Validating a CSV file: either all rows are accepted or no rows are accepted

So close, ok so I have the error and the success streams. I am rejoining them. When I have any error, I want the filename to be have a .err extension. When I have no errors I want the filename to have a .csv extension.

If only there was an if error file exists then merge files and set file extension to err else no errors so set file extension to csv that would allow this to work.

I thought about running one pass creating a status file that contains either 0 or 1 and then using that status to define the output file extension.