If you want a way to update the status bar, Tk::after might be what you need.

It allows time delayed callbacks to be made to a particular subroutine. So, you could have a subroutine that checks progress, and updates the status bar variable. This would be called by the $w->after command. (you can set a reference to the callback and the delay in milliseconds between calls.

The widget example that I referred to is found in the standard distribution. Just in case you can't get your hands on a copy, I'm pasting it in here. Unfortunately, all my scripts that use Tk::ProgressBar are back at home :o) several thousand miles away...

# ProgressBar - display various progress bars.

use strict;
use Tk;
use Tk::ProgressBar;
use Tk::Scale;

my $mw = MainWindow->new;

my $status_var = 0;

my($fromv,$tov) = (0,100);
foreach my $loop (0..1) {
    my $res = 0;
    my $blks = 10;
    my @p = qw(top bottom left right);
    foreach my $dir (qw(n s w e)) {
        $mw->ProgressBar(
        -borderwidth => 2,
        -relief => 'sunken',
        -width => 20,
        -padx => 2,
        -pady => 2,
        -variable => \$status_var,
        -colors => [0 => 'green', 50 => 'yellow' , 80 => 'red'],
        -resolution => $res,
        -blocks => $blks,
        -anchor => $dir,
        -from => $fromv,
        -to => $tov
        )->pack(
        -padx => 10,
        -pady => 10,
        -side => pop(@p),
        -fill => 'both',
        -expand => 1
    );
    $blks = abs($blks - ($res * 2));
    $res = abs(5 - $res);
    }
    ($fromv,$tov) = ($tov,$fromv);
}

$mw->Scale(-from => 0, -to => 100, -variable => \$status_var)->pack;

MainLoop;
[download]

What I'd suggest is that you have a method that updates the variable $status_var in a callback.
ie:

 
# Your script should have
$MainWindow->after(10,\&update_var);

# this is the update variable callback.
sub update_var {
    $status_var = $work_done/$total;
    $status_var = $status_var * 100; # get percentage
}
[download]