Running Scala from a script using terminal

Question

I am really sorry, this seems basic. I am using Programming in Scala and I have got to step 4:

Put this into a file named hello.scala:

@main def m():
        println("Hello world from a script!"

At first I got an illegal start of definition error, since pivoting to using vs code I get the following:

(base) *dir* scala % scala hello.scala
Compiling project (Scala 3.5.1, JVM (21))
[error] ./hello.scala:2:12
[error] end of toplevel definition expected but '(' found
[error]     println("hello world from script")
[error]            ^
[error] ./hello.scala:1:11
[error] Declaration of method m not allowed here: only classes can have declared but undefined members
[error] @main def m():
[error]           ^
Error compiling project (Scala 3.5.1, JVM (21))

I thought it might be a new line issue, so I moved everything onto one line like @main def m(): println("hello world from script") and I get the following:

(base) *dir* scala % scala hello.scala
Compiling project (Scala 3.5.1, JVM (21))
[error] ./hello.scala:1:23
[error] end of toplevel definition expected but '(' found
[error] @main def m(): println("hello world from script")
[error]                       ^
[error] ./hello.scala:1:11
[error] Declaration of method m not allowed here: only classes can have declared but undefined members
[error] @main def m(): println("hello world from script")
[error]           ^
Error compiling project (Scala 3.5.1, JVM (21))

Using scalac hello.scala does not work either.

You are missing an = methods don't start with :, rather : is used to specify the return type. — Luis Miguel Mejía Suárez
– Luis Miguel Mejía Suárez, Commented Nov 18, 2024 at 23:03

tgkprog · Accepted Answer · 2024-11-18 23:11:12Z

1

You need to keep something like this in the file:

object HelloWorld {
  def main(args: Array[String]): Unit = {
    println("Hello, World!")
  }
}

Then save that file say hello.scala

from same folder in terminal

scalac HelloWorld.scala

then

scala HelloWorld

Another way is to do a script like

@main def m(): Unit =
  println("Hello, world from a script!")

This you can run directly by calling

scala hello.scala

Its great to read a book but might help to also watch a few videos that have screen share on so can see the actions and maybe get some code ~ search like this

edited Nov 18, 2024 at 23:11

answered Nov 18, 2024 at 23:04

tgkprog

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2 Comments

clueless Over a year ago

Thank you for the answer and the resources, apologies I knew it was a very simple question

tgkprog Over a year ago

Np if it helped mark the answer as accepted

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