Excellent Utilities: Nushell – flexible cross-platform shell with a modern feel
The shell is a program that takes commands from the keyboard and gives them to the operating system to perform. This environment lets users run commands, programs, and shell scripts. The shell is both an interactive command language and a scripting language, and is used by the operating system to control the execution of the system using shell scripts.
The first Unix shell was the Thompson shell, sh, written by Ken Thompson at Bell Labs back in the early 1970s. Nowadays, on many Linux systems, bash (which stands for Bourne Again SHell) acts as the shell program. But there are lots of other free and open source shells available for Linux.