#!/usr/bin/perl -w

use strict;
use constant CHAPTER_LENGTH => 56;

open INFILE, "< $ARGV[0]"
  or die "Could not open file $ARGV[0]: $!";

my $page = 1;

until(eof INFILE) {
  open OUTFILE, "> chapterx_page_$page.html"
    or die "Could not open file chapter_$page: $!";

  while(<INFILE>) {
    print OUTFILE;
    last unless $. % CHAPTER_LENGTH; #will return true when the line
                                     #no. is equally divisible by 56
  }

  ++$page;
}