Trying to figure out if there's a way to select these files:
x1.txt.001
x1.txt.002
x1.txt.003
x2.txt.001
x2.txt.002
x3.txt.001
x3.txt.002
x3.txt.003
And have the joined files x1.txt, x2.txt, x3.txt created in one go, instead of doing three separate join operations.