The push keyword

The push function treats ARRAY as a stack by appending LIST values to ARRAY. Returns the number of elements in the ARRAY after push is completed.

From Perl 5.14.0 onwards, a scalar EXPRESSION can be passed that should hold a reference to an unblessed array. The argument is dereferenced automatically. This is a highly experimental aspect of push and may change in future Perl versions.

  push ARRAY, LIST
  push EXPRESSION, LIST