diff --git a/org.eclipse.jgit.pgm.test/tst/org/eclipse/jgit/pgm/DiffToolTest.java b/org.eclipse.jgit.pgm.test/tst/org/eclipse/jgit/pgm/DiffToolTest.java
index e7bf484..e2ff189 100644
--- a/org.eclipse.jgit.pgm.test/tst/org/eclipse/jgit/pgm/DiffToolTest.java
+++ b/org.eclipse.jgit.pgm.test/tst/org/eclipse/jgit/pgm/DiffToolTest.java
@@ -9,7 +9,13 @@
  */
 package org.eclipse.jgit.pgm;
 
+import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_DIFFTOOL_SECTION;
+import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_DIFF_SECTION;
+import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_CMD;
+import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_PROMPT;
+import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_TOOL;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -19,6 +25,7 @@
 import org.eclipse.jgit.diff.DiffEntry;
 import org.eclipse.jgit.internal.diffmergetool.CommandLineDiffTool;
 import org.eclipse.jgit.lib.CLIRepositoryTestCase;
+import org.eclipse.jgit.lib.StoredConfig;
 import org.eclipse.jgit.pgm.opt.CmdLineParser;
 import org.eclipse.jgit.pgm.opt.SubcommandHandler;
 import org.eclipse.jgit.revwalk.RevCommit;
@@ -60,6 +67,7 @@ public static class GitCliJGitWrapperParser {
 		return result.outLines().toArray(new String[0]);
 	}
 
+	private static final String TOOL_NAME = "some_tool";
 	private Git git;
 
 	@Override
@@ -68,6 +76,15 @@ public void setUp() throws Exception {
 		super.setUp();
 		git = new Git(db);
 		git.commit().setMessage("initial commit").call();
+		configureEchoTool(TOOL_NAME);
+	}
+
+	@Test(expected = Die.class)
+	public void testNotDefinedTool() throws Exception {
+		createUnstagedChanges();
+
+		runAndCaptureUsingInitRaw("difftool", "--tool", "undefined");
+		fail("Expected exception when trying to run undefined tool");
 	}
 
 	@Test
@@ -85,7 +102,7 @@ public void testTool() throws Exception {
 			assertArrayOfLinesEquals("Incorrect output for option: " + option,
 					expectedOutput,
 					runAndCaptureUsingInitRaw("difftool", option,
-							"some_tool"));
+							TOOL_NAME));
 		}
 	}
 
@@ -100,7 +117,7 @@ public void testToolTrustExitCode() throws Exception {
 		for (String option : options) {
 			assertArrayOfLinesEquals("Incorrect output for option: " + option,
 					expectedOutput, runAndCaptureUsingInitRaw("difftool",
-							"--trust-exit-code", option, "some_tool"));
+							"--trust-exit-code", option, TOOL_NAME));
 		}
 	}
 
@@ -116,7 +133,7 @@ public void testToolNoGuiNoPromptNoTrustExitcode() throws Exception {
 			assertArrayOfLinesEquals("Incorrect output for option: " + option,
 					expectedOutput, runAndCaptureUsingInitRaw("difftool",
 							"--no-gui", "--no-prompt", "--no-trust-exit-code",
-							option, "some_tool"));
+							option, TOOL_NAME));
 		}
 	}
 
@@ -131,7 +148,7 @@ public void testToolCached() throws Exception {
 		for (String option : options) {
 			assertArrayOfLinesEquals("Incorrect output for option: " + option,
 					expectedOutput, runAndCaptureUsingInitRaw("difftool",
-							option, "--tool", "some_tool"));
+							option, "--tool", TOOL_NAME));
 		}
 	}
 
@@ -144,8 +161,11 @@ public void testToolHelp() throws Exception {
 			String toolName = defaultTool.name();
 			expectedOutput.add(toolName);
 		}
+		String customToolHelpLine = TOOL_NAME + "." + CONFIG_KEY_CMD + " "
+				+ getEchoCommand();
+		expectedOutput.add("user-defined:");
+		expectedOutput.add(customToolHelpLine);
 		String[] userDefinedToolsHelp = {
-				"user-defined:",
 				"The following tools are valid, but not currently available:",
 				"Some of the tools listed above only work in a windowed",
 				"environment. If run in a terminal-only session, they will fail.",
@@ -157,6 +177,25 @@ public void testToolHelp() throws Exception {
 				expectedOutput.toArray(new String[0]), runAndCaptureUsingInitRaw("difftool", option));
 	}
 
