settings-outputDir

scala> java.nio.file.Files.exists(java.nio.file.Files.createDirectories(java.nio.file.Paths.get("target", "test-repl-settings-outDir")))
val res0: Boolean = true

scala> val x = 1
val x: Int = 1

scala>:settings -d target/test-repl-settings-outDir

scala> val y = 2
val y: Int = 2

scala> x
val res1: Int = 1

scala> y
val res2: Int = 2

scala> java.nio.file.Files.walk(java.nio.file.Paths.get("target", "test-repl-settings-outDir")).sorted(java.util.Comparator.reverseOrder).forEach(java.nio.file.Files.delete)