It needed the code "my $buffer = $textview_nav->get_buffer".

Doh!!! I shouldn't have missed that. I see the problem now.... in your code you create the textview (with a an automatic buffer ), and you thought it was using $buffer.

#my $textview_nav = Gtk2::TextView->new; 
# should have been
my $textview_nav = Gtk2::TextView->new_with_buffer($buffer);
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If you had used new_with_buffer($buffer) , then reading from the global $buffer would have worked. As it now is written, your global $buffer is unused.

P.S. You might also want to add a line to make the textview have the cursor when it opens.

my $rc = 
Gtk2::Gdk->keyboard_grab($textview_nav->window, 0 ,
                                     Gtk2->get_current_event_time);
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