Because I was trying a variety of things, the solution below is rather untidy (stuff left over from things that didn't work)

However, I am running short of time, so I simply give you something that might be what you are looking for.

Main points:
1. Use $mainWindow->update() within loops. It keeps Tk alive
2. Launching process using after allows you to continue processing within your current process (kinda like thread?)
3. If you are using a system command that blocks your process, you should look at fileevent and pipes.

Good luck.

use strict; 
use warnings; 
use Tk; 
my $excelflag;
 
my $mainWindow = MainWindow->new; 
my $textBox = $mainWindow->Scrolled("Text", -width=>80, -height=>7, 
      -scrollbars=>"ose", -wrap=>"word")->pack(); 
 
#my $goBut = $mainWindow->Button(-foreground=>"blue", -text=>"Click", 
#                   -command=>sub { $thr = threads->new(\&excecute) } 
+)->pack(); 
 
my $goBut = $mainWindow->Button(-foreground=>"blue", -text=>"Click", 
                   -command=>sub { excecute() } )->pack(); 

my $stopBut = $mainWindow->Button(-foreground=>"red", -text=>"Stop", 
                   -command=>sub{ $excelflag = 1 })->pack(); 
 
my $exitBut = $mainWindow->Button(-foreground=>"red", -text=>"Exit", 
                   -command=>sub{ $excelflag = 1; exit })->pack(); 
 
MainLoop; 
 
sub excecute 
{ 
        $goBut->configure(-state=>"disabled"); 
        $textBox->configure(-state=>"normal"); 
        $excelflag = 0;
        $textBox->after(2,\&excel);
        open(FILE,"C:/file.txt") or die "Can't open file.\n"; 
        while(<FILE>) 
        { 
                my $message = $_; 
                $textBox->insert('end', $message); 
        } 
        close(FILE); 
 
        $textBox->configure(-state=>"disabled"); 
        $textBox->see('end'); 
        return;
}

sub excel {
        use Win32::OLE; 
        use Win32::OLE::Const 'Microsoft Excel'; 
 
        my ($Excel,$Workbook,$fileOutput,$CurrentSheet,$Range); 
        $fileOutput = "C:/test.xls"; 
 
        $Excel = Win32::OLE->new('Excel.Application', 'Quit') || 
        die "Can't create Excel object. \n"; 
        $Excel->{'Visible'}                  = 1;    #0 is hidden, 1 i
+s visible 
        $Excel->{DisplayAlerts}              = 0;    #0 is hide alerts
+ 
        $Excel->{SheetsInNewWorkbook}        = 1; 
        $Workbook = $Excel->Workbooks->Add(); 
 
        $Workbook->SaveAs($fileOutput) or die "Can't save Excel.\n"; 
        $CurrentSheet = $Workbook->Worksheets(1); 
        $CurrentSheet->Select; 
 
        for (my $i=1; $i<=6500; $i++) 
        { 
                $Range = $CurrentSheet->Range("A$i"); 
                $Range->{Value} = $i; 
                sleep(0.01); 
                $mainWindow->update();
                last if $excelflag;
        } 
 
        $Workbook->Save(); 
        $Workbook->Close(); 
        $Excel->Quit(); 
        Win32::OLE->FreeUnusedLibraries(); 
        $goBut->configure(-state=>"normal");
        return;
}
[download]

Sandy

Thanks for the code Sandy. When I test the code you gave to me, I get my GUI to freeze up until it's done running the Excel part. It's the same way I have before, and this is why I switch to threads to prevent the GUI from freezing up.

1. You cannot spawn a thread from a Tk Button callback.

2. You cannot access a Tk widget from a thread.

Here is some code to show you how to use shared variables and Tk with threads. I don't use win32, so OLE stuff is left out and may be a bigger problem yet.

#!/usr/bin/perl
use strict;
use warnings;
use Tk;
use threads;
use threads::shared;

my $data:shared = '';
my $go_control:shared = 0;
my $die_control:shared = 0;

#create thread before any Tk
my $thr = threads->new(\&excecute);


my $mainWindow = MainWindow->new;

my $textBox = $mainWindow->Scrolled("Text", -width=>80, -height=>7,
      -scrollbars=>"ose", -wrap=>"word")->pack();

my $goBut; # need to declare here so can be used in -command
$goBut = $mainWindow->Button(-foreground=>"blue", -text=>"Click",
                   -command=>sub { $goBut->configure(-state=>"disabled
+");
                               $textBox->configure(-state=>"normal");
                   $go_control = 1; #start thread
                   } )->pack();

my $stopBut = $mainWindow->Button(-foreground=>"red", -text=>"Exit",
                   -command=>sub{  $die_control = 1;
                   $thr->join;    
                   exit;
                   })->pack();

#use a timer to read the shared variable and deal with Tk stuff

my $repeater = $mainWindow->repeat(20,sub{
                
                $textBox->insert('end',$data);
                $textBox->see('end');


             });


MainLoop;


sub excecute{
   
#   require Win32::OLE;
#   require Win32::OLE::Const 'Microsoft Excel';
   
   while(1){
      
      #wait for $go_control  
      if($go_control){      
           open(FILE,$0 ) or die "Can't open file.\n";
             while(<FILE>){
              if($die_control){return} 
              $data = $_;
         }
       close(FILE);
     }else{ select(undef,undef,undef,.25); }# sleep until awakened 
   }
    
return;
}
[download]