EOF: how to generate one in a string

I am trying to use a command line program in Linux using this form: $result = /path/prog $arg; But this doesn't work as the program is expecting and EOF that never comes. If I use the program on the command line when I am finished entering all the data I need to hit return and then CTRL-D to give an EOF. How can I simulate this using the backticks? Thanks! Jc