Just Enough Terminal

Programs are started from a terminal: a window where you type commands instead of clicking on things. Most people have never opened one on purpose, and it can look unfriendly, a dark box with a blinking cursor and no buttons. The good news is that this book needs only four things from it: open it, see where you are, move between folders, and run a command.

Think of it as giving directions over the phone instead of pointing at a map. At first it is slower than clicking. But it is exact every time, it can be repeated word for word, and it works in places where there is nothing to click. Every tool a programmer uses, Python included, starts from here.

What the Terminal Is

A terminal is a text conversation with your computer. You type a command, press Enter, and the computer answers in text. Then it waits for the next command. There is no hidden magic: each command is just the name of a program, followed by whatever you want to give it.

At every moment the terminal is standing inside one folder, called the current folder (you will also see it called the working directory). It is the same idea as an open window in your file manager: the folder you are looking at right now. Commands work in that folder unless you tell them otherwise.

Opening One

On Windows, open the Start menu, type Terminal, and choose Terminal. It opens PowerShell, the standard Windows command line. On a Mac, press Command and Space to open Spotlight, type Terminal, and press Enter.

Either way, you see a line ending in a symbol, usually a greater-than sign on Windows or a percent sign on a Mac, followed by a blinking cursor. That line is the prompt. It is the terminal saying: I am ready, type a command. On Windows the prompt also shows the current folder; on a Mac it shows the folder's short name.

Where Am I, and What Is Here?

Two commands answer those questions, and both work on Windows and on a Mac. The first is pwd, short for print working directory. It prints the full path of the current folder. When a terminal first opens, that is your home folder, the one with your user name.

PS C:\Users\you> pwd

Path
----
C:\Users\you

you@mac ~ % pwd
/Users/you

Windows prints the answer under a small heading and uses backslashes between folder names; a Mac prints the bare path with forward slashes. Different punctuation, same meaning: your home folder.

The second command is ls, which lists what is in the current folder. You will recognise the names: Desktop, Documents, Downloads. They are the same folders you see in your file manager, just shown as text. On Windows the list comes as a table with dates and sizes; on a Mac it is just the names.

Moving Around

To step into a folder, type cd followed by its name. The letters stand for change directory. To go back up one level, type cd followed by a space and two dots. Two dots always mean the folder that contains this one.

Now make the folder this book works in. The command mkdir, short for make directory, creates a new folder in the current one. From your home folder, type the two commands below. The first creates a folder named python-course; the second steps into it. Run pwd afterwards and you will see the new folder at the end of the path.

mkdir python-course
cd python-course

One habit will save you a great deal of typing and many typos: the Tab key. Type the first few letters of a folder name and press Tab, and the terminal completes the rest for you. If several names start with those letters, PowerShell fills in the first one and each further Tab moves to the next; a Mac terminal fills in as much as the names share and shows you the choices. If nothing happens at all, no name starts with those letters.

Running a Command

Everything you type at the prompt has the same shape: the name of a program, then whatever you want to give it, separated by spaces. The cd command is a program name, and python-course is what you gave it. In the next topic, the first command you run will be the Python program itself, asked to report its version. From then on, running your own programs will look exactly the same.

A last reassurance. The commands on this page only look and move, apart from creating one empty folder. Nothing in this book asks you to delete anything from the terminal. If you make a typo, the worst that happens is a message saying the command was not recognised, and a fresh prompt waiting for you to try again.