change grib source cli default

grib_processor/main.py

@@ -86,8 +86,10 @@ def setup() -> tuple[Iterable[GribPayload], Callable[[GribPayload], None]]:
     )
     parser.add_argument(
         "grib_src",
+        nargs="?",
+        default=None,
         metavar="grib_source",
-        help="Directory to watch for new grib files, file to read grib paths from, or '--' to read file paths from stdin.",
+        help="Where to get grib files from. Either stdin (default), a directory to watch, or a grib file itself.",
     )
     parser.add_argument(
         "-v",
@@ -161,7 +163,10 @@ def setup() -> tuple[Iterable[GribPayload], Callable[[GribPayload], None]]:
 
     # Get an iterator over grib files to process
     file_iter: Iterable[str]
-    if os.path.isdir(args.grib_src):
+    if args.grib_src is None:
+        LOG.info("Sourcing grib files from stdin, realtime=%s", args.realtime)
+        file_iter = map(str.strip, iter(sys.stdin.readline, ""))
+    elif os.path.isdir(args.grib_src):
         LOG.info(
             "Sourcing grib files from directory watch @ %s realtime=%s",
             args.grib_src,
@@ -177,11 +182,8 @@ def setup() -> tuple[Iterable[GribPayload], Callable[[GribPayload], None]]:
             args.grib_src, debounce=debounce, recursive=args.recursive
         )
     elif os.path.isfile(args.grib_src):
-        LOG.info("Sourcing grib file directly from CLI, %s", args.grib_src)
+        LOG.info("Grib source is a file, parsing directly, %s", args.grib_src)
         file_iter = (str(args.grib_src),)
-    elif args.grib_src == "--":
-        LOG.info("Sourcing grib files from stdin, realtime=%s", args.realtime)
-        file_iter = map(str.strip, iter(sys.stdin.readline, ""))
     else:
         parser.error("{0} is not a valid source!".format(args.grib_src))