Make `show` output on stdout rather than to the logger

Fixes #4184

main/src/main/scala/sbt/Main.scala

@@ -678,7 +678,10 @@ object BuiltinCommands {
   def act: Command = Command.customHelp(Act.actParser, actHelp)
 
   def actHelp: State => Help =
-    s => CommandStrings.showHelp ++ CommandStrings.multiTaskHelp ++ keysHelp(s)
+    s =>
+      CommandStrings.showHelp ++ CommandStrings.printHelp ++ CommandStrings.multiTaskHelp ++ keysHelp(
+        s
+    )
 
   def keysHelp(s: State): Help =
     if (Project.isProjectLoaded(s))
@@ -824,7 +827,7 @@ object BuiltinCommands {
         if (version != app.id.version()) {
           state.log.warn(s"""sbt version mismatch, current: ${app.id
             .version()}, in build.properties: "$version", use 'reboot' to use the new value.""")
-        }
+      }
     )
   }
 

main/src/main/scala/sbt/internal/Act.scala

@@ -15,7 +15,7 @@ import Aggregation.{ KeyValue, Values }
 import DefaultParsers._
 import sbt.internal.util.Types.idFun
 import java.net.URI
-import sbt.internal.CommandStrings.{ MultiTaskCommand, ShowCommand }
+import sbt.internal.CommandStrings.{ MultiTaskCommand, ShowCommand, PrintCommand }
 import sbt.internal.util.{ AttributeEntry, AttributeKey, AttributeMap, IMap, Settings, Util }
 import sbt.util.Show
 
@@ -427,7 +427,12 @@ object Act {
       val akp = aggregatedKeyParser(extracted)
       def evaluate(kvs: Seq[ScopedKey[_]]): Parser[() => State] = {
         val preparedPairs = anyKeyValues(structure, kvs)
-        val showConfig = Aggregation.defaultShow(state, showTasks = action == ShowAction)
+        val showConfig = if (action == PrintAction) {
+          Aggregation.ShowConfig(true, true, println, false)
+        } else {
+          Aggregation.defaultShow(state, showTasks = action == ShowAction)
+        }
+
         evaluatingParser(state, showConfig)(preparedPairs) map { evaluate => () =>
           {
             val keyStrings = preparedPairs.map(pp => showKey.show(pp.key)).mkString(", ")
@@ -438,18 +443,19 @@ object Act {
       }
       action match {
         case SingleAction => akp flatMap evaluate
-        case ShowAction | MultiAction =>
+        case ShowAction | PrintAction | MultiAction =>
           rep1sep(akp, token(Space)).flatMap(kvss => evaluate(kvss.flatten))
       }
     }
   }
 
   private[this] final class ActAction
-  private[this] final val ShowAction, MultiAction, SingleAction = new ActAction
+  private[this] final val ShowAction, MultiAction, SingleAction, PrintAction = new ActAction
 
   private[this] def actionParser: Parser[ActAction] =
     token(
       ((ShowCommand ^^^ ShowAction) |
+        (PrintCommand ^^^ PrintAction) |
         (MultiTaskCommand ^^^ MultiAction)) <~ Space
     ) ?? SingleAction
 

main/src/main/scala/sbt/internal/CommandStrings.scala

@@ -19,6 +19,7 @@ object CommandStrings {
   val ProjectCommand = "project"
   val ProjectsCommand = "projects"
   val ShowCommand = "show"
+  val PrintCommand = "print"
   val MultiTaskCommand = "all"
   val BootCommand = "boot"
 
@@ -51,6 +52,18 @@ $ShowCommand <task>
 
 	Evaluates the specified task and display the value returned by the task."""
 
+  def printHelp = Help(PrintCommand, (s"$PrintCommand <key>", printBrief), printDetailed)
+  def printBrief =
+    "Prints the result of evaluating the setting or task associated with 'key' to standard output."
+  def printDetailed =
+    s"""$PrintCommand <setting>
+
+	Prints the value of the specified setting.
+
+$PrintCommand <task>
+
+	Evaluates the specified task and print the value returned by the task."""
+
   val PluginsCommand = "plugins"
   val PluginCommand = "plugin"
   def pluginsBrief = "Lists currently available plugins."