my $number;  

PROMPT_FOR_NUMBER:{
        print "Enter a number 0-9\n";
        GET_NUMBER:{
            $number=<STDIN>;
            chomp($number);
            unless(length($number) ==1  && $number =~ /[0-9]/){
                print "You don't want to give me one number ?\n";  
                redo PROMPT_FOR_NUMBER;
            }
        } 
}