Sumac is a command line option parser and library. It tries to differentiate itself from other libraries by making it dead simple to define arguments, removing boilerplate and repetition. It is a very small, lightweight scala library.

It is available on maven central. The last stable release is 0.4.1. An sbt dependency would look like:

"com.quantifind" %% "sumac" % "0.4.1"

Integration with 3rd party libraries (in particular, Joda-Time and Typesafe Config) is available through the sumac-ext package:

"com.quantifind" %% "sumac-ext" % "0.4.1"

Usage

Full usage can be found on the wiki, but we can go over the basics quickly. Define a basic container object which extends FieldArgs. Every field of the object becomes a command line argument with the same name. Then use parse() to process the command line arguments.

import com.quantifind.sumac.FieldArgs

class Arguments extends FieldArgs {
  var name: Option[String] = None
  var count: Int = _
}

object MyApp {
  def main(args: Array[String]) {
    val myArgs = new Arguments()
    myArgs.parse(args)
    ...
  }
}

Now MyApp has two arguments, "name" and "count". You can run it like:

java -cp <path>/<to>/<compiled>/<code> MyApp --name foobar --count 17

ArgMain

You don't even have to call parse() yourself. The arguments are automatically parsed for you if you extend ArgMain

import com.quantifind.sumac.{ArgMain, FieldArgs}

class Arguments extends FieldArgs {
  var name: String = _
  var count: Int = _
}

object MyApp extends ArgMain[Arguments]{
   def main(args: Arguments) {
     //the cmd line arguments get parsed, and then passed into this function
     println(args.name)
   }
}

you could then run these programs with

java -cp <path>/<to>/<compiled>/<code> MyApp --name foobar --count 17

Mixing In Multiple Traits

You can use traits to create "sets" of arguments that tend to go together. Because you can mix in multiple traits into one argument object, this lets you put together the arguments that want, without duplicating argument definitions.

For example, lets say that you have some set of arguments for a database connection, another set of arguments for a screen resolution, and another set of arguments for the username. You can define traits for each of these groups:

import com.quantifind.sumac.FieldArgs

trait DBConnectionArgs extends FieldArgs {
  var dbHost : String = _
  var dbPort : Int = 4000
  def getDbConnection = { ... }
}

trait ScreenResolutionArgs extends FieldArgs {
  var width: Int = 800
  var height: Int = 600
}

trait UsernameArgs extends FieldArgs {
  var username: String = _
}

Then one application that needs a database connection and a user name could be written as:

import com.quantifind.sumac.{ArgMain, FieldArgs}

class AppNumberOneArgs extends DBConnectionArgs with UsernameArgs
object AppNumberOne extends ArgMain[AppNumberOneArgs]{
  def main(args: AppNumberOneArgs) = {
    val db = args.getDbConnection()
    ...
  }
}

And another application that needs a database connection and screen resolution:

import com.quantifind.sumac.{ArgMain, FieldArgs}

class AppNumeroDosArgs extends DBConnectionArgs with ScreenResolutionArgs
object AppNumeroDos extends ArgMain[AppNumeroDosArgs]{
  def main(args: AppNumeroDosArgs) = {
    val db = args.getDbConnection()
    ...
  }
}

Note that you are sharing the argument names and types, AND the definition of helper methods like getDbConnection()

Builtin Help

Every set of arguments get support for "--help" added automatically. If that appears anywhere in the list of arguments you give when calling FieldArgs.parse, then you'll get a help message listing all options and their types

bash-3.2$ java -cp core/target/scala-2.9.3/classes/:$SCALA_HOME/lib/scala-library.jar com.quantifind.sumac.examples.SimpleApp --count 1 --help
Exception in thread "main" com.quantifind.sumac.ArgException: usage:
--name  class java.lang.String  name

--count int     count

Validation

Every argument holder can ensure it received valid arguments via custom validation rules.

import com.quantifind.sumac.{FieldArgs, ArgException}

trait MyArgs extends FieldsArgs {
  var count: Int = 1
  addValidation{ if (count < 0) throw new ArgException("count must be >= 0")}
}

More Info

Lots more details about using Sumac can be found on the wiki.

Sumac is open source, and we hope to get involvement from the community. We'd love to get some pull requests. Also, even if you don't have a fix, feel free to report bugs or just request new features through the github issue tracker.

Credits

This was inspired by the optional package from alexy, which in turn came from:

Idea and prototype implementation: DRMacIver.

Fleshing out and awesomification: paulp.

This is a total rewrite, though.

Contributing

Sumac is released under the Apache License and we welcome any contributions within this license. Any pull request is welcome and will be reviewed and merged as quickly as possible.

Because this open source project is released by Quantifind as a company, if you want to submit a pull request, you will have to sign the following simple contributors agreement:

• If you are an individual, please sign this contributors agreement and send it back to contributors@quantifind.com
• If you are contributing changes that you did as part of your work, please sign this contributors agreement and send it back to contributors@quantifind.com