There is also Tk::ProgressIndicator which may be a bit simpler.

#!/usr/bin/perl
use strict;
use warnings;
use Tk;
use Tk::ProgressIndicator;
my $MainWindow = MainWindow->new();
my $total = 100;    # this will vary 
my $ProgressIndicator = $MainWindow->ProgressIndicator
(
              '-current' => 0,
              '-limit' => 100,   # this is fixed! 
              '-increment' => 1,
              '-height' => 20,
              '-width' => 400
)->pack;

foreach my $offset (0..$total)
{
     $ProgressIndicator->configure ('-current' => $offset*100/$total,)
+;
     $MainWindow->update;
}
MainLoop;
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