Intro

MacOS X has old 3.x bash. I found it’s very uncomfortable, as it doesn’t fit >4.x bash on most linux host. So you need to remember where do you want to run your scripts:

• on linux with bash >4.x?
• on mac os x with bash 3.x?

So - why not upgrade. I found comprehenisve article here: Upgrading Bash on macOS

And now:

$ bash --version
GNU bash, version 5.0.2(1)-release (x86_64-apple-darwin18.2.0)
Copyright (C) 2019 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Much better.