use Tk::IO;

# callback for 'Run' Button
sub RunCB {
  $fh = new Tk::IO->new(-linecommand => \&guiReadTestHandle,
                       -childcommand => \&guiCloseTestHandle);
  $fh->exec("test.pl");
}

# callback for when $fh is readable<BR>
sub guiReadTestHandle {
  if (<$fh>) {
    $txtRunRslt->insert(end, $data);
  }
}

# callback for when $fh reaches EOF
sub guiCloseTestHandle {
  $fh->close();
}