I had the same problem with the same Tk version (which happens to be the ActiveState distributes with ActivePerl 5.8).

See RT Bug 13400. You could try upgrading to a newer Tk. I simply chose not to use the ProgressBar.

Commenting out the last line (#$mw->update();) I found that the program runs as before (update is not needed) and there is no more memory leak.

The strange thing is that the same effect (no leak) can be obtained commenting out the $percent=rand(100); line instead of the update line.

In this last version I occasionally get this message in console:

Tk::Error: Usage $widget->update(...)
MainWindow=HASH(0x8286464) is not a Tk object at ./x.pl line 28.
 Tk callback for .button
 <ButtonRelease-1>
 (command bound to event)
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IMHO this seems to imply that the update method is not fully reentrant and so repeated calls to it may cause a problem. I don't know if this can be related to the memory leak problem that looks like a var reference not correctly freed...

I tested your code on my Linux box (Debian Sarge Etch) and I detected the same problem: about 40 KByte of overhead every click.

10x, the problem is when using the ProgressBar in more complicated application and the build up is much more. It just eats memory. Maybe I should build my own progressbar and see whether it will help.

#!/usr/bin/perl
use strict;
use Tk;
use Tk::ProgressBar;

my $mw=MainWindow->new;

my $percent;

my $pb=$mw->ProgressBar(
   -height      => 0,
   -width       => 20,
   -length      => 100,
   -colors=>[0,'blue'],
   -blocks=>100,
  )->pack;

my $btn=$mw->Button(
   -command => \&show_progress,
   -text    => 'Run program',
  )->pack;
  
MainLoop;

sub show_progress{
    for (1..100) {
        $percent=rand(100);
       $pb->value($percent);
    }
}
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#!/usr/bin/perl
use strict;
use Tk;

my $mw=MainWindow->new;

my $percent;

my $pb= $mw->Label(
    -bg => 'white',
    -fg => 'blue',
    -width       => 60,
    -justify => 'left',
    -anchor => 'w',
    )->pack();

my $label1 = $mw->Label(
      -textvariable=> \$percent,
  )->pack();


my $timer = $mw->repeat(10,\&show_progress);
  
MainLoop;

sub show_progress{
        $percent += 1;
        if($percent >= 100){$percent = 0}

        my $str = '|' x $percent;                               
        $pb->configure(-text => $str );   
}
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#!/usr/bin/perl
use strict;
use warnings;
use Tk::Carp qw/fatalsToDialog/;
use Tk::Carp qw/warningsToDialog/;
use Tk;

my (
    $in_file_name,
    $out_file_name,
    $MW,
    $message,
    $count_runs
);
$MW = MainWindow->new(-title=>"Open/read times");

my $Frame=$MW->Labelframe(
   -text               => 'Input Parameters',
  )->pack();
  
my $Ent_In_File_Name=$Frame->Entry(
   -textvariable => \$in_file_name,
  )->grid(
   -row    => 0,
   -column => 0,
   -sticky => 'w',
  );
  
my $Btn_Open_File=$Frame->Button(
   -command => 'main::open_file',
   -text    => 'Open File',
  )->grid(
   -row    => 0,
   -column => 1,
   -sticky => 'w',
  );
  
my $Btn_run=$Frame->Button(
   -command => 'main::run_program',
   -text    => 'Run program',
  )->grid(
   -row    => 3,
   -column => 0,
   -sticky => 'w',
  );
  
my $Ent_Run=$Frame->Entry(
  )->grid(
   -row    => 3,
   -column => 1,
   -sticky => 'w',
  );
  
###### SUBROUTINES ###################################################
+##########
sub open_file {
    my $file_name_open=$MW->getOpenFile();
    $Ent_In_File_Name->delete(0,'end');
    $Ent_In_File_Name->insert(0,$file_name_open);
}
sub run_program {
    $count_runs++;
    my @data;
    open MYFILE ,$in_file_name or die "Could not open file to read:$in
+_file_name\n";
    while(<MYFILE>) {
        my $temp=$_;
        chomp $temp;
        my @array=split("\t",$temp);
        push(@data,[@array]);
    }
    close MYFILE;
    $Ent_Run->delete(0,'end');
    $Ent_Run->Insert("open/read N:$count_runs");
}

MainLoop();
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#!/usr/bin/perl
use warnings;
use strict;

my $in_file="\\in_file\.txt";
my $count_runs=0;


while (1) {
    $count_runs++;
    my @data;
    open MYFILE ,$in_file or die "Could not open file to read:$in_file
+\n";
    while(<MYFILE>) {
        my $temp=$_;
        chomp $temp;
        my @array=split("\t",$temp);
        push(@data,[@array]);
    }
    close MYFILE;
    print "run $count_runs\n";
    <>;
}
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#!/usr/bin/perl
use warnings;
use strict;

my $in_file="\\in_dile\.txt";
my $count_runs=0;


while (1) {
    $count_runs++;
    read_file();
    print "run $count_runs\n";
    <>;
}

sub read_file {
    my @data;
    open MYFILE ,$in_file or die "Could not open file to read:$in_file
+\n";
    while(<MYFILE>) {
        my $temp=$_;
        chomp $temp;
        my @array=split("\t",$temp);
        push(@data,[@array]);
    }
    close MYFILE;
}
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