A single Application can host multiple commands. The first CLI argument selects the command name, and remaining arguments are parsed according to that command’s declared parameters.

¶Creating a multi-command app

$app = new Application(
	"Multi-command example",
	new ArgumentList(...$argv),
	$sumCommand,
	$repeatCommand
);
$app->run();

In example/06-multi-command.php:

• sum left right validates numeric input and prints a total
• repeat text [count] repeats user text with an optional count
• help is automatically available for global and per-command usage

Command-level errors can throw CommandException, which is caught by the application and displayed on the error stream.

if(!is_numeric($left) || !is_numeric($right)) {
	throw new CommandException("Both values must be numeric");
}

This keeps command logic focused while preserving consistent output and exit handling.

For manual error output inside a command, pass StreamName::ERROR to writeLine():

$this->writeLine("Could not read input file", StreamName::ERROR);

Commands may also return explicit exit codes from run():

• 0 indicates success.
• Any non-zero value exits the application with that code.

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Next, refer to output streams for stream selection, or examples for complete runnable scripts.