1.4 Terminal and CLI for Beginners

🖥️ What Is the Terminal

O terminal is a program that receives text commands and executes them on the operating system. It’s the most direct and powerful interface to a computer — predating graphical interfaces and far more efficient for automation.

🖥️ Where to find the terminal

🍎 macOS

Spotlight (⌘+Space) → "Terminal" or install the iTerm2 for a better experience.

🐧 Linux

Comes with terminals (gnome-terminal, konsole, xterm). Shortcut: Ctrl+Alt+T on most distros.

🪟 Windows

Use WSL2 (Windows Subsystem for Linux) for a real Unix environment. PowerShell works, but there are differences.

💡 Tip: The prompt tells you where you are

The prompt user@mac ~/projetos/meu-app $ has three parts: user@machine, current directory (~ = home), and $ indicating that you can type. Read the prompt before typing any command.

Shell

bash/zsh — command interpreter

Prompt

Where you type (ends in $)

stdout

Command's standard output

Exit code

0 = success, ≠0 = error

📂 Folders and paths

The file system is a tree: one root, with folders inside folders inside folders. Knowing where you are and how to reference files is terminal skill #1.

🌳 Typical directory structure

/ ← root — absolute

├── home/

│ └── user/ ← ~ (user's home)

│ ├── projetos/

│ │ └── meu-app/ ← you're here

│ │ ├── src/

│ │ └── package.json

│ └── Downloads/

# Absolute path: /home/user/projetos/meu-app

# Relative path (from ~/projetos): ./meu-app

# Go up one level: ../ (goes to ~/projetos)

✓ Absolute path

/home/user/projetos/app
/etc/nginx/nginx.conf
/usr/local/bin/node

Starts with / — works from anywhere

→ Relative path

./src/index.ts
../config/env.json
../../outro-projeto/

Relative to the current directory — shorter

System root

User's home

Current directory

Parent directory

⚡ Essential commands

You don't need to memorize 200 Unix commands. With 10 commands you can navigate, create, move, and inspect any project with Claude Code.

📖 Quick reference — 10 essential commands

pwd # print working directory — where am I?

→ /home/user/projetos/meu-app

ls # list — what's here?

ls -la # with details and hidden files

→ src/ package.json .gitignore node_modules/

cd folder # change directory — navigate

cd .. # go up one level

cd ~ # go back to home

mkdir name # make directory — create folder

mkdir -p a/b/c # creates complete hierarchy

cat file # view file contents

cp src dest # copy file

mv src dest # move/rename file

How Claude Code uses these commands day to day

→

`ls` — explore the structure

The agent uses ls to understand the project before taking action. It's the first thing it does in new sessions.

→

`mkdir -p` — create structure

To create features, the agent creates the necessary folders before writing the files.

→

`mv` — refactoring

Moving files to a new folder structure during refactoring is a daily task.

cd/pwd/ls

Basic navigation

mkdir/cp/mv

File management

cat/grep

Inspect content

man cmd

Help for any command

🔌 What Is a CLI

A CLI (Command-Line Interface) is a program you control by typing text commands. Git, npm, Python, Docker, and Claude Code are all CLIs. Understanding the anatomy of a CLI command is a skill that transfers to all of them.

🔍 Anatomy of a CLI Command

# General structure:

program [subcommand] [--flags] [arguments]

# Real examples:

git commit -m "message"

npm install --save-dev TypeScript

claude --dangerously-skip-permissions -p "task"

# Help is always available:

claude --help

git --help

npm help install

✓ CLI best practices

✓Always use --help before guessing
✓Tab completion — press Tab to autocomplete
✓Use the ↑↓ arrows to navigate command history
✓Ctrl+C cancels the current command

✗ CLI pitfalls

✗Copying a command from the internet without reading it
✗Ignore error messages
✗Use sudo unnecessarily
✗Typing commands in the wrong folder

Flags

--flag or -f (short form)

Subcommand

git commit, npm install

--help

Inline help always available

Tab

Autocomplete — always use it

📦 Install tools

To use Claude Code, you need to install Node.js and the npm package. Understand package managers is essential — they're the standard way to install CLIs on any system.

Installing Claude Code — step by step

Install Node.js

# macOS (Homebrew)

brew install node

# Linux (Ubuntu/Debian)

curl -fsSL https://deb.nodesource.com/setup_lts.x | sudo -E bash -

sudo apt-get install -y nodejs

Verify installation

node --version # should show v18+

npm --version # should show 9+

Install Claude Code

npm install -g @anthropic-ai/claude-code

# verify:

which claude # should show the path

claude --version

💡 What PATH is

When you type claude, the shell looks for the executable in the folders listed in the variable PATH. If you get "command not found," the global npm folder isn’t in your PATH. Solution: export PATH="$PATH:$(npm root -g)/../.bin".

npm

Node Package Manager

-g flag

Installs globally on the system

PATH

Where the shell looks for executables

which

Shows where an executable is located

🔒 Terminal Security

The terminal has real power about the system. A wrong command can delete unrecoverable files, expose credentials, or install malicious software. These simple rules prevent 99% of problems.

⚠️ Commands you should NEVER copy without understanding

rm -rf / ← erases the entire system

rm -rf ~ ← deletes all your files

curl URL | bash ← runs unknown code

sudo chmod -R 777 / ← removes system security

> file.conf ← erases the file's contents!

Rule: if you can’t explain what a command does, don’t run it.

✓ Security best practices

✓Use .env for secrets, and never commit this file
✓Check what you're about to delete first with ls
✓Prefer mv to the Trash instead of rm
✓Read confirmation messages (y/n) carefully

✗ Common security errors

✗Commit API keys or passwords to git
✗Use sudo indiscriminately
✗Run third-party scripts without reviewing them
✗Leaving environment variables in the history

💡 Security with Claude Code

Claude Code can run any Bash command. Configure the settings.json with a denylist for destructive commands you never want it to run automatically. That way, you have autonomy with safeguards.

"deny": ["Bash(rm -rf:*)", "Bash(git push --force:*)"]

.env

File for secret variables

.gitignore

Lists files not to commit

sudo

Superuser—use with care

denylist

Block dangerous commands in Claude

✅ Module 1.4 Summary

✓

Terminal = text interface — where Claude Code lives

✓

Directory tree — /, ~, ., .., and absolute/relative paths

✓

10 essential commands — cd, ls, mkdir, pwd, cat, cp, mv, rm, grep, man

✓

CLI: program + subcommand + flags + args — universal pattern

✓

npm installs Claude Code — npm install -g @anthropic-ai/claude-code

✓

Security: read before running — never copy commands without understanding them

🎉 Track 1 complete!

You have the complete foundation: what Claude Code is, how it thinks, how it manages context, and how to use the terminal. Next step: install Claude Code for real in Track 2 — Installation.

← Module 1.3 Track 2: Installation →