Your First Terminal Session

Working Code

Open a terminal and type your first command. On macOS, press Spotlight (Cmd+Space) and search for "Terminal," or go to Applications > Utilities > Terminal.

Example 1: Printing text

echo "Hello, Terminal!"

Output:

Hello, Terminal!

echo prints text to the screen. It's one of the simplest commands.

Example 2: Checking your current location and listing files

pwd

Example output:

/Users/dale

ls

Example output:

Desktop  Documents  Downloads  Movies  Music  Pictures

Example 3: Adding options to a command

ls -l

Example output:

drwx------   5 dale staff   160 Jan 15 10:30 Desktop
drwx------  10 dale staff   320 Jan 14 09:00 Documents
drwx------   3 dale staff    96 Jan 13 15:20 Downloads

Characters like -l that start with - are called flags (or options). They modify how a command behaves.

Try It Yourself

Once you understand command structure, picking up new commands becomes easy.

Command structure: verb + flags + arguments

ls    -la    Documents
^      ^        ^
verb  flags   argument (target)

• Verb (command): what to do (ls, echo, pwd)
• Flags (options): how to do it (-l, -a, -r)
• Arguments: what to do it on (Documents, file.txt)

Try combining different commands:

# Detailed list including hidden files
ls -la

# View contents of a specific directory
ls -l Documents

# Save a message to a file
echo "My first file" > hello.txt

# Read file contents
cat hello.txt

You can combine multiple flags. ls -l -a and ls -la are identical.

"Why?" — Why Use the Terminal?

The terminal is a text-based interface for giving commands to your computer. Tasks that require multiple clicks in a GUI can be done with a single command.

| Scenario | GUI | Terminal | | ---------------------- | ----------------------------------------- | ---------------------- | | Rename 1000 files | Click one by one (practically impossible) | One command | | Connect to a server | No GUI available | SSH | | Run automation scripts | Not possible | Instant | | Search/replace text | One at a time in an editor | One line with grep/sed |

Understanding the Prompt

When you open the terminal, you see something like this:

dale@macbook ~ %

• dale — current username
• macbook — computer name
• ~ — current location (~ means the home directory)
• % — waiting for input (bash uses $, zsh uses %)

stdin and stdout — The Flow of Data

This is a core terminal concept:

Keyboard -> [stdin] -> Command -> [stdout] -> Screen

• stdin (standard input): the input channel where a command receives data (default: keyboard)
• stdout (standard output): the output channel where a command sends results (default: screen)

When you type echo "hello":

• echo receives "hello" as an argument (not through stdin)
• It outputs hello to stdout (the screen)

This concept matters because it's the foundation for pipes (|) and redirection (>) that you'll learn later.

Common Mistakes

Mistake 1: Case sensitivity

# Wrong
LS
Echo "hello"

# Correct
ls
echo "hello"

Terminal commands are case-sensitive. LS is not the same as ls.

Mistake 2: Watch out for spaces

# This treats "hello" and "world.txt" as two separate files
ls hello world.txt

# This treats "hello world.txt" as one filename
ls "hello world.txt"

If a filename contains spaces, always wrap it in quotes.

Mistake 3: Command not found

zsh: command not found: sl

Either you made a typo or the program isn't installed. Check that you typed ls, not sl.

Deep Dive

echo $SHELL

/bin/zsh

# Type "ls Doc" then press Tab:
ls Documents/