Hope this helps. Try the following demo code, first run it as is, then comment out that $mw->update() line, run it again, and see what happens.

• With update() line, the status is reported back to you right the way from time to time.
• Without it, your GUI hangs, and nothing gets reported until the whole process is done.

(When you try it, you may want to adjust those big numbers base on the speed of your machine.)

use Tk;
use Tk::ProgressBar;
use strict;
use warnings;

my $count;

my $mw = new MainWindow(-title => "demo");
$mw->Button(-command => [\&a_long_process, \$count], -text => "A Long 
+Process")->pack();
my $pb = $mw->ProgressBar(
        -from => 0,
        -to => 100000,
        -blocks => 100000,
        -colors => [0, 'green', 30000, 'yellow' , 60000, 'red'],
        -variable => \$count
)->pack();
MainLoop;

sub a_long_process {
    my $hash = {};
    for (0..100000) {
        $hash->{$_} = $_;
        $count ++;
        $mw->update(); #try to comment and uncomment this
        ;
    }
}
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