In a process flow, variables are useful if you want multiple activities in the process flow to reference the same file. Using a variable, can define the file in one place, then reference the variable in all downstream activities that need to reference the file. If the file ever changes, you can modify the variable definition without having to modify all the downstream activities.
When you add a job activity to a process flow, the activity automatically creates variables for each source and sink in the dataflow. If there are files you want to use in the process flow that are not defined in the source or sink of a job, you can create variables.
When you add a Run Program activity, no variables are created by default. If you want to use variables with a Run Program activity you must create them.
This procedure describes how to create a variable in a job activity or a Run Program activity.