fix: accept a FIFO .env file in dotenv run

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]
+- `dotenv run` now accepts a `.env` file that is a FIFO (named pipe), such as a 1Password-mounted `.env` or a `<(...)` process substitution, like `load_dotenv` and `dotenv list`/`get` already do, instead of failing with "does not exist" by [@sungbin1015] in [#723]
 
 ## [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
+[#723]: https://github.com/theskumar/python-dotenv/pull/723
 [790c5c0]: https://github.com/theskumar/python-dotenv/commit/790c5c02991100aa1bf41ee5330aca75edc51311
 
 <!-- contributors -->
@@ -520,6 +522,7 @@ os.PathLike]` instead of just `os.PathLike` (#347 by [@bbc2]).
 [@ShamikOfficial]: https://github.com/ShamikOfficial
 [@sidharth-sudhir]: https://github.com/sidharth-sudhir
 [@snobu]: https://github.com/snobu
+[@sungbin1015]: https://github.com/sungbin1015
 [@techalchemy]: https://github.com/techalchemy
 [@theGOTOguy]: https://github.com/theGOTOguy
 [@theskumar]: https://github.com/theskumar

src/dotenv/cli.py

@@ -17,7 +17,7 @@
     )
     sys.exit(1)
 
-from .main import DotEnv, dotenv_values, set_key, unset_key
+from .main import DotEnv, _is_file_or_fifo, dotenv_values, set_key, unset_key
 from .version import __version__
 
 
@@ -193,7 +193,7 @@ def unset(ctx: click.Context, key: Any) -> None:
 def run(ctx: click.Context, override: bool, commandline: tuple[str, ...]) -> None:
     """Run command with environment variables present."""
     file = ctx.obj["FILE"]
-    if not os.path.isfile(file):
+    if not _is_file_or_fifo(file):
         raise click.BadParameter(
             f"Invalid value for '-f' \"{file}\" does not exist.", ctx=ctx
         )

tests/test_fifo_dotenv.py

@@ -6,6 +6,7 @@
 import pytest
 
 from dotenv import load_dotenv
+from tests.test_lib import check_process, run_dotenv
 
 pytestmark = pytest.mark.skipif(sys.platform == "win32", reason="FIFOs are Unix-only")
 
@@ -29,3 +30,22 @@ def writer():
 
     assert ok is True
     assert os.getenv("MY_PASSWORD") == "pipe-secret"
+
+
+def test_cli_run_from_fifo(tmp_path: pathlib.Path):
+    fifo = tmp_path / ".env"
+    os.mkfifo(fifo)
+
+    def writer():
+        with open(fifo, "w", encoding="utf-8") as w:
+            w.write("MY_PASSWORD=pipe-secret\n")
+
+    # A daemon thread, so that a reader which never opens the FIFO can't hang
+    # the test session.
+    t = threading.Thread(target=writer, daemon=True)
+    t.start()
+
+    result = run_dotenv(["run", "printenv", "MY_PASSWORD"], cwd=tmp_path)
+    t.join(timeout=2)
+
+    check_process(result, exit_code=0, stdout="pipe-secret\n")