+	private void configureEchoTool(String toolName) {
+		StoredConfig config = db.getConfig();
+		// the default diff tool is configured without a subsection
+		String subsection = null;
+		config.setString(CONFIG_DIFF_SECTION, subsection, CONFIG_KEY_TOOL,
+				toolName);
+
+		String command = getEchoCommand();
+
+		config.setString(CONFIG_DIFFTOOL_SECTION, toolName, CONFIG_KEY_CMD,
+				command);
+		/*
+		 * prevent prompts as we are running in tests and there is no user to
+		 * interact with on the command line
+		 */
+		config.setString(CONFIG_DIFFTOOL_SECTION, toolName, CONFIG_KEY_PROMPT,
+				String.valueOf(false));
+	}
+
 	private RevCommit createUnstagedChanges() throws Exception {
 		writeTrashFile("a", "Hello world a");
 		writeTrashFile("b", "Hello world b");
@@ -188,11 +227,7 @@ private List<DiffEntry> getRepositoryChanges(RevCommit commit)
 		for (int i = 0; i < changes.size(); ++i) {
 			DiffEntry change = changes.get(i);
 			String newPath = change.getNewPath();
-			String oldPath = change.getOldPath();
-			String newIdName = change.getNewId().name();
-			String oldIdName = change.getOldId().name();
-			String expectedLine = "M\t" + newPath + " (" + newIdName + ")"
-					+ "\t" + oldPath + " (" + oldIdName + ")";
+			String expectedLine = newPath;
 			expectedToolOutput[i] = expectedLine;
 		}
 		return expectedToolOutput;
@@ -202,4 +237,12 @@ private static void assertArrayOfLinesEquals(String failMessage,
 			String[] expected, String[] actual) {
 		assertEquals(failMessage, toString(expected), toString(actual));
 	}
+
+	private static String getEchoCommand() {
+		/*
+		 * use 'MERGED' placeholder, as both 'LOCAL' and 'REMOTE' will be
+		 * replaced with full paths to a temporary file during some of the tests
+		 */
+		return "(echo \"$MERGED\")";
+	}
 }
diff --git a/org.eclipse.jgit.pgm/resources/org/eclipse/jgit/pgm/internal/CLIText.properties b/org.eclipse.jgit.pgm/resources/org/eclipse/jgit/pgm/internal/CLIText.properties
index fda0bf6..3653b9d 100644
--- a/org.eclipse.jgit.pgm/resources/org/eclipse/jgit/pgm/internal/CLIText.properties
+++ b/org.eclipse.jgit.pgm/resources/org/eclipse/jgit/pgm/internal/CLIText.properties
@@ -60,7 +60,7 @@
 deletedRemoteBranch=Deleted remote branch {0}
 diffToolHelpSetToFollowing='git difftool --tool=<tool>' may be set to one of the following:\n{0}\n\tuser-defined:\n{1}\nThe following tools are valid, but not currently available:\n{2}\nSome of the tools listed above only work in a windowed\nenvironment. If run in a terminal-only session, they will fail.
 diffToolLaunch=Viewing ({0}/{1}): '{2}'\nLaunch '{3}' [Y/n]?
-diffToolDied=external diff died, stopping at {0}
+diffToolDied=external diff died, stopping at path ''{0}'' due to exception: {1}
 doesNotExist={0} does not exist
 dontOverwriteLocalChanges=error: Your local changes to the following file would be overwritten by merge:
 everythingUpToDate=Everything up-to-date
diff --git a/org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/DiffTool.java b/org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/DiffTool.java
index 1288817..2f74177 100644
--- a/org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/DiffTool.java
+++ b/org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/DiffTool.java
@@ -21,8 +21,10 @@
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
-
+import org.eclipse.jgit.diff.ContentSource;
+import org.eclipse.jgit.diff.ContentSource.Pair;
 import org.eclipse.jgit.diff.DiffEntry;
+import org.eclipse.jgit.diff.DiffEntry.Side;
 import org.eclipse.jgit.diff.DiffFormatter;
 import org.eclipse.jgit.dircache.DirCacheIterator;
 import org.eclipse.jgit.errors.AmbiguousObjectException;
@@ -30,8 +32,11 @@
 import org.eclipse.jgit.errors.RevisionSyntaxException;
 import org.eclipse.jgit.internal.diffmergetool.DiffTools;
 import org.eclipse.jgit.internal.diffmergetool.ExternalDiffTool;
+import org.eclipse.jgit.internal.diffmergetool.FileElement;
+import org.eclipse.jgit.internal.diffmergetool.ToolException;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.ObjectReader;
+import org.eclipse.jgit.lib.ObjectStream;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.lib.TextProgressMonitor;
 import org.eclipse.jgit.lib.internal.BooleanTriState;
@@ -40,8 +45,10 @@
 import org.eclipse.jgit.treewalk.AbstractTreeIterator;
 import org.eclipse.jgit.treewalk.CanonicalTreeParser;
 import org.eclipse.jgit.treewalk.FileTreeIterator;
+import org.eclipse.jgit.treewalk.WorkingTreeIterator;
 import org.eclipse.jgit.treewalk.filter.TreeFilter;
 import org.eclipse.jgit.util.StringUtils;
+import org.eclipse.jgit.util.FS.ExecutionResult;
 import org.kohsuke.args4j.Argument;
 import org.kohsuke.args4j.Option;
 
@@ -145,40 +152,54 @@ protected void run() {
 
 	private void compare(List<DiffEntry> files, boolean showPrompt,
 			String toolNamePrompt) throws IOException {
-		for (int fileIndex = 0; fileIndex < files.size(); fileIndex++) {
-			DiffEntry ent = files.get(fileIndex);
-			String mergedFilePath = ent.getNewPath();
-			if (mergedFilePath.equals(DiffEntry.DEV_NULL)) {
-				mergedFilePath = ent.getOldPath();
-			}
-			// check if user wants to launch compare
-			boolean launchCompare = true;
-			if (showPrompt) {
-				launchCompare = isLaunchCompare(fileIndex + 1, files.size(),
-						mergedFilePath, toolNamePrompt);
-			}
-			if (launchCompare) {
-				switch (ent.getChangeType()) {
-				case MODIFY:
-					outw.println("M\t" + ent.getNewPath() //$NON-NLS-1$
-							+ " (" + ent.getNewId().name() + ")" //$NON-NLS-1$ //$NON-NLS-2$
-							+ "\t" + ent.getOldPath() //$NON-NLS-1$
-							+ " (" + ent.getOldId().name() + ")"); //$NON-NLS-1$ //$NON-NLS-2$
-					int ret = diffTools.compare(ent.getNewPath(),
-							ent.getOldPath(), ent.getNewId().name(),
-							ent.getOldId().name(), toolName, prompt, gui,
-							trustExitCode);
-					if (ret != 0) {
+		ContentSource.Pair sourcePair = new ContentSource.Pair(source(oldTree),
+				source(newTree));
+		try {
+			for (int fileIndex = 0; fileIndex < files.size(); fileIndex++) {
+				DiffEntry ent = files.get(fileIndex);
+				String mergedFilePath = ent.getNewPath();
+				if (mergedFilePath.equals(DiffEntry.DEV_NULL)) {
+					mergedFilePath = ent.getOldPath();
+				}
+				FileElement local = new FileElement(ent.getOldPath(),
+						ent.getOldId().name(),
+						getObjectStream(sourcePair, Side.OLD, ent));
+				FileElement remote = new FileElement(ent.getNewPath(),
+						ent.getNewId().name(),
+						getObjectStream(sourcePair, Side.NEW, ent));
+				// check if user wants to launch compare
+				boolean launchCompare = true;
+				if (showPrompt) {
+					launchCompare = isLaunchCompare(fileIndex + 1, files.size(),
+							mergedFilePath, toolNamePrompt);
+				}
+				if (launchCompare) {
+					try {
+						// TODO: check how to return the exit-code of
+						// the
+						// tool
+						// to
+						// jgit / java runtime ?
+						// int rc =...
+						ExecutionResult result = diffTools.compare(db, local,
+								remote, mergedFilePath,
+								toolName, prompt, gui, trustExitCode);
+						outw.println(new String(result.getStdout().toByteArray()));
+						errw.println(
+								new String(result.getStderr().toByteArray()));
+					} catch (ToolException e) {
+						outw.println(e.getResultStdout());
+						outw.flush();
+						errw.println(e.getMessage());
 						throw die(MessageFormat.format(
-								CLIText.get().diffToolDied, mergedFilePath));
+								CLIText.get().diffToolDied, mergedFilePath, e));
 					}
-					break;
-				default:
+				} else {
 					break;
 				}
-			} else {
-				break;
 			}
+		} finally {
+			sourcePair.close();
 		}
 	}
 
