Add cli_flag_prefix_char config option.

docs/index.md

@@ -1207,6 +1207,31 @@ sub_model options:
 """
 ```
 
+#### Change the CLI Flag Prefix Character
+
+Change The CLI flag prefix character used in CLI optional arguments by settings `cli_flag_prefix_char`.
+
+```py
+import sys
+
+from pydantic import AliasChoices, Field
+
+from pydantic_settings import BaseSettings
+
+
+class Settings(BaseSettings, cli_parse_args=True, cli_flag_prefix_char='+'):
+    my_arg: str = Field(validation_alias=AliasChoices('m', 'my-arg'))
+
+
+sys.argv = ['example.py', '++my-arg', 'hi']
+print(Settings().model_dump())
+#> {'my_arg': 'hi'}
+
+sys.argv = ['example.py', '+m', 'hi']
+print(Settings().model_dump())
+#> {'my_arg': 'hi'}
+```
+
 ### Integrating with Existing Parsers
 
 A CLI settings source can be integrated with existing parsers by overriding the default CLI settings source with a user

pydantic_settings/main.py

@@ -41,6 +41,7 @@ class SettingsConfigDict(ConfigDict, total=False):
     cli_use_class_docs_for_groups: bool
     cli_exit_on_error: bool
     cli_prefix: str
+    cli_flag_prefix_char: str
     cli_implicit_flags: bool | None
     cli_ignore_unknown_args: bool | None
     secrets_dir: PathType | None
@@ -119,6 +120,7 @@ class BaseSettings(BaseModel):
         _cli_exit_on_error: Determines whether or not the internal parser exits with error info when an error occurs.
             Defaults to `True`.
         _cli_prefix: The root parser command line arguments prefix. Defaults to "".
+        _cli_flag_prefix_char: The flag prefix character to use for CLI optional arguments. Defaults to '-'.
         _cli_implicit_flags: Whether `bool` fields should be implicitly converted into CLI boolean flags.
             (e.g. --flag, --no-flag). Defaults to `False`.
         _cli_ignore_unknown_args: Whether to ignore unknown CLI args and parse only known ones. Defaults to `False`.
@@ -146,6 +148,7 @@ def __init__(
         _cli_use_class_docs_for_groups: bool | None = None,
         _cli_exit_on_error: bool | None = None,
         _cli_prefix: str | None = None,
+        _cli_flag_prefix_char: str | None = None,
         _cli_implicit_flags: bool | None = None,
         _cli_ignore_unknown_args: bool | None = None,
         _secrets_dir: PathType | None = None,
@@ -174,6 +177,7 @@ def __init__(
                 _cli_use_class_docs_for_groups=_cli_use_class_docs_for_groups,
                 _cli_exit_on_error=_cli_exit_on_error,
                 _cli_prefix=_cli_prefix,
+                _cli_flag_prefix_char=_cli_flag_prefix_char,
                 _cli_implicit_flags=_cli_implicit_flags,
                 _cli_ignore_unknown_args=_cli_ignore_unknown_args,
                 _secrets_dir=_secrets_dir,
@@ -226,6 +230,7 @@ def _settings_build_values(
         _cli_use_class_docs_for_groups: bool | None = None,
         _cli_exit_on_error: bool | None = None,
         _cli_prefix: str | None = None,
+        _cli_flag_prefix_char: str | None = None,
         _cli_implicit_flags: bool | None = None,
         _cli_ignore_unknown_args: bool | None = None,
         _secrets_dir: PathType | None = None,
@@ -282,6 +287,11 @@ def _settings_build_values(
             _cli_exit_on_error if _cli_exit_on_error is not None else self.model_config.get('cli_exit_on_error')
         )
         cli_prefix = _cli_prefix if _cli_prefix is not None else self.model_config.get('cli_prefix')
+        cli_flag_prefix_char = (
+            _cli_flag_prefix_char
+            if _cli_flag_prefix_char is not None
+            else self.model_config.get('cli_flag_prefix_char')
+        )
         cli_implicit_flags = (
             _cli_implicit_flags if _cli_implicit_flags is not None else self.model_config.get('cli_implicit_flags')
         )
@@ -348,6 +358,7 @@ def _settings_build_values(
                         cli_use_class_docs_for_groups=cli_use_class_docs_for_groups,
                         cli_exit_on_error=cli_exit_on_error,
                         cli_prefix=cli_prefix,
+                        cli_flag_prefix_char=cli_flag_prefix_char,
                         cli_implicit_flags=cli_implicit_flags,
                         cli_ignore_unknown_args=cli_ignore_unknown_args,
                         case_sensitive=case_sensitive,
@@ -398,6 +409,7 @@ def _settings_build_values(
         cli_use_class_docs_for_groups=False,
         cli_exit_on_error=True,
         cli_prefix='',
+        cli_flag_prefix_char='-',
         cli_implicit_flags=False,
         cli_ignore_unknown_args=False,
         json_file=None,

pydantic_settings/sources.py

@@ -1026,6 +1026,7 @@ class CliSettingsSource(EnvSettingsSource, Generic[T]):
         cli_exit_on_error: Determines whether or not the internal parser exits with error info when an error occurs.
