Okay, in the interest of moving this along, here's a teaser.

I wrote a Perl script which produces the following output from the following suspected input:

C:\Steve\Dev\PerlMonks\P-2013-10-18@1712-DataMergeCSV>type hello.csv
abc,2,3,4,5,6
abc,7,5,2,1,6,2,3
abc,8,2,1,3,1,4
def,8,9,4,5,6
def,5,6,2,1

C:\Steve\Dev\PerlMonks\P-2013-10-18@1712-DataMergeCSV>perl mergetest99
+.pl hello.csv

C:\Steve\Dev\PerlMonks\P-2013-10-18@1712-DataMergeCSV>type hello.csv.o
+ut.csv
abc,2,3,4,5,6,7,5,2,1,6,2,3,8,2,1,3,1,4
def,8,9,4,5,6,5,6,2,1
[download]

If this is what you are looking for and if you want to see how I did this, let's get your code working and I'd be glad to get you moving on this again.

On the other hand, if this is not what you are looking for, I suppose this demonstrates why you need to post the input file.  :-)