I am just using the rename function in command line.
rename 001.tabular 3972
As I read your code, it is renaming the files by simply adding the extension of .foobar to each one. I need to completely rename them, so I need to designate $old as $ARGV and $new as $ARGV1 from a text file but it needs to be the column and not the element of the array.
Even when the file doesn't exist, if I change the "%03d" it still says won't clobber. If I can fix that code to rename the files as the value of column 1 that I am sorting on, I don't have to worry about the renaming code. But when I make changes to the code, I either get won't clobber or still get the exact same names as before (that have no meaning and need to be changed).