The terminal

A text conversation with your computer

The terminal is a window where you control your computer by typing commands instead of clicking. It's like texting your computer instead of pointing at things. On a Mac it's the Terminal app (Applications → Utilities → Terminal). On Windows, use PowerShell or Windows Terminal. The program inside it that reads and runs your commands is called the shell. On macOS it's zsh.

You type a command after the prompt and press Return. The shell runs it, prints any output, and shows a new prompt. A prompt often looks something like this:

sam@MacBook campaign-report %

That's your username, your computer's name, the folder you're in, and %, which means "ready". You never type the prompt itself.

Most commands follow the same shape:

1. a program name,
2. optional flags, which change how it behaves (they start with -),
3. arguments, which say what to act on.

ls -l data

Here ls is the program (list files). -l is a flag (long format, with sizes and dates). And data is the argument (which folder to list).

Note: In documentation you'll often see commands written as $ ls -l. The $ stands for the prompt. Don't type it.

Where am I?

Your files are arranged as a tree of folders. The terminal also calls them directories. At any moment the shell has a current working directory: the folder your commands act on. It's like the room you're standing in. Three commands do most of the work of finding your way around:

A few shortcuts make cd fast:

• cd .. moves up one level, to the folder that contains this one. .. always means "the parent folder", and . means "this folder".
• cd ~, or just cd on its own, goes to your home folder, /Users/yourname. The ~ is shorthand for it.
• cd ~/projects/campaign-report jumps straight to a folder from anywhere.

Paths come in two kinds, like a full street address versus "two doors down":

• An absolute path starts at the top of the tree with /, or at your home folder with ~. It works from anywhere: /Users/sam/projects/campaign-report/notes.txt.
• A relative path starts from wherever you are now. If you're already in campaign-report, the same file is just notes.txt, and the spending data is data/spend.csv.

Files whose names start with a dot, like .gitignore or .env, are hidden. Plain ls skips them, and ls -a shows them. You'll meet both of those files in later lessons, and both matter.

Tip: Press Tab to finish a file or folder name for you. Type cd da and press Tab, and the shell completes it to cd data/. It saves typing and catches typos.

Try it below. The terminal starts inside a small project folder.

path = "/Users/ann/projects/shop"
parts = path.split("/")
print(parts[-1])

Making and changing files

echo prints whatever you give it. On its own it prints to the screen. The > sign redirects that output into a file instead. One > replaces the file's contents, and two >> add to the end of it. Mixing them up is a classic way to wipe a file, so give it a moment's thought every time.

Watch out: rm doesn't use the Trash. A deleted file is gone, with no "are you sure?" and no undo. rm -r on the wrong folder can remove a whole project. Run pwd and ls first so you know exactly what you're deleting.

Running programs

Every command you've typed so far is actually a small program. Python is a program too. To run a Python file, give its name to python3:

python3 report.py

On a Mac the command is python3, not python. Older guides say python, which on many Macs either doesn't exist or points at something else. (On Windows it's usually python or py.) Two quick checks:

python3 --version
which python3

The first prints the version. The academy's browser Python is 3.14, and your computer may have an older one. which shows the full path of the program a command will run. That helps when something "isn't found" or the wrong version runs.

A few habits that save time:

• Up arrow brings back your previous command, so you can rerun or edit it.
• history lists the commands you've typed recently.
• Ctrl+C stops a program that's running too long or stuck in a loop.
• clear wipes the screen when it gets cluttered (your files are untouched).

Reading a README's instructions

Open-source AI projects explain setup as a list of commands. Now you can read one:

cd ~/projects
git clone https://github.com/example/ad-analyzer.git
cd ad-analyzer
python3 -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt
python3 analyze.py

You already know cd and python3. git clone downloads a project (next lesson). The venv, source and pip lines set up the project's own Python packages (the lesson after that).

Sometimes two commands are joined with &&, as in cd ad-analyzer && python3 analyze.py. That means "run the second only if the first worked".

Watch out: Don't paste commands you don't understand into your terminal. Be most careful with ones that start with sudo (run as administrator), or that send a download straight into the shell, like curl ... | sh. Those can change anything on your computer. If an AI assistant or a website suggests one, ask what each part does first.

Worked example: set up a report folder

Here's a short session from start to finish. Lines starting with % are what you type, and the other lines are what the terminal prints back:

% cd ~/projects
% mkdir -p q4-report/data
% cd q4-report
% echo "Q4 report notes" > notes.txt
% echo "Check search CPC" >> notes.txt
% cat notes.txt
Q4 report notes
Check search CPC
% ls
data  notes.txt
% pwd
/Users/sam/projects/q4-report

Step by step:

1. mkdir -p makes q4-report and the data folder inside it in one go.
2. cd moves into the new project folder.
3. The first echo uses >, so it creates notes.txt with one line. The second uses >>, so it adds a line instead of replacing the first.
4. cat shows both lines, ls shows the folder and the file, and pwd confirms where you are.

If the second echo had used a single >, cat would show only "Check search CPC".