liverpole's thread example is pretty good, but for many reasons you really don't want to launch a thread for something as simple as a non-blocking execution of a function.

For instance, the code in liverpole's example

sub button_press {
    my $sthread = threads->new(sub { worker_thread() });
    $sthread->detach();
    # Here we "return immediately" :)
    return;
}
[download]

where the thread is created in a button callback, after Tk code has been invoked in main, has a possible problem. Many nodes have been posted previously, on how some of the "copy-on-write" Tk code gets copied into the thread, and sometimes causes "free to wrong pool" errors. The example works, but it is a very simple button press. I'm just saying, beware of the non-thread-safety of the Tk module. The general advice to absolutely avoid the possible problem, is shown in PerlTk on a thread....... the copy-on-write thread action combined with the non-thread safety of Tk, means you need to follow alot of restrictions for foolproof operation of your Tk-threaded program.

However, threads aside, if you just want to execute something and move on, you can fork it off with a piped open, IPC::Open3, etc. Then use Tk::fileevent, or i used a timer in the first code block, to read the results as they come back in.

#!/usr/bin/perl
use warnings;
use strict;
use Tk;

my $mw = MainWindow->new(-background => 'gray50');

my $text = $mw->Scrolled('Text')->pack();

my $pid;
my $startb = $mw->Button( -text => 'Start',
                -command=> \&work,
                 )->pack();

my $count = 0;
my $label = $mw->Label(-textvariable=>\$count)->pack();

my $testtimer = $mw->repeat(500,
                   sub { $count++}  );

my $stopb = $mw->Button( -text => 'Exit',
                -command=>sub{
                 kill 9,$pid;
                 exit;
              },
                 )->pack();

MainLoop;
#####################################

sub work{

$startb->configure(-state=>'disabled');

use Fcntl;                                                            
+             
  my $flags;                                                          
+               
 
  #long 10 second delay between outputs
  $pid = open (my $fh, "top -b -d 10 |" ) or warn "$!\n";

  fcntl($fh, F_SETFL, O_NONBLOCK) || die "$!\n"; # Set the non-block f
+lags  

   my $repeater; 
   $repeater = $mw->repeat(10,
          sub {
                if(my $bytes = sysread( $fh, my $buf, 1024)){;
            $text->insert('end',$buf);    
                $text->see('end');         
          }
      }
     );             
}
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and reading with a fileevent

#!/usr/bin/perl 
use warnings;
use strict;
use IPC::Open3;
use Tk;

$|=1;
my $pid=open3(\*IN,\*OUT,0,'/bin/bash');

my $mw=new MainWindow;
$mw->geometry("600x400");

my $t=$mw->Scrolled('Text',-width => 80,
     -height => 80,
     )->pack;

&refresh;

$mw->fileevent(\*OUT,'readable',\&write_t);
my $id = Tk::After->new($mw,2000,'repeat',\&refresh);

MainLoop;

sub refresh{
print IN "top b n 1";
print IN "\n";  #absolutely needed and on separate line
}

sub write_t {
  my $str= <OUT>;
  $t->insert("1.0",$str);
#  $t->see("0.0");
}
__END__
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