Hello, World

Hello, World

This page assumes you've installed sbt.

Create a project directory with source code

A valid sbt project can be a directory containing a single source file. Try creating a directory hello with a file hw.scala, containing the following:

object Hi {
  def main(args: Array[String]) = println("Hi!")
}

Now from inside the hello directory, start sbt and type run at the sbt interactive console. On Linux or OS X the commands might look like this:

$ mkdir hello
$ cd hello
$ echo 'object Hi { def main(args: Array[String]) = println("Hi!") }' > hw.scala
$ sbt
...
> run
...
Hi!

In this case, sbt works purely by convention. sbt will find the following automatically:

  • Sources in the base directory
  • Sources in src/main/scala or src/main/java
  • Tests in src/test/scala or src/test/java
  • Data files in src/main/resources or src/test/resources
  • jars in lib

By default, sbt will build projects with the same version of Scala used to run sbt itself.

You can run the project with sbt run or enter the Scala REPL with sbt console. sbt console sets up your project's classpath so you can try out live Scala examples based on your project's code.

Build definition

Most projects will need some manual setup. Basic build settings go in a file called build.sbt, located in the project's base directory.

For example, if your project is in the directory hello, in hello/build.sbt you might write:

name := "hello"

version := "1.0"

scalaVersion := "2.10.3"

Notice the blank line between every item. This isn't just for show; they're actually required in order to separate each item. In .sbt build definition you'll learn more about how to write a build.sbt file.

If you plan to package your project in a jar, you will want to set at least the name and version in a build.sbt.

Setting the sbt version

You can force a particular version of sbt by creating a file hello/project/build.properties. In this file, write:

sbt.version=0.13.2

to force the use of sbt 0.13.2. sbt is 99% source compatible from release to release. Still, setting the sbt version in project/build.properties avoids any potential confusion.