Here is a test script. Run it with a -g as the first parameter.

On a machine without Tk, it will correctly die.
On a machine with Tk, it *should* bring up a simple Tk window, but it exits instead. If I replace the 'require' and 'import' with the 'use', then it works.

if ($ARGV[0] =~ /-g/) {
   # do gui
   
   die "You need Tk." unless (eval("require Tk;"));

   #use Tk;
   require Tk;
   Tk->import;

   $mw = MainWindow->new;
   $mw->Button(-text=>"EXIT",
               -command=>sub{exit})->pack(-side=>"bottom",
                                          -fill=>"both");
   MainLoop;

   print "gui done.\n";

} else {
   # do non-gui

   print "non-gui stuff\n";
}
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