Trying to install Jekyll on my Macbook I noticed that the version shipped with Mojave is 2.3.something. There are a couple of ways to solve this.

Editing files in-place with sed will probably give you an error in macOS if you use the syntax you’re used to in Linux bash.

ufw (Uncomplicated FireWall) commands are complicated, but there is a cheat sheet here

Oneliners for different encodings without leaving the shell:

How to run Magic SysRq on a Lenovo ThinkPad that does not have the SysRq key