Command line --get-pref may be used without name of the target pref.

If pref name is missing, all prefs are printed on stdout.
Should fix/mitigate #2982

app/src/cc/arduino/view/SplashScreenHelper.java

@@ -90,7 +90,7 @@ public void close() {
   }
 
   private void printText(String str) {
-    System.out.println(str);
+    System.err.println(str);
   }
 
 }

app/src/processing/app/Base.java

@@ -477,13 +477,7 @@ protected void onProgress(Progress progress) {
       // Do nothing (intended for only changing preferences)
       System.exit(0);
     } else if (parser.isGetPrefMode()) {
-      String value = PreferencesData.get(parser.getGetPref(), null);
-      if (value != null) {
-        System.out.println(value);
-        System.exit(0);
-      } else {
-        System.exit(4);
-      }
+      BaseNoGui.dumpPrefs(parser);
     }
   }
 

arduino-core/src/processing/app/BaseNoGui.java

@@ -570,13 +570,26 @@ static public void init(String[] args) throws Exception {
       System.exit(0);
     }
     else if (parser.isGetPrefMode()) {
+      dumpPrefs(parser);
+    }
+  }
+
+  protected static void dumpPrefs(CommandlineParser parser) {
+    if (parser.getGetPref() != null) {
       String value = PreferencesData.get(parser.getGetPref(), null);
       if (value != null) {
         System.out.println(value);
         System.exit(0);
       } else {
         System.exit(4);
       }
+    } else {
+      System.out.println("#PREFDUMP#");
+      PreferencesMap prefs = PreferencesData.getMap();
+      for (Map.Entry<String, String> entry : prefs.entrySet()) {
+        System.out.println(entry.getKey() + "=" + entry.getValue());
+      }
+      System.exit(0);
     }
   }
 

arduino-core/src/processing/app/debug/LegacyTargetBoard.java

@@ -58,7 +58,7 @@ public LegacyTargetBoard(String _id, PreferencesMap _prefs,
       String board = containerPlatform.getId() + "_" + id;
       board = board.toUpperCase();
       prefs.put("build.board", board);
-      System.out
+      System.err
           .println(format(_("Board {0}:{1}:{2} doesn''t define a ''build.board'' preference. Auto-set to: {3}"),
                           containerPlatform.getContainerPackage().getId(),
                           containerPlatform.getId(), id, board));

arduino-core/src/processing/app/debug/LegacyTargetPackage.java

@@ -51,7 +51,7 @@ public LegacyTargetPackage(String _id, File _folder) throws TargetPlatformExcept
         TargetPlatform platform = new LegacyTargetPlatform(arch, subFolder, this);
         platforms.put(arch, platform);
       } catch (TargetPlatformException e) {
-        System.out.println(e.getMessage());
+        System.err.println(e.getMessage());
       }
     }
 

arduino-core/src/processing/app/helpers/CommandlineParser.java

@@ -73,10 +73,9 @@ private void parseArguments(String[] args) {
         }
         if (a == ACTION.GET_PREF) {
           i++;
-          if (i >= args.length) {
-            BaseNoGui.showError(null, I18n.format(_("Argument required for {0}"), a.value), 3);
+          if (i < args.length) {
+            getPref = args[i];
           }
-          getPref = args[i];
         }
         if (a == ACTION.INSTALL_BOARD) {
           i++;

build/shared/manpage.adoc

@@ -27,7 +27,7 @@ SYNOPSIS
 
 *arduino* [*--verify*|*--upload*] [*--board* __package__:__arch__:__board__[:__parameters__]] [*--port* __portname__] [*--pref* __name__=__value__] [*-v*|*--verbose*] [--preserve-temp-files] [__FILE.ino__]
 
-*arduino* [*--get-pref* __preference__]
+*arduino* [*--get-pref* [__preference__]]
 
 *arduino* [*--install-boards* __package name__:__platform architecture__[:__version__]]
 
@@ -63,10 +63,11 @@ ACTIONS
 *--upload*::
 	Build and upload the sketch.
 
-*--get-pref* __preference__::
+*--get-pref* [__preference__]::
 	Prints the value of the given preference to the standard output
 	stream. When the value does not exist, nothing is printed and
 	the exit status is set (see EXIT STATUS below).
+	If no preference is given as parameter, it prints all preferences.
 
 *--install-boards* __package name__:__platform architecture__[:__version__]::
 	Fetches available board support (platform) list and install the specified one, along with its related tools. If __version__ is omitted, the latest is installed. If a platform with the same version is already installed, nothing is installed and program exits with exit code 1. If a platform with a different version is already installed, it's replaced.