Here's another way to split one large HTML page down into smaller 56-line pages:

#!/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;
}
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This will iterate over each line in <INFILE>, and on every 56th line, it will start a new chapter. The last chapter will be 56 lines or less.

If your file size ever gets large I would suggest using this method. Reading a large file into an array, then slicing the aray after, will be more expensive than iterating over the source file one line at a time.