Yes, use File.expand. It will expand the tilde ~
to be the the home directory of the user running this cookbook. Alternatively, you could do:
"#{ENV['HOME']}/Pictures/SCREEN SAVER NEW MACS"
Like the previous comment, this is not chef DSL or ruby code. What is the source of this code or is it just pseudo-code to ask the question?
Also, chef-client is not frequently run as multiple users in a chef server deployment. It's usually run in a sudo context. So maybe you are referring to a --local-mode or chef-zero application?