An unopinionated command line parser for Swift CLI projects.

What's New


  • adopts UserDefaults Style for function names
  • adds index support to all types


DashDashSwift Logo

An unopinionated command line parser for Swift CLI projects. DashDashSwift gives straightforward, sophisticated key-value access to command line arguments.


DashDashSwift is available as a Swift package. Here's a quick guide from Apple about integrating packages into your application.

(You could also just drag the contents of Sources/DashDashSwift into your project direcly, if you like.)

Getting Started

You can use an instance of CommandLineParser to parse an array of arguments. Generally, you'd get these from an instance of CommandLine, but the args(from:) function can produce these from a plain string.

From there, a parser has methods to extract strings, ints, doubles, bools and more.

// example --name Chris --age 8
var parser = CommandLineParser()
parser.arguments = CommandLine.arguments
let name = parser.string(forKey: "name") // -> Optional("Chris")
let age = parser.int(forKey: "age")      // -> Optional(8)

The parser expects multi-character flags to be prefixed with --, and allows single-character boolean flags to be grouped together eith a single -. For example:

let command = `-rf --path ./input.json -o ./output.json`
var parser = CommandLineParser()
parser.arguments = CommandLineParser.args(from: command)

let inputPath = parser.string(forKey: "path") // -> Optional("./input.json")
let outputPath = parser.string(forKey: "o")   // -> Optional("./output.json")

let isRecursive = parser.bool(forKey: "r")    // -> true
let isForced = parser.bool(forKey: "f")       // -> true


The Bare Minimum

import DashDashSwift

// create a parser
var parser = CommandLineParser()

let name = parser.string(forKey: "name", shortKey: "n", args: CommandLine.arguments) ?? "Anonymous"

let age = parser.int(forKey: "age", args: CommandLine.arguments) ?? 21

let height = parser.double(forKey: "height", shortKey:"h" args: CommandLine.arguments) ?? 180.0

More Flair

import DashDashSwift

// create a parser, passing in a title and description.
// this will be printed when a user requests help
var parser = CommandLineParser(title: "Chotchkie", description: "Chotchkie is a command line program to control the amount of flair on your uniform.")

// optionally register the command line arguments to parse.
// you may also pass this value in to any of the parser's functions
parser.arguments = CommandLine.arguments

// optionally register your commands with the parser.
// this allows you to ask for `key` and get `shortKey` automatically,
// as well as printing a help message with all the commands automatically.
parser.register(key: "input", shortKey: "i", index: 0, description: "The location where files should be read from.")
parser.register(key: "output",  shortKey: "o", index: 1, description: "The location where files should be saved.")
parser.register(key: "size", shortKey: "s", description: "The desired file size, in bytes")
parser.register(key: "all", shortKey: "a", description: "Boolean. Whether or not all directories should be included.")
parser.register(key: "help", shortKey: "h", description: "Print this help message")

if (parser.bool(forKey: "h")) {

if parser.bool(forKey: "all") {
    // ...

let size = parser.int(forKey: "size") ?? 1024

// Be flexible! Allow users to pass in unnamed arguments, 
// and fall back to them by index. 
// The below code allows
//    script ./path1 ./path2
// or
//    script -i ./path1 -o ./path2
// or
//    script --input ./path1 --output ./path2
let input = parser.stringFor(key: "input")
let output = parser.stringFor(key: "output")

// you can also grab these on the fly like so:
// parser.string(forKey: "path", index: 0)

if let input = input, let output = output {
   // ...

Who made this?

Great question. I'm Chris—I make iOS apps like ChordBank and Better Notes, in addition to selected client dev and design work. In the process, I write lots and lots of command line utilities.

Do you have an interesting and well-financed iOS project you'd like help with? Let's talk!


  • Swift Tools 5.1.0
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Last updated: Mon Nov 07 2022 20:43:06 GMT-0500 (GMT-05:00)