#!/usr/bin/perl
use strict;
use warnings;

for my $f ( @ARGV ) {
    local $/;
    open( I, '<', $f );
    open( O, '>', "$f.bak" );
    my $count = 0;
    my $line = <I>;

    $line =~ s{ (<\/div>) }
              { if (++$count == 2){
                  "\t<?php include(\$_SERVER['DOCUMENT_ROOT'].\"\/includes\/footer.php\"); ?>\n\n".$1;
                } else {
                  $1;
                }
              }gex;

    print O $line;
}