It dies because you call get_cb_values at line 63 without the program's interface actually running yet. How do you want that to work?

I changed that line as follows, and the interface comes up, apparently ready to search:

my $s_button = $mw->Button(-text => 'Search', -command => sub{search(g
+et_cb_values())} );
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Now the routine isn't called until the button is clicked.