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 @_ 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 {}", "INIT {}", "CHECK {}", and "END {}" 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.