The repeat() call is only there to demo the progress bar; your actual code will probably not need to use repeat() at all. Write your Perl/TK program as normal, but whenever an event occurs that marks a further step toward the completion of the task, update $Progress at the end of that event. For example:

use strict;
use warnings;
use Tk;
use Tk::StatusBar;

my $mw = MainWindow->new();

$mw->Label(  -text => 'Mission: knock three times' )->pack();
$mw->Button( -text => 'Knock', -command => \&knock )->pack();

my $sb = $mw->StatusBar();

my $Label1 = 'Progress in knocking:';
$sb->addLabel( -textvariable => \$Label1 );

my $Progress = 0;
sub knock {
    print "Knocking\n";
    $Progress += 33;
    $Label1 = 'Done!' if $Progress >= 99;
}
$sb->addProgressBar(
    -length         =>  60,
    -from           =>   0,
    -to             =>  99,
    -variable       => \$Progress,
);

MainLoop();
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