I'm new to regular expressions in general, and in prepping for a Perl class that I am taking in the fall semester, I wanted to get my feet wet early. I'm still wrapping my head around them, and doing very basic things to get an idea of how matching and substitution works. So I wrote a simple script that checks to see if an employee's id number is valid. The simple requirements I came up with are:

1. Has to start with a 9
2. Can only have one zero in the whole number

I cannot for the life of me figure out how to make the condition fail if it has more than one zero. My code looks like this:

```
$s;
print("Please enter your id number: ");
$s = <STDIN>;

if(($s =~ /^9/) && ($s =~ /0{1}/))
{
    print("ID is valid\n");
}
else
{
    print("ID not valid\n");
}

```

The second part of the condition ($s =~ /0{1}/) I am reading as, "Match only one zero" but it will not work if the number is something that contains multiple zeros as long as they aren't repeated (ex: 90401 is returned as valid, where 90091 is not valid). I know this has go to be possible, but I've tried quite a few combinations with no solution. Any point in the right direction would be most helpful.