I'm using the function for caching multiple javascript files into one:
<%= javascript_include_tag :all, :cache => true %>
The way I understand it this creates the all.js file the first time a HTML file using it is generated.
But if the app is configured to use an asset host on a seperate server that does not deliver HTML the file will not be created. Is there a way to generate all.js manually on deploy?
You need to configure your deploy task in order to compress and create the file. If you use Capistrano, you can add a callback to be executed on deploy.
Otherwise, the are a couple of alternatives that offers also a more efficient solution. The standard Rails strategy only merges all files into a single one. But you can gain additional benefit by compressing and minifying the final result. For more information you can read the GitHub asset deployment strategy or the Jammit documentation.
A great project for javascript concatenation is sprockets, which can be found here: http://getsprockets.org/
It's really easy to setup and integrate with capistrano. Might be worth a look.