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 "$F\n"' *.csv
-n = loop over lines but do NOT print them -a = autosplit by ' ' -F, = replace the split string by ','
You want to make sure all the rows are 4 elements long. Print out file name and line number of all the bad rows.
perl -a -F, -n -e 'print "$ARGV:$.\n" if @F != 4' data.csv