Add Set And Show Heroku Env Variables as a Heroku til

heroku/set-and-show-heroku-env-variables.md

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+# Set And Show Heroku Env Variables
+
+The `heroku` CLI includes the `config` command which will show all the env
+variables for the current app.
+
+```bash
+$ heroku config
+=== my-app Config Vars
+
+```
+
+At this point I have none set.
+
+I can set one with the `config:set` command and a key-value parameter.
+
+```bash
+$ heroku config:set PUBLIC_NEXT_URL=http://localhost:1235
+Setting PUBLIC_NEXT_URL and restarting ⬢ my-app... done, v3
+PUBLIC_NEXT_URL: http://localhost:1235
+```
+
+I can see the value that this specific variable is set to by calling it with
+`config:get`.
+
+```bash
+$ heroku config:get PUBLIC_NEXT_URL
+http://localhost:1235
+```
+
+[source](https://devcenter.heroku.com/articles/config-vars#using-the-heroku-cli)