I don't always know how variable arrives in a script.  To be general, I have a function ClearVar($Name) that accepts the name of a variable, and goes through all of the global arrays to clear it.

This appears to work properly with HTTP_GET_VARS and HTTP_POST_VARS, but the GLOBALS array is a funny fish.

In fact, playing around to try to figure it out, I tried:

$Piano = "Hemmingway";
print "Before: Piano = $Piano<br>\n";
unset($GLOBALS["Piano"]);
print "After: Piano = $Piano<br>\n";

Which outputs:

Before: Piano = Hemmingway
After: Piano = ??0????

or some variant of that.

More surprisingly, if I use unset on an element of the GLOBALS array within a function even odder things happen.  The following code:

$Piano = "Hemmingway";
print "Before: Piano = $Piano<br>\n";
ClearTest();
print "After: Piano = $Piano<br>\n";

$Piano = "Brahmbach";

print "Before: Piano = $Piano<br>\n";
ClearTest();
print "After: Piano = $Piano<br>\n";


function ClearTest()
{
	global $Piano;	
	print "Before[ClearTest]: Piano = $Piano<br>\n";
	MyClearVar("Piano");
	print "After[ClearTest]: Piano = $Piano<br>\n";

}
function MyClearVar($Name)
{
	unset($GLOBALS[$Name]);
}

Produces the following:

Before: Piano = Hemmingway
Before[ClearTest]: Piano = Hemmingway
After[ClearTest]: Piano = Hemmingway
After: Piano = |6(
Before: Piano = Brahmbach
Before[ClearTest]: Piano = 
After[ClearTest]: Piano = 
After: Piano = Brahmbach

So apparently not all is simple with $GLOBALS.  There maybe something I'm missing, I may be abusing a convenience method, but boy are the results strange.