open(INFILE, $filename) or die "Can't open $filename: $!";
my @lines = <INFILE>;
my @chapters;
$chapters[1] = @lines[0 .. 55];
$chapters[2] = @lines[56 .. 112];
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Update: merlyn's right. That's what happens when you switch approaches while typing out your code. If you don't want to use references, do instead:

@chapter1 = @lines[0 .. 55];
@chapter2 = @lines[56 .. 112];
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$chapters[1] = @lines[0 .. 55]; 
$chapters[2] = @lines[56 .. 112];
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Ooops... you're slipping. You need an extra anon-array constructor there:

$chapters[1] = [@lines[0 .. 55]]; 
$chapters[2] = [@lines[56 .. 112]];
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-- Randal L. Schwartz, Perl hacker

Seems pretty straightforward:

open (INFILE,$filename) or die "a slow, suffocating death: $!";
$segment=1;
ENDLESS: while (1) {
    open (OUTFILE,">".$filename.$segment.$extension);
    foreach (1..56) {
        $line=<INFILE> or end ENDLESS;
        print OUTFILE $line;
    }
    close OUTFILE;
    $segment++;
}
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The variable names should be pretty self-explanatory. Hope that helps, Brother Ade

$lines = 56;
$filename = 'chapterx.html';
$nameformat = 'chapterx_page_%d.html';

open(INFILE, "<$filename") or die $!;
while(<INFILE>) {
    if ($. % $lines == 1) {
        open(OUTFILE, '>'.sprintf($nameformat, $. / $lines + 1)) or di
+e $!;
    }                                                           
    print OUTFILE $_;                                           
}
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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;
}
[download]

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.