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OptionKit - Option Parsing in Swift

OptionKit is an OS X framework to parse basic command-line options in pure Swift. Currently, it has the most basic functionality necessary, but will probably expand to include more advanced features as the need arises.


OptionKit currently supports three types of options:

  • Short options, triggered by flags of type -f
  • Long options, triggered by flags of type --long-option
  • Mixed options, triggered by either type, such as -v or --version

An option can have zero or more required parameters. Parameters are restricted in that they cannot begin with - or --, as they would be confused with triggers.

OptionKit's OptionParser class returns a ParseData type, which consists of:

  • A dictionary of Option objects mapped to their (possibly empty) parameter list.
  • A list of remaining arguments.


A simple, full example called optionsTest.swift might be:

#!/usr/bin/env xcrun swift -F /Library/Frameworks

import Foundation
import OptionKit

let opt1 = Option(trigger:.Mixed("e", "echo"))
let opt2 = Option(trigger:.Mixed("h", "help"))
let opt3 = Option(trigger:.Mixed("a", "allow-nothing"))
let opt4 = Option(trigger:.Mixed("b", "break-everything"))
let opt5 = Option(trigger:.Mixed("c", "counterstrike"))
let parser = OptionParser(definitions:[opt1, opt3, opt4, opt5])

let actualArguments = Array(Process.arguments[1..<Process.arguments.count])

do {
    let (options, rest) = try parser.parse(actualArguments)

    if options[opt1] != nil {

    if options[opt2] != nil {
} catch let OptionKitError.InvalidOption(description: description) {

The output would be:

~: ./optionTest.swift -e hello
~: ./optionTest.swift --echo hello world
[hello, world]
~: ./optionTest.swift -h
usage: optionTest [-e|--echo] [-a|--allow-nothing] [-b|--break-everything]
                  [-c|--counterstrike] [-h|--help]

~: ./optionTest.swift --help
usage: optionTest [-e|--echo] [-a|--allow-nothing] [-b|--break-everything]
                  [-c|--counterstrike] [-h|--help]

~: ./optionTest.swift -d
Invalid option: -d


Minimum system requirements:

  • Xcode 7
  • OS X Yosemite 10.10


  1. Clone this github repository, and build the project.
  2. Run the tests, just for sanity. They should all pass.
  3. Copy OptionKit.framework from the DerivedData directory to /Library/Frameworks (this will require sudo access)

OptionKit should now be available for use from a command line script. The shebang needs to read:

#!/usr/bin/env xcrun swift -F /Library/Frameworks

This is because the Swift compiler, unlike Clang, doesn't automatically pick up frameworks in /Library/Frameworks.

Including OptionKit in Other Libraries

Use Carthage. OptionKit uses semantic versioning, so the corresponding Cartfile line should be:

github "nomothetis/OptionKit" ~> 1.0.0

To Do

  • Add support for sub-parsers.
  • Make help string include per-option help.