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Using scala-cli to run Scala Scripts

Scala Scripts​

Scala scripts are files that contain Scala code without a main method. These source code files don't require build-tool configurations. To run Scala scripts very quickly without waiting the need for build tools, use scala-cli.

Run​

For example, given this simple script:

HelloScript.sc
val sv = scala.util.Properties.versionNumberString

val message = s"Hello from Scala ${sv}, Java ${System.getProperty("java.version")}"
println(message)

You can run it directly with scala-cli — there's no need for a build tool or additional configuration:

scala-cli run HelloScript.sc

Alternatively, you can add a "shebang" header to your script, make it executable, and execute it directly with scala-cli. For example, given this script with a header that invokes scala-cli:

HelloScriptSheBang.sc
#!/usr/bin/env -S scala-cli shebang

val sv = scala.util.Properties.versionNumberString

def printMessage(): Unit =
  val message = s"Hello from Scala ${sv}, Java ${System.getProperty("java.version")}"
  println(message)

printMessage()

You can make it executable and then run it like this:

chmod +x HelloScriptSheBang.sc
./HelloScriptSheBang.sc
# Hello from Scala 2.13.6, Java 16.0.1

You can also pass command line arguments to Scala scripts:

ScriptArguments.sc
#!/usr/bin/env -S scala-cli shebang
println(args(1))
chmod +x ScriptArguments.sc
./ScriptArguments.sc foo bar
# bar

As shown, command line arguments are accessed through the special args variable.

Features​

All of the features shown for non-scripts work for Scala scripts as well, such as waiting for changes (watch mode), dependency menagement, packaging, compiling, etc.

Package​

For example, run the package sub-command to package your script as a lightweight executable JAR file:

scala-cli package HelloScript.sc
./HelloScript

Watch mode​

As another example, pass --watch to scala-cli to watch all source files for changes, and then re-run them when there is a change:

scala-cli --watch HelloScript.sc