Ruby on Rails: How can I specify runner script environment

I am using a shell script to run some runner scripts in my Ruby on Rails app. I need to run it on the production database, but the following:

#!/bin/bash
/usr/bin/ruby RAILS_ENV=production ../script/runner ../lib/tasks.rb 

gives an error:

/usr/bin/ruby: No such file or directory -- RAILS_ENV=production (LoadError)

I have tried to force it in config/environment.rb

ENV['RAILS_ENV'] ||= 'production'

or even

ENV['RAILS_ENV'] = 'production'

but even with that it still runs in development environment.

Update: I can force the scripts to connect to the right database by editing the config/database.yml file, but I wonder what's the proper way of doing it.