$ perl -e" Demo(); "
Undefined subroutine &main::Demo called at -e line 1.

$ perl -e" sub demo {warn 666} Demo(); "
Undefined subroutine &main::Demo called at -e line 1.

$ perl -e" package Demo;sub Demo {warn 666}; package main; Demo(); "
Undefined subroutine &main::Demo called at -e line 1.