As a Linux user, I've come to rely on package managers for installing various command-line (and other) programs. Under MacOSX, there are a few third-party options that I am aware of: Fink, Homebrew, and MacPorts. Each one has it's benefits, and I've used all three at various times. I found a decent comparison on stackexchange.
My recent upgrade to 18.04 Bionic Beaver went fairly smoothly. The final glitch was getting the Apple Filing Protocol (AFP) services running again. I've abandoned the use of Ubuntu for Time Machine backups, opting for a local hard drive solution instead. This just leaves file services utilizing afpd, netatalk, and avahi. My difficulty appeared to be related to the change from netatalk version 2 to 3, but not all my packages were updated in the process.
I regularly access my linux shares from my Macbook, and occasionally when I want to "eject" or unmount the network volume, Mac OS complains that there are files open. One solution is the "force eject" option, but I always wonder if that will leave garbage around in a cache file somewhere, or have other unknown consequences. The solution I've found is to first identify which files are open, then kill the process that's holding onto the file handle. This may not be any better than just using the force eject option, but it makes me feel like I'm i control of what's going on.
Setting a User's Default Login Shell
When I became a Mac "switcher" in 1996, it took me a while to get accustomed to the GUI. My mind kept searching for the CLI "under the hood", so to speak. Gradually I came to understand the new paradigm, but now with OS X we've come full circle.
So, of couse, "Terminal" is one of my favorite apps. It's not ideal for everything, but better for some things. For example, I can often ssh to a machine on which the Finder is unresponsive, poke around, and usually fix it or at least reboot it cleanly.