fulcrumgenomics / sopt   1.1.0

MIT License GitHub

An argument parsing library for Scala

Scala versions: 2.13 2.12 2.11

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sopt - Scala Option Parsing Library

sopt is a scala library for command line option parsing with minimal dependencies. It is designed for toolkits that have multiple "commands" such as dagr and fgbio. The latest API documentation can be found here.

It has the following high level features:

  • Support for GNU/posix style argument names and conventions
    • Camel case names in scala are auto-translated to GNU style options (e.g. inputFile -> input-file)
  • Argument configuration via annotations on scala classes
  • Reflectively builds typed strongly typed argument values for most simple types:
    • Primitive types like Int and Double
    • Any type that has a constructor from String or a companion apply(String)
    • Option types, e.g. Option[Int] or Option[String], etc.
    • Collection types, e.g. Seq[Int] or Set[String], etc.
  • Typedefs used for argument types and will be used in usage & documentation
  • Argument file support similar to Python's Argparse
  • Command usage and argument documentation in GitHub flavored MarkDown, formatted appropriately for the terminal
  • Terminal output using ANSI escape sequences to color and highlight usage
  • APIs to retrieve command and argument metadata, e.g. to create offline documentation

Getting Started

To use sopt you will need to add it to your build. For sbt this looks like:

libraryDependencies +=  "com.fulcrumgenomics" %% "sopt" % "1.1.0"

You'll then need the following:

  1. A trait which all your commands or tools will extend
  2. One or more command classes
  3. An object with a main method that invokes sopt to parse the command line

A Short Example

The following is a minimal example of a use of sopt.

package example

import com.fulcrumgenomics.sopt._
import com.fulcrumgenomics.sopt.Sopt._
import example.Types._

/** All command classes exposed on the command-line will extend or mix-in this trait. */
trait Tool { def execute(): Unit }

object Types {
  type Name = String

/** An example command. */
     |An example program that greets people. The `greeting` argument is optional
     |since it has a default.
class Greet(
  @arg(flag='g', doc="The greeting.")   val greeting: String = "Hello",
  @arg(flag='n', doc="Someone's name.") val name: Name
) extends Tool {
  override def execute(): Unit = System.out.println(s"$greeting $name!")

/** The main class that invokes sopt. */
object Main {
  def main(args: Array[String]): Unit = {
    val commands = Sopt.find[Tool](packages=Seq("example"))
    Sopt.parseCommand[Tool](name="example-kit", args=args, commands=commands) match {
      case Failure(usage) => 
      case CommandSuccess(tool) => 

The Tool trait is not required, but it is generally useful to have a trait which is implemented by all commands, so that not only can they have a common method (ex. execute()) that can be invoked to do something, the available commands can be found using the Tool trait and Sopt.find. Alternatively you could invoke Sopt.parseCommand[AnyRef] directly! To do so, you would need to manually construct the list of commands instead of searching for subclasses with Sopt.find[AnyRef](packages).

In this example, the Main class is implemented only once and can act as a dispatcher to any number of commands that implement Tool. It also acts as a central point to add consistent behaviour amongst tools, for example printing out the date and time at the start and end of execution.

Running the Main class from the command line yields the following output:

USAGE: example-kit [command] [arguments]
Version: 1.0

Available Sub-Commands:
Clps:                                 Various command line programs.
    GreetingCommand                    An example program that greets people.

No sub-command given.

Running the Main class and specifying the Greet command without any arguments produces the following output:

USAGE: Greet [arguments]
Version: 0.2.0-SNAPSHOT
An example program that greets people. The greeting argument is optional since it has a default.

Greet Required Arguments:
-n String, --name=Name      Someone's name.

Greet Optional Arguments:
-h [true|false], --help[=true|false]
                              Display the help message. Default: false.
-g String, --greeting=String  The greeting. Default: Hello.
--version[=true|false]        Display the version number for this tool. Default: false.

Error: Argument 'name' is required.


API documentation for all versions can be viewed on javadoc.io.

Argument Naming & Formatting

Each argument may have a long name and optionally a short name.

Short Names

Short names are single-character names. Arguments with short names may be formatted on the command line as follows:

  • -<name><value>
  • -<name>=<value>
  • -<name> <value>

Long names

Long names may be of any length and are generally specified as one or more lower-case words separated with hyphens (e.g. --input-files). Long names may be used on the command line with the following formats:

  • --<name>=<value>
  • --<name> <value>

Name must be [A-Za-z0-9?][-A-Za-Z0-9?]*

The following is not supported:

  • --<name><value>

due to the prefix support described below.


Prefixes of option names are supported, as long as the a prefix is unambiguous, and either a (whitespace) or = delimiter is used.

In a command with no other options beginning with foo the following are equivalent:

  • --foobar <value>
  • --fooba <value>
  • --foob <value>
  • --foo <value>

But if we have another option, e.g. --football <value>, then using --foo <value> will cause a DuplicateOptionNameException to be thrown.

Argument Types


Flags are arguments with a boolean (true or false) value. The value may be ommitted, in which case it is interpreted as if true were provided. The following are all equivalent:

  • -x
  • -xtrue
  • -x=true
  • -xT
  • -x=T

Yes and Y are also interpreted as true; No and N are interpreted as false. Both are case insensitive.

Single-value arguments

Single value arguments may only be specified once on the command line. If the argument has a default value, the value from the command line will override it. Single-value arguments may be specified using long or short names, in the following ways:

  • -x <value>
  • -x<value>
  • -x=<value>
  • --extra <value>
  • --extra=<value>

Multi-value arguments

Arguments that accept multiple values may be specified up to the maximum number of times specified by the tool. If an argument has a default value, the value(s) specified on the command line replace the default value (i.e. they do not add to it).

Multiple values can specified via multiple name/value pairs, e.g.:

  • --input=foo.txt --input=bar.txt --input=whee.txt
  • --input foo.txt --input bar.txt --input whee.txt

or with multiple values following a single argument name:

  • --input foo.txt bar.txt whee.txt
  • --input *.txt

Optional arguments

Arguments are optional on the command line if any of the following are true:

  • The argument has a default value
  • The argument's type is Option[_]
  • The argument's type is a collection type (e.g. Seq) and minElements is set to 0

Option and collection arguments that are optional, but have default values may be cleared by specifying the special argument value :none:.

Argument files

Argument files are modeled after the implementation in Python's Argparse library. In short:

  • Any argument prefixed with @ is expected to be an argument file (e.g. -foo=bar @whee.txt species one parameter on the command line, and then a file called whee.txt)
  • The arguments present in an argument file are substituted into the command line at the point where the argument file is specified
  • Each line in the argument file is treated as a single token or argument

The latter is especially useful when passing many arguments that include spaces or special characters. For example the following file:

Hello World!
I'm a shooting *star*

is equivalent to --funny-strings 'Hello World!' 'I\'m a shooting *star*'.