You don't indicate how you are running the nas script so the answer here will vary.
If this is an AO profile that's running a script, on the profile definition there's a place to put arguments. In your LUA code you'd access that argument value with something like:
local recipient = SCRIPT_ARGUMENT
If you are running the script from the command line, it puts the parameters into a table called arg. At least that's my recollection.
-Garin