Make the output command line argument optional for SURFEX binary tasks

Some applications do not need to produce (or store) output files after
running SURFEX but current implementation requires an output file
(a PGD, PREP or an OFFLINE restart file) to be always stored. This
commit relaxes that requirement.

pysurfex/cli.py

@@ -582,7 +582,7 @@ def run_surfex_binary(mode, **kwargs):
         else:
             raise FileNotFoundError("File not found: " + archive)
 
-    if not os.path.exists(output) or force:
+    if not (output is not None and os.path.exists(output)) or force:
         if os.path.isfile(namelist_path):
             with open(namelist_path, mode="r", encoding="utf-8") as file_handler:
                 nam_defs = yaml.safe_load(file_handler)

pysurfex/cmd_parsing.py

@@ -947,7 +947,7 @@ def parse_args_surfex_binary(argv, mode):
     parser.add_argument(
         "--domain", type=str, required=False, help="JSON file with domain"
     )
-    parser.add_argument("--output", "-o", type=str, required=True)
+    parser.add_argument("--output", "-o", type=str, required=False, default=None)
     parser.add_argument("--dtg", type=str, required=False, default=None)
     parser.add_argument("--basetime", type=str, required=False, default=None)
     if pert: