Command Line Basics - Programming Fundamentals

🤔 What Is the Command Line?

The command line (also called the terminal, shell, or console) is a text-based way to interact with your computer. Instead of clicking icons and menus, you type commands and press Enter.

It might feel slower at first, but once you learn the basics, it's actually faster for many tasks — especially running code. Every professional developer uses the command line daily.

Key vocabulary:

Terminal — The application window where you type commands.
Shell — The program that interprets your commands (bash, zsh, PowerShell).
Prompt — The text that appears before your cursor, showing you where you are (e.g., C:\Users\you> or ~/projects$).
Directory — Another word for "folder."
Path — The address of a file or folder (e.g., /home/user/projects/hello.py).

🚪 Opening Your Terminal

Windows

PowerShell: Press Win, type "PowerShell", press Enter.
Command Prompt: Press Win+R, type cmd, press Enter.
VS Code: Press Ctrl+` (backtick) to open the built-in terminal.

This course recommends PowerShell or the VS Code terminal on Windows.

macOS

Terminal.app: Open Finder → Applications → Utilities → Terminal.
Spotlight: Press Cmd+Space, type "Terminal", press Enter.
VS Code: Press Ctrl+` to open the built-in terminal.

Linux

Press Ctrl+Alt+T on most distributions.
Or find "Terminal" in your applications menu.

🧭 Navigating the File System

These are the commands you'll use constantly. They work the same in almost every terminal.

Where am I? — `pwd`

Print Working Directory. Shows the full path to your current location.

# Type:
# pwd

# Output example:
# /home/yourname/projects

// Type:
// pwd
// (or: Get-Location)

// Output example:
// C:\Users\yourname\projects

// Type:
// cd
// (with no arguments, cmd shows current directory)

// Output example:
// C:\Users\yourname\projects

What's in here? — `ls` / `dir`

List the contents of the current directory.

# List files and folders:
# ls

# With details (size, date, permissions):
# ls -la

# Show only .py files:
# ls *.py

// List files and folders:
// ls
// (or: Get-ChildItem)
// (or: dir)

// Show only .js files:
// ls *.js

// List files and folders:
// dir

// Show only .cs files:
// dir *.cs

Go somewhere — `cd`

Change Directory. Move into a folder, move up, or jump to a specific path.

# Move into a folder:
cd projects

# Move up one level:
cd ..

# Move up two levels:
cd ../..

# Go to your home directory:
cd ~

# Go to a specific path:
cd /home/yourname/projects/my-app

Pro tip: Type the first few letters of a folder name and press Tab — the terminal will auto-complete it for you.

📁 Creating & Managing Files

Create a folder — `mkdir`

Make Directory. Creates a new folder.

# Create a single folder:
mkdir my-project

# Create nested folders at once:
mkdir -p my-project/src/utils

On Windows cmd, use mkdir my-project\src\utils (backslashes, and it auto-creates parents).

Create / view a file

# Create an empty file:
# touch hello.py

# View a file's contents:
# cat hello.py

# View a long file with scrolling:
# less hello.py

// Create an empty file:
// New-Item hello.js

// View a file's contents:
// Get-Content hello.js
// (or: cat hello.js)

// Create an empty file:
// type nul > hello.cs

// View a file's contents:
// type hello.cs

Copy, move, and delete

Action	macOS / Linux	Windows (PowerShell)	Windows (cmd)
Copy a file	`cp file.py backup.py`	`Copy-Item file.js backup.js`	`copy file.cs backup.cs`
Move / rename	`mv old.py new.py`	`Move-Item old.js new.js`	`move old.cs new.cs`
Delete a file	`rm file.py`	`Remove-Item file.js`	`del file.cs`
Delete a folder	`rm -r folder/`	`Remove-Item -Recurse folder`	`rmdir /s folder`

⚠️ Be careful with delete commands. There's no recycle bin in the terminal — deleted files are gone for good.

▶️ Running Your Programs

This is what you'll do most often in this course: write code in VS Code, then switch to the terminal to run it.

# Run a Python file:
# python hello.py
# (or on macOS/Linux:)
# python3 hello.py

# Run with arguments:
# python hello.py --name Ray

# Start an interactive Python session:
# python
# (type exit() to leave)

// Run a JavaScript file with Node.js:
// node hello.js

// Run with arguments:
// node hello.js --name Ray

// Start an interactive Node session (REPL):
// node
// (press Ctrl+C twice to leave)

// First, create a project (if you haven't):
// dotnet new console -n MyApp
// cd MyApp

// Run the project:
// dotnet run

// Build without running:
// dotnet build

🎓 Instructor Note: Terminal Workflow

Demonstrate the "edit-save-switch-run" loop early and often. Many beginners forget to save their file before running, or they run the command in the wrong directory. Encourage using VS Code's built-in terminal so they don't have to switch windows.

⌨️ Time-Saving Shortcuts

These keyboard tricks will make you faster in the terminal immediately:

Shortcut	What It Does
`Tab`	Auto-complete file and folder names. Press twice to see all options.
`↑` / `↓`	Scroll through your command history. Re-run previous commands quickly.
`Ctrl+C`	Cancel the currently running command. Use when a program is stuck.
`Ctrl+L`	Clear the screen (same as typing `clear`).
`Ctrl+A`	Move cursor to the beginning of the line.
`Ctrl+E`	Move cursor to the end of the line.
`history`	Show all recent commands. On Windows PowerShell: `Get-History`.
`clear`	Clear the terminal screen. On Windows cmd: `cls`.

🚫 Common Mistakes

Running code from the wrong directory

If you see "file not found" when running python hello.py, you're probably in the wrong folder. Use pwd to check where you are and ls to confirm your file is there.

Forgetting to save before running

Your terminal runs whatever is saved on disk, not what's on screen in your editor. Press Ctrl+S (or Cmd+S on Mac) before switching to the terminal.

Spaces in folder names

Folder names with spaces cause problems in the terminal. Use hyphens or underscores instead: my-project not my project. If you must use a path with spaces, wrap it in quotes: cd "My Documents".

Backslashes vs. forward slashes

Windows uses backslashes (\) in paths; macOS and Linux use forward slashes (/). PowerShell accepts both. If you copy a path from Windows Explorer, it will have backslashes — that's fine in PowerShell but won't work in bash/zsh.

📋 Quick Reference

Task	macOS / Linux	Windows (PowerShell)
Where am I?	`pwd`	`pwd`
List files	`ls`	`ls` or `dir`
Change directory	`cd folder`	`cd folder`
Go up one level	`cd ..`	`cd ..`
Home directory	`cd ~`	`cd ~`
Create folder	`mkdir name`	`mkdir name`
Create file	`touch file.txt`	`New-Item file.txt`
View file	`cat file.txt`	`cat file.txt`
Copy file	`cp a.txt b.txt`	`cp a.txt b.txt`
Move / rename	`mv a.txt b.txt`	`mv a.txt b.txt`
Delete file	`rm file.txt`	`rm file.txt`
Clear screen	`clear`	`cls` or `clear`
Run Python	`python3 file.py`	`python file.py`
Run JavaScript	`node file.js`	`node file.js`
Run C#	`dotnet run`	`dotnet run`

💻 Command Line Basics

📑 Jump To

🤔 What Is the Command Line?

🚪 Opening Your Terminal

Windows

macOS

Linux

🧭 Navigating the File System

Where am I? — `pwd`

What's in here? — `ls` / `dir`

Go somewhere — `cd`

📁 Creating & Managing Files

Create a folder — `mkdir`

Create / view a file

Copy, move, and delete

▶️ Running Your Programs

⌨️ Time-Saving Shortcuts

🚫 Common Mistakes

Running code from the wrong directory

Forgetting to save before running

Spaces in folder names

Backslashes vs. forward slashes

📋 Quick Reference

📑 Jump To

🤔 What Is the Command Line?

🚪 Opening Your Terminal

Windows

macOS

Linux

🧭 Navigating the File System

Where am I? — pwd

What's in here? — ls / dir

Go somewhere — cd

📁 Creating & Managing Files

Create a folder — mkdir

Create / view a file

Copy, move, and delete

▶️ Running Your Programs

⌨️ Time-Saving Shortcuts

🚫 Common Mistakes

Running code from the wrong directory

Forgetting to save before running

Spaces in folder names

Backslashes vs. forward slashes

📋 Quick Reference

Where am I? — `pwd`

What's in here? — `ls` / `dir`

Go somewhere — `cd`

Create a folder — `mkdir`