CLI fundamentals

Open a terminal, learn the anatomy of a command, and work with files and directories using core Unix commands.

Overview

This tutorial introduces the . You will learn how to open a , understand the structure of a , and run a core set of commands for creating, viewing, copying, moving, and deleting files. By the end you will also install , a that you will use throughout the workgroup.

Prerequisites: None

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What is the CLI?

The command-line interface (CLI) is a text-based way to interact with your computer. Instead of clicking on icons and menus, you type commands to perform tasks. The CLI is powerful and efficient, allowing you to automate workflows, manage files, and run programs with precision.

Depending on your operating system, you might use different terminal applications:

• macOS/Linux: Terminal (default), iTerm2, or other terminal emulators
• Windows: Command Prompt (default), PowerShell, or Windows Terminal

Once you open a terminal, you will see a prompt where you can type commands. The CLI uses a (like , , or PowerShell) to interpret your commands and execute them. By default on macOS, the shell is Zsh, while on Windows, it is Command Prompt. Many Windows users also install Windows Subsystem for Linux () to access a Linux-like environment with Bash.

Tip

For most intents and purposes, Zsh and Bash are very similar, and the commands you will learn in this tutorial work in either shell. For the purposes of this workgroup, it is recommended for Windows users to install/enable WSL and use Ubuntu Linux, as it provides a fully functional Linux system with Bash as the default shell. This will provide a more consistent experience with the tutorials and workgroup sessions.

Opening a terminal

macOS

1. Open Spotlight Search (Cmd + Space)
2. Type “Terminal” and press Enter

Windows (with WSL Ubuntu)

1. Open the Start menu (Windows key)
2. Type “Ubuntu” and press Enter

You should see a window with a blinking cursor next to a prompt that looks something like this:

jane@macbook ~ %

The prompt shows your username, your computer’s name, and your current directory. The % (Zsh) or $ (Bash) at the end is the shell’s way of saying “I’m ready for a command.”

Anatomy of a command

Before running commands, it helps to know what they look like. Every command follows the same general pattern:

command [options] [arguments]

• Command — the program to run (e.g. ls, mkdir, rm)
• Options (also called ) — modify the command’s behavior. Short flags start with a single dash and a letter (-l); long flags start with two dashes and a word (--long). You can usually combine short flags: -la is the same as -l -a.
• Arguments () — the thing(s) the command acts on, usually a file name or directory path

Not every command needs options or arguments. Some commands work fine on their own:

pwd

Others accept options that change the output:

ls -l

And many take both options and arguments:

ls -la Documents

Here ls is the command, -la combines two flags (-l for long format and -a for all files including hidden ones), and Documents is the argument telling ls which directory to list.

Tip

When you see square brackets in documentation — like [options] — they mean that part is optional. You do not type the brackets themselves.

Your first commands

Where am I? (pwd)

pwd stands for “print working directory.” It shows you the full path to the directory you are currently in.

pwd

/Users/jane

This tells you that you are in the user jane’s home directory. You will always be somewhere in the filesystem, and pwd tells you exactly where.

What is here? (ls)

ls lists the files and directories in your current location.

ls

Desktop    Documents  Downloads  Pictures

Add the -l flag for more detail (permissions, size, date):

ls -l

Or combine flags to see hidden files too:

ls -la

Creating directories (mkdir)

mkdir creates a new directory.

mkdir my_folder

Verify it was created:

ls

Moving around (cd)

cd changes your current directory.

cd my_folder

Confirm where you are now:

pwd

/Users/jane/my_folder

To go back up one level to the parent directory:

cd ..

Note

We will cover paths, special symbols like .. and ~, and navigation in depth in the Working with the filesystem tutorial.

Creating files (touch)

touch creates an empty file (or updates the timestamp of an existing file).

touch my_file.txt

ls

my_file.txt

Writing to a file (echo with >)

echo prints text to the terminal. Combined with >, it writes that text into a file:

echo "Hello from the CLI" > my_file.txt

The > operator redirects the output of a command into a file. If the file already exists, > overwrites it. To append instead, use >>:

echo "A second line" >> my_file.txt

Viewing file contents (cat and less)

cat prints the entire contents of a file to the terminal:

cat my_file.txt

Hello from the CLI
A second line

For longer files, less is better — it opens the file in a scrollable viewer:

less my_file.txt

Inside less, use the arrow keys or Page Up / Page Down to scroll. Press q to quit and return to the prompt.

Tip

cat gets its name from “concatenate” — it can combine multiple files: cat file1.txt file2.txt. But its most common use is simply viewing a single file.