             Defaults to `True`.
         cli_prefix: Prefix for command line arguments added under the root parser. Defaults to "".
+        cli_flag_prefix_char: The flag prefix character to use for CLI optional arguments. Defaults to '-'.
         cli_implicit_flags: Whether `bool` fields should be implicitly converted into CLI boolean flags.
             (e.g. --flag, --no-flag). Defaults to `False`.
         cli_ignore_unknown_args: Whether to ignore unknown CLI args and parse only known ones. Defaults to `False`.
@@ -1056,6 +1057,7 @@ def __init__(
         cli_use_class_docs_for_groups: bool | None = None,
         cli_exit_on_error: bool | None = None,
         cli_prefix: str | None = None,
+        cli_flag_prefix_char: str | None = None,
         cli_implicit_flags: bool | None = None,
         cli_ignore_unknown_args: bool | None = None,
         case_sensitive: bool | None = True,
@@ -1097,6 +1099,12 @@ def __init__(
             else settings_cls.model_config.get('cli_exit_on_error', True)
         )
         self.cli_prefix = cli_prefix if cli_prefix is not None else settings_cls.model_config.get('cli_prefix', '')
+        self.cli_flag_prefix_char = (
+            cli_flag_prefix_char
+            if cli_flag_prefix_char is not None
+            else settings_cls.model_config.get('cli_flag_prefix_char', '-')
+        )
+        self._cli_flag_prefix = self.cli_flag_prefix_char * 2
         if self.cli_prefix:
             if cli_prefix.startswith('.') or cli_prefix.endswith('.') or not cli_prefix.replace('.', '').isidentifier():  # type: ignore
                 raise SettingsError(f'CLI settings source prefix is invalid: {cli_prefix}')
@@ -1131,6 +1139,7 @@ def __init__(
                 prog=self.cli_prog_name,
                 description=None if settings_cls.__doc__ is None else dedent(settings_cls.__doc__),
                 formatter_class=formatter_class,
+                prefix_chars=self.cli_flag_prefix_char,
             )
             if root_parser is None
             else root_parser
@@ -1503,7 +1512,8 @@ def parse_args_insensitive_method(
             ) -> Any:
                 insensitive_args = []
                 for arg in shlex.split(shlex.join(args)) if args else []:
-                    matched = re.match(r'^(--[^\s=]+)(.*)', arg)
+                    flag_prefix = rf'\{self.cli_flag_prefix_char}{{1,2}}'
+                    matched = re.match(rf'^({flag_prefix}[^\s=]+)(.*)', arg)
                     if matched:
                         arg = matched.group(1).lower() + matched.group(2)
                     insensitive_args.append(arg)
@@ -1621,7 +1631,7 @@ def _add_parser_args(
                         model_default=PydanticUndefined,
                     )
             else:
-                arg_flag: str = '--'
+                flag_prefix: str = self._cli_flag_prefix
                 is_append_action = _annotation_contains_types(
                     field_info.annotation, (list, set, dict, Sequence, Mapping), is_strip_annotated=True
                 )
@@ -1655,7 +1665,7 @@ def _add_parser_args(
                     arg_names = [kwargs['dest']]
                     del kwargs['dest']
                     del kwargs['required']
-                    arg_flag = ''
+                    flag_prefix = ''
 
                 self._convert_bool_flag(kwargs, field_info, model_default)
 
@@ -1666,7 +1676,7 @@ def _add_parser_args(
                         added_args,
                         arg_prefix,
                         subcommand_prefix,
-                        arg_flag,
+                        flag_prefix,
                         arg_names,
                         kwargs,
                         field_name,
@@ -1679,10 +1689,12 @@ def _add_parser_args(
                         if isinstance(group, dict):
                             group = self._add_argument_group(parser, **group)
                         added_args += list(arg_names)
-                        self._add_argument(group, *(f'{arg_flag[:len(name)]}{name}' for name in arg_names), **kwargs)
+                        self._add_argument(group, *(f'{flag_prefix[:len(name)]}{name}' for name in arg_names), **kwargs)
                     else:
                         added_args += list(arg_names)
