my @blacklist = ('evil', 'bad', 'wrong');
my $a = "this string contains no blacklisted tokens";
my $b = "this string is evil and wrong";

my $regex = join '|', @blacklist;

# The !~ is a better way to do !(foo =~ /regex/)
if ($a !~ /$regex/) {
    print "Success with a!\n";
}
else {
    print "Failure with a\n";
}

if ($b !~ /$regex/) {
    print "Success with b!\n";
}
else {
    print "Failure with b\n";
}

##</code><code>##

my $regex = '.(?!evil)';

if ("this is so evil" =~ /($regex)/) {
    print "yay: $1\n";
}