added unique and first modifiers to lookup subcommand

filetags.py

@@ -389,7 +389,17 @@ if __name__ == "__main__":
       for file_hash in common_file_hashes:
         lookup_results[file_hash] = get_tags_by_hash(storage_directory, file_hash)
 
-    print(json.dumps(lookup_results))
+    if 'unique' in command:
+      if(len(lookup_results)==1):
+        print(json.dumps(lookup_results))
+      else:
+        print("More than one matching file found.", file=sys.stderr)
+        sys.exit(GENERAL_ERROR)
+    elif 'first' in command:
+      file_hash, tags = list(lookup_results.items())[0]
+      print(json.dumps({file_hash : tags}))
+    else:
+      print(json.dumps(lookup_results))