Merge pull request #273 from dgilleland/patch-1

Document built-in environment variables

Author: knolleary

docs/user-guide/environment-variables.md

@@ -60,6 +60,24 @@ function:
 let foo = env.get("FOO");
 ```
 
+### Built-In Environment Variables
+
+*Since Node-RED 2.2*
+
+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).
+
+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.
 
 ### Subflow Instance properties