#!/usr/bin/perl

use strict;
use warnings;

my $input = ( @ARGV and -f $ARGV[0] ) ?  shift : "C:/csv_in/test.csv";
open( $ifh, "<", $input ) or die "$input: open failed: $!\n";

my $out_num = my $out_count = 0;
my $ofh;

while ( <$ifh> ) {
    if ( ! defined( $ofh ) or $out_count == 5 ) {
        if ( $ofh ) {
            # print closing html stuff (page trailer, etc)...
            close $ofh;
        }
        my $out_name = sprintf( "C:/html_out/output_%d.html", ++$out_num );
        open( $ofh, ">", $out_name ) or die "$out_name: cannot open: $!\n";
        # print opening html stuff...
        $out_count = 0;
    }
    # extract fields from data row and stuff it into html...
    print $ofh ...
    $out_count++;
}
# print closing html content to current $ofh ...