$comment =~ s/$l/****/g;

##</code><code>##

my $foo = "man, that's some badass motherfucking shit!";
my @badwords = qw/ass fuck shit/;

foreach my $word (@badwords) {
    my $bleep = "*" x length($word);
    $foo =~ s/$word/$bleep/g;
}

print $foo, "\n";

##</code><code>##

man, that's some bad*** mother****ing ****!