Update iCalendar generation tool: add output suffix option

docs/examples.md

@@ -599,7 +599,7 @@ the [icalendar](https://github.com/collective/icalendar) package.
 For user convenience, the library includes `holidays-ics` tool for generating iCalendar (.ics)
 files from holiday calendars provided by the library. It supports country, subdivision,
 and financial market calendars, holiday category filtering, localized holiday names,
-year selection, and custom output file names.
+year selection, custom output file names, and suffixes for generated output file names.
 
 The tool can be run either as an installed command:
 
@@ -661,6 +661,12 @@ Generate a holiday calendar for multiple years and save it to a custom file:
 holidays-ics US --years 2025-2027 --output us_holidays.ics
 ```
 
+Append a custom suffix to the generated file name:
+
+```shell
+holidays-ics CH --subdiv ZH --years 2025 --output-suffix -personal.ics
+```
+
 Generate a calendar containing only bank holidays:
 
 ```shell

holidays/generate_ics.py

@@ -61,7 +61,13 @@ def __init__(self):
         parser.add_argument(
             "-l", "--language", help="Language code for holiday names (e.g., en_US, es)"
         )
-        parser.add_argument("-o", "--output", help="Output file path (e.g., holidays.ics)")
+
+        output_group = parser.add_mutually_exclusive_group()
+        output_group.add_argument("-o", "--output", help="Output file path (e.g., holidays.ics)")
+        output_group.add_argument(
+            "--output-suffix",
+            help="Suffix to append to the generated output filename base (e.g., -MYNOTE.ics)",
+        )
 
         list_group = parser.add_mutually_exclusive_group()
         list_group.add_argument(
@@ -73,7 +79,23 @@ def __init__(self):
         list_group.add_argument(
             "--list-languages", action="store_true", help="List supported languages"
         )
-        self.args = parser.parse_args()
+        self.args = parser.parse_args(self.normalize_output_suffix_args(sys.argv[1:]))
+
+    @staticmethod
+    def normalize_output_suffix_args(args: list[str]) -> list[str]:
+        """Allow suffix values that begin with '-' without requiring '=' syntax."""
+        normalized_args = list(args)
+        try:
+            option_index = normalized_args.index("--output-suffix")
+        except ValueError:
+            return normalized_args
+
+        value_index = option_index + 1
+        if value_index < len(normalized_args):
+            suffix = normalized_args[value_index]
+            if suffix.startswith("-") and not suffix.startswith("--"):
+                normalized_args[option_index : value_index + 1] = [f"--output-suffix={suffix}"]
+        return normalized_args
 
     @staticmethod
     def parse_years(years: str) -> tuple[int, int]:
@@ -196,7 +218,10 @@ def run(self) -> None:
         start_year, end_year = self.args.years
         years_part = f"{start_year}_{end_year}" if start_year != end_year else f"{start_year}"
         subdiv_part = f"_{self.args.subdiv.upper().replace(' ', '_')}" if self.args.subdiv else ""
-        output_path = self.args.output or f"{self.args.code}{subdiv_part}_{years_part}.ics"
+        output_suffix = self.args.output_suffix or ".ics"
+        output_path = (
+            self.args.output or f"{self.args.code}{subdiv_part}_{years_part}{output_suffix}"
+        )
 
         try:
             holiday_obj = self.entity_loader(

tests/test_generate_ics.py

@@ -127,6 +127,30 @@ def test_parse_categories(self):
             IcsGenerator.parse_categories("BANK,Public,optional"), ["bank", "public", "optional"]
         )
 
+    def test_normalize_output_suffix_args(self):
+        self.assertEqual(
+            IcsGenerator.normalize_output_suffix_args(["US", "--output-suffix", "-personal.ics"]),
+            ["US", "--output-suffix=-personal.ics"],
+        )
+        self.assertEqual(
+            IcsGenerator.normalize_output_suffix_args(["US", "--output-suffix", "personal.ics"]),
+            ["US", "--output-suffix", "personal.ics"],
+        )
+        self.assertEqual(
+            IcsGenerator.normalize_output_suffix_args(["US", "--output-suffix=-personal.ics"]),
+            ["US", "--output-suffix=-personal.ics"],
+        )
+        self.assertEqual(
+            IcsGenerator.normalize_output_suffix_args(
+                ["US", "--output-suffix", "--list-categories"]
+            ),
+            ["US", "--output-suffix", "--list-categories"],
+        )
+        self.assertEqual(
+            IcsGenerator.normalize_output_suffix_args(["US", "--output-suffix"]),
+            ["US", "--output-suffix"],
+        )
+
     def test_validate_country_code(self):
         with self.argv("US"):
             generator = IcsGenerator()
@@ -425,6 +449,36 @@ def test_filename_subdivision(self):
 
             self.assertTrue((temp_dir / "US_CA_2025.ics").exists())
 
+    def test_filename_output_suffix(self):
+        with self.temp_cwd() as temp_dir:
+            with self.argv(
+                "CH", "--subdiv", "ZH", "--years", "2020", "--output-suffix", "-MYNOTE.ics"
+            ):
+                IcsGenerator().run()
+
+            self.assertTrue((temp_dir / "CH_ZH_2020-MYNOTE.ics").exists())
+            self.assertFalse((temp_dir / "CH_ZH_2020.ics").exists())
+
+    def test_filename_output_suffix_does_not_append_extension(self):
+        with self.temp_cwd() as temp_dir:
+            with self.argv("US", "--years", "2025", "--output-suffix", "-personal"):
+                IcsGenerator().run()
+
+            self.assertTrue((temp_dir / "US_2025-personal").exists())
+            self.assertFalse((temp_dir / "US_2025-personal.ics").exists())
+
+    def test_filename_output_and_suffix_are_mutually_exclusive(self):
+        with (
+            self.argv("US", "--output", "calendar.ics", "--output-suffix", "-personal.ics"),
+            self.assertRaises(SystemExit),
+        ):
+            IcsGenerator()
+
+    def test_output_suffix_equals_form_is_unchanged(self):
+        args = IcsGenerator.normalize_output_suffix_args(["US", "--output-suffix=-personal.ics"])
+
+        self.assertEqual(args, ["US", "--output-suffix=-personal.ics"])
+
     def test_generate_calendar_error(self):
         with patch(
             "holidays.ical.ICalExporter.save_ics",