use 5.010;

sub old     { say "$_ " . ($_[0] // '<undef>' ) }
sub new (_) { say "$_ " . ($_[0] // '<undef>' ) }

old() for qw/ global /;
new() for qw/ global /;

local $_ = 'global';
my $_;
old() for qw/ lexical /;
new() for qw/ lexical /;

__END__
global <undef>
global global
global <undef>
global lexical