and when I ran it on a perl module like Tie::Scalar (path supplied by perldoc -l) it gave me nothing, since the module doesn't export globals.

Well, the script I provided is for the case you mentioned - just a file with subs in it, without any package declaration whatsoever (and inspecting the symbol table hasn't anything to do with what is exported - the ad-hoc package Query doen't export anything, either). Now, Tie::Scalar has a package declaration - package Tie::Scalar; - and the script isn't suitable for that case. You would have to inspect %Tie::Scalar. I'd reach for something else for the general case, maybe even PPI.

I think the right answer to this is to simply grep the file for /^sub/, unless you're trying to get a list of dynamically generated coderefs??

That heavily depends on what is "right" for you and the task at hand. More general would be grepping for /^\s*sub/. But that won't give you not only dynamically generated subrefs, but also typeglob-bound code generated at module use, such as generated by Class::Accessor:

package Foo;
BEGIN {
   our ($VERSION, @ISA, @METHODS);
   @METHODS = qw(foo bar quux);
 
   for my $field (@METHODS) {
       *{__PACKAGE__.'::'.$field} = sub {
          my $self = shift @_;
          if (@_) {
            return $self->set($field, @_);
          } else {
            return $self->get($field);
          }
      };
   }
   for (qw(set get)) {
      *{__PACKAGE__.'::'.$_} = sub {
          my $self = shift @_;
          if (@_ == 1) {
            return $$self{$_[0]};
          } elsif (@_ > 1) {
            return $self->{$_[0]} = $_[1];
          } else {
            $self->_croak('Wrong number of arguments received');
          }
      };
   }
}
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