Scalaでスクリプトとか書くときのコマンドライン引数の解析

echo.scala

#!/bin/sh
exec scala "$0" "$@"
!#

val helpMessage = """
Usage:
       -n     do not output the trailing newline

       -x     repeat x times

       --help display this help and exit

"""


// オプションを表すcase class
case class Args(newLine: Boolean, repeat: Int, help: Boolean, message: String)

def parseArgs(args: List[String]): Option[Args] = {

  // デフォルト値
  var newLine = true
  var repeat = 1
  var help = false

  // こんな感じで再帰関数作る
  @scala.annotation.tailrec
  def parseArgsHelper(args: List[String]): Args = {
    args match {
      case "-n" :: rest => {
        newLine = false
        parseArgsHelper(rest)
      }
      case "-x" :: x :: rest => {
        repeat = x.toInt
        parseArgsHelper(rest)
      }
      case "--help" :: rest => Args(newLine, repeat, true, "")
      case message => Args(newLine, repeat, false, message.mkString(" "))
    }
  }

  try { Some(parseArgsHelper(args)) } catch { case _ =>  None }

}

def doEcho(args: Args): Unit =  args match {
  case Args(_, _, true, _) => println(helpMessage)
  case Args(true, repeat, _,  message) => (1 to repeat) foreach { _ => println(message) }
  case Args(false, repeat, _, message) => (1 to repeat) foreach { _ => print(message) }
}


def main = parseArgs(args.toList) match {
  case Some(args) => doEcho(args)
  case None => println("Invalid Arguments ヽ(`Д´)ﾉ!!")
}

main


/*

 $ ./echo.scala -x a
Invalid Arguments ヽ(`Д´)ﾉ!!
 $ ./echo.scala -x 3 foo
foo
foo
foo
 $ ./echo.scala -n -x 3 foo
foofoofoo%
 $ ./echo.scala -n -x 3 foo bar baz
foo bar bazfoo bar bazfoo bar baz%
 $ ./echo.scala -x 3 foo bar baz
foo bar baz
foo bar baz
foo bar baz

*/