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Terminal Basics

1. What is the terminal and why learn it

The terminal (also called command line, command prompt, or shell) is how you give instructions to the computer using text instead of clicking icons.

For Java developers, the terminal is essential for:

  • Compiling and running Java without opening an IDE
  • Using Maven / Gradle to build projects
  • Running servers, checking logs, managing processes
  • Using Git to manage source code

You don't need to memorize hundreds of commands. This lesson focuses on the 10 most-used commands you will type every day.

2. Opening the terminal

Windows has two main terminals:

Command Prompt (CMD) — the classic terminal: - Press Windows + R, type cmd, press Enter. - Or: search "Command Prompt" in the Start Menu.

PowerShell — more modern, supports most Unix commands: - Press Windows + X, choose Windows PowerShell or Terminal. - Or: search "PowerShell" in the Start Menu.

Recommendation: use Windows Terminal

Install Windows Terminal from the Microsoft Store — supports tabs, a clean interface, and integrates both CMD and PowerShell. Search "Windows Terminal" in the Microsoft Store and install for free.

Terminal is built in: - Press Cmd + Space, type Terminal, press Enter. - Or: Finder → Applications → Utilities → Terminal.

The default shell on macOS is Zsh (since macOS Catalina).

iTerm2 — a better terminal for macOS

iTerm2 provides more features than the default Terminal: search, split panes, rich color themes. Free download at iterm2.com.

  • Ubuntu: Ctrl + Alt + T
  • GNOME: search "Terminal" in the launcher
  • KDE: search "Konsole"

3. Understanding the prompt

When you open the terminal, you see a line like this:

C:\Users\YourName>_
  • C:\Users\YourName — your current directory
  • > — the prompt, waiting for your input
  • _ — the cursor
yourname@MacBook ~ %_
  • yourname — your username
  • MacBook — your computer's name
  • ~ — your home directory (shorthand for /Users/YourName on macOS)
  • % or $ — the prompt

4. Navigating directories

See your current directory

cd

pwd

Example output: /Users/yourname — this is where you currently are.

List files and directories

dir

ls

More detail (size, permissions, date):

ls -l

Include hidden files:

ls -la

Move into a directory

cd directory-name

Example — go into Documents:

cd Documents

Go into a nested directory:

cd Documents/java-projects

Go up one level to the parent directory:

cd ..

Go back to the home directory:

cd ~

cd %USERPROFILE%

Absolute vs relative paths

Type Example Meaning
Absolute cd /Users/yourname/Documents Starts from the root, works from any location
Relative cd Documents Relative to your current directory

5. Managing files and directories

Create a new directory

mkdir directory-name

Create multiple levels at once:

mkdir -p projects/java/hello-world

mkdir projects\java\hello-world

Delete a file

rm file.txt

Delete a directory and everything inside it:

rm -rf directory-name/

Be careful with rm -rf

This permanently deletes files — they do not go to the Trash. Double-check the directory name before running.

del file.txt
rmdir /s /q directory-name

Copy and move files

cp source.txt destination.txt          # copy file
cp -r source-dir/ destination-dir/     # copy directory
mv source.txt destination.txt          # move (or rename)

copy source.txt destination.txt
xcopy source-dir destination-dir /E /I
move source.txt destination.txt

6. Read file contents

cat file.txt        # print the entire file
head -20 file.txt   # first 20 lines
tail -20 file.txt   # last 20 lines

type file.txt

7. Compile and run Java from the terminal

This is the most important part of this lesson.

Example directory structure

hello-java/
└── HelloWorld.java

Create the Java file

Create the directory and navigate into it:

mkdir hello-java
cd hello-java

Use a text editor to create HelloWorld.java with this content:

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

The filename must match the class name

A file named HelloWorld.java must contain public class HelloWorld. A mismatch causes javac to report an error.

Compile

javac HelloWorld.java

If there are no errors, this produces a HelloWorld.class file in the same directory.

Run

java HelloWorld

Do not add .class when running

The correct command is java HelloWorld, not java HelloWorld.class.

Output:

Hello, World!

The full workflow

HelloWorld.java  →  javac  →  HelloWorld.class  →  java  →  Output
(source code)      (compile)    (bytecode)          (run)

8. Other useful commands

Clear the screen

clear

cls

View command history

history

Press the ↑ key to repeat the previous command — no need to retype it.

Stop a running program

Press Ctrl + C to stop any currently running command (very useful when running a server).

Search inside a file

grep "search-term" file.txt
grep -r "search-term" directory/   # search recursively through a directory

findstr "search-term" file.txt

9. Essential command reference

Action Windows CMD macOS / Linux
Show current directory cd pwd
List contents dir ls
Enter a directory cd dirname cd dirname
Go up one level cd .. cd ..
Create directory mkdir name mkdir name
Delete file del file.txt rm file.txt
Delete directory rmdir /s /q name rm -rf name/
Copy file copy a.txt b.txt cp a.txt b.txt
Move/rename move a.txt b.txt mv a.txt b.txt
Read file type file.txt cat file.txt
Clear screen cls clear
Stop program Ctrl + C Ctrl + C
Compile Java javac File.java javac File.java
Run Java java ClassName java ClassName

10. Tips for working efficiently in the terminal

  • Tab to autocomplete: type the first few letters of a file or directory name and press Tab — the terminal fills in the rest.
  • ↑ ↓ to browse history: no need to retype previous commands.
  • Ctrl + C to exit: when any command gets stuck or runs too long — press Ctrl + C to stop it immediately.
  • Ctrl + L to clear the screen: shortcut for clear / cls.
  • Drag and drop paths: drag a file or folder from Finder (macOS) or Explorer (Windows) into the terminal window — it automatically pastes the full path.

Next: Git and GitHub — learn how to save your code history and collaborate with others.

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