Merge pull request #285 from drmibell/master

Update environment-variables.md

Author: knolleary

docs/user-guide/environment-variables.md

@@ -60,24 +60,14 @@ function:
 let foo = env.get("FOO");
 ```
 
-### Built-In Environment Variables
-
-*Since Node-RED 2.2*
+### Template node
 
-Node-RED maintains its own set of environment variables for exposing information about the node itself. This information helps "locate" the node in your [workspace](/docs/user-guide/editor/workspace/index.md). Nodes in your workspace exist as part of a [flow](/docs/user-guide/editor/workspace/flows.md). Likewise, a node may (or may not) be part of a [group](/docs/user-guide/editor/workspace/groups.md). Nodes, flows and groups are each given unique IDs that are generated by Node-RED.
-
-Nodes, flows and groups all support the `name` property, which you can change when [editing properties](/docs/user-guide/editor/workspace/nodes.md#editing-node-properties).
+*Since [Node-RED 3.0](https://nodered.org/blog/2022/07/14/version-3-0-released#environment-variables-in-the-template-node)*
 
-The following environment variables can be used to access this contextual information for the node.
-
-    - `NR_NODE_ID`
-    - `NR_NODE_NAME`
-    - `NR_GROUP_ID`
-    - `NR_GROUP_NAME`
-    - `NR_FLOW_ID`
-    - `NR_FLOW_NAME`
-
-Note that while the IDs generated by Node-RED are guaranteed to be unique, the names are not. If a node, flow or group is not given a name, then the corresponding environment variable will return an empty string. If a node is not part of a group, its group id environment variable will also return an empty string.
+The `template` node  can access environment variables using the syntax:
+```
+My favourite colour is {{env.COLOUR}}
+```
 
 ### Subflow Instance properties
 
@@ -90,28 +80,61 @@ a subflow could be created to access the API and handle the response, using an
 environment variable to identify which type of record should be accessed. Individual
 instances of the Subflow can then be customised for those particular types.
 
-### Flow/Group level environment variable 
 
-Since 2.21, environment variables can be set for Flow or Group on their settings panel.
 
-### Predefined environment variable
+### Flow/Group level environment variables
 
-Since 2.22, following predefined environment variables has been added that provides access to information about the node, group and flow.
+*Since [Node-RED 2.1](https://nodered.org/blog/2021/10/21/version-2-1-released#flowgroup-level-environment-variables)*
+
+Environment variables can be set at the flow or group level. This is done in the appropriate tab in the edit dialog for the flow or group.
+
+### Accessing nested environment variables
+
+When accessing an environment variable in a subflow, Node-RED will search the
+subflow properties, then the flow containing the subflow (which could be a subflow
+itself).
+
+In some cases it is useful to access the 'parent' levels environment variables
+without reference the 'local' value. This can be achieved by prefixing the
+variable name with `$parent.`.
+
+
+### Running as a service
+
+When Node-RED is running as a service having been installed using the provided [script](https://nodered.org/docs/getting-started/raspberrypi), it will not have access to environment variables that are defined only in the calling process. In this instance, environment variables can be defined in the settings file by adding:
+
+```
+process.env.FOO='World';
+```
+
+placed outside the `module.exports` section. Alternatively, variables can be defined as part of the `systemd` service by placing statements of the form
+
+```
+ENV_VAR='foobar'
+```
+in a file named `environment` within the Node-RED user directory, `~/.node-red`.
+
+
+### Built-In Environment Variables
+
+*Since Node-RED 2.2*
+
+Node-RED defines a set of environment variables for exposing information about the nodes, flows and groups.
+
+This information helps "locate" the node in your [workspace](/docs/user-guide/editor/workspace/index.md). Nodes in your workspace exist as part of a [flow](/docs/user-guide/editor/workspace/flows.md). Likewise, a node may (or may not) be part of a [group](/docs/user-guide/editor/workspace/groups.md). Nodes, flows and groups are each given unique IDs that are generated by Node-RED.
+
+Nodes, flows and groups all support the `name` property, which you can change when [editing properties](/docs/user-guide/editor/workspace/nodes.md#editing-node-properties).
+
+The following environment variables can be used to access this information for a given node:
 
 - `NR_NODE_ID` - the ID of the node
 - `NR_NODE_NAME` - the Name of the node
-- `NR_NODE_NAME` - the Path of the node
-
-   The node's path represents a node's hierarchy in a flow.  It is `/`
-   delimited IDs of the flow, enclosing subflows, and the node.
+- `NR_NODE_NAME` - the Path of the node. This represents a node's position in a flow.  It is `/` delimited IDs of the flow, enclosing subflows, and the node.
 - `NR_GROUP_ID` - the ID of the containing group
 - `NR_GROUP_NAME` - the Name of the containing group
 - `NR_FLOW_ID` - the ID of the flow the node is on
 - `NR_FLOW_NAME` - the Name of the flow the node is on
 
-### Accessing nested environment variable
+Note that while the IDs generated by Node-RED are guaranteed to be unique, the names are not. If a node, flow or group does not have a given name, the corresponding environment variable will be an empty string. If a node is not part of a group, its group id environment variable will also return an empty string.
+
 
-Environment variable definition is searched from the bottom to the top
-of the node's definition hierarchy. `$ parent.` prefix can be added to
-environment variable name (e.g. `$parent.NR_GROUP_NAME`) to move the
-start position of this search up one level in the hierarchy.