make flag printing optional

chio.py

@@ -479,6 +479,7 @@ def add_argument(parser, arg, **kwargs):
     add_argument(_parser, "--challenge_depth", type=int, default=1, nargs='?', help="the complexity (in terms of nested expressions) of the arithmetic problems")
     add_argument(_parser, "--password", type=str, nargs='?', help="the challenge will check for a hardcoded password over stdin")
     add_argument(_parser, "--num_signals", type=int, nargs='?', help="the challenge will require the parent to send number of signals")
+    add_argument(_parser, "--reward", type=str, nargs='?', help="the challenge will output a reward file (e.g., /flag) if all the tests pass")
 
     # remaining arguments
     _parser.add_argument("old_args", nargs=argparse.REMAINDER)
@@ -520,6 +521,8 @@ def add_argument(parser, arg, **kwargs):
         print(f"[FAIL]    {_e}")
         sys.exit(2)
 
-    print("[GOOD] Success! You have satisfied all execution requirements. Here is your flag:")
-    print(open("/flag").read())
+    print("[GOOD] Success! You have satisfied all execution requirements.")
+    if _args.reward:
+        print("Here is your flag:")
+        print(open(_args.reward).read()) #pylint:disable=unspecified-encoding,consider-using-with
     sys.exit(0)