scallop / scallop

a simple Scala CLI parsing library

Version Matrix


A simple command-line arguments parsing library for Scala, written in spirit of Ruby's Trollop. Cross-built for Scala 2.10, 2.11, 2.12, 2.13, Dotty, supports Scala Native and Scala JS.

Scallop supports:

  • flag, single-value and multiple value options
  • POSIX-style short option names (-a) with grouping (-abc)
  • GNU-style long option names (--opt, --opt=value)
  • unnamed integer options, like GNU tail (-42)
  • Property arguments (-Dkey=value, -D key1=value key2=value)
  • Non-string types of options and properties values (with extendable converters)
  • Powerful matching on trailing args
  • Subcommands

For more info and information on usage, you can look into the project wiki or consult the API docs.

Also, I wrote a blog post and another one about Scallop.


Add following to your build.sbt:

libraryDependencies += "org.rogach" %% "scallop" % "3.5.1"

For use with Scala Native and Scala.js, use %%%:

libraryDependencies += "org.rogach" %%% "scallop" % "3.5.1"

If you were using 2.x version or older, please see migration notes.

Quick example

import org.rogach.scallop._

class Conf(arguments: Seq[String]) extends ScallopConf(arguments) {
  val apples = opt[Int](required = true)
  val bananas = opt[Int]()
  val name = trailArg[String]()

object Main {
  def main(args: Array[String]) {
    val conf = new Conf(args)  // Note: This line also works for "object Main extends App"
    println("apples are: " + conf.apples())

This snippet above defined simple configuration that will parse argument lines like these:

--apples 4 --bananas 10 strangeTree
-a 4 appleTree

For more examples, you can look at Scallop's wiki and test suite.

Fancy things

Scallop supports quite powerful matching on trailing arguments. For example:

object Conf extends ScallopConf(
       List("-Ekey1=value1", "key2=value2", "key3=value3",
            "first", "1","2","3","second","4","5","6")) {
  val props = props[String]('E')
  val firstListName = trailArg[String]()
  val firstList = trailArg[List[Int]]()
  val secondListName = trailArg[String]()
  val secondList = trailArg[List[Double]]()
Conf.props("key1") should equal (Some("value1"))
Conf.firstListName() should equal ("first")
Conf.secondListName() should equal ("second")
Conf.firstList() should equal (List(1,2,3))
Conf.secondList() should equal (List[Double](4,5,6))

In this case, Scallop's backtracking parser is clever enough to distinguish the boundaries of the arguments lists.

Also, Scallop supports parsing of subcommands. Not only subcommands, but nested subcommands!

object Conf extends ScallopConf(Seq("sub1", "sub2", "sub3", "sub4", "win!")) {
  val sub1 = new Subcommand("sub1") {
    val sub2 = new Subcommand("sub2") {
      val sub3 = new Subcommand("sub3") {
        val sub4 = new Subcommand("sub4") {
          val opts = trailArg[List[String]]()
Conf.subcommands should equal (List(Conf.sub1, Conf.sub1.sub2, Conf.sub1.sub2.sub3, Conf.sub1.sub2.sub3.sub4))
Conf.sub1.sub2.sub3.sub4.opts() should equal (List("win!"))


... and the whole Scala community for help and explanations.


Scallop is distributed under MIT license.