# Installing Scala: Scala CLI, sbt and the REPL — Scala

Source: https://www.geekswithgeeks.com/en/scala/f-setup

> Set up Scala with Coursier, run scripts with Scala CLI and build projects with sbt.

## The Scala toolchain

The recommended installer is **Coursier** (`cs setup`), which installs a JDK if needed plus the Scala tools. Since Scala 3.5, the **`scala` command is Scala CLI**, a fast tool for scripts, small projects, the REPL, tests and packaging: `scala run hello.scala`, `scala repl`, `scala test .` and `scala package`. Dependencies and settings go in **`//> using` directives** at the top of a file, such as `//> using dep com.lihaoyi::os-lib:0.11.3`. For larger, multi-module projects, **sbt** is the most widely used build tool: `build.sbt` declares the Scala version and `libraryDependencies`, and sbt's interactive shell compiles incrementally (`~compile` recompiles on every save). **Mill** and Gradle or Maven with Scala plugins are alternatives. Library coordinates use **`%%`** in sbt (or **`::`** in Scala CLI) to append the Scala binary version (such as `_3`) to the artifact name. For editing, use **Metals** (the Scala language server) in VS Code or other editors, or **IntelliJ IDEA** with the Scala plugin.

## Scala CLI directives and an sbt build

Scripts declare dependencies inline; sbt builds larger projects.

```scala
// hello.scala  (run with: scala run hello.scala)
//> using scala 3.3
//> using dep com.lihaoyi::upickle:4.1.0

import upickle.default.*

case class Item(sku: String, price: Int) derives ReadWriter

@main def hello(): Unit =
  val json = write(Item("pen", 4950))
  println(json)                              // {"sku":"pen","price":4950}
  println(read[Item](json).sku)

// build.sbt for a larger project
// ThisBuild / scalaVersion := "3.3.6"
// lazy val root = project
//   .in(file("."))
//   .settings(
//     name := "orders-service",
//     libraryDependencies ++= Seq(
//       "com.lihaoyi"   %% "upickle" % "4.1.0",
//       "org.scalameta" %% "munit"   % "1.1.0" % Test
//     )
//   )
```

## A scooter and a truck

Scala CLI is a scooter: perfect for quick trips such as scripts, experiments and small tools. sbt is a truck: slower to start, but built to carry large multi-module projects and long build pipelines.

**Quiz:** What does %% do in an sbt dependency?

- [ ] Marks the dependency as optional
- [ ] Downloads the source code
- [ ] Excludes transitive dependencies
- [x] Appends the Scala binary version (such as _3) to the artifact name

*Answer:* Appends the Scala binary version (such as _3) to the artifact name. Scala libraries are published per Scala binary version, and %% selects the right one.