#!/usr/bin/perl -w
use strict;

my $string = 'copyright 2001, 2002';

if ( index($string,'2003') == -1 ) {
    $string .= ', 2003';
}

##</code><code>##

#!/usr/bin/perl -w
use strict;

my $string = 'copyright 2000-2003';
$string .= ', 2003' if $string ~= /\b2003\b/;