c:\@Work\Perl\monks>perl -wMstrict -le
"print 'Perl version ', $];
 ;;
 my $s = '123456';
 ;;
 printf qq{'$_' } for $s =~ m{ (\d\d) }xmsg;
 print ''
 ;;
 printf qq{'$_' } for $s =~ m{ (?= (\d\d)) }xmsg;
"
Perl version 5.008009
'12' '34' '56'
'12' '23' '34' '45' '56'