Perl 5 version 24.0 documentation
Pops and returns the last value of the array, shortening the array by one element.
Returns the undefined value if the array is empty, although this may also happen at other times. If ARRAY is omitted, pops the @ARGV array in the main program, but the @_ array in subroutines, just like shift.
Starting with Perl 5.14, an experimental feature allowed pop to take a scalar expression. This experiment has been deemed unsuccessful, and was removed as of Perl 5.24.