/^(?!.*(?:evil|bad|wrong))/ seems to work for me. The key was the ^ at the begining. With that, it's forced to try from the begining. Otherwise, it keeps searching until it finds a place that doesn't have any of the blacklisted words (for instace, at the end of the string) and then succeeds. 
#!/usr/bin/perl -l

use strict;
use warnings;

my @blacklist = ('evil', 'bad', 'wrong');
#$a and $b are bad variable names due to sorting things
my $aa = "this string contains no blacklisted tokens";
my $bb = "this string is evil and wrong";

# The regex should express the blacklist is such a way that
# # it will match on any string which DOES NOT contain any of
# # the tokens in the blacklist, and it will fail to match on
# # any string which DOES contain tokens from the blacklist.
#
my $regex = qr/^(?!.*(?:evil|bad|wrong))/;

if (($aa =~ m/$regex/) && !($bb =~ m/$regex/)) {
   print "Woohoo";
}

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In reply to Re: Blacklisting with a Regular Expression by Eimi Metamorphoumai
in thread Blacklisting with a Regular Expression by BenjiSmith

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