How to set Heroku config var with contents of a file

Take a look at the heroku-config plugin, which adds a heroku config:push command to push key-value pairs in a file named .env to the app.

It also has a heroku config:pull command to do the opposite and works very well with foreman for running the app locally with the config in .env.

https://github.com/xavdid/heroku-config

Example

heroku config:push --file=.env.production