my $fh = new FileHandle;
my $pid = open( $fh , "tail -f -n 25 command_file  | ") or die ;
#.....
# now you can check the output of ps to see if you get a shell $pid 
# or just your process $pid
# then to make sure you kill all shells and commands, if you see
# the $pid is the shell

use Proc::Killfam;
$mw->protocol('WM_DELETE_WINDOW' => sub {
                       killfam 9,$pid;
                       exit;
                      });
# or put the killfam in the callback of an Exit button, etc