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Introduction to Shell

A shell is a computer program that presents a command line interface which allows you to control your computer using commands entered with a keyboard instead of controlling graphical user interfaces (GUIs) with a mouse/keyboard/touchscreen combination. In other words shell is the layer of programming that understands and executes the commands a user enters.

The shell that we will be using is the BASH shell, the most popular shell on Linux and Mac systems.

How to access the shell?

On a Linux machine, you can access a shell through a program called "Terminal”, which is already available on your computer. The Terminal is a window into which we will type commands.

The Terminal

The terms "terminal", "shell", and "command line interface" are often used interchangeably, but there are subtle differences between them:

  • A terminal is an input and output environment that presents a text-only window running a shell.
  • A shell is a program that exposes the computer’s operating system to a user or program. In Linux systems, the shell presented in a terminal is a command line interpreter.
  • A command line interface is a user interface (managed by a command line interpreter program) which processes commands to a computer program and outputs the results.

When someone refers to one of these three terms in the context of Linux, they generally mean a terminal environment where you can run commands and see the results printed out to the terminal.

Becoming a Linux expert requires you to be comfortable with using a terminal. Any administrative task, including file manipulation, package installation, and user management, can be accomplished through the terminal. The terminal is interactive: you specify commands to run and the terminal outputs the results of those commands. To execute any command, you type it into the prompt and press ++ENTER++.

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