How to Use the Command 'scala-cli' (with Examples)

The ‘scala-cli’ command offers a versatile way to interact with the Scala programming language. It provides various functionalities such as starting a REPL, compiling and executing scripts, testing, formatting, and even setting up IDE support for Scala projects. The command is a powerful tool for both Scala beginners and seasoned developers who seek to streamline their development workflow.

Use Case 1: Start a REPL (Interactive Shell) Using a Specific Scala and JVM Version

Code:

scala-cli --scala 3.1.0 --jvm temurin:17

Motivation:

Using a REPL (Read Eval Print Loop) allows developers to interactively test and experiment with Scala code snippets without having to write an entire script or application. Specifying a particular Scala and JVM version ensures compatibility and lets developers leverage new language features or library updates that may not be available in previous versions.

Explanation:

• --scala 3.1.0: This argument specifies the version of Scala to be used. By choosing version 3.1.0, you gain access to any new features or advancements in that version while ensuring your code aligns with its syntax and behavior.
• --jvm temurin:17: Specifies the JVM implementation and version. Temurin is a popular OpenJDK distribution, and version 17 is selected for its modern features and support. This pairing ensures your Scala code runs optimally on a stable and up-to-date JVM.

Example Output:

Upon execution, the terminal launches an interactive Scala shell where you can input and evaluate Scala code dynamically, displaying immediate results or errors for each snippet entered.

Use Case 2: Compile and Run a Scala Script

Code:

scala-cli run path/to/script.scala

Motivation:

The ability to compile and run Scala scripts directly from the command line simplifies the development process, letting you quickly test functionalities or showcase concepts without setting up a complex project structure. This is particularly useful for development environments, learning scenarios, or debugging.

Explanation:

• run: This part of the command tells scala-cli to compile and execute the specified script.
• path/to/script.scala: The path indicates the location of your Scala script. Replace this with the actual path to your file. This places a focus on the specific script you intend to run, maintaining clarity and control over the execution process.

Example Output:

The system compiles the provided Scala script and executes it, displaying the output, errors, or any exceptions directly on the console.

Use Case 3: Compile and Test a Scala Script

Code:

scala-cli test path/to/script.scala

Motivation:

Testing is a crucial part of software development. This command facilitates automated testing of your Scala scripts, allowing you to verify functionality and ensure code quality. It is vital for developers who follow Test-Driven Development (TDD) or need to maintain code integrity over time.

Explanation:

• test: Signals scala-cli to compile the script and run test cases present in the file.
• path/to/script.scala: This denotes the actual location of your Scala file. By targeting the specific file, you ensure tests are only performed on the relevant code, promoting efficient bug tracking and code validation.

Example Output:

Executing this command runs the test cases found within your script, giving you a summary of passed tests, failures, and errors, essentially guiding you to areas of the code that may require attention.

Use Case 4: Format a Scala Script, Updating the File In-Place

Code:

scala-cli fmt path/to/script.scala

Motivation:

Code formatting is essential for maintaining readability and consistency within a codebase. This command automatically formats your Scala script following predefined style guidelines, helping ensure compliance with team coding standards or personal preferences.

Explanation:

• fmt: Calls upon the formatting feature of scala-cli to apply standard styling to your script.
• path/to/script.scala: This specifies the script you wish to format. It identifies the target file to be beautified, ensuring that alterations are contained and intentional.

Example Output:

After execution, the script is altered in place to reflect cleaner, more maintainable code format, potentially offering improved readability and more consistent styling across your project.

Use Case 5: Generate Files for IDE (VSCode and IntelliJ) Support

Code:

scala-cli setup-ide path/to/script.scala

Motivation:

IDE integration is vital for feature-rich development experiences. This command generates necessary files, improving code navigation, syntax checking, and offering autocomplete support for your Scala projects within IDEs like VSCode and IntelliJ.

Explanation:

• setup-ide: Instructs scala-cli to prepare the project for IDE compatibility by generating appropriate configuration files.
• path/to/script.scala: While this typically refers to the starting script, it contextualizes the setup process, helping the IDE assess dependencies and environment configurations specific to your script’s location.

Example Output:

Upon run, this command outputs configuration files for the specified IDE, allowing you to immediately enjoy enhanced IDE functionality such as better project organization, auto-import features, and effective debugging tools.

Conclusion:

The ‘scala-cli’ command offers a remarkable range of functionalities that enhance the development process for Scala applications. From facilitating interactive programming sessions in a REPL to ensuring code quality with testing and formatting, this tool empowers developers with necessary utilities to efficiently work with Scala. Its seamless integration with popular IDEs further elevates productivity by furnishing comprehensive support throughout the development cycle.