You can use the input() function in the script to ask a user for a value, store that in a variable, then use the variable in your file path.
Input(str cue [, str caption])
This function can be used in the script only and opens an input box that prompts the user for a value during the script execution. The parameters cue and caption are used as message and caption texts, respectively. The function returns the entered value.
The input box function returns NULL if the dialog is cancelled, closed or cannot be shown.
Load Input('Enter value', 'Input box') as v, Recno () as r autogenerate 3;