%MESSAGE% ##
##

#!/usr/bin/perl -w

use strict;

open HTML, "test.html" or die "can't open html file!\n";

# read the whole file in a variable
my $htmldata=join '', ;

close HTML;

# prepare the message to display
my $parameter=shift;
my $message;

if ($parameter >0) { $message="Oh no!"}
elsif ($parameter<0) { $message="Really?"}
else {$message="Mwahahahaha!"}

# replace %MESSAGE% by whatever you want
$htmldata =~ s/\%MESSAGE%/$message/;

# display the modified html
print $htmldata