(First, nitpick: it's 'csv' files. 'comma-separated-values'. cvs is a version control system.)

It's probably a good idea to use the Text::CSV_XS module to parse and recombine your csv files. This easily lets you get them into convenient array form.

Then, I'd store the arrays in a hash based on the first key. If the hash already has an array assigned to it, you can append to the existing array. (Or whatever you need to do. It's not exceedingly clear from the question. But this should be a good way to group them together.)

At the end, you can do a foreach on the keys of the hash, and combine the fields using the module, and write that out to a new csv file.

Hope this points you in the right direction!