gistfile1.rb

  set :site_path, Proc.new { Capistrano::CLI.ui.ask "Site to export (e.g. 'all', 'JGP' etc.): " }
  
  # we don't want exporting all sites if nothing is provided
  # that would be a costly mistake...
  raise ArgumentError, "Site path must be specified" if site_path == ""
  
  # site_path here is whatever we specify, 'JGP' for example
  
  # if 'all' was provided, reset site_path to .../sites/
  site_path = "" if site_path == "all"
  
  # it becomes "" here EVEN if site_path != "all"