Scala 3 for Beginners: Install Scala and Run Your First Program

Step 1: Understand what you are installing

Scala source code is compiled to JVM bytecode, so it needs a Java Development Kit to run. Install a long-term support JDK such as 17 or 21 from a vendor like Eclipse Temurin. On top of the JDK you need the Scala compiler and a build tool. The simplest route is Coursier, the official Scala installer, which downloads a JDK if needed, the Scala command-line tools, and sbt, the standard build tool for larger projects. Because everything runs on the JVM, Scala programs can use any Java library, which is a big part of its appeal.

Step 2: Install with Coursier

Follow the instructions on the Scala website's install page for your operating system to get the Coursier launcher, called cs. Running its setup command then installs the standard Scala tools and places them on your path. Open a new terminal window afterwards so the path change takes effect. If a command is not found, the new terminal is the first thing to check. Installers change over time, so the official page is the most reliable reference for the exact steps on your platform.

cs setup
java -version
scala-cli version
sbt --version

Step 3: Write and run a script

Scala CLI runs a single file without any project setup, which is ideal for learning. Create a file named hello.scala. The main annotation marks a function as the program entry point, replacing the verbose static main method that Scala 2 and Java require. Indentation defines blocks in Scala 3, so there are no braces here. Run the file with scala-cli run, and the first run may take a little longer while it compiles and downloads the compiler.

// hello.scala
@main def hello(): Unit =
  println("Hello, CaliberTek!")

Step 4: Try the REPL for quick experiments

The REPL, which stands for read-eval-print loop, evaluates each line you type and prints the result with its type. It is the quickest way to try an idea or learn a library method. Each result is stored in a generated name such as res0, so you can reuse it. Exit with Ctrl+D or the :quit command. Use the REPL for tiny experiments and files for anything you want to keep.

scala-cli repl

scala> 2 + 3
val res0: Int = 5

scala> "scala".toUpperCase
val res1: String = SCALA

Step 5: Pass arguments and read input

A main function can take command-line arguments as a sequence of strings. This small program greets each name given on the command line, and it introduces two ideas you will use constantly: the for loop with the do keyword, and string interpolation with the s prefix, which inserts values into text. Anything after the script name on the command line is passed to the program. If no arguments are given, the loop simply does nothing.

@main def greet(names: String*): Unit =
  for name <- names do
    println(s"Hello, $name!")

// scala-cli run greet.scala -- Asha Ben

Step 6: Choose an editor

Scala has first-class support in IntelliJ IDEA with the Scala plugin and in Visual Studio Code or other editors through Metals, a language server that gives completion, error messages, and navigation. For a Scala CLI file, open the folder in VS Code with the Metals extension and let it import the project. A good editor matters more in Scala than in many languages, because the type information it shows on hover teaches you what the compiler infers. Do not worry about configuring everything on day one, because the REPL and a text file are enough for the first lessons.