print help if you don't give a namespace

tools/Tool.cpp

@@ -34,6 +34,11 @@ mongo::Tool::~Tool(){
 void mongo::Tool::printExtraHelp( ostream & out ){
 }
 
+void mongo::Tool::printHelp(ostream &out) {
+    _options->print(out);
+    printExtraHelp(out);
+}
+
 int mongo::Tool::main( int argc , char ** argv ){
     boost::filesystem::path::default_name_check( boost::filesystem::no_check );
 
@@ -44,8 +49,7 @@ int mongo::Tool::main( int argc , char ** argv ){
     po::notify( _params );
 
     if ( _params.count( "help" ) ){
-        _options->print( cerr );
-        printExtraHelp( cerr );
+        printHelp(cerr);
         return 0;
     }
 

tools/Tool.h

@@ -50,6 +50,8 @@ namespace mongo {
 
         virtual int run() = 0;
 
+        virtual void printHelp(ostream &out);
+
         virtual void printExtraHelp( ostream & out );
 
     protected:

tools/export.cpp

@@ -44,7 +44,7 @@ public:
     }
 
     int run(){
-        const string ns = getNS();
+        string ns;
         const bool csv = hasParam( "csv" );
         ostream *outPtr = &cout;
         string outfile = getParam( "out" );
@@ -57,6 +57,13 @@ public:
 
         vector<string> fields;
 
+        try {
+            ns = getNS();
+        } catch (...) {
+            printHelp(cerr);
+            return 1;
+        }
+
         if ( hasParam( "fields" ) ){
 
             BSONObjBuilder b;