sbt scala script setup fail

Question

I'm want setup scala script by sbt ways according to document here.
A error encountered when execute java -Dsbt.main.class=sbt.ScriptMain -Dsbt.boot.directory=/home/user/.sbt/boot -jar sbt-launch.jar "$@"

Error message:

Getting org.scala-sbt sbt 1.0.0 ...
:: retrieving :: org.scala-sbt#boot-app
    confs: [default]
    69 artifacts copied, 0 already retrieved (21983kB/69ms)
Getting Scala 2.12.3 (for sbt)...
:: retrieving :: org.scala-sbt#boot-scala
    confs: [default]
    5 artifacts copied, 0 already retrieved (19004kB/48ms)
[error] java.lang.RuntimeException: No script file specified
[error]     at scala.sys.package$.error(package.scala:27)
[error]     at sbt.internal.Script$.$anonfun$command$3(Script.scala:24)
[error]     at scala.Option.getOrElse(Option.scala:121)
[error]     at sbt.internal.Script$.$anonfun$command$1(Script.scala:23)
[error]     at sbt.Command$.$anonfun$command$2(Command.scala:79)
[error]     at sbt.MainLoop$.processCommand(MainLoop.scala:121)
[error]     at sbt.MainLoop$.$anonfun$next$2(MainLoop.scala:105)
[error]     at sbt.State$$anon$1.runCmd$1(State.scala:228)
[error]     at sbt.State$$anon$1.process(State.scala:234)
[error]     at sbt.MainLoop$.$anonfun$next$1(MainLoop.scala:105)
[error]     at sbt.internal.util.ErrorHandling$.wideConvert(ErrorHandling.scala:17)
[error]     at sbt.MainLoop$.next(MainLoop.scala:105)
[error]     at sbt.MainLoop$.run(MainLoop.scala:98)
[error]     at sbt.MainLoop$.$anonfun$runWithNewLog$1(MainLoop.scala:76)
[error]     at sbt.io.Using.apply(Using.scala:23)
[error]     at sbt.MainLoop$.runWithNewLog(MainLoop.scala:70)
[error]     at sbt.MainLoop$.runAndClearLast(MainLoop.scala:52)
[error]     at sbt.MainLoop$.runLoggedLoop(MainLoop.scala:37)
[error]     at sbt.MainLoop$.runLogged(MainLoop.scala:29)
[error]     at sbt.StandardMain$.runManaged(Main.scala:104)
[error]     at sbt.ScriptMain.run(Main.scala:82)
[error]     at xsbt.boot.Launch$$anonfun$run$1.apply(Launch.scala:109)
[error]     at xsbt.boot.Launch$.withContextLoader(Launch.scala:128)
[error]     at xsbt.boot.Launch$.run(Launch.scala:109)
[error]     at xsbt.boot.Launch$$anonfun$apply$1.apply(Launch.scala:35)
[error]     at xsbt.boot.Launch$.launch(Launch.scala:117)
[error]     at xsbt.boot.Launch$.apply(Launch.scala:18)
[error]     at xsbt.boot.Boot$.runImpl(Boot.scala:41)
[error]     at xsbt.boot.Boot$.main(Boot.scala:17)
[error]     at xsbt.boot.Boot.main(Boot.scala)
[error] No script file specified
[error] Use 'last' for the full log.

I'm not sure show does -Dsbt.main.class=sbt.ScriptMain means.

This document is also confusing:

Duplicate your standard sbt script, which was set up according to Setup, as scalas and screpl (or whatever names you like).

What's the standard sbt script?

scalas is the script runner and should use sbt.ScriptMain as the main class

Where is sbt.ScriptMain or how to define it?