The following demonstrates a Tk app that updates the screen in response to the output from another Perl process in real time:

#!perl -slw
use strict;
use threads;
use threads::shared;

## A shared var to communicate progress between work thread and TK
my $progress : shared = 0;

sub work{
    open PROC, 
      'perl -le"$|=1; print and select(undef,undef,undef,0.1) for 1 ..
+ 1000" |'
        or die $!;
    while( <PROC> ) {
        lock $progress;
        $progress = $_;
    }
    close PROC;
}

threads->new( \&work )->detach;

require Tk::ProgressBar;

my $mw = MainWindow->new;
my $pb = $mw->ProgressBar()->pack();

my $repeat;
$repeat = $mw->repeat( 100 => sub {
#    print $progress;
    $repeat->cancel if $progress == 100;
    $pb->value( $progress ) }
);


$mw->MainLoop;
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