Commands

Core annotations and patterns for defining CLI commands, options, and argument handling in Crest.

Crest turns Java methods into CLI commands through a small set of annotations. A method annotated with @Command becomes a command. Its parameters become options and positional arguments. The framework handles parsing, type conversion, validation, and help generation automatically.

This section covers everything you need to define and organize commands:

• Annotations – @Command, @Option, @Default, and @Required form the foundation of every CLI tool built with Crest.
• Options Classes – Bundle related options into reusable @Options classes and compose them across commands.
• Command Groups – Organize commands into groups with sub-commands using class-level @Command.
• Return Types – Choose from String, StreamingOutput, PrintOutput, Stream, and more to control command output.
• I/O Streams – Inject stdin, stdout, and stderr into commands with @In, @Out, and @Err.
• Help – Built-in help command, man page generation, and option description sources.