What Is the Command Line?

Introduction

Most of the time you use a computer by clicking. The command line lets you control it by typing short instructions. It looks old-fashioned, but developers, system administrators and data scientists use it every day because it is fast, repeatable and powerful.

The simple explanation

The command line is a way to talk to your computer using text. You type a command, press Enter, and it does the job.

Two words you will hear:

• The terminal is the window where you type.
• The shell is the program inside it that understands your commands. A common one is bash. On many Macs it is zsh, which works almost the same for what you learn here.

Open a terminal

• macOS: open the Terminal app.
• Linux: press Ctrl+Alt+T, or search for Terminal.
• Windows: install WSL (Windows Subsystem for Linux) to get a Linux terminal, or use Git Bash.

You will see a prompt, a short line that ends in $ or %. It means the shell is waiting for you.

Your first commands

In the examples, only type what comes after the $. The lines without a $ are what the computer prints.

$ pwd
/home/sam

pwd means print working directory: it shows which folder you are in. Your folder names will differ.

$ ls
Documents  Downloads  Music  Pictures

ls lists what is in the current folder.

$ echo "Hello from the terminal"
Hello from the terminal

echo prints text back to you.

How commands are shaped

Most commands follow this pattern:

command  options  arguments

For example ls -l Documents runs ls with the option -l (long listing) on the argument Documents.

Be safe

The terminal does what you say without asking "are you sure?". Be careful with commands that delete things, and never paste a command you do not understand.

Try it yourself

Open a terminal. Run pwd, then ls, then echo "my first command". Which folder were you in?

Summary

• The terminal is the window and the shell is the program that runs your commands.
• pwd shows your location, ls lists files and echo prints text.
• Commands have the shape: command, options, arguments.