I think I see the problem. You put the code in a script, made it executable. When you open it in your file manager you get asked if you want to "Run in Terminal", "Display", Cancel, Run, right? You clicked run in terminal, but the processing of the 6 files was too fast to see anything.
Either you run the script in a terminal (NOT from file manager) or you add
sleep 5 at the end of the script and try again.
Oh, one other thing, you said your files are like SG1130113000247.CAPNFXS, but they are more like SG1130113000247.CAPNFXS.csv
If you want the output to be 130113000247, both scripts will produce right output.
If you want the output to be 130113000247.csv, substitute "$new" with "$new.csv"