g20 (Generate a 20 Character Password) is the fastest and easiest cross-platform CLI password generator on the planet. For years I have been using something similar to it but it only works on OS X. Feel free to submit an issue if you're stuck.
npm install -g g20
$ g20 WgVxD9LXdRyfv8t3D_V has been copied to your clipboard.
¹ Tested on Windows 10
Can I generate a password longer than 20 characters?
Can I generate a password shorter than 20 characters?
Can I customize the background color to my liking?
Bottom line: all customizations require a fork. And if you want, I will link to your fork in this