$retval = fork();
if ($retval == -1) {
    die "fork() failed: $!\n";
} elsif ($retval == 0) {
    exec("$find / -type f > tmp.txt 2>&1") || die "Error\n";
} else {
     while(!waitpid ($retval, WNOHANG)) {
     if ( $percent_done == 150) { $percent_done=0 } else { $percent_done++; $toplw->update(); sleep 1; }
     } 
}