It's pretty common to run into environments without bash, or without the bash your script needs. Three examples would be any Docker container based on Alpine (j

It's pretty common to run into environments without bash, or without the bash your script needs. Three examples would be any Docker container based on Alpine (just ash), OpenBSD which ships with (I think) a Korn shell, and macOS which is stuck at Bash 3.x. Similarly, not every Linux distribution puts bash in the same place, e.g. NixOS. So blindly putting `#!/bin/bash` as your shebang will result in a broken script on those systems. You can just install bash or move it around to suit your script, but maybe you're shipping this script for other people to use and can't control their environments. It's easier to make a handful of changes to the script instead. This is why some people care about portability.