Please use <code> tags to format your example input and expected output, and show the code you've tried so far (How do I post a question effectively?). In general, it sounds like you probably want to use Text::CSV to read the file (with the sep_char set to |), and break down the group and pid with split (if it is guaranteed that the strings don't contain any escaped commas, otherwise it's better to use Text::CSV for that too), and then loop over the results.