@@ -254,4 +275,23 @@ private List<DiffEntry> getFiles()
 		return files;
 	}
 
+	private ObjectStream getObjectStream(Pair pair, Side side, DiffEntry ent) {
+		ObjectStream stream = null;
+		if (!pair.isWorkingTreeSource(side)) {
+			try {
+				stream = pair.open(side, ent).openStream();
+			} catch (Exception e) {
+				stream = null;
+			}
+		}
+		return stream;
+	}
+
+	private ContentSource source(AbstractTreeIterator iterator) {
+		if (iterator instanceof WorkingTreeIterator) {
+			return ContentSource.create((WorkingTreeIterator) iterator);
+		}
+		return ContentSource.create(db.newObjectReader());
+	}
+
 }
diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/diffmergetool/ExternalDiffToolTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/diffmergetool/ExternalDiffToolTest.java
index c9ebec7..ebc67c8 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/diffmergetool/ExternalDiffToolTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/diffmergetool/ExternalDiffToolTest.java
@@ -10,13 +10,17 @@
 package org.eclipse.jgit.internal.diffmergetool;
 
 import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_DIFFTOOL_SECTION;
+import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_DIFF_SECTION;
 import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_CMD;
 import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_GUITOOL;
 import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_PATH;
 import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_PROMPT;
+import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_TOOL;
 import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_TRUST_EXIT_CODE;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
 
 import java.util.Collections;
 import java.util.LinkedHashSet;
@@ -25,6 +29,7 @@
 
 import org.eclipse.jgit.lib.internal.BooleanTriState;
 import org.eclipse.jgit.storage.file.FileBasedConfig;
+import org.eclipse.jgit.util.FS.ExecutionResult;
 import org.junit.Test;
 
 /**
@@ -32,6 +37,54 @@
  */
 public class ExternalDiffToolTest extends ExternalToolTestCase {
 
+	@Test(expected = ToolException.class)
+	public void testUserToolWithError() throws Exception {
+		String toolName = "customTool";
+
+		int errorReturnCode = 1;
+		String command = "exit " + errorReturnCode;
+
+		FileBasedConfig config = db.getConfig();
+		config.setString(CONFIG_DIFFTOOL_SECTION, toolName, CONFIG_KEY_CMD,
+				command);
+
+		DiffTools manager = new DiffTools(db);
+
+		BooleanTriState prompt = BooleanTriState.UNSET;
+		BooleanTriState gui = BooleanTriState.UNSET;
+		BooleanTriState trustExitCode = BooleanTriState.TRUE;
+
+		manager.compare(db, local, remote, merged.getPath(), toolName, prompt,
+				gui, trustExitCode);
+
+		fail("Expected exception to be thrown due to external tool exiting with error code: "
+				+ errorReturnCode);
+	}
+
+	@Test(expected = ToolException.class)
+	public void testUserToolWithCommandNotFoundError() throws Exception {
+		String toolName = "customTool";
+
+		int errorReturnCode = 127; // command not found
+		String command = "exit " + errorReturnCode;
+
+		FileBasedConfig config = db.getConfig();
+		config.setString(CONFIG_DIFFTOOL_SECTION, toolName, CONFIG_KEY_CMD,
+				command);
+
+		DiffTools manager = new DiffTools(db);
+
+		BooleanTriState prompt = BooleanTriState.UNSET;
+		BooleanTriState gui = BooleanTriState.UNSET;
+		BooleanTriState trustExitCode = BooleanTriState.FALSE;
+
+		manager.compare(db, local, remote, merged.getPath(), toolName, prompt,
+				gui, trustExitCode);
+
+		fail("Expected exception to be thrown due to external tool exiting with error code: "
+				+ errorReturnCode);
+	}
+
 	@Test
 	public void testToolNames() {
 		DiffTools manager = new DiffTools(db);
@@ -86,11 +139,11 @@ public void testUserDefinedTools() {
 		config.setString(CONFIG_DIFFTOOL_SECTION, customToolname,
 				CONFIG_KEY_PATH, "/usr/bin/echo");
 		config.setString(CONFIG_DIFFTOOL_SECTION, customToolname,
-				CONFIG_KEY_PROMPT, "--no-prompt");
+				CONFIG_KEY_PROMPT, String.valueOf(false));
 		config.setString(CONFIG_DIFFTOOL_SECTION, customToolname,
-				CONFIG_KEY_GUITOOL, "--no-gui");
+				CONFIG_KEY_GUITOOL, String.valueOf(false));
 		config.setString(CONFIG_DIFFTOOL_SECTION, customToolname,
-				CONFIG_KEY_TRUST_EXIT_CODE, "--no-trust-exit-code");
+				CONFIG_KEY_TRUST_EXIT_CODE, String.valueOf(false));
 		DiffTools manager = new DiffTools(db);
 		Set<String> actualToolNames = manager.getUserDefinedTools().keySet();
 		Set<String> expectedToolNames = new LinkedHashSet<>();
@@ -109,38 +162,50 @@ public void testNotAvailableTools() {
 	}
 
 	@Test
-	public void testCompare() {
-		DiffTools manager = new DiffTools(db);
+	public void testCompare() throws ToolException {
+		String toolName = "customTool";
 
