shift
shift - remove the first element of an array, and return it
shift ARRAY
shift
Shifts the first value of the array off and returns it, shortening the
array by 1 and moving everything down.  If there are no elements in the
array, returns the undefined value.  If ARRAY is omitted, shifts the
@ARGV
 array in the main program, and the @_ array in subroutines.
(This is determined lexically.)  See also 
unshift()
, 
push()
, and 
pop()
.
Shift() and 
unshift()
 do the same thing to the left end of an array
that 
push()
 and 
pop()
 do to the right end.