Use the debugger... put a breakpoint on the line before the call $DB::single = 1;:
$DB::single = 1;
$des->all();
Then run it from the command line with the -d param: perl -d script.pl. You'll be dropped into the debugger. Simply type c to 'continue' all the way to your breakpoint, then s to 'step' into the next line of code which should give you some insight:
main::(test.pl:6): my $des = Devel::Examine::Subs->new({file => 'sh
+ift.pl'});
DB<1> c
main::(test.pl:9): $des->all();
DB<1> s
Devel::Examine::Subs::all(/usr/lib/perl5/site_perl/5.22.0/Devel/Examin
+e/Subs.pm:382):
382: my $self = shift;
-stevieb