-		String newPath = "";
-		String oldPath = "";
-		String newId = "";
-		String oldId = "";
-		String toolName = "";
+		FileBasedConfig config = db.getConfig();
+		// the default diff tool is configured without a subsection
+		String subsection = null;
+		config.setString(CONFIG_DIFF_SECTION, subsection, CONFIG_KEY_TOOL,
+				toolName);
+
+		String command = getEchoCommand();
+
+		config.setString(CONFIG_DIFFTOOL_SECTION, toolName, CONFIG_KEY_CMD,
+				command);
+
 		BooleanTriState prompt = BooleanTriState.UNSET;
 		BooleanTriState gui = BooleanTriState.UNSET;
 		BooleanTriState trustExitCode = BooleanTriState.UNSET;
 
+		DiffTools manager = new DiffTools(db);
+
 		int expectedCompareResult = 0;
-		int compareResult = manager.compare(newPath, oldPath, newId, oldId,
-				toolName, prompt, gui, trustExitCode);
+		ExecutionResult compareResult = manager.compare(db, local, remote,
+				merged.getPath(), toolName, prompt, gui, trustExitCode);
 		assertEquals("Incorrect compare result for external diff tool",
-				expectedCompareResult, compareResult);
+				expectedCompareResult, compareResult.getRc());
 	}
 
 	@Test
 	public void testDefaultTool() throws Exception {
+		String toolName = "customTool";
+		String guiToolName = "customGuiTool";
+
 		FileBasedConfig config = db.getConfig();
 		// the default diff tool is configured without a subsection
 		String subsection = null;
-		config.setString("diff", subsection, "tool", "customTool");
+		config.setString(CONFIG_DIFF_SECTION, subsection, CONFIG_KEY_TOOL,
+				toolName);
 
 		DiffTools manager = new DiffTools(db);
 		BooleanTriState gui = BooleanTriState.UNSET;
 		String defaultToolName = manager.getDefaultToolName(gui);
 		assertEquals(
 				"Expected configured difftool to be the default external diff tool",
-				"my_default_toolname", defaultToolName);
+				toolName, defaultToolName);
 
 		gui = BooleanTriState.TRUE;
 		String defaultGuiToolName = manager.getDefaultToolName(gui);
@@ -148,11 +213,63 @@ public void testDefaultTool() throws Exception {
 				"Expected configured difftool to be the default external diff tool",
 				"my_gui_tool", defaultGuiToolName);
 
-		config.setString("diff", subsection, "guitool", "customGuiTool");
+		config.setString(CONFIG_DIFF_SECTION, subsection, CONFIG_KEY_GUITOOL,
+				guiToolName);
 		manager = new DiffTools(db);
 		defaultGuiToolName = manager.getDefaultToolName(gui);
 		assertEquals(
 				"Expected configured difftool to be the default external diff guitool",
 				"my_gui_tool", defaultGuiToolName);
 	}
+
+	@Test
+	public void testOverridePreDefinedToolPath() {
+		String newToolPath = "/tmp/path/";
+
+		CommandLineDiffTool[] defaultTools = CommandLineDiffTool.values();
+		assertTrue("Expected to find pre-defined external diff tools",
+				defaultTools.length > 0);
+
+		CommandLineDiffTool overridenTool = defaultTools[0];
+		String overridenToolName = overridenTool.name();
+		String overridenToolPath = newToolPath + overridenToolName;
+		FileBasedConfig config = db.getConfig();
+		config.setString(CONFIG_DIFFTOOL_SECTION, overridenToolName,
+				CONFIG_KEY_PATH, overridenToolPath);
+
+		DiffTools manager = new DiffTools(db);
+		Map<String, ExternalDiffTool> availableTools = manager
+				.getAvailableTools();
+		ExternalDiffTool externalDiffTool = availableTools
+				.get(overridenToolName);
+		String actualDiffToolPath = externalDiffTool.getPath();
+		assertEquals(
+				"Expected pre-defined external diff tool to have overriden path",
+				overridenToolPath, actualDiffToolPath);
+		String expectedDiffToolCommand = overridenToolPath + " "
+				+ overridenTool.getParameters();
+		String actualDiffToolCommand = externalDiffTool.getCommand();
+		assertEquals(
+				"Expected pre-defined external diff tool to have overriden command",
+				expectedDiffToolCommand, actualDiffToolCommand);
+	}
+
+	@Test(expected = ToolException.class)
+	public void testUndefinedTool() throws Exception {
+		DiffTools manager = new DiffTools(db);
+
+		String toolName = "undefined";
+		BooleanTriState prompt = BooleanTriState.UNSET;
+		BooleanTriState gui = BooleanTriState.UNSET;
+		BooleanTriState trustExitCode = BooleanTriState.UNSET;
+
+		manager.compare(db, local, remote, merged.getPath(), toolName, prompt,
+				gui, trustExitCode);
+		fail("Expected exception to be thrown due to not defined external diff tool");
+	}
+
+	private String getEchoCommand() {
+		return "(echo \"$LOCAL\" \"$REMOTE\") > "
+				+ commandResult.getAbsolutePath();
+	}
 }
diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/diffmergetool/ExternalToolTestCase.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/diffmergetool/ExternalToolTestCase.java
index 0cc1297..6757eb4 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/diffmergetool/ExternalToolTestCase.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/diffmergetool/ExternalToolTestCase.java
@@ -36,6 +36,14 @@ public abstract class ExternalToolTestCase extends RepositoryTestCase {
 
 	protected File commandResult;
 
+	protected FileElement local;
+
+	protected FileElement remote;
+
+	protected FileElement merged;
+
+	protected FileElement base;
+
 	@Before
 	@Override
 	public void setUp() throws Exception {
@@ -51,6 +59,11 @@ public void setUp() throws Exception {
 		baseFile.deleteOnExit();
 		commandResult = writeTrashFile("commandResult.txt", "");
 		commandResult.deleteOnExit();
+
+		local = new FileElement(localFile.getAbsolutePath(), "LOCAL");
+		remote = new FileElement(remoteFile.getAbsolutePath(), "REMOTE");
+		merged = new FileElement(mergedFile.getAbsolutePath(), "MERGED");
+		base = new FileElement(baseFile.getAbsolutePath(), "BASE");
 	}
 
