fix: ModelTrainer generates sm_train.sh with CRLF line endings on Windows causing tra (5904)

sagemaker-train/src/sagemaker/train/model_trainer.py

@@ -1061,7 +1061,7 @@ def _prepare_train_script(
             execute_driver=execute_driver,
         )
 
-        with open(os.path.join(tmp_dir.name, TRAIN_SCRIPT), "w") as f:
+        with open(os.path.join(tmp_dir.name, TRAIN_SCRIPT), "w", newline="\n") as f:
             f.write(train_script)
 
     @classmethod

sagemaker-train/tests/unit/train/test_model_trainer.py

@@ -1287,6 +1287,49 @@ def mock_upload_data(path, bucket, key_prefix):
     assert kwargs["tensor_board_output_config"].local_path == "/opt/ml/output/tensorboard"
 
 
+@patch("sagemaker.train.model_trainer.TrainingJob")
+@patch("sagemaker.train.model_trainer.TemporaryDirectory")
+def test_prepare_train_script_uses_lf_line_endings(
+    mock_tmp_dir, mock_training_job, modules_session
+):
+    """Test that _prepare_train_script generates sm_train.sh with LF line endings only."""
+    modules_session.upload_data.return_value = (
+        f"s3://{DEFAULT_BUCKET}/{DEFAULT_BASE_NAME}-job/input/test"
+    )
+
+    tmp_dir = tempfile.TemporaryDirectory()
+    tmp_dir._cleanup = False
+    tmp_dir.cleanup = lambda: None
+    mock_tmp_dir.return_value = tmp_dir
+
+    try:
+        model_trainer = ModelTrainer(
+            sagemaker_session=modules_session,
+            training_image=DEFAULT_IMAGE,
+            source_code=DEFAULT_SOURCE_CODE,
+            role=DEFAULT_ROLE,
+        )
+
+        model_trainer.train()
+
+        train_script_path = os.path.join(tmp_dir.name, TRAIN_SCRIPT)
+        assert os.path.exists(train_script_path)
+
+        with open(train_script_path, "rb") as f:
+            content = f.read()
+
+        # Verify no CRLF line endings exist
+        assert b"\r\n" not in content, (
+            "sm_train.sh contains CRLF line endings; expected LF only"
+        )
+        # Verify LF line endings are present
+        assert b"\n" in content, (
+            "sm_train.sh does not contain any LF line endings"
+        )
+    finally:
+        shutil.rmtree(tmp_dir.name, ignore_errors=True)
+
+
 @patch("sagemaker.train.model_trainer.TrainingJob")
 def test_input_merge(mock_training_job, modules_session):
     model_input = InputData(channel_name="model", data_source="s3://bucket/model/model.tar.gz")