my $open = 0;   
LOOP: while ($test =~ /(.)/g) {   
    my $char = $1;  
    if ($char eq '[' or $char eq ']') {    
        $open = $char eq '[' ? 1 : 0;    
    }    
    else {  
        if ($char eq ',' and $open == 0) {  
            print "INVALID";  
            last LOOP;  
        }  
    }  
}