 	@After
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/diff/ContentSource.java b/org.eclipse.jgit/src/org/eclipse/jgit/diff/ContentSource.java
index 1a41df3..64ff19c 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/diff/ContentSource.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/diff/ContentSource.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2010, 2020 Google Inc. and others
+ * Copyright (C) 2010, 2021 Google Inc. and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -91,6 +91,29 @@ public static ContentSource create(WorkingTreeIterator iterator) {
 	public abstract ObjectLoader open(String path, ObjectId id)
 			throws IOException;
 
+	/**
+	 * Closes the used resources like ObjectReader, TreeWalk etc. Default
+	 * implementation does nothing.
+	 *
+	 * @since 6.2
+	 */
+	public void close() {
+		// Do nothing
+	}
+
+	/**
+	 * Checks if the source is from "working tree", so it can be accessed as a
+	 * file directly.
+	 *
+	 * @since 6.2
+	 *
+	 * @return true if working tree source and false otherwise (loader must be
+	 *         used)
+	 */
+	public boolean isWorkingTreeSource() {
+		return false;
+	}
+
 	private static class ObjectReaderSource extends ContentSource {
 		private final ObjectReader reader;
 
@@ -111,6 +134,16 @@ public long size(String path, ObjectId id) throws IOException {
 		public ObjectLoader open(String path, ObjectId id) throws IOException {
 			return reader.open(id, Constants.OBJ_BLOB);
 		}
+
+		@Override
+		public void close() {
+			reader.close();
+		}
+
+		@Override
+		public boolean isWorkingTreeSource() {
+			return false;
+		}
 	}
 
 	private static class WorkingTreeSource extends ContentSource {
@@ -194,6 +227,16 @@ private void seek(String path) throws IOException {
 					throw new FileNotFoundException(path);
 			}
 		}
+
+		@Override
+		public void close() {
+			tw.close();
+		}
+
+		@Override
+		public boolean isWorkingTreeSource() {
+			return true;
+		}
 	}
 
 	/** A pair of sources to access the old and new sides of a DiffEntry. */
@@ -261,5 +304,37 @@ public ObjectLoader open(DiffEntry.Side side, DiffEntry ent)
 				throw new IllegalArgumentException();
 			}
 		}
+
+		/**
+		 * Closes used resources.
+		 *
+		 * @since 6.2
+		 */
+		public void close() {
+			oldSource.close();
+			newSource.close();
+		}
+
+		/**
+		 * Checks if source (side) is a "working tree".
+		 *
+		 * @since 6.2
+		 *
+		 * @param side
+		 *            which side of the entry to read (OLD or NEW).
+		 * @return is the source a "working tree"
+		 *
+		 */
+		public boolean isWorkingTreeSource(DiffEntry.Side side) {
+			switch (side) {
+			case OLD:
+				return oldSource.isWorkingTreeSource();
+			case NEW:
+				return newSource.isWorkingTreeSource();
+			default:
+				throw new IllegalArgumentException();
+			}
+		}
+
 	}
 }
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/CommandExecutor.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/CommandExecutor.java
new file mode 100644
index 0000000..0dde9b5
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/CommandExecutor.java
@@ -0,0 +1,182 @@
+/*
+ * Copyright (C) 2018-2021, Andre Bossert <andre.bossert@siemens.com>
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+package org.eclipse.jgit.internal.diffmergetool;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.util.Arrays;
+import java.util.Map;
+import org.eclipse.jgit.util.FS;
+import org.eclipse.jgit.util.FS.ExecutionResult;
+import org.eclipse.jgit.util.FS_POSIX;
+import org.eclipse.jgit.util.FS_Win32;
+import org.eclipse.jgit.util.FS_Win32_Cygwin;
+
+/**
+ * Runs a command with help of FS.
+ */
+public class CommandExecutor {
+
+	private FS fs;
+
+	private boolean checkExitCode;
+
+	private File commandFile;
+
+	private boolean useMsys2;
+
+	/**
+	 * @param fs
+	 *            the file system
+	 * @param checkExitCode
+	 *            should the exit code be checked for errors ?
+	 */
+	public CommandExecutor(FS fs, boolean checkExitCode) {
+		this.fs = fs;
+		this.checkExitCode = checkExitCode;
+	}
+
+	/**
+	 * @param command
+	 *            the command string
+	 * @param workingDir
+	 *            the working directory
+	 * @param env
+	 *            the environment
+	 * @return the execution result
+	 * @throws ToolException
+	 * @throws InterruptedException
+	 * @throws IOException
+	 */
+	public ExecutionResult run(String command, File workingDir,
+			Map<String, String> env)
+			throws ToolException, IOException, InterruptedException {
+		String[] commandArray = createCommandArray(command);
+		try {
+			ProcessBuilder pb = fs.runInShell(commandArray[0],
+					Arrays.copyOfRange(commandArray, 1, commandArray.length));
+			pb.directory(workingDir);
+			Map<String, String> envp = pb.environment();