-                        self._add_argument(parser, *(f'{arg_flag[:len(name)]}{name}' for name in arg_names), **kwargs)
+                        self._add_argument(
+                            parser, *(f'{flag_prefix[:len(name)]}{name}' for name in arg_names), **kwargs
+                        )
 
         self._add_parser_alias_paths(parser, alias_path_args, added_args, arg_prefix, subcommand_prefix, group)
         return parser
@@ -1723,7 +1735,7 @@ def _add_parser_submodels(
         added_args: list[str],
         arg_prefix: str,
         subcommand_prefix: str,
-        arg_flag: str,
+        flag_prefix: str,
         arg_names: list[str],
         kwargs: dict[str, Any],
         field_name: str,
@@ -1758,7 +1770,7 @@ def _add_parser_submodels(
             added_args.append(arg_names[0])
             kwargs['help'] = f'set {arg_names[0]} from JSON string'
             model_group = self._add_argument_group(parser, **model_group_kwargs)
-            self._add_argument(model_group, *(f'{arg_flag}{name}' for name in arg_names), **kwargs)
+            self._add_argument(model_group, *(f'{flag_prefix}{name}' for name in arg_names), **kwargs)
         for model in sub_models:
             self._add_parser_args(
                 parser=parser,
@@ -1804,7 +1816,7 @@ def _add_parser_alias_paths(
                     kwargs['metavar'] = 'list'
                 if arg_name not in added_args:
                     added_args.append(arg_name)
-                    self._add_argument(context, f'--{arg_name}', **kwargs)
+                    self._add_argument(context, f'{self._cli_flag_prefix}{arg_name}', **kwargs)
 
     def _get_modified_args(self, obj: Any) -> tuple[str, ...]:
         if not self.cli_hide_none_type:

tests/test_settings.py

@@ -2694,18 +2694,39 @@ class BadCliPositionalArg(BaseSettings):
 
 def test_cli_case_insensitive_arg():
     class Cfg(BaseSettings, cli_exit_on_error=False):
-        Foo: str
-        Bar: str
+        foo: str = Field(validation_alias=AliasChoices('F', 'Foo'))
+        bar: str = Field(validation_alias=AliasChoices('B', 'Bar'))
 
-    cfg = Cfg(_cli_parse_args=['--FOO=--VAL', '--BAR', '"--VAL"'])
-    assert cfg.model_dump() == {'Foo': '--VAL', 'Bar': '"--VAL"'}
+    cfg = Cfg(
+        _cli_parse_args=[
+            '--FOO=--VAL',
+            '--BAR',
+            '"--VAL"',
+        ]
+    )
+    assert cfg.model_dump() == {'foo': '--VAL', 'bar': '"--VAL"'}
+
+    cfg = Cfg(
+        _cli_parse_args=[
+            '-f=-V',
+            '-b',
+            '"-V"',
+        ]
+    )
+    assert cfg.model_dump() == {'foo': '-V', 'bar': '"-V"'}
 
     cfg = Cfg(_cli_parse_args=['--Foo=--VAL', '--Bar', '"--VAL"'], _case_sensitive=True)
-    assert cfg.model_dump() == {'Foo': '--VAL', 'Bar': '"--VAL"'}
+    assert cfg.model_dump() == {'foo': '--VAL', 'bar': '"--VAL"'}
+
+    cfg = Cfg(_cli_parse_args=['-F=-V', '-B', '"-V"'], _case_sensitive=True)
+    assert cfg.model_dump() == {'foo': '-V', 'bar': '"-V"'}
 
     with pytest.raises(SettingsError, match='error parsing CLI: unrecognized arguments: --FOO=--VAL --BAR "--VAL"'):
         Cfg(_cli_parse_args=['--FOO=--VAL', '--BAR', '"--VAL"'], _case_sensitive=True)
 
+    with pytest.raises(SettingsError, match='error parsing CLI: unrecognized arguments: -f=-V -b "-V"'):
+        Cfg(_cli_parse_args=['-f=-V', '-b', '"-V"'], _case_sensitive=True)
+
     with pytest.raises(SettingsError, match='Case-insensitive matching is only supported on the internal root parser'):
         CliSettingsSource(Cfg, root_parser=CliDummyParser(), case_sensitive=False)
 
@@ -3993,6 +4014,17 @@ class Cfg(BaseSettings, cli_ignore_unknown_args=True):
     assert cfg.model_dump() == {'this': 'goodbye', 'that': 789}
 
 
+def test_cli_flag_prefix_char():
+    class Cfg(BaseSettings, cli_flag_prefix_char='+'):
+        my_var: str = Field(validation_alias=AliasChoices('m', 'my-var'))
+
+    cfg = Cfg(_cli_parse_args=['++my-var=hello'])
+    assert cfg.model_dump() == {'my_var': 'hello'}
+
+    cfg = Cfg(_cli_parse_args=['+m=hello'])
+    assert cfg.model_dump() == {'my_var': 'hello'}
+
+
 @pytest.mark.parametrize('parser_type', [pytest.Parser, argparse.ArgumentParser, CliDummyParser])
 @pytest.mark.parametrize('prefix', ['', 'cfg'])
 def test_cli_user_settings_source(parser_type, prefix):