Assume that you want to share the CGI.pm object (I will use $q) between your modules. For example, you create it in script.pl, but you want it to be visible in My::HTML. First, you make $q global.

  script.pl:
  ----------------
  use vars qw($q);
  use CGI;
  use lib qw(.); 
  use My::HTML qw($q); # My/HTML.pm is in the same dir as script.pl
  $q = CGI->new;

  My::HTML::printmyheader();

Note that I have imported $q from My::HTML. And My::HTML does the export of $q:

  My/HTML.pm
  ----------------
  package My::HTML;
  use strict;

  BEGIN {
    use Exporter ();

    @My::HTML::ISA         = qw(Exporter);
    @My::HTML::EXPORT      = qw();
    @My::HTML::EXPORT_OK   = qw($q);

  }

  use vars qw($q);

  sub printmyheader{
    # Whatever you want to do with $q... e.g.
    print $q->header();
  }
  1;

So the $q is shared between the My::HTML package and script.pl. It will work vice versa as well, if you create the object in My::HTML but use it in script.pl. You have true sharing, since if you change $q in script.pl, it will be changed in My::HTML as well.

What if you need to share $q between more than two packages? For example you want My::Doc to share $q as well.

You leave My::HTML untouched, and modify script.pl to include:

 use My::Doc qw($q);

Then you add the same Exporter code that I used in My::HTML, into My::Doc, so that it also exports $q.

One possible pitfall is when you want to use My::Doc in both My::HTML and script.pl. Only if you add

  use My::Doc qw($q);

into My::HTML will $q be shared. Otherwise My::Doc will not share $q any more. To make things clear here is the code:

  script.pl:
  ----------------
  use vars qw($q);
  use CGI;
  use lib qw(.); 
  use My::HTML qw($q); # My/HTML.pm is in the same dir as script.pl
  use My::Doc  qw($q); # Ditto
  $q = new CGI;

  My::HTML::printmyheader();

  My/HTML.pm
  ----------------
  package My::HTML;
  use strict;

  BEGIN {
    use Exporter ();

    @My::HTML::ISA         = qw(Exporter);
    @My::HTML::EXPORT      = qw();
    @My::HTML::EXPORT_OK   = qw($q);

  }

  use vars     qw($q);
  use My::Doc  qw($q);

  sub printmyheader{
    # Whatever you want to do with $q... e.g.
    print $q->header();

    My::Doc::printtitle('Guide');
  }
  1;

  My/Doc.pm
  ----------------
  package My::Doc;
  use strict;

  BEGIN {
    use Exporter ();

    @My::Doc::ISA         = qw(Exporter);
    @My::Doc::EXPORT      = qw();
    @My::Doc::EXPORT_OK   = qw($q);

  }

  use vars qw($q);

  sub printtitle{
    my $title = shift || 'None';

    print $q->h1($title);
  }
  1;