Scala Command Line Options

A Scala approach to parsing command-line options. This supports both long options (--longopt ) and short options (-o).

Short options do not work combined (-asdf), but must be provided individually, eg. '-a -s -d -f'. There is an additional restriction that short options are boolean switches only and do not take arguments. Long options, on the other hand, must have arguments.

Conveniently ParseOpts will additionally support non-options as long as they are provided last:

myApp -f -d --foo1 bar argX argY argZ

To support this feature, options are returned as a scala.collection.immutable.Map of options and List of remaining arguments.

This approach works well for use with Apache Spark, and at the least, provides the flexibility of allowing options to be clearly defined and provided in any order.

#!/bin/bash
MYCLASS="com.foo.bar.example"
MYJAR="myexample-0.1.jar"

spark-submit --master yarn \
  $SPARK_CONF_ARGS \
  --class $MYCLASS \
  $MYJAR \
  $@

Code

The code for performing the parsing is relatively straight-forward and consists primarily of the following scala function:

import scala.collection.immutable.{List, Map}

object ParseOpts {

  type OptMap  = Map[String, String]
  type OptList = List[String]

  def parseOpts ( args: OptList ) : (OptMap, OptList)  =
  {
    def nextOpt ( argList: OptList, optMap: OptMap ) : (OptMap, OptList) = {
      val longOpt = "^--(\\S+)".r
      val regOpt  = "^-(\\S+)".r

      argList match {
        case Nil => (optMap, argList)
        case longOpt(opt) :: value :: tail => nextOpt(tail, optMap ++ Map(opt -> value))
        case regOpt(opt)           :: tail => nextOpt(tail, optMap ++ Map(opt -> null))
        case _ => (optMap, argList)
      }
    }
    nextOpt(args, Map())
  }

}

Building

Builds are Scala Version specific and provided as profiles to Maven. Currently supported Scala versions by profile:

scala-2.12
scala-2.13 (default)

Build the jar file via mvn package

$ mvn package -Pscala-2.12
[ ... ]
INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ scala-parseopts ---
[INFO] Building jar: /home/tca/src/github/scala-parseopts/target/scala-parseopts-1.5.2_2.12.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  15.643 s
[INFO] Finished at: 2021-04-18T12:48:14-07:00
[INFO] ------------------------------------------------------------------------

Note that the POM currently sets the artifactId version with a variable which causes Maven to throw a Warning that version contains an expression. This is a known cross-compile issue with Scala binary versions and maven.

This project was tested with the following versions:

Maven 3.6.x
Java 8, Java 11, Java 17
Scala 2.12, 2.13

Using ParseOpts

The project has a GitHub based Maven Repository, which requires authentication by GitHub. This generally involves configuring settings.xml and the project POM.

  <repositories>
      <repository>
          <id>scala-parseopts</id>
          <url>https://maven.pkg.github.com/tcarland/scala-parseopts</url>
      </repository>
  </repositories>

Optionally create a local maven entry from the build of this repo Note the scala binary version as described above, which should match the parent project.

mvn install:install-file \
  -Dpackaging=jar -DgroupId=com.trace3.util \
  -DartifactId=scala-parseopts -Dversion=1.5.5_2.13 \
  -Dfile=target/scala-parseopts-1.5.5_2.13.jar

The maven artifact for this dependency:

  <dependency>
      <groupId>com.trace3.util</groupId>
      <artifactId>scala-parseopts</artifactId>
      <version>1.5.5_2.13</version>
  </dependency>