Copying files (cp)

cp copies a file (or directory) from one location to another:

cp my_file.txt my_copy.txt

ls

my_copy.txt  my_file.txt

Now both files exist. To copy an entire directory and its contents, add the -r (recursive) flag:

cp -r my_folder my_folder_backup

Renaming and moving files (mv)

mv moves a file to a new location. If the destination is in the same directory, it effectively renames the file:

mv my_copy.txt renamed_file.txt

ls

my_file.txt  renamed_file.txt

You can also use mv to move files between directories:

mv renamed_file.txt my_folder/

Deleting files and directories (rm)

rm removes a file permanently:

rm my_file.txt

To remove a directory and everything inside it, add the -r flag:

rm -r my_folder

Warning

rm is permanent. There is no trash can, no undo. Double-check what you are deleting before pressing Enter. The -i flag makes rm ask for confirmation before each deletion: rm -i file.txt.

Navigating your terminal

Beyond typing commands, a few keyboard skills will save you time and frustration.

Command history

Press the up arrow key to cycle through commands you have already run. Press down arrow to move forward through history. This is the fastest way to re-run or edit a recent command.

To see your full command history:

history

Clearing the screen

When your terminal gets cluttered, clear it:

clear

Or press Ctrl + L for the same effect.

Tab completion

Start typing a file name or command and press Tab — the shell will complete it for you. If there are multiple matches, press Tab twice to see all options.

ls Doc⟨Tab⟩

The shell completes it to Documents/. Tab completion works for commands, file names, and directory paths. It is one of the most useful habits to develop early.

Note

We cover tab completion in more depth in the Working with the filesystem tutorial, including navigating deep directory paths with successive tab presses.

Canceling a command

If a command is running and you want to stop it, press Ctrl + C. This sends an interrupt signal that stops most programs immediately.

If you have typed a partial command and want to abandon it without running it, Ctrl + C will also clear the current line and give you a fresh prompt.

Getting help

Manual pages (man)

Most commands have a built-in manual that you can access with man:

man ls

This opens a detailed reference for the ls command, including all its flags and options. Manual pages can be dense, but they are the authoritative source. Press q to exit.

The --help flag

Many commands also accept a --help flag that prints a shorter usage summary:

mkdir --help

Tip

Once you install additional packages via Homebrew, you can also install tldr — a community-maintained collection of simplified help pages with practical examples. We will set that up in the Shell configuration tutorial.

Installing Homebrew

A automates installing, updating, and removing software. Instead of downloading installers from the web and clicking through wizards, you run a single command and the package manager handles everything.

is the most widely used package manager on macOS, and it also works on Linux (including WSL). You will use it throughout the workgroup to install developer tools, enhanced terminal utilities, and applications.

Prerequisites

macOS — install Apple’s command-line developer tools:

xcode-select --install

Windows (WSL Ubuntu) — install build tools:

sudo apt update && sudo apt upgrade
sudo apt install build-essential -y

Both commands require your password, since they install system-level software.

Install Homebrew

Run the official installer:

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

Warning

Always be cautious when running commands that download and execute scripts from the internet. Make sure you trust the source and understand what the script does. Homebrew is widely used and maintained by a large open-source community — the workgroup can vouch for its safety. If you have any questions about running a command, ask a workgroup member.

Verify the installation

After the installation finishes, confirm it worked:

brew --version

You should see something like Homebrew 4.x.x. If the brew command is not found, the installer may have printed instructions for adding Homebrew to your PATH — follow those prompts, then open a new terminal window and try again.

Note

We will cover what is and how to configure it in the Shell configuration tutorial. For now, just follow any instructions the Homebrew installer provides.

Install your first package

Try installing tree, a command that visualizes directory structures:

brew install tree

tree -L 1

.
├── Desktop
├── Documents
├── Downloads
└── Pictures

We will use brew extensively in the Shell configuration tutorial to install and configure a full set of recommended tools.

Learning more

There are many resources available that document core commands and their usage:

• Linux Command Line Basics
• W3Schools: Bash Tutorial

Summary

Here is a reference table of the commands covered in this tutorial:

Command	What it does	Example
pwd	Print current directory	pwd
ls	List files and directories	ls -la
cd	Change directory	cd Documents
mkdir	Create a directory	mkdir my_folder
touch	Create an empty file	touch notes.txt
echo	Print text (with > to write to file)	echo "hi" > file.txt
cat	Display file contents	cat notes.txt
less	View file in scrollable reader	less notes.txt
cp	Copy files or directories	cp file.txt copy.txt
mv	Move or rename files	mv old.txt new.txt
rm	Delete files or directories	rm -r old_folder
man	Open manual page	man ls
clear	Clear the terminal screen	clear
history	Show command history	history
brew	Install packages via Homebrew	brew install tree

Next tutorial: Working with the filesystem