#!/usr/bin/perl
use strict;
use CGI;
use File::Slurp qw/read_file/;

my $includepath  = "c:/temp/";
my $file_to_read = 'aa.html';
my $html = read_file($file_to_read); 

$html =~ s{<!--#include file="([^"]+)"-->}
          {&add_template($includepath.$1)}gei ;

print CGI::header();
print $html;

sub add_template{
  my $file = shift;
  if (-e $file){
    return read_file($file);
  } else {
    warn "$file not found";
    return '<!-- $file not found to include -->';
  }
}