Update documentation

docs/userguide/deployment.rst

@@ -17,17 +17,18 @@ Running the launcher is very straightfoward:
 
 .. code-block:: bash
 
-    asphalt run yourconfig.yaml [your-overrides.yml...]
+    asphalt run yourconfig.yaml [your-overrides.yml...] [--set your.component.param=your_value]
 
 Or alternatively:
 
-    python -m asphalt run yourconfig.yaml [your-overrides.yml...]
+    python -m asphalt run yourconfig.yaml [your-overrides.yml...] [--set your.component.param=your_value]
 
 What this will do is:
 
 #. read all the given configuration files, starting from ``yourconfig.yaml``
-#. merge the configuration files' contents into a single configuration dictionary using
-   :func:`~asphalt.core.utils.merge_config`
+#. read the command line configuration options passed with ``--set``, if any
+#. merge the configuration files' contents and the command line configuration options into a single configuration dictionary using
+   :func:`~asphalt.core.utils.merge_config`. The command line configuration options have precedence over the configuration files.
 #. call :func:`~asphalt.core.runner.run_application` using the configuration dictionary as keyword
    arguments
 
@@ -105,6 +106,16 @@ least ``INFO`` level to the console. You may want to set up more granular loggin
 configuration file. See the
 :ref:`Python standard library documentation <python:logging-config-dictschema>` for details.
 
+Passing configuration at the command line
+-----------------------------------------
+
+With the above configuration file saved as ``config.yaml``, you could override the mailer's host
+and the ``data_directory`` with:
+
+.. code-block:: bash
+
+    asphalt run config.yaml --set mailer.host=smtp.my_other_company.com --set data_directory=/some/other/file/somewhere
+
 Using data from environment variables and files
 -----------------------------------------------
 

src/asphalt/core/cli.py

@@ -93,13 +93,12 @@ def run(
         if "." in key:
             ks = key.split(".")
             last_i = len(ks) - 1
-            d = config["component"]["components"]
+            d = config["component"].setdefault("components", {})
             for i, k in enumerate(ks):
                 if i == last_i:
                     d[k] = value
                 else:
-                    d[k] = d.get(k, {})
-                    d = d[k]
+                    d = d.setdefault(k, {})
         else:
             config["component"][key] = value