After playing around a bit, here's an example of  STDIN accessibility both before and after the  MainLoop function. I don't know how kosher this may be. Again, this code is launched from the command line.

>perl -wMstrict -le
"use Tk;
 ;;
 my $text;
 ;;
 my $mw = MainWindow->new;
 ;;
 $mw->Label(-text => 'Enter text: ')->pack();
 $mw->Entry(-textvariable => \$text)->pack();
 $mw->Button(-text => 'Submit', -command => sub { $mw->destroy }
   )->pack();
 ;;
 print qq{before MainLoop: enter text: };
 my $pre_ml = <STDIN>;
 chomp $pre_ml;
 ;;
 MainLoop;
 ;;
 seek STDIN, 0, 2;
 print qq{after MainLoop: enter more text: };
 my $post_ml = <STDIN>;
 chomp $post_ml;
 ;;
 print qq{before MainLoop: '$pre_ml'};
 print qq{in MainLoop: '$text'};
 print qq{after MainLoop: '$post_ml'};
"
before MainLoop: enter text:
Before
after MainLoop: enter more text:
After all
before MainLoop: 'Before'
in MainLoop: 'hi there'
after MainLoop: 'After all'
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