error,warn,info,debug commands to set log level, useful in conjunction with early combinator --. Fixes #806.

main/command/src/main/scala/sbt/BasicCommandStrings.scala

@@ -37,6 +37,29 @@ object BasicCommandStrings
 
 	def exitBrief = "Terminates the build."
 
+	def logLevelHelp =
+	{
+		val levels = Level.values.toSeq
+		val levelList = levels.mkString(", ")
+		val brief = ("<log-level>", "Sets the logging level to 'log-level'.  Valid levels: " + levelList)
+		val detailed = levels.map(l => (l.toString, logLevelDetail(l))).toMap
+		Help(brief, detailed)
+	}
+	private[this] def logLevelDetail(level: Level.Value): String =
+s"""$level
+
+	Sets the global logging level to $level.
+	This will be used as the default level for logging from commands, settings, and tasks.
+	Any explicit `logLevel` configuration in a project overrides this setting.
+
+${runEarly(level.toString)}
+
+	Sets the global logging level as described above, but does so before any other commands are executed on startup, including project loading.
+	This is useful as a startup option:
+		* it takes effect before any logging occurs
+		* if no other commands are passed, interactive mode is still entered
+"""
+
 	def runEarly(command: String) = {
 		val sep = if(command.isEmpty || Character.isLetter(command.charAt(0))) "" else " "
 		s"$EarlyCommand$sep$command"

main/src/main/scala/sbt/LogManager.scala

@@ -86,6 +86,14 @@ object LogManager
 			s
 		}
 
+	def setGlobalLogLevel(s: State, level: Level.Value): State = {
+		s.globalLogging.full match {
+			case a: AbstractLogger => a.setLevel(level)
+			case _ => ()
+		}
+		s.put(BasicKeys.explicitGlobalLogLevels, true).put(Keys.logLevel.key, level)
+	}
+
 	private[this] def setExplicitGlobalLogLevels(s: State, flag: Boolean): State =
 		s.put(BasicKeys.explicitGlobalLogLevels, flag)
 	private[this] def hasExplicitGlobalLogLevels(s: State): Boolean =

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

@@ -85,11 +85,11 @@ object BuiltinCommands
 {
 	def initialAttributes = AttributeMap.empty
 
-	def ConsoleCommands: Seq[Command] = Seq(ignore, exit, IvyConsole.command, early, act, nop)
-	def ScriptCommands: Seq[Command] = Seq(ignore, exit, Script.command, early, act, nop)
+	def ConsoleCommands: Seq[Command] = Seq(ignore, exit, IvyConsole.command, setLogLevel, early, act, nop)
+	def ScriptCommands: Seq[Command] = Seq(ignore, exit, Script.command, setLogLevel, early, act, nop)
 	def DefaultCommands: Seq[Command] = Seq(ignore, help, about, tasks, settingsCommand, loadProject,
 		projects, project, reboot, read, history, set, sessionCommand, inspect, loadProjectImpl, loadFailed, Cross.crossBuild, Cross.switchVersion,
-		setOnFailure, clearOnFailure, stashOnFailure, popOnFailure,
+		setOnFailure, clearOnFailure, stashOnFailure, popOnFailure, setLogLevel,
 		ifLast, multi, shell, continuous, eval, alias, append, last, lastGrep, export, boot, nop, call, exit, early, initialize, act) ++
 		compatCommands
 	def DefaultBootCommands: Seq[String] = LoadProject :: (IfLast + " " + Shell) :: Nil
@@ -98,6 +98,9 @@ object BuiltinCommands
 
 	def about = Command.command(AboutCommand, aboutBrief, aboutDetailed) { s => s.log.info(aboutString(s)); s }
 
+	def setLogLevel = Command.arb(const(logLevelParser), logLevelHelp)(LogManager.setGlobalLogLevel)
+	private[this] def logLevelParser: Parser[Level.Value] = oneOf(Level.values.toSeq.map(v => v.toString ^^^ v))
+
 	// This parser schedules the default boot commands unless overridden by an alias
 	def bootParser(s: State) =
 	{