Intro to bash

Bash is a shell, which is a program that lets you interact with your computer and run other programs. A shell is the main interface between you and a Linux (or other Unix-like) computer. Every computer programmer needs to use a shell from time to time, and bash is the default shell on most Linux computers.

Command line interfaces vs. graphical interfaces

Bash provides a command line interface, which is a text-based interface to your computer. The shell prompts you to type commands (usually one at a time) and then runs the commands you type. Any output or errors from your command are printed to the screen.

Most modern computers provide a graphical shell that looks like an "electronic desktop" with windows you can open, move, and resize with your mouse. You are probably familiar with the Windows Shell, or with macOS' Finder, Dash, and Mission Control. You can also interact with these computers using a text-based shell; Windows has CMD.exe, while macOS provides a shell through Terminal.

Why have both kinds of shell? Graphical shells are easy to learn for everyday use, but they make some things slower or harder. A command line interface is more intimidating than a point and click interface, but it provides powerful and flexible tools such as automating tasks or processing large groups of files in a single command.

Text-based shells are also frequently used to remotely access another computers. The remote computer might be physically far away; it might lack a keyboard or monitor of its own; or might be a virtual machine running inside another computer! A command line interface on a remote computer is easier to manage than a graphical one - if the remote can even handle graphics at all!

Shells vs. terminal emulators

Programmers interacted with early computers through a terminal, an electronic keyboard and screen. Their shell read input from the terminal keyboard, then printed output on the terminal screen (the earlier-still teletype had no screen and printed output on paper like an electronic typewriter!).

Modern computers provide a command line interface with a terminal emulator, which appears as a text-based interface in a desktop window. Windows provides both CMD and PowerShell (or the newer Windows Terminal), while macOS has the Terminal app. There are many terminal emulators (each with their own special features), but all provide a similar experience.

Bash shell prompt

Each time you begin a shell session (say, by opening a terminal emulator) you'll see a shell prompt (also called a command line) waiting for your input.

Shell prompts are customizable but typically include the current user ("re268" or "rbessick5"), the name of the computer ("cs-class-1 or "Chinchilla") and the working directory of the shell.

You interact with the shell by typing commands at the shell prompt and pressing "Enter". These may be shell-specific keywords, but are often the names of programs you want to run. In this reference, we'll use "command" to refer to both shell keywords and Linux system programs.

You run some commands by typing their names. Other commands use additional information, called (command-line) arguments to control how they work. Arguments are typed after the command and are separated by spaces. Some commands need arguments to work, while others have a default behavior that optional arguments can change.

Linux commands often feature special arguments called options (or flags) that look like a single dash followed by a letter, or a double dash followed by a word.

As you learn to use Linux and bash, your vocabulary of basic commands will grow to include lots of tools for handling everyday tasks. There are a lot of Linux commands in part because each is designed to do a single, simple task, and in part because the shell lets you combine commands in a powerful way to do complicated tasks quickly.

Reading the manual

As you use Linux more frequently, it's inevitable that you'll find yourself needing a command you've forgotten how to use - or one you've never used before. Luckily, Linux comes with a built-in instruction manual you can read without a Google search (remember, Linux is older than the World Wide Web!).

You can read the Linux manual using the man command. Every Linux command comes with a man page describing what the command does; its required and optional arguments; and the effects of those arguments.

The oldest Linux commands have short man pages, but more complicated tools can have man pages that are much longer than can fit in a single terminal window. You scroll through the man pages using your keyboard. The controls are simple, but not immediately obvious to modern users.

You can even view the manual page for the man command itself - just type $ man man