show history with !: or !:n

sbt/src/main/scala/sbt/LineReader.scala

@@ -36,10 +36,6 @@ abstract class JLine extends LineReader
 			case null => None
 			case x => Some(x.trim)
 		}
-	def getHistory: Array[String]  =
-		JLine.synchronized {
-			reader.getHistory.getHistoryList.toArray(new Array[String](0))
-		}
 }
 private object JLine
 {
@@ -71,10 +67,13 @@ private object JLine
 			Control.trapAndLog(log)
 			{
 				historyFile.getParentFile.mkdirs()
-				cr.getHistory.setHistoryFile(historyFile)
+				val history = cr.getHistory
+				history.setMaxSize(MaxHistorySize)
+				history.setHistoryFile(historyFile)
 			}
 		}
 	def simple(historyPath: Option[Path], log: Logger): SimpleReader = new SimpleReader(historyPath, log)
+	val MaxHistorySize = 500
 }
 class SimpleReader private[sbt] (historyPath: Option[Path], log: Logger) extends JLine
 {

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

@@ -199,11 +199,11 @@ class xMain extends xsbti.AppMain
 					}
 
 				case action :: tail if action.startsWith(HistoryPrefix) =>
-					historyCommand(action.substring(HistoryPrefix.length).trim, baseProject.historyPath, project.log) match
+					historyCommand(action.substring(HistoryPrefix.length).trim, baseProject.historyPath, JLine.MaxHistorySize, project.log) match
 					{
-						case Some(command) =>
-							println(command)  //better to print it than to log it
-							continue(project, command :: tail, failAction)
+						case Some(commands) =>
+							commands.foreach(println)  //better to print it than to log it
+							continue(project, commands ::: tail, failAction)
 						case None => failed(UsageErrorExitCode)
 					}
 					
@@ -280,7 +280,7 @@ class xMain extends xsbti.AppMain
 			if(message eq null) None else Some(message)
 		}
 	}
-	private def historyCommand(s: String, historyPath: Option[Path], log: Logger): Option[String] =
+	private def historyCommand(s: String, historyPath: Option[Path], maxLines: Int, log: Logger): Option[List[String]] =
 	{
 		val lines = historyPath.toList.flatMap(h => xsbt.FileUtilities.readLines(h.asFile) ).toArray
 		if(lines.isEmpty)
@@ -290,15 +290,24 @@ class xMain extends xsbti.AppMain
 		}
 		else
 		{
-			def replaceLastCommand(s: String) {
-				lines(lines.length - 1) = s
-				historyPath foreach { h => xsbt.FileUtilities.writeLines(h.asFile, lines) }
+			val ListPrefix = ":"
+			val history = complete.History(lines, log)
+			if(s.startsWith(ListPrefix))
+			{
+				val rest = s.substring(ListPrefix.length)
+				val show = complete.History.number(rest).getOrElse(lines.length)
+				printHistory(history, maxLines, show)
+				Some(Nil)
+			}
+			else {
+				val command = historyCommand(history, s, log)
+				command.foreach(lines(lines.length - 1) = _)
+				historyPath foreach { h => xsbt.FileUtilities.writeLines(h.asFile, lines) }
+				Some(command.toList)
 			}
-			val command = historyCommand(complete.History(lines, log), s, log)
-			command.foreach(replaceLastCommand)
-			command
 		}
 	}
+	private def printHistory(history: complete.History, historySize: Int, show: Int): Unit = history.list(historySize, show).foreach(println)
 	private def historyCommand(history: complete.History, s: String, log: Logger): Option[String] =
 	{
 		val ContainsPrefix = "?"

sbt/src/main/scala/sbt/complete/History.scala

@@ -30,13 +30,16 @@ final class History private(lines: Array[String], log: Logger) extends NotNull
 		}
 		else
 			act
+
+	def list(historySize: Int, show: Int): Seq[String] =
+		lines.toList.drop((lines.size - historySize) max 0).zipWithIndex.map { case (line, number) => "   " + number + "  " + line }.takeRight(show max 1)
 }
 
 object History
 {
 	def apply(lines: Seq[String], log: Logger): History = new History(lines.toArray, log)
 
-	private def number(s: String): Option[Int] =
+	def number(s: String): Option[Int] =
 		try { Some(s.toInt) }
 		catch { case e: NumberFormatException => None }
 }