How to use the command 'crystal' (with examples)

The ‘crystal’ command is a powerful tool for managing Crystal source code. It provides various functionalities such as running Crystal files, compiling code, generating API documentation, running specification suites, starting an interactive server, and more.

Use case 1: Run a Crystal file

Code:

crystal path/to/file.cr

Motivation: Running a Crystal file allows testing and executing the code within the file. This is useful for quick testing and debugging purposes.

Explanation:

• crystal: The command to execute the Crystal compiler.
• path/to/file.cr: The path to the Crystal file that you want to run.

Example output:

Hello, Crystal!

Use case 2: Compile a file and all dependencies to a single executable

Code:

crystal build path/to/file.cr

Motivation: Compiling a Crystal file along with its dependencies into a single executable simplifies the distribution and deployment of an application. It allows running the program without the need for the Crystal compiler.

Explanation:

• crystal: The command to execute the Crystal compiler.
• build: Indicates that we want to build the file.
• path/to/file.cr: The path to the Crystal file that you want to compile.

Example output:

Generated executable 'file' in path/to/

Use case 3: Read Crystal source code from the command line or stdin, and execute it

Code:

crystal eval 'code'

Motivation: With the ‘crystal eval’ command, you can directly execute Crystal code without the need for a file. This comes in handy for quickly testing snippets of code or performing one-off evaluations.

Explanation:

• crystal: The command to execute the Crystal compiler.
• eval: Indicates that we want to evaluate code.
• 'code': The Crystal code that you want to execute.

Example output:

1 + 2 = 3

Use case 4: Generate API documentation from inline docstrings in Crystal files

Code:

crystal docs

Motivation: Generating API documentation is essential for documenting the functionality, usage, and structure of a Crystal project. It improves code maintainability and helps other developers understand how to interact with your project.

Explanation:

• crystal: The command to execute the Crystal compiler.
• docs: Indicates that we want to generate API documentation.

Example output:

Documentation generated at doc/index.html

Use case 5: Compile and run a Crystal specification suite

Code:

crystal spec

Motivation: Running a Crystal specification suite allows you to verify the correctness of your code through automated tests. It helps ensure that your code behaves as intended and detects any regressions or issues.

Explanation:

• crystal: The command to execute the Crystal compiler.
• spec: Indicates that we want to run the specification suite.

Example output:

............................

Finished in 0.073 seconds (files took 1.3 seconds to load)
30 examples, 0 failures, 0 pending

Use case 6: Start a local interactive server for testing the language

Code:

crystal play

Motivation: Starting a local interactive server allows you to experiment with the Crystal language. It provides a playground environment where you can write and execute code snippets, test out features, and learn the language interactively.

Explanation:

• crystal: The command to execute the Crystal compiler.
• play: Indicates that we want to start the interactive server.

Example output: The interactive server starts, and you can interact with it through a user interface in the web browser.

Use case 7: Create a project directory for a Crystal application

Code:

crystal init app application_name

Motivation: Creating a project directory for a Crystal application is the first step in starting a new project. It sets up the basic file structure and configuration files needed to organize and develop your application.

Explanation:

• crystal: The command to execute the Crystal compiler.
• init: Indicates that we want to initialize a new project.
• app: Specifies the type of project to create (in this case, an application).
• application_name: The name of the application, which will be used for the project directory.

Example output:

      create  application_name/.gitignore
      create  application_name/LICENSE
      create  application_name/README.md
      create  application_name/.editorconfig
      create  application_name/application_name.cr
      create  application_name/spec/spec_helper.cr
      create  application_name/spec/application_name_spec.cr
      create  application_name/.travis.yml
      create  application_name/shard.yml

Use case 8: Display all help options

Code:

crystal help

Motivation: When you need help with the ‘crystal’ command, using the ‘crystal help’ command will display a list of all available options, their usage, and brief descriptions. It serves as a quick reference for understanding the command and its functionalities.

Explanation:

• crystal: The command to execute the Crystal compiler.
• help: Indicates that we want to display help information.

Example output:

Usage: crystal [command] [switches] [program file] [--] [arguments]
...

Conclusion:

The ‘crystal’ command is a versatile tool for managing Crystal source code. It provides a range of functionalities, from running and compiling code to generating documentation and running tests. By understanding and utilizing these different use cases, developers can efficiently develop, test, and maintain Crystal projects.