my @numbers4 = $text =~ /\b \d{4} \b/gx;
foreach $unit4 (@numbers4) {
$text =~ s/$unit4/\<a href=\"script.pl?do=view&unit=$unit4\"\>\<b\>$unit4\<\/b\>\<\/a\>/i;
}
##</code><code>##

<a href="script.pl?do=view&unit=<a href="script.pl?do=view&unit=2003"><b>2003</b>