Added usage message.

build.gradle

@@ -3,7 +3,7 @@ apply plugin: "application"
 apply plugin: "maven"
 
 group = "com.jdblabs"
-version = "1.2"
+version = "1.3"
 mainClassName = "com.jdblabs.file.treediff.TreeDiff"
 
 repositories {

src/main/groovy/com/jdblabs/file/treediff/TreeDiff.groovy

@@ -8,7 +8,7 @@ import org.apache.commons.codec.digest.DigestUtils
 
 public class TreeDiff {
 
-    public static final String VERSION = "1.2"
+    public static final String VERSION = "1.3"
 
     private ObjectMapper objectMapper = new ObjectMapper()
     private PrintStream stdout
@@ -54,7 +54,7 @@ public class TreeDiff {
 
         def opts = LightOptionParser.parseOptions(cliDef, args)
 
-        if (opts.h) { /* TODO */ return }
+        if (opts.h) { println this.usage; return }
 
         if (opts.V) {
             stdout.println "JDB Labs TreeDiff v${VERSION}"
@@ -280,4 +280,103 @@ public class TreeDiff {
 
     private void verboseErr(String msg) { if (verbose) stderr.println msg }
 
+    public String getUsage() {
+        return """\
+JDB Labs TreeDiff v${VERSION}
+
+Gather and display information about the differences between two file trees,
+including files found in only one side and not the other, files that match on
+both sides, files which share the same contents but reside in differing paths
+on each side, and files that reside at the same location on both sides but
+whose contents differ.
+
+usage: treediff [options] <left-direction> <right-directory>
+
+where options are:
+
+    -h, --help      Output this usage information.
+    -v, --verbose   Enable verbose output.
+    -V, --version   Output the version information for the utility.
+    -g, --gui       Launch the graphical interface (not yet implemented).
+
+    -s, --same
+    
+        Output information about files that are the same on both sides.
+
+    -S, --exclude-same
+    
+        Do not output information about files that are the same on both sides.
+
+    -c, --content-mismatch
+    
+        Output information about files that have the same relative path on both
+        side but whose contents differ.
+
+    -c, --exclude-content-mismatch
+
+        Do not output information about files that have the same relative path
+        on both side but whose contents differ.
+
+    -p, --path-mismatch
+
+        Output information about files that have the same content but reside at
+        different relative paths on each side.
+
+    -P, --exclude-path-mismatch
+
+        Do not output information about files that have the same content but
+        reside at different relative paths on each side.
+
+    -l, --left-only
+
+        Output information about files found on only the left side (missing
+        from the right entirely).
+
+    -L, --exclude-left-only
+
+        Do not output information about files found on the left side only
+        (missing from the right entirely).
+
+    -r, --right-only
+
+        Output information about files found on only the right side (missing
+        from the left entirely).
+
+    -R, --exclude-right-only
+
+        Do not output information about files found on the right side only
+        (missing from the left entirely).
+
+    -q, --quiet
+
+        Suppress all output and error messages except for the progress
+        indicator.
+
+    -Q, --very-quiet
+
+        Suppress all output and error messages including the progress
+        indicator.
+
+    -rd, --direction <directory-path>
+
+        Use <directory-path> as the root for all relative file paths (input
+        directories to scan for example).
+
+    -i, --analysis-in   <left-dir-analysis> <right-dir-analysis>
+    
+        Use pre-calculated directory analysis in place of reading local
+        directories. This is useful if you wish to do diffs between two
+        directory trees that are not on the same filesystem, or if you wish to
+        display different output about a diff without re-scanning the
+        filesystem.
+
+    -o, --analysis-out  <file-name-root>
+
+        In addition to the requested output on STDOUT, write the analysis for
+        each of the scanned directories to files named <file-name-root>.left
+        and <file-name-root>.right. These analysis files are formatted so that
+        they can be used as inputs to the --analysis-in option.
+
+""";
+    }
 }