use Benchmark qw[ cmpthese ];

@good = map{ join'',map{ rand() < .5 ? 1 : 0 } 1..1000 } 1..100;

@bad = map{ substr( $s=$_, rand( 1000 ), 1 ) = 2 } @good;

cmpthese( -3, { 
    '+ve' => q[ $n1 = grep /^[01]+$/, @good, @bad ], 
    '-ve' => q[ $n2 = grep !/[^01]/, @good, @bad ] 
});
      Rate  -ve  +ve
-ve  467/s   -- -80%
+ve 2363/s 406%   --

print $n1, $n2;
100 100