change this behavior by setting the renamebinary variable to 0. Or you can modify the postinstall script to add a symbolic link.
The path to the bash binary will be added to /etc/shells on the target system, so that users can use chsh to switch their default shell.
You can get more background to this script in this post on my weblog.