use strict;
use warnings;
use diagnostics;

my( $first, $second ) = ( "a1b2c3d4e5f6", "AaBbCc" );

while( $first =~ m/(\d)/g ) {
    print "\$first matched on $1\n";
    while( $second =~ m/([a-z])/g ) {
        print "\t\$second matched on $1\n";
    }
}