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Scala CLI as an implementation of the scala command

As of Scala 3.5.0, Scala CLI has become the official runner for the language, replacing the old runner implementation under the scala script.

Since Scala CLI is quite feature-packed, we do not want to expose all the features and options to all the Scala users from the very beginning. Why is that?

  • We want to make sure that the options / commands are stable.
  • We do not want to overwhelm users with multiple options and commands.

That is why we built in a mechanism to limit the commands, options, directives in Scala CLI by default. However, it's still possible to enable all features by explicitly passing the --power flag on the command line, or by setting it globally running:

scala config power true

Alternatively, it is also possible to rely on the SCALA_CLI_POWER environment variable to achieve the same:

export SCALA_CLI_POWER=true

To check which options, commands and directives are supported when running Scala CLI with limited functionalities, refer to options, commands and using directives, respectively.

Installing Scala CLI as scala​

Refer to the official instructions for installing Scala.

note

A given Scala version has a paired Scala CLI version which is used by the scala command installed alongside it, as per the official instructions. This means that even when installing the latest Scala version, its scala command may refer to an older Scala CLI version.

To get the latest stable Scala CLI launcher, refer to the separate scala-cli installation instructions.

Alternatively, you can use the --cli-version launcher option to specify the Scala CLI version to use. This will run the JVM launcher of the specified Scala CLI version under the hood, so do keep in mind that it may be a bit slower than a native launcher. Also, the specified version (and potentially any of its dependencies, if they are not already installed) would be downloaded if it's not available in the local cache, so it may require additional setup for isolated environments.

scala --cli-version 1.5.0 version
# Scala CLI version: 1.5.0
# Scala version (default): 3.5.0

If the bleeding edge is what you are after, you can use the nightly version this way. Just keep in mind that there are no guarantees about the stability of nightly versions.

scala --cli-version nightly version
# Scala CLI version: 1.5.0-17-g00e4c88c1-SNAPSHOT
# Scala version (default): 3.5.0

Migrating from the old scala runner to Scala CLI​

If you have been using the old scala runner and want to migrate to Scala CLI, refer to the migration guide.

Using the old (deprecated) scala runner with Scala 3.5+​

You can still use the (deprecated as of Scala 3.5.0) legacy runner with Scala 3.5+ installed. It is available under the scala_legacy command.

caution

Even though this enables usage of the old runner under a new alias, it is recommended to migrate any existing scripts and automations to Scala CLI under either scala or scala-cli, as the scala_legacy command may be dropped at some point in the future.

scala_legacy -version
# [warning] MainGenericRunner class is deprecated since Scala 3.5.0, and Scala CLI features will not work.
# [warning] Please be sure to update to the Scala CLI launcher to use the new features.
# [warning] Check the Scala 3.5.0 release notes to troubleshoot your installation.
# Scala code runner version 3.5.0 -- Copyright 2002-2024, LAMP/EPFL