+			if (env != null) {
+				envp.putAll(env);
+			}
+			ExecutionResult result = fs.execute(pb, null);
+			int rc = result.getRc();
+			if ((rc != 0) && (checkExitCode
+					|| isCommandExecutionError(rc))) {
+				throw new ToolException(
+						new String(result.getStderr().toByteArray()), result);
+			}
+			return result;
+		} finally {
+			deleteCommandArray();
+		}
+	}
+
+	private void deleteCommandArray() {
+		deleteCommandFile();
+	}
+
+	private String[] createCommandArray(String command)
+			throws ToolException, IOException {
+		String[] commandArray = null;
+		checkUseMsys2(command);
+		createCommandFile(command);
+		if (fs instanceof FS_POSIX) {
+			commandArray = new String[1];
+			commandArray[0] = commandFile.getCanonicalPath();
+		} else if (fs instanceof FS_Win32) {
+			if (useMsys2) {
+				commandArray = new String[3];
+				commandArray[0] = "bash.exe"; //$NON-NLS-1$
+				commandArray[1] = "-c"; //$NON-NLS-1$
+				commandArray[2] = commandFile.getCanonicalPath().replace("\\", //$NON-NLS-1$
+						"/"); //$NON-NLS-1$
+			} else {
+				commandArray = new String[1];
+				commandArray[0] = commandFile.getCanonicalPath();
+			}
+		} else if (fs instanceof FS_Win32_Cygwin) {
+			commandArray = new String[1];
+			commandArray[0] = commandFile.getCanonicalPath().replace("\\", "/"); //$NON-NLS-1$ //$NON-NLS-2$
+		} else {
+			throw new ToolException(
+					"JGit: file system not supported: " + fs.toString()); //$NON-NLS-1$
+		}
+		return commandArray;
+	}
+
+	private void checkUseMsys2(String command) {
+		useMsys2 = false;
+		String useMsys2Str = System.getProperty("jgit.usemsys2bash"); //$NON-NLS-1$
+		if (useMsys2Str != null && !useMsys2Str.isEmpty()) {
+			if (useMsys2Str.equalsIgnoreCase("auto")) { //$NON-NLS-1$
+				useMsys2 = command.contains(".sh"); //$NON-NLS-1$
+			} else {
+				useMsys2 = Boolean.parseBoolean(useMsys2Str);
+			}
+		}
+	}
+
+	private void createCommandFile(String command)
+			throws ToolException, IOException {
+		String fileExtension = null;
+		if (useMsys2 || fs instanceof FS_POSIX
+				|| fs instanceof FS_Win32_Cygwin) {
+			fileExtension = ".sh"; //$NON-NLS-1$
+		} else if (fs instanceof FS_Win32) {
+			fileExtension = ".cmd"; //$NON-NLS-1$
+			command = "@echo off" + System.lineSeparator() + command //$NON-NLS-1$
+					+ System.lineSeparator() + "exit /B %ERRORLEVEL%"; //$NON-NLS-1$
+		} else {
+			throw new ToolException(
+					"JGit: file system not supported: " + fs.toString()); //$NON-NLS-1$
+		}
+		commandFile = File.createTempFile(".__", //$NON-NLS-1$
+				"__jgit_tool" + fileExtension); //$NON-NLS-1$
+		try (OutputStream outStream = new FileOutputStream(commandFile)) {
+			byte[] strToBytes = command.getBytes();
+			outStream.write(strToBytes);
+			outStream.close();
+		}
+		commandFile.setExecutable(true);
+	}
+
+	private void deleteCommandFile() {
+		if (commandFile != null && commandFile.exists()) {
+			commandFile.delete();
+		}
+	}
+
+	private boolean isCommandExecutionError(int rc) {
+		if (useMsys2 || fs instanceof FS_POSIX
+				|| fs instanceof FS_Win32_Cygwin) {
+			// 126: permission for executing command denied
+			// 127: command not found
+			if ((rc == 126) || (rc == 127)) {
+				return true;
+			}
+		}
+		else if (fs instanceof FS_Win32) {
+			// 9009, 0x2331: Program is not recognized as an internal or
+			// external command, operable program or batch file. Indicates that
+			// command, application name or path has been misspelled when
+			// configuring the Action.
+			if (rc == 9009) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/DiffToolConfig.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/DiffToolConfig.java
index 551f634..c8b04f9 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/DiffToolConfig.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/DiffToolConfig.java
@@ -49,9 +49,10 @@ private DiffToolConfig(Config rc) {
 		toolName = rc.getString(CONFIG_DIFF_SECTION, null, CONFIG_KEY_TOOL);
 		guiToolName = rc.getString(CONFIG_DIFF_SECTION, null,
 				CONFIG_KEY_GUITOOL);
-		prompt = rc.getBoolean(CONFIG_DIFFTOOL_SECTION, CONFIG_KEY_PROMPT,
+		prompt = rc.getBoolean(CONFIG_DIFFTOOL_SECTION, toolName,
+				CONFIG_KEY_PROMPT,
 				true);
-		String trustStr = rc.getString(CONFIG_DIFFTOOL_SECTION, null,
+		String trustStr = rc.getString(CONFIG_DIFFTOOL_SECTION, toolName,
 				CONFIG_KEY_TRUST_EXIT_CODE);
 		if (trustStr != null) {
 			trustExitCode = Boolean.parseBoolean(trustStr)
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/DiffTools.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/DiffTools.java
index 39729a4..b15cbdc 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/DiffTools.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/DiffTools.java
@@ -12,11 +12,16 @@
 
