Argument

Use the @Argument wrapper to define a property of your custom command as a positional argument. A positional argument for a command-line tool is specified without a label and must appear in declaration order. @Argument properties with Optional type or a default value are optional for the user of your command-line tool.

For example, the following program has two positional arguments. The name argument is required, while greeting is optional because it has a default value.

@main
struct Greet: ParsableCommand {
    @Argument var name: String
    @Argument var greeting: String = "Hello"

    mutating func run() {
        print("\(greeting) \(name)!")
    }
}

You can call this program with just a name or with a name and a greeting. When you supply both arguments, the first argument is always treated as the name, due to the order of the property declarations.

$ greet Nadia
Hello Nadia!
$ greet Tamara Hi
Hi Tamara!

Single Arguments

• init(help: ArgumentHelp?, completion: CompletionKind?)

  Creates a property with no default value.

• init<T>(help: ArgumentHelp?, completion: CompletionKind?)

  Creates an optional property that reads its value from an argument.

• init(help: ArgumentHelp?, completion: CompletionKind?, transform: @escaping (String) throws -> Value)

  Creates a property with no default value, parsing with the given closure.

• init<T>(help: ArgumentHelp?, completion: CompletionKind?, transform: @escaping (String) throws -> T)

  Creates an optional property that reads its value from an argument.

• init(wrappedValue:help:completion:)
• init(wrappedValue:help:completion:transform:)

Array Arguments

• init<T>(parsing: ArgumentArrayParsingStrategy, help: ArgumentHelp?, completion: CompletionKind?)

  Creates a property with no default value that reads an array from zero or more arguments.

• init<T>(parsing: ArgumentArrayParsingStrategy, help: ArgumentHelp?, completion: CompletionKind?, transform: @escaping (String) throws -> T)

  Creates a property with no default value that reads an array from zero or more arguments, parsing each element with the given closure.

• init<T>(wrappedValue: Array<T>, parsing: ArgumentArrayParsingStrategy, help: ArgumentHelp?, completion: CompletionKind?)

  Creates a property that reads an array from zero or more arguments.

• init<T>(wrappedValue: Array<T>, parsing: ArgumentArrayParsingStrategy, help: ArgumentHelp?, completion: CompletionKind?, transform: @escaping (String) throws -> T)

  Creates a property that reads an array from zero or more arguments, parsing each element with the given closure.

• struct ArgumentArrayParsingStrategy

  The strategy to use when parsing multiple values from positional arguments into an array.

Infrequently Used APIs

• var wrappedValue: Value

  The value presented by this property wrapper.