$ perl -e'
   use Carp qw( croak );
   sub foo { croak "bar" }
   foo();
'
bar at -e line 3.
        main::foo() called at -e line 4

##</code><code>##

$ perl -e'
   use Carp qw( croak );
   BEGIN { *foo = sub { croak "bar" }; }
   foo();
'
bar at -e line 3.
        main::__ANON__() called at -e line 4

##</code><code>##

$ perl -e'
   use Carp qw( croak );
   use Sub::Util qw( set_subname );
   BEGIN { *foo = set_subname "foo", sub { croak "bar" }; }
   foo();
'
bar at -e line 4.
        main::foo() called at -e line 5