Updated environment documentation in guides to account for env files.

docs/guide/environment.rst

@@ -23,25 +23,76 @@ simply to use the optional ``--env`` argument when running bonobo from the shell
 syntax ``VAR_NAME=VAR_VALUE``. Multiple environment variables can be passed by using multiple ``--env`` / ``-e`` flags
 (i.e. ``bonobo run --env FIZZ=buzz ...`` and ``bonobo run --env FIZZ=buzz --env Foo=bar ...``). Additionally, in bash
 you can also set environment variables by listing those you wish to set before the `bonobo run` command with space
-separating the key-value pairs (i.e. ``FIZZ=buzz bonobo run ...`` or ``FIZZ=buzz FOO=bar bonobo run ...``).
+separating the key-value pairs (i.e. ``FIZZ=buzz bonobo run ...`` or ``FIZZ=buzz FOO=bar bonobo run ...``). Additionally,
+bonobo is able to pull environment variables from local '.env' files rather than having to pass each key-value pair
+individually at runtime. Importantly, a strict 'order of priority' is followed when setting environment variables so
+it is advisable to read and understand the order listed below to prevent
+
+
+The order of priority is from lower to higher with the higher "winning" if set:
+
+    1. default values
+            ``os.getenv("VARNAME", default_value)``
+            The user/writer/creator of the graph is responsible for setting these.
+
+    2. ``--default-env-file`` values
+            Specify file to read default env values from. Each env var in the file is used if the var isn't already a corresponding value set at the system environment (system environment vars not overwritten).
+
+    3. ``--default-env`` values
+            Works like #2 but the default ``NAME=var`` are passed individually, with one ``key=value`` pair for each ``--default-env`` flag rather than gathered from a specified file.
+
+    4. system environment values
+            Env vars already set at the system level. It is worth noting that passed env vars via ``NAME=value bonobo run ...`` falls here in the order of priority.
+
+    5. ``--env-file`` values
+            Env vars specified here are set like those in #2 albeit that these values have priority over those set at the system level.
+
+    6. ``--env`` values
+            Env vars set using the ``--env`` / ``-e`` flag work like #3 but take priority over all other env vars.
+
+
+
+Examples
+::::::::
 
 The Examples below demonstrate setting one or multiple variables using both of these methods:
 
 .. code-block:: bash
 
-    # Using one environment variable via --env flag:
+    # Using one environment variable via --env and --defualt-env flags:
     bonobo run csvsanitizer --env SECRET_TOKEN=secret123
+    bonobo run csvsanitizer --defaul-env SECRET_TOKEN=secret123
 
-    # Using multiple environment variables via -e (env) flag:
+    # Using multiple environment variables via -e (env) and --default-env flags:
     bonobo run csvsanitizer -e SRC_FILE=inventory.txt -e DST_FILE=inventory_processed.csv
+    bonobo run csvsanitizer --default-env SRC_FILE=inventory.txt --default-env DST_FILE=inventory_processed.csv
 
-    # Using one environment variable inline (bash only):
+    # Using one environment variable inline (bash-like shells only):
     SECRET_TOKEN=secret123 bonobo run csvsanitizer
 
-    # Using multiple environment variables inline (bash only):
+    # Using multiple environment variables inline (bash-like shells only):
     SRC_FILE=inventory.txt DST_FILE=inventory_processed.csv bonobo run csvsanitizer
 
-*Though not-yet implemented, the bonobo roadmap includes implementing environment / .env files as well.*
+    # Using an env file for default env values:
+    bonobo run csvsanitizer --default-env-file .default_env
+
+    # Using an env file for env values:
+    bonobo run csvsanitizer --env-file '.env'
+
+
+ENV File Structure
+::::::::::::::::::
+
+The file structure for env files is incredibly simple. The only text in the file
+should be `NAME=value` pairs with one pair per line like the below.
+
+.. code-block:: text
+
+    # .env
+
+    DB_USER='bonobo'
+    DB_PASS='cicero'
+
 
 Accessing Environment Variables from within the Graph Context
 :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::