array_shift() shifts the first value of the
array off and returns it, shortening the
array by one element and moving everything
down. All numerical array keys will be modified to start counting from zero
while literal keys won't be touched. If array is empty
(or is not an array),
NULL will be returned.
This function will reset() the array pointer after use.
$stack = array("orange", "banana", "apple", "raspberry");
$fruit = array_shift($stack);
This would result in
$stack having 3 elements left:
 => banana
 => apple
 => raspberry
orange will be assigned to