Jonathan :
I want to launch some controller methods in application.rb from a script, so I'm trying to use the console to help write it.
?> require "app/controllers/application.rb" => true
you don't have to require it in script/console.
>> ApplicationController.post_render(:id => 119) NoMethodError: undefined method `post_render' for ApplicationController:Class from (irb):5
>> ApplicationController.instance_methods => ["methods", "web_service_object", "render_nothing".........................."post_render", ............................. "gem", "transition", "silence_stream"]
What really silly thing am I doing wrong?
#post_render is an instance method and you're invoking it
as a class method, so it doesn't work 
If you want to test your action in script/console, call it as if it were a browser :
app.get 'my_url'
(like app.get 'article/show/2' )
and inspect it :
app.response.body app.controller.params ...
-- Jean-François.