Don't rewrite the .env file when unset_key finds no such key

CHANGELOG.md

@@ -14,6 +14,7 @@ project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 - `set_key` and `unset_key` no longer leave a `.tmp_*` file behind on Windows when writing a read-only `.env` fails, and the error raised is the one from the failed write rather than from cleaning up the temporary file by [@MohammedAlkindi] in [#686]
 - `load_dotenv`, `dotenv_values`, `get_key`, `set_key`, `unset_key` and the CLI `--file` option now expand a leading `~` to the user's home directory by [@veeceey] in [#615]
 - `find_dotenv` and the IPython `%dotenv` magic now expand a leading `~` in the file name by [@theskumar] in [#714]
+- `unset_key` and `dotenv unset` no longer rewrite the `.env` file when the key isn't in it, so a symlinked `.env` stays a symlink and its line endings and permissions are left alone by [@PDGGK] in [#734]
 
 ## [1.2.4] - 2026-10-01
 
@@ -467,6 +468,7 @@ os.PathLike]` instead of just `os.PathLike` (#347 by [@bbc2]).
 [#700]: https://github.com/theskumar/python-dotenv/pull/700
 [#711]: https://github.com/theskumar/python-dotenv/pull/711
 [#714]: https://github.com/theskumar/python-dotenv/pull/714
+[#734]: https://github.com/theskumar/python-dotenv/pull/734
 [790c5c0]: https://github.com/theskumar/python-dotenv/commit/790c5c02991100aa1bf41ee5330aca75edc51311
 
 <!-- contributors -->
@@ -477,6 +479,7 @@ os.PathLike]` instead of just `os.PathLike` (#347 by [@bbc2]).
 [@MohammedAlkindi]: https://github.com/MohammedAlkindi
 [@Nicals]: https://github.com/Nicals
 [@Nougat-Waffle]: https://github.com/Nougat-Waffle
+[@PDGGK]: https://github.com/PDGGK
 [@Qwerty-133]: https://github.com/Qwerty-133
 [@ReinerBRO]: https://github.com/ReinerBRO
 [@ROTl24]: https://github.com/ROTl24

src/dotenv/main.py

@@ -285,6 +285,10 @@ def set_key(
     return True, key_to_set, value_to_set
 
 
+class _KeyNotFound(Exception):
+    pass
+
+
 def unset_key(
     dotenv_path: StrPath,
     key_to_unset: str,
@@ -311,17 +315,21 @@ def unset_key(
         return None, key_to_unset
 
     removed = False
-    with rewrite(dotenv_path, encoding=encoding, follow_symlinks=follow_symlinks) as (
-        source,
-        dest,
-    ):
-        for mapping in with_warn_for_invalid_lines(parse_stream(source)):
-            if mapping.key == key_to_unset:
-                removed = True
-            else:
-                dest.write(mapping.original.string)
-
-    if not removed:
+    try:
+        with rewrite(
+            dotenv_path, encoding=encoding, follow_symlinks=follow_symlinks
+        ) as (source, dest):
+            for mapping in with_warn_for_invalid_lines(parse_stream(source)):
+                if mapping.key == key_to_unset:
+                    removed = True
+                else:
+                    dest.write(mapping.original.string)
+            if not removed:
+                # Abandon the rewrite: there is nothing to change, and replacing
+                # the file anyway would, for instance, turn a symlink into a
+                # regular file.
+                raise _KeyNotFound()
+    except _KeyNotFound:
         logger.warning(
             "Key %s not removed from %s - key doesn't exist.", key_to_unset, dotenv_path
         )

tests/test_main.py

@@ -512,6 +512,41 @@ def test_unset_key_symlink_to_existing_file(tmp_path):
     assert symlink.read_text() == ""
 
 
+def test_unset_non_existent_value_leaves_file_untouched(dotenv_path):
+    dotenv_path.write_bytes(b"a=b\r\nc=d\r\n")
+    inode_before = dotenv_path.stat().st_ino
+    logger = logging.getLogger("dotenv.main")
+
+    with mock.patch.object(logger, "warning") as mock_warning:
+        result = dotenv.unset_key(dotenv_path, "x")
+
+    assert result == (None, "x")
+    assert dotenv_path.read_bytes() == b"a=b\r\nc=d\r\n"
+    assert dotenv_path.stat().st_ino == inode_before
+    assert list(dotenv_path.parent.iterdir()) == [dotenv_path]
+    mock_warning.assert_called_once_with(
+        "Key %s not removed from %s - key doesn't exist.", "x", dotenv_path
+    )
+
+
+@pytest.mark.skipif(
+    sys.platform == "win32", reason="symlinks require elevated privileges on Windows"
+)
+def test_unset_key_symlink_non_existent_value(tmp_path):
+    target = tmp_path / "target.env"
+    target.write_text("a=x\n")
+    symlink = tmp_path / ".env"
+    symlink.symlink_to(target)
+    logger = logging.getLogger("dotenv.main")
+
+    with mock.patch.object(logger, "warning"):
+        result = dotenv.unset_key(symlink, "b")
+
+    assert result == (None, "b")
+    assert symlink.is_symlink()
+    assert target.read_text() == "a=x\n"
+
+
 @pytest.mark.skipif(
     sys.platform == "win32", reason="symlinks require elevated privileges on Windows"
 )