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 @_ array within the lexical scope of subroutines and formats, and the @ARGV array at file scopes or within the lexical scopes established by the eval '', BEGIN {}, END {}, and INIT {} constructs. See also unshift(), push(), and pop(). Shift() and unshift() do the same thing to the left end of an array that pop() and push() do to the right end.