command line 'arrrrg processor

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Pirate is a functional Scala library that provides a mechanism for parsing command line arguments and producing usage strings.

Pirate defines a set of applicative combinators for constructing commands from a set of flags and positional parameters in a natural manner. Each component has an attached function that is executed as arguments are processed, to transform it into its final form. Flags, switches, positionals, and subcommands are all easy to create and combine for simple and complex programs alike.

Pirate also provides a number of utilities such as a standard dispatch mechanism for parsing arguments and executing a program based upon the result.


To get started, import the pirate package:

import pirate._

This will expose the required type constructors, extra helper functions are available with

import Pirate._

Define an argument object, which could be anything from a simple map, tuple, or list through to a case class (which is recommended).

case class MyArgs(flag: Boolean, author: Option[String], delim: String, dryRun: Boolean, path: String)

Construct a command line, combining in flags and positional parameters.

val cmd = (MyArgs |*| (
    switch(both('f',"flag"), description("enable flag."))
  , flag[String](long("author"), metavar("<pattern>")).option
  , flag[String](long("delim"), metavar("[|]")).default("|")
  , switch(long("dry-run"), empty)
  , argument[String](metavar("<path>"))
  )) ~ "myprogram" ~~ "My description"

Extend PirateMain or PirateMainIO to use:

object MyApp extends PirateMain[MyArgs] {

  def command = cmd

  def run(args: MyArgs): Unit = ???

Or run directly:

Runners.runOrFail(args.toList, cmd).map {
  args => ???

When run with incorrect parameters, a custom help text will be generated, e.g.,

  myprogram [(-f|--flag)] [--author <pattern>] [--delim [|]] [--dry-run] <path>

My description

Available options:
  -f|--flag               enable flag.
  --author <pattern>
  --delim [|]

Positional arguments:

Consult the api and demos for more advanced/complete documentation.


The pirate library is currently very usable and in use by the engineering team at Ambiata, who provide builds in an Ivy repo via https://ambiata-oss.s3.amazonaws.com

The API however, is not yet frozen and is still being refined, and may therefore be subject to breaking changes future. In particular, we would like to allow user definable parser configurations for how and when the usage text is displayed, and other parser properties such as backtracking are used. Further refinement of the usage texts is also expected.


Much of Pirate is inspired by optparse-applicative by Paolo Capriotti.


  1. Official repository https://github.com/markhibberd/pirate
  2. Site and documentation http://pirate.mth.io
  3. License (3 point BSD style) https://github.com/markhibberd/pirate/blob/master/LICENSE