How to retrieve data from txt files only

Hi,
i tried the following sample complex_output_0x00_separated_java_user_class.ktr
It works fine but i want to know to modify it if i want to retrieve data from all txt file, i mean i don' t want to specify the filename.
Because i receive 12 txt files every 2h with different names.
so i could not start ETL and specify every 2h for 12 different filename

Thank you