c:\@Work\Perl\monks>perl -wMstrict -le "for my $Disc (qw( 00000000 00000001 00000002 00000003 00000004 00000005 00000006 00000007 00000008 00000009 0 00 000 0000 00000 000000 0000000 000000000 FFFFFFFF ffffffff 6C163512 x00000000 00000000x x00000000x x0000000 0000000x x0000000x x000000000 000000000x x000000000x ), '') { ;; my $proper_word = my ($righmost_digit) = $Disc =~ m{ \A 0{7} (\d) \z }xms; ;; if ($proper_word) { print qq{'$Disc' ok, rightmost digit '$righmost_digit'}; } else { print qq{'$Disc' is bad}; } } " '00000000' ok, rightmost digit '0' '00000001' ok, rightmost digit '1' '00000002' ok, rightmost digit '2' '00000003' ok, rightmost digit '3' '00000004' ok, rightmost digit '4' '00000005' ok, rightmost digit '5' '00000006' ok, rightmost digit '6' '00000007' ok, rightmost digit '7' '00000008' ok, rightmost digit '8' '00000009' ok, rightmost digit '9' '0' is bad '00' is bad '000' is bad '0000' is bad '00000' is bad '000000' is bad '0000000' is bad '000000000' is bad 'FFFFFFFF' is bad 'ffffffff' is bad '6C163512' is bad 'x00000000' is bad '00000000x' is bad 'x00000000x' is bad 'x0000000' is bad '0000000x' is bad 'x0000000x' is bad 'x000000000' is bad '000000000x' is bad 'x000000000x' is bad '' is bad