You actually want this: 
if (exists $USER{coffee} && $USER{coffee} > 5){$msg='You drink too muc
+h coffee'}

[download]

It checks that the coffee key exists in %USER. You can just use 

if ($USER{coffee} && $USER{coffee} > 5){$msg='You drink too much coffe
+e'}

[download]
It will get rid of the warning, but won't actually do anything useful. exists checks that the coffee key was created. This check actually tells you a potentially relevant piece of information. e.g 
if (! exists $USER{coffee}){
    $msg = 'You drank no coffee?!?!';
}
elsif ($USER{coffee} > 5){
    $msg='You drink too much coffee';
}
else {
    $msg='You drank a moderate amount of coffee';
}

[download]
There is no point in adding code just to get rid of a warning if the new code does nothing useful! It is a poor practice to get into and can be confusing to the people that have to maintain you application. Like Abigail said check your input to make sure no one made a mistake inputting a value (or is pulling a fast one on you).

This doesn't seem to be the behaviour that you want.

HTH,
Clayton

Update:
I removed a section that said testing if a non exsistant key was defined would autovivify it and added my support for Abigail's answer. I swear with God as my witness...

In reply to Re: -w in production environment by clscott
in thread -w in production environment by gwhite

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