$ cat pm_1207659_out.csv
X,Y,Z
C,what,ever
some,thing,else
$ pm_1207659_csv_append.pl
$ cat pm_1207659_out.csv
X,Y,Z
C,what,ever
some,thing,else
B,F2-1,F3-1
A,F2-3,F3-3
D,F2-5,F3-5