You are making it complicated by doing a rename and in place edit.

I would do -

open (IN, 'origdata.csv');  # Open the file for read
open (OUT,'>','copy.csv');  # Open the file for write. Will overwrite 
+if exists

while(<IN>) {   # read contents of input file
  # <IN>, typucally used inside a while will populate variable $_
  # more proecessing
   print OUT ($_); # Write out to new file
}
[download]

I think you should start reading more about how to work with files and other perl idioms.

I would recommend that you start with "Learning perl book". Also there are lot of stuff in Categorized Questions and Answers section!

-SK