Added support for default value when environment variable is missing (#8484)

* Added support for a default value when an environment variable is missing

* Shouldn't have used docstring

homeassistant/util/yaml.py

@@ -205,8 +205,13 @@ def _construct_seq(loader: SafeLineLoader, node: yaml.nodes.Node):
 def _env_var_yaml(loader: SafeLineLoader,
                   node: yaml.nodes.Node):
     """Load environment variables and embed it into the configuration YAML."""
-    if node.value in os.environ:
-        return os.environ[node.value]
+    args = node.value.split()
+
+    # Check for a default value
+    if len(args) > 1:
+        return os.getenv(args[0], ' '.join(args[1:]))
+    elif args[0] in os.environ:
+        return os.environ[args[0]]
     else:
         _LOGGER.error("Environment variable %s not defined.", node.value)
         raise HomeAssistantError(node.value)

tests/util/test_yaml.py

@@ -60,6 +60,13 @@ class TestYaml(unittest.TestCase):
         assert doc['password'] == "secret_password"
         del os.environ["PASSWORD"]
 
+    def test_environment_variable_default(self):
+        """Test config file with default value for environment variable."""
+        conf = "password: !env_var PASSWORD secret_password"
+        with io.StringIO(conf) as file:
+            doc = yaml.yaml.safe_load(file)
+        assert doc['password'] == "secret_password"
+
     def test_invalid_enviroment_variable(self):
         """Test config file with no enviroment variable sat."""
         conf = "password: !env_var PASSWORD"