Perl - Split CSV by field value and retain header

split_csv_by_field_values.pl

open $fh, '<', $ARGV[0];
while ($line = <$fh>) {
    print $line;
    if ($. == 1) {
        $header = $line;
    } else {
        # $fields[2] is the 3rd column
        @fields = split /,/, $line;
        # save line into hash %c
        $c{"$fields[2].csv"} .= $line;
    }
}
close $fh;
for $file (keys %c) {
    print "$file\n";
    open $fh, '>', $file;
    print $fh $header;
    print $fh $c{$file};
    close $fh;
}