#!/usr/bin/perl -wT
use strict;
use CGI;
use HTML::Entities;

my $query = CGI->new;
my $tainted_number = $query->param( "bob" );
my ( $clean_number ) = ( $tainted_number =~ /^\s*(\d+)\s*$/ );

print $query->header,
      $query->start_html( -title => "Input test" );

if ( defined $clean_number ) {
    print $query->p( "You entered '$clean_number'." );
} else {
    print $query->p( "You're only supposed to enter numbers, dummy." ),
          $query->p( "You entered '" . encode_entities( $tainted_number ) . "'" );
}

print $query->end_html;