 import java.util.TreeMap;
 import java.util.Collections;
+import java.io.File;
+import java.io.IOException;
 import java.util.Map;
 import java.util.Set;
 
+import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.lib.internal.BooleanTriState;
+import org.eclipse.jgit.util.FS.ExecutionResult;
+import org.eclipse.jgit.util.StringUtils;
 
 /**
  * Manages diff tools.
@@ -25,9 +30,9 @@ public class DiffTools {
 
 	private final DiffToolConfig config;
 
-	private Map<String, ExternalDiffTool> predefinedTools;
+	private final Map<String, ExternalDiffTool> predefinedTools;
 
-	private Map<String, ExternalDiffTool> userDefinedTools;
+	private final Map<String, ExternalDiffTool> userDefinedTools;
 
 	/**
 	 * Creates the external diff-tools manager for given repository.
@@ -37,21 +42,22 @@ public class DiffTools {
 	 */
 	public DiffTools(Repository repo) {
 		config = repo.getConfig().get(DiffToolConfig.KEY);
-		setupPredefinedTools();
-		setupUserDefinedTools();
+		predefinedTools = setupPredefinedTools();
+		userDefinedTools = setupUserDefinedTools(config, predefinedTools);
 	}
 
 	/**
 	 * Compare two versions of a file.
 	 *
-	 * @param newPath
-	 *            the new file path
-	 * @param oldPath
-	 *            the old file path
-	 * @param newId
-	 *            the new object ID
-	 * @param oldId
-	 *            the old object ID
+	 * @param repo
+	 *            the repository
+	 * @param localFile
+	 *            the local file element
+	 * @param remoteFile
+	 *            the remote file element
+	 * @param mergedFilePath
+	 *            the path of 'merged' file, it equals local or remote path for
+	 *            difftool
 	 * @param toolName
 	 *            the selected tool name (can be null)
 	 * @param prompt
@@ -61,11 +67,39 @@ public DiffTools(Repository repo) {
 	 * @param trustExitCode
 	 *            the "trust exit code" option
 	 * @return the return code from executed tool
+	 * @throws ToolException
 	 */
-	public int compare(String newPath, String oldPath, String newId,
-			String oldId, String toolName, BooleanTriState prompt,
-			BooleanTriState gui, BooleanTriState trustExitCode) {
-		return 0;
+	public ExecutionResult compare(Repository repo, FileElement localFile,
+			FileElement remoteFile, String mergedFilePath, String toolName,
+			BooleanTriState prompt, BooleanTriState gui,
+			BooleanTriState trustExitCode) throws ToolException {
+		ExternalDiffTool tool = guessTool(toolName, gui);
+		try {
+			File workingDir = repo.getWorkTree();
+			String localFilePath = localFile.getFile().getPath();
+			String remoteFilePath = remoteFile.getFile().getPath();
+			String command = tool.getCommand();
+			command = command.replace("$LOCAL", localFilePath); //$NON-NLS-1$
+			command = command.replace("$REMOTE", remoteFilePath); //$NON-NLS-1$
+			command = command.replace("$MERGED", mergedFilePath); //$NON-NLS-1$
+			Map<String, String> env = new TreeMap<>();
+			env.put(Constants.GIT_DIR_KEY,
+					repo.getDirectory().getAbsolutePath());
+			env.put("LOCAL", localFilePath); //$NON-NLS-1$
+			env.put("REMOTE", remoteFilePath); //$NON-NLS-1$
+			env.put("MERGED", mergedFilePath); //$NON-NLS-1$
+			boolean trust = config.isTrustExitCode();
+			if (trustExitCode != BooleanTriState.UNSET) {
+				trust = trustExitCode == BooleanTriState.TRUE;
+			}
+			CommandExecutor cmdExec = new CommandExecutor(repo.getFS(), trust);
+			return cmdExec.run(command, workingDir, env);
+		} catch (IOException | InterruptedException e) {
+			throw new ToolException(e);
+		} finally {
+			localFile.cleanTemporaries();
+			remoteFile.cleanTemporaries();
+		}
 	}
 
 	/**
@@ -103,41 +137,64 @@ public Map<String, ExternalDiffTool> getNotAvailableTools() {
 	 */
 	public String getDefaultToolName(BooleanTriState gui) {
 		return gui != BooleanTriState.UNSET ? "my_gui_tool" //$NON-NLS-1$
-				: "my_default_toolname"; //$NON-NLS-1$
+				: config.getDefaultToolName();
 	}
 
 	/**
 	 * @return is interactive (config prompt enabled) ?
 	 */
 	public boolean isInteractive() {
-		return false;
+		return config.isPrompt();
 	}
 
-	private void setupPredefinedTools() {
-		predefinedTools = new TreeMap<>();
-		for (CommandLineDiffTool tool : CommandLineDiffTool.values()) {
-			predefinedTools.put(tool.name(), new PreDefinedDiffTool(tool));
+	private ExternalDiffTool guessTool(String toolName, BooleanTriState gui)
+			throws ToolException {
+		if (StringUtils.isEmptyOrNull(toolName)) {
+			toolName = getDefaultToolName(gui);
 		}
+		ExternalDiffTool tool = getTool(toolName);
+		if (tool == null) {
+			throw new ToolException("Unknown diff tool " + toolName); //$NON-NLS-1$
+		}
+		return tool;
 	}
 
-	private void setupUserDefinedTools() {
-		userDefinedTools = new TreeMap<>();
-		Map<String, ExternalDiffTool> userTools = config.getTools();
+	private ExternalDiffTool getTool(final String name) {
+		ExternalDiffTool tool = userDefinedTools.get(name);
+		if (tool == null) {
+			tool = predefinedTools.get(name);
+		}
+		return tool;
+	}
+
+	private static Map<String, ExternalDiffTool> setupPredefinedTools() {
+		Map<String, ExternalDiffTool> tools = new TreeMap<>();
+		for (CommandLineDiffTool tool : CommandLineDiffTool.values()) {
+			tools.put(tool.name(), new PreDefinedDiffTool(tool));
+		}
+		return tools;
+	}
+
+	private static Map<String, ExternalDiffTool> setupUserDefinedTools(
+			DiffToolConfig cfg, Map<String, ExternalDiffTool> predefTools) {
+		Map<String, ExternalDiffTool> tools = new TreeMap<>();
+		Map<String, ExternalDiffTool> userTools = cfg.getTools();
 		for (String name : userTools.keySet()) {
 			ExternalDiffTool userTool = userTools.get(name);
 			// if difftool.<name>.cmd is defined we have user defined tool
 			if (userTool.getCommand() != null) {
-				userDefinedTools.put(name, userTool);
+				tools.put(name, userTool);
 			} else if (userTool.getPath() != null) {
 				// if difftool.<name>.path is defined we just overload the path
 				// of predefined tool
-				PreDefinedDiffTool predefTool = (PreDefinedDiffTool) predefinedTools
+				PreDefinedDiffTool predefTool = (PreDefinedDiffTool) predefTools
 						.get(name);
 				if (predefTool != null) {
 					predefTool.setPath(userTool.getPath());
 				}
 			}
 		}
+		return tools;
 	}
 
