Add command-line option handling and usage message in main function

krash_main.cpp

@@ -61,6 +61,7 @@ int main(int argc, char** argv) {
     vector<string> testnames;
 
     int c;
+    bool no_opt = true;
     while ((c = getopt(argc, argv, "hf:rdt:x")) != -1) {
         switch (c) {
             case 'h':
@@ -88,8 +89,19 @@ int main(int argc, char** argv) {
                 cout << "Invalid option. Use -h for help.\n";
                 return 1;
         }
+        no_opt = false;
     }
 
+    if (no_opt == true) {
+        cout << "Usage: " << argv[0] << " -f <filename> [-r <truncate>] [-t <testnames>] [-h]\n";
+
+        cout << "\tOptions:\n";
+        cout << "\t\t-f => Specify .datalog file name\n";
+        cout << "\t\t-t => Specify tests to be extracted seprated by space\n";
+        cout << "\t\t-r => Truncate or replace generated files (default is append)\n";
+        cout << "\t\t-x => Exract all tests, overrides tests specified in -t\n\n";
+        return 1;
+    }
     if (filename == "") {
         return 0;
     }