Note that KSSV's answer will not process the files in alphanumeric order as you probably expect, it will concatenate them in the order that the names are returned by the OS, most likely this order:
results1.txt
results10.txt
results100.txt
results1000.txt
results101.txt
results102.txt
results103.txt
results104.txt
results105.txt
results106.txt
results107.txt
results108.txt
results109.txt
results11.txt
results110.txt
... etc.
results988.txt
results989.txt
results99.txt
results990.txt
results991.txt
results992.txt
results993.txt
results994.txt
results995.txt
results996.txt
results997.txt
results998.txt
results999.txt
which means that your data will be concatenated together in an order that is unlikely to make much sense.
If you want the file data concatenated in an order that follows the number in the filename then you will have to sort the filenames yourself, e.g. downloading and using my FEX submission natsortfiles:
