How to pass input in scala through command line

Question

  import scala.io._    

  object Sum {    
     def main(args :Array[String]):Unit = {    

      println("Enter some numbers and press ctrl-c")

     val input = Source.fromInputStream(System.in)

     val lines = input.getLines.toList

     println("Sum "+sum(lines))

   }

   def toInt(in:String):Option[Int] =

      try{

        Some(Integer.parseInt(in.trim))

      }

      catch    {
       case e: NumberFormatException => None    
   } 

   def sum(in :Seq[String]) = {

     val ints = in.flatMap(s=>toInt(s))

      ints.foldLeft(0) ((a,b) => a +b)

     } }

I am trying to run this program after passing input I have press ctrl + c but

It gives this message E:\\Scala>scala HelloWord.scala Enter some numbers and press ctrl-c 1 2 3 Terminate batch job (Y/N)?

Answer 1

Additional observations, note trait App to make an object executable, hence not having to declare a main(...) function, for instance like this,

object Sum extends App {
  import scala.io._
  import scala.util._

  val nums = Source.stdin.getLines.flatMap(v => Try(v.toInt).toOption)
  println(s"Sum: ${nums.sum}")
}

Using Try , non successful conversions from String to Int are turned to None and flattened out.

Also note objects and classes are capitalized, hence instead of object sum by convention we write object Sum .

Answer 2

You can also use an external API. I really like scallop API

Answer 3

Try this piece of code. It should work as intended.

object Sum {
    def main(args: Array[String]) {
        val lines = io.Source.stdin.getLines
        val numbers = lines.map(_.toInt)
        println(s"Sum: ${numbers.sum}")
    }
}

Plus, the correct shortcut to end the input stream is Ctrl + D .