 }
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/FileElement.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/FileElement.java
new file mode 100644
index 0000000..cdc8f01
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/FileElement.java
@@ -0,0 +1,160 @@
+/*
+ * Copyright (C) 2018-2021, Andre Bossert <andre.bossert@siemens.com>
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+package org.eclipse.jgit.internal.diffmergetool;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+
+import org.eclipse.jgit.diff.DiffEntry;
+import org.eclipse.jgit.lib.ObjectStream;
+
+/**
+ * The element used as left or right file for compare.
+ *
+ */
+public class FileElement {
+
+	private final String path;
+
+	private final String id;
+
+	private ObjectStream stream;
+
+	private File tempFile;
+
+	/**
+	 * @param path
+	 *            the file path
+	 * @param id
+	 *            the file id
+	 */
+	public FileElement(final String path, final String id) {
+		this(path, id, null);
+	}
+
+	/**
+	 * @param path
+	 *            the file path
+	 * @param id
+	 *            the file id
+	 * @param stream
+	 *            the object stream to load instead of file
+	 */
+	public FileElement(final String path, final String id,
+			ObjectStream stream) {
+		this.path = path;
+		this.id = id;
+		this.stream = stream;
+	}
+
+	/**
+	 * @return the file path
+	 */
+	public String getPath() {
+		return path;
+	}
+
+	/**
+	 * @return the file id
+	 */
+	public String getId() {
+		return id;
+	}
+
+	/**
+	 * @param stream
+	 *            the object stream
+	 */
+	public void setStream(ObjectStream stream) {
+		this.stream = stream;
+	}
+
+	/**
+	 * @param workingDir the working directory used if file cannot be found (e.g. /dev/null)
+	 * @return the object stream
+	 * @throws IOException
+	 */
+	public File getFile(File workingDir) throws IOException {
+		if (tempFile != null) {
+			return tempFile;
+		}
+		File file = new File(path);
+		String name = file.getName();
+		if (path.equals(DiffEntry.DEV_NULL)) {
+			file = new File(workingDir, "nul"); //$NON-NLS-1$
+		}
+		else if (stream != null) {
+			tempFile = File.createTempFile(".__", "__" + name); //$NON-NLS-1$ //$NON-NLS-2$
+			try (OutputStream outStream = new FileOutputStream(tempFile)) {
+				int read = 0;
+				byte[] bytes = new byte[8 * 1024];
+				while ((read = stream.read(bytes)) != -1) {
+					outStream.write(bytes, 0, read);
+				}
+			} finally {
+				// stream can only be consumed once --> close it
+				stream.close();
+				stream = null;
+			}
+			return tempFile;
+		}
+		return file;
+	}
+
+	/**
+	 * Returns a real file from work tree or a temporary file with content if
+	 * stream is valid or if path is "/dev/null"
+	 *
+	 * @return the object stream
+	 * @throws IOException
+	 */
+	public File getFile() throws IOException {
+		if (tempFile != null) {
+			return tempFile;
+		}
+		File file = new File(path);
+		String name = file.getName();
+		// if we have a stream or file is missing ("/dev/null") then create
+		// temporary file
+		if ((stream != null) || path.equals(DiffEntry.DEV_NULL)) {
+			// TODO: avoid long random file name (number generated by
+			// createTempFile)
+			tempFile = File.createTempFile(".__", "__" + name); //$NON-NLS-1$ //$NON-NLS-2$
+			if (stream != null) {
+				try (OutputStream outStream = new FileOutputStream(tempFile)) {
+					int read = 0;
+					byte[] bytes = new byte[8 * 1024];
+					while ((read = stream.read(bytes)) != -1) {
+						outStream.write(bytes, 0, read);
+					}
+				} finally {
+					// stream can only be consumed once --> close it
+					stream.close();
+					stream = null;
+				}
+			}
+			return tempFile;
+		}
+		return file;
+	}
+
+	/**
+	 * Deletes and invalidates temporary file if necessary.
+	 */
+	public void cleanTemporaries() {
+		if (tempFile != null && tempFile.exists())
+		tempFile.delete();
+		tempFile = null;
+	}
+
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/PreDefinedDiffTool.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/PreDefinedDiffTool.java
index 1c69fb4..092cb60 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/PreDefinedDiffTool.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/PreDefinedDiffTool.java
@@ -46,17 +46,6 @@ public PreDefinedDiffTool(CommandLineDiffTool tool) {
 	 */
 	@Override
 	public void setPath(String path) {
-		// handling of spaces in path
-		if (path.contains(" ")) { //$NON-NLS-1$
-			// add quotes before if needed
-			if (!path.startsWith("\"")) { //$NON-NLS-1$
-				path = "\"" + path; //$NON-NLS-1$
-			}
-			// add quotes after if needed
-			if (!path.endsWith("\"")) { //$NON-NLS-1$
-				path = path + "\""; //$NON-NLS-1$
-			}
-		}
 		super.setPath(path);
 	}
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/ToolException.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/ToolException.java
new file mode 100644
index 0000000..7862cf5
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/diffmergetool/ToolException.java
@@ -0,0 +1,120 @@
+/*
+ * Copyright (C) 2018-2021, Andre Bossert <andre.bossert@siemens.com>
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+package org.eclipse.jgit.internal.diffmergetool;
+
+import org.eclipse.jgit.util.FS.ExecutionResult;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Tool exception for differentiation.
+ *
+ */
+public class ToolException extends Exception {
+
+	private final static Logger LOG = LoggerFactory
+			.getLogger(ToolException.class);
+
+	private final ExecutionResult result;
+
+	/**
+	 * the serial version UID
+	 */
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 *
+	 */
+	public ToolException() {
+		super();
+		result = null;
+	}
+
+	/**
+	 * @param message
+	 *            the exception message
+	 */
+	public ToolException(String message) {
+		super(message);
+		result = null;
+	}
+
+	/**
+	 * @param message
+	 *            the exception message
+	 * @param result
+	 *            the execution result
+	 */
+	public ToolException(String message, ExecutionResult result) {
+		super(message);
+		this.result = result;
+	}
+
+	/**
+	 * @param message
+	 *            the exception message
+	 * @param cause
+	 *            the cause for throw
+	 */
+	public ToolException(String message, Throwable cause) {
+		super(message, cause);
+		result = null;
+	}
+
+	/**
+	 * @param cause
+	 *            the cause for throw
+	 */
+	public ToolException(Throwable cause) {
+		super(cause);
+		result = null;
+	}
+
+	/**
+	 * @return true if result is valid, false else
+	 */
+	public boolean isResult() {
+		return result != null;
+	}
+
+	/**
+	 * @return the execution result
+	 */
+	public ExecutionResult getResult() {
+		return result;
+	}
+
+	/**
+	 * @return the result Stderr
+	 */
+	public String getResultStderr() {
+		try {
+			return new String(result.getStderr().toByteArray());
+		} catch (Exception e) {
+			LOG.warn(e.getMessage());
+		}
+		return ""; //$NON-NLS-1$
+	}
+
+	/**
+	 * @return the result Stdout
+	 */
+	public String getResultStdout() {
+		try {
+			return new String(result.getStdout().toByteArray());
+		} catch (Exception e) {
+			LOG.warn(e.getMessage());
+		}
+		return ""; //$NON-NLS-1$
+	}
+
+}