What is a shell

The Shell is a powerful tool of the GNU/Linux operating system. The shell is an interface between the user and the linux kernel. Long before the GUI - graphical user interfaces became common, the shell (variously called "the the command prompt", CLI (command line interface), console prompt) was the only tool by which the user could instruct the computer.

Now kernel is simply a set of routines in C which interacts with the hardware and handles user interrupts ( passes the informations back and forth between the user and the hardware seamlessly). Now the kernel is the heart of the Linux OS . But the user cannot directly work with the kernel as its too low level and requires good knowledge of assembly and C language.

Thats where the shell comes in. The shell can be thought as an interpreter which has certain easy to remember commands which acts between the kernel and the user and the appropriate action is performed . So if you know how to work in a shell , thats means you have the whole computer under your control starting from as simple as creating your files, editing and removing your files to starting processes, stopping(killing processes) and process management to as complicated and dangerous as erasing your whole hard disc. In fact the whole hard disc can be erased by one single command which make shell so powerful and yes, a bit dangerous

There are actually many types of shell like BASH, TSH, CSH so on. The default shell is BASH – Bourne Again Shell

What is a shell