This is not an error, it is a warning.

Your data do not seem to be comma separated, but the script sets $column_separator to qr/,/.

Also, please check the closing code tag. It is missing a slash.

Update: use Text::CSV is a step in the right direction. The script does not profit from the module in any way, though.

Update 2: To read from a file, you have to open it for reading, not appending.