You have a number of csv files, 
you want to print the 3rd field of each row of each file.

perl -n -a -F, -e 'print "$F[2]\n"' *.csv

-n  = loop over lines but do NOT print them 
-a  = autosplit by ' '
-F, = replace the split string by ','

You want to make sure all the rows are 4 elements long. Print out file name and line number of all the bad rows.

perl -a -F, -n -e 'print "$ARGV:$.\n" if @F != 4' data.csv