Render template inside a Rails runner script

with_runner.rb

view_assigns = {widgets: Widget.all}
av = ActionView::Base.new(ActionController::Base.view_paths, view_assigns)
av.class_eval do
  # include any needed helpers (for the view)
  include ApplicationHelper
end

# normal render statement
content = av.render template: 'widgets/index.xlsx.axlsx'
# do something with content, such as:
File.open("/tmp/with_runner.xlsx","w+b") {|f| f.puts content }

If you’re writing a view spec or similar, and your template contains instance variables, you can add/change locals to assigns in the above snippet from @delbetu

# if your .xlsx.aslsx file needs access to a `@posts`
# instance variable rather than local variable, use this:

content = ApplicationController.render(
  template: "exports/demo/index",
  assigns: { posts: Post.all.limit(3) },
  handlers: [:axlsx],
  formats: [:xlsx]
)