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argparse4s is an argument parsing library for Scala built on argparse4j, which in turn is inspired by the Python argparse module.

Project Status

I (Michael Ekstrand) am not actively using or maintaining this project. Happy to turn it over to anyone interested in carrying it forward.

Using argparse4s

First, add argparse4s to your project dependencies. In SBT:

libraryDependencies += "net.elehack.argparse4s" %% "argparse4s" % "0.2.1"

The main entry point for argparse4s is the Command trait. To use argparse4s, create an object extending Command whose main method calls Command's run(Array[String]) method. It will then parse the arugments, prepare an ExecutionContext, and pass it to your command's run() method.

Options are defined using the option, flag, and argument methods (from CommandLike). These methods return objects representing the arguments which can in turn be used to set additional parameters (defaults, help messages, etc.) and to get the actual value (using the get method, which requires an implicit execution context).

An example:

object MyCommand extends Command {
    /* characters are short options (-v), strings long (--verbose). */
    val verbose = flag('v', "verbose").
                  help("emit verbose output")
    /* Option-typed options are optional. Files have a default
       metavar of FILE. /
    val outputFile = option[Option[File]]('o', "output-file").
                     help("output to FILE")
    /* Options can have defaults. */
    val count = option[Int]('n', "count").
                help("run up to N iterations")

    /* accumulate all arguments as an input */
    val inputs = argument[Seq[File]]()

     * The run() method contains your program logic.
    def run()(implicit exc: ExecutionContext) {
        /* get argument values with the get method */
        for (i <- 1 to count.get) {
            /* do something */

     * main calls out to argparse4s.
    def main(args: Array[String]) {

For more details see the scaladoc.

Customizing argument types

The OptionType typeclass allows you to specify behavior for specific option/argument types, including parsing strategies and the default metavar name.


argparse4s inherits from argparse4j the ability to have subcommands. To support subcommands, extend the MasterCommand trait. Each subcommand must extends Subcommand.


Scala argument parsing library wrapping argparse4j