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Substitute ${name:-default} when the variable is set but empty (POSIX) #684

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Substitute ${name:-default} when the variable is set but empty (POSIX) #684

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6 changes: 4 additions & 2 deletions src/dotenv/variables.py
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Original file line number Diff line number Diff line change
Expand Up @@ -62,8 +62,10 @@ def __hash__(self) -> int:
return hash((self.__class__, self.name, self.default))

def resolve(self, env: Mapping[str, Optional[str]]) -> str:
default = self.default if self.default is not None else ""
result = env.get(self.name, default)
result = env.get(self.name)
if not result and self.default is not None:
# POSIX ${name:-default} substitutes when name is unset OR null.
return self.default
return result if result is not None else ""


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5 changes: 5 additions & 0 deletions tests/test_main.py
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Expand Up @@ -702,6 +702,11 @@ def test_dotenv_values_file(dotenv_path):
# Undefined
({}, "a=${b}", True, {"a": ""}),
({}, "a=${b:-d}", True, {"a": "d"}),
# Defined but empty: POSIX ${name:-default} substitutes on null too
({"b": ""}, "a=${b:-d}", True, {"a": "d"}),
({}, "b=\na=${b:-d}", True, {"a": "d", "b": ""}),
({"b": ""}, "a=${b}", True, {"a": ""}),
({"b": ""}, "a=${b:-}", True, {"a": ""}),
# With quotes
({"b": "c"}, 'a="${b}"', True, {"a": "c"}),
({"b": "c"}, "a='${b}'", True, {"a": "c"}),
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