in reply to undef-ing an active subroutine

So deactivate it:

>perl -wle"sub real_AUTOLOAD { undef &AUTOLOAD; } sub AUTOLOAD { print + 'A'; goto &real_AUTOLOAD } f() for 1..2;" A Undefined subroutine &main::f called at -e line 1.

Getting rid of the whole glob works too:

>perl -wle"sub AUTOLOAD { print 'A'; undef *AUTOLOAD; } f() for 1..2;" A Undefined subroutine &main::f called at -e line 1.