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apple/swift-argument-parser 1.2.0
Straightforward, type-safe argument parsing for Swift
⭐️ 2,827
🕓 2 weeks ago
.package(url: "https://github.com/apple/swift-argument-parser.git", from: "1.2.0")

Swift Argument Parser


Begin by declaring a type that defines the information that you need to collect from the command line. Decorate each stored property with one of ArgumentParser's property wrappers, and then declare conformance to ParsableCommand and add the @main attribute. Finally, implement your command's logic in the run() method.

import ArgumentParser

struct Repeat: ParsableCommand {
    @Flag(help: "Include a counter with each repetition.")
    var includeCounter = false

    @Option(name: .shortAndLong, help: "The number of times to repeat 'phrase'.")
    var count: Int? = nil

    @Argument(help: "The phrase to repeat.")
    var phrase: String

    mutating func run() throws {
        let repeatCount = count ?? 2

        for i in 1...repeatCount {
            if includeCounter {
                print("\(i): \(phrase)")
            } else {

The ArgumentParser library parses the command-line arguments, instantiates your command type, and then either executes your run() method or exits with a useful message.

ArgumentParser uses your properties' names and type information, along with the details you provide using property wrappers, to supply useful error messages and detailed help:

$ repeat hello --count 3
$ repeat --count 3
Error: Missing expected argument 'phrase'.
Help:  <phrase>  The phrase to repeat.
Usage: repeat [--count <count>] [--include-counter] <phrase>
  See 'repeat --help' for more information.
$ repeat --help
USAGE: repeat [--count <count>] [--include-counter] <phrase>

  <phrase>                The phrase to repeat.

  --include-counter       Include a counter with each repetition.
  -c, --count <count>     The number of times to repeat 'phrase'.
  -h, --help              Show help for this command.


For guides, articles, and API documentation see the library's documentation on the Web or in Xcode.


This repository includes a few examples of using the library:

  • repeat is the example shown above.
  • roll is a simple utility implemented as a straight-line script.
  • math is an annotated example of using nested commands and subcommands.
  • count-lines uses async/await code in its implementation.

You can also see examples of ArgumentParser adoption among Swift project tools:

  • swift-format uses some advanced features, like custom option values and hidden flags.
  • swift-package-manager includes a deep command hierarchy and extensive use of option groups.

Project Status

The Swift Argument Parser package is source stable; version numbers follow semantic versioning. Source breaking changes to public API can only land in a new major version.

The public API of version 1.0.0 of the swift-argument-parser package consists of non-underscored declarations that are marked public in the ArgumentParser module. Interfaces that aren't part of the public API may continue to change in any release, including the exact wording and formatting of the autogenerated help and error messages, as well as the package’s examples, tests, utilities, and documentation.

Future minor versions of the package may introduce changes to these rules as needed.

We'd like this package to quickly embrace Swift language and toolchain improvements that are relevant to its mandate. Accordingly, from time to time, we expect that new versions of this package will require clients to upgrade to a more recent Swift toolchain release. Requiring a new Swift release will only require a minor version bump.

Adding ArgumentParser as a Dependency

To use the ArgumentParser library in a SwiftPM project, add it to the dependencies for your package and your command-line executable target:

let package = Package(
    // name, platforms, products, etc.
    dependencies: [
        // other dependencies
        .package(url: "https://github.com/apple/swift-argument-parser", from: "1.2.0"),
    targets: [
        .executableTarget(name: "<command-line-tool>", dependencies: [
            // other dependencies
            .product(name: "ArgumentParser", package: "swift-argument-parser"),
        // other targets

Supported Versions

The most recent versions of swift-argument-parser support Swift 5.5 and newer. The minimum Swift version supported by swift-argument-parser releases are detailed below:

swift-argument-parser Minimum Swift Version
0.0.1 ..< 0.2.0 5.1
0.2.0 ..< 1.1.0 5.2
1.1.0 ... 5.5


Stars: 2827
Last commit: 2 days ago
jonrohan Something's broken? Yell at me @ptrpavlik. Praise and feedback (and money) is also welcome.

Release Notes

ArgumentParser 1.2.0
2 weeks ago


  • You can now provide a title in an @OptionGroup declaration. Titled option groups are listed separately in the help screen under that title as a heading. (#492)

  • Two new parsing strategies have been added for @Argument array properties:

    • .allUnrecognized captures all unrecognized inputs after parsing known flags, options, and arguments.
    • .postTerminator collects any inputs that follow the -- terminator.

    See the ArgumentArrayParsingStrategy documentation for more. (#496)

  • Default values are now supported for @Argument or @Option properties with optional type, allowing you to initialize those properties with nil. Providing a non-nil default value results in a warning, since optional properties with non-nil defaults don't need to be declared as optionals. (#477, #480)


  • The .unconditionalRemaining array parsing strategy has been deprecated and renamed to .captureForPassthrough, to better fit its semantic behavior and intended usage. See the ArgumentArrayParsingStrategy documentation for more. (#496)


  • Invalid init(from:) decoding initializers are now correctly diagnosed by ArgumentParser's validators. (#487)
  • Default values are now correctly displayed as flags for @Flag properties with inversions or EnumerableFlag types. (#486)
  • The help display for non-string-backed raw representable types has been corrected to not show raw Swift values. Instead, the help display uses the type's customized defaultValueDescription and allValues implementations. (#494)
  • Properties at different levels of a command hierarchy with the same Swift name but different argument names no longer collide. (#495)
  • The generate-manual plugin name is improved when used from within Xcode. (#505)
  • Documentation fixes and improvements.

The 1.2.0 release includes contributions from @allevato, @clayellis, @compnerd, @d-ronnqvist, @natecook1000, @randomeizer, and @rauhul. Thank you!

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