Execute Process Task; How to use user variable as an argument

I am trying to call a executable that takes an argument. I am using an "execute process task" and have declared a user string variable "file_name" (c:\file.txt)

How do I use this variable so that the executable will see it as an argument.

You can use expressions to define the path and parameters of you executable... Then you don't pass the variable but construct the "command line" with an expression including the parameter (which is the value of your variable)...