I have a directory of subdirectories corresponding to months/ years with each subdirectory named (subyymm, ex: sub1712). I have subdirectories for each month from sub1712 - sub1812. Within each subdirectory is a .txt file called "sub_data.txt', and this is consistent across all subdirectories. I was wondering would would be a quick way to loop through each subdirectory and append all 13 sub_data.txt files together? Right now I append one at a time, and this seems inefficient.

Thank you!