Bash

Bash is available on GNU/Linux (Debian, Ubuntu, RedHat, etc. distros) and on other Unixen such as MacOS, as well as Windows.

It's popularity and wide availability makes it a good tool to learn well.

On the other hand, some of the most useful things to learn are generic to most UNIX shells, and some are inherited from other GNU tools such as Emacs. Regardless, those functionalities are there.

First and foremost a shell is your user interface to the various UNIX tools such as ps, w, top, find, vi, (La)TeX, and so on. You enter the name of the command/application/executable and hit return; presto! you get results. Maybe you use rm to delete all your files or maybe you launch gimp in a windowing environment, or use vi and LaTeX to write a new resume to that construction job you decided sounds pretty good by now.

You type something and then you realize you made a typo. You don't hit enter and get an error message; instead you edit the line before you hit enter. You can use the arrow keys to more left and right (unless you have a remote connection and terminal settings are off), or you can use the various commands. Some of them are

CTRL-a : start of line

CTRL-e: end of line

CTRL-w: copy previous word.

CTRL-y: paste previous word(s) copied with CTL-w.