fix: interpolate output_file attribute from YAML

Co-Authored-By: Joe Moura <joao@crewai.com>

src/crewai/task.py

@@ -213,8 +213,14 @@ class Task(BaseModel):
 
     @field_validator("output_file")
     @classmethod
-    def output_file_validation(cls, value: str) -> str:
-        """Validate the output file path by removing the / from the beginning of the path."""
+    def output_file_validation(cls, value: Optional[str]) -> Optional[str]:
+        """Validate the output file path."""
+        if value is None:
+            return None
+        # Don't strip leading slash if it's a template path with variables
+        if "{" in value or "}" in value:
+            return value
+        # Strip leading slash for regular paths
         if value.startswith("/"):
             return value[1:]
         return value
@@ -394,17 +400,23 @@ class Task(BaseModel):
         return "\n".join(tasks_slices)
 
     def interpolate_inputs(self, inputs: Dict[str, Any]) -> None:
-        """Interpolate inputs into the task description and expected output."""
+        """Interpolate inputs into the task description, expected output, and output file path."""
         if self._original_description is None:
             self._original_description = self.description
         if self._original_expected_output is None:
             self._original_expected_output = self.expected_output
+        if self.output_file is not None and not hasattr(self, "_original_output_file"):
+            self._original_output_file = self.output_file
 
         if inputs:
             self.description = self._original_description.format(**inputs)
             self.expected_output = self.interpolate_only(
                 input_string=self._original_expected_output, inputs=inputs
             )
+            if self.output_file is not None:
+                self.output_file = self.interpolate_only(
+                    input_string=self._original_output_file, inputs=inputs
+                )
 
     def interpolate_only(self, input_string: str, inputs: Dict[str, Any]) -> str:
         """Interpolate placeholders (e.g., {key}) in a string while leaving JSON untouched."""

tests/task_test.py

@@ -719,21 +719,24 @@ def test_interpolate_inputs():
     task = Task(
         description="Give me a list of 5 interesting ideas about {topic} to explore for an article, what makes them unique and interesting.",
         expected_output="Bullet point list of 5 interesting ideas about {topic}.",
+        output_file="/tmp/{topic}/output_{date}.txt"
     )
 
-    task.interpolate_inputs(inputs={"topic": "AI"})
+    task.interpolate_inputs(inputs={"topic": "AI", "date": "2024"})
     assert (
         task.description
         == "Give me a list of 5 interesting ideas about AI to explore for an article, what makes them unique and interesting."
     )
     assert task.expected_output == "Bullet point list of 5 interesting ideas about AI."
+    assert task.output_file == "/tmp/AI/output_2024.txt"
 
-    task.interpolate_inputs(inputs={"topic": "ML"})
+    task.interpolate_inputs(inputs={"topic": "ML", "date": "2025"})
     assert (
         task.description
         == "Give me a list of 5 interesting ideas about ML to explore for an article, what makes them unique and interesting."
     )
     assert task.expected_output == "Bullet point list of 5 interesting ideas about ML."
+    assert task.output_file == "/tmp/ML/output_2025.txt"
 
 
 def test_interpolate_only():