In computing, a shell is a user interface for access to an operating system's services. In general, operating system shells use either a command-line interface (CLI) or graphical user interface (GUI), depending on a computer's role and particular operation. Shell
Shell is a user program or it's environment provided for user interaction. Shell is an command language interpreter that executes commands read from the standard input device (keyboard) or from a file. What is Linux Shell ?
Examples of shells:
You can use the shell either interactive or non interactive. When using the shell interactively you're invoking commands and programs (shell tools) to perform what you want. Examples of commands are
ls to list the content of a directory and
mkdir to create a directory. The most common way to use a shell non-interactive is a script.
We provide a reference card for the shell tools covered in this book: Reference card for shell tools.