$string =~ s{
                (?<![-\w./])
                (
                    \s?
                    [-\w.]*
                    $item
                    [-\w.]*
                    \s?
                )
            }{<b>$1<\/b>}gimsx;

##</code><code>##

$ regex_slash_prob.pl
<a href="/cgi-programming-with-perl.zip"><b>cgi-programming-with-perl.zip</b></a>

##</code><code>##

my $string = qq|
        <a href="/cgi-programming-with-perl.zip">
            cgi-programming-with-perl.zip
        </a>
|;

##</code><code>##

        <a href="/cgi-programming-with-perl.zip">
           <b> cgi-programming-with-perl.zip
</b>        </a>

##</code><code>##

        <a href="/cgi-programming-with-perl.zip">
            <b>cgi-programming-with-perl.zip</b>
        </a>

##</code><code>##

$string =~ s{
                (?<![-\w./])
                (
                    [-\w.]*
                    $item
                    [-\w.]*
                )
            }{<b>$1<\/b>}gimsx;