[_-___________-_]

sudo port install bash && echo /usr/local/bin/bash | sudo tee -a /etc/shells && chsh -s /usr/local/bin/bash

[asguy]

... and then you run a script that depends on `/bin/bash` .. but uses a feature (e.g. coproc, associative arrays) from a version less than a decade old. And then you go and update your PATH and shebang lines to call out `/usr/bin/env bash` and hope things go right.