[GitHub] alexkli commented on a change in pull request #2848: Support reading param.json from stdin #2837

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alexkli commented on a change in pull request #2848: Support reading param.json from stdin #2837
URL: https://github.com/apache/incubator-openwhisk/pull/2848#discussion_r145554426
 
 

 ##########
 File path: docs/actions.md
 ##########
 @@ -202,6 +202,39 @@ Parameters can be passed to the action when it is invoked.
       "payload": "Hello, Bernie from Vermont"
   }
   ```
+4.  It is possible to pipe JSON parameters to the `wsk` command by using the special filename `-` with `--params-file` or `-P`:
+  
+  ```
+  cat parameters.json | envsubst | wsk action invoke -r hello -P -
+  ```
+  
+  This example uses `envsubst` to replace environment variables in the JSON before passing them to the action invocation.
 
 Review comment:
   I thought it's nice to have a more "real world" use case example.
   
   The echo example can also be done simpler using `-p name Alice`. I chose `envsubst` as that's an actual case where you need to pipe from a file since some processing is going on, and I happened to be using `envsubst` in my case.
   
   Do you think there is a need to be as simple as possible?

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