Eugene Yokota Eugene Yokota - 4 months ago 61
Scala Question

Scala: Best way to parse command-line parameters (CLI)?

What's the best way to parse command-line parameters in Scala?
I personally prefer something lightweight that does not require external jar.

Related:


Answer

scopt/scopt

val parser = new scopt.OptionParser[Config]("scopt") {
  head("scopt", "3.x")

  opt[Int]('f', "foo") action { (x, c) =>
    c.copy(foo = x) } text("foo is an integer property")

  opt[File]('o', "out") required() valueName("<file>") action { (x, c) =>
    c.copy(out = x) } text("out is a required file property")

  opt[(String, Int)]("max") action { case ((k, v), c) =>
    c.copy(libName = k, maxCount = v) } validate { x =>
    if (x._2 > 0) success
    else failure("Value <max> must be >0") 
  } keyValueName("<libname>", "<max>") text("maximum count for <libname>")

  opt[Unit]("verbose") action { (_, c) =>
    c.copy(verbose = true) } text("verbose is a flag")

  note("some notes.\n")

  help("help") text("prints this usage text")

  arg[File]("<file>...") unbounded() optional() action { (x, c) =>
    c.copy(files = c.files :+ x) } text("optional unbounded args")

  cmd("update") action { (_, c) =>
    c.copy(mode = "update") } text("update is a command.") children(
    opt[Unit]("not-keepalive") abbr("nk") action { (_, c) =>
      c.copy(keepalive = false) } text("disable keepalive"),
    opt[Boolean]("xyz") action { (x, c) =>
      c.copy(xyz = x) } text("xyz is a boolean property")
  )
}
// parser.parse returns Option[C]
parser.parse(args, Config()) map { config =>
  // do stuff
} getOrElse {
  // arguments are bad, usage message will have been displayed
}

The above generates the following usage text:

scopt 3.x
Usage: scopt [update] [options] [<file>...]

  -f <value> | --foo <value>
        foo is an integer property
  -o <file> | --out <file>
        out is a required file property
  --max:<libname>=<max>
        maximum count for <libname>
  --verbose
        verbose is a flag
some notes.

  --help
        prints this usage text
  <file>...
        optional unbounded args

Command: update
update is a command.

  -nk | --not-keepalive
        disable keepalive    
  --xyz <value>
        xyz is a boolean property

This is what I currently use. Clean usage without too much baggage. (Disclaimer: I now maintain this project)