Alert Windows - How To

Help!! I urgently need (by EoD tomorrow) need to find out how to invoke pop up alert windows. I've never really used perl but am doing for a contract. I've managed to get the rest of the stuff I need working but I can't find out about alert windows anywhere. You know what I mean, those annoying little boxes that pop up and tell you when something has gone wrong.

Can anybody tell me how I would do the following:

I have a fill out form and I need a alert window to appear when the user hasn't entered a mandatory field. On pressing ok I need the form page to still be displayed with the already entered text.

Any help would be REALLY appreciated.

Thanks.

Nick Gushlow.
Email: nickg@dynamicweb.co.uk

Is the form HTML? If so, then just use javascript...here is an example of a function that will check if the field is empty or not:
function check_null(form) {
if(form.CompSearch.value < 1)
{alert('Enter a part to search for!');
document.Searcher.CompSearch.focus();
return false}
else
return true
}
Note: you might want to change form.CompSearch.value < 1

Yeah the form is HTML, and the data collection is Perl. I hadn't thought of using Javascript, which I suppose was a bit narrow-minded of me, thanks.

Yes, especially since that can't be done in perl.