use strict;
use warnings;
use Benchmark;

my @strings = qw(exception:tex exception:mex asdf tex:exception:mex);

Benchmark::cmpthese( -5, {
    'one' => sub { my @filtered = grep { /exception:(?!tex)/} @strings; },
    'two' => sub { my @filtered = grep { /exception/ && !/tex/ } @strings; },
    'three' => sub { my @filtered = grep { pos = 0; /exception:/g && !/\Gtex/ } @strings; },
});
__END__
          Rate three   one   two
three  99554/s    --  -18%  -38%
one   121692/s   22%    --  -24%
two   161067/s   62%   32%    --