my $consensus = 'abc*def*ghi';
my( @index_c, @index_n );
my $idx = 0;
my $len = length( $consensus );

while( $idx < $len ) {
    if( substr( $consensus, $idx, 1 ) eq '*' ) {
        push @index_c, $idx;
    }
    else {
        push @index_n, $idx;
    }
    $idx++;
}

print "C: @index_c\n";
print "N: @index_n\n";