...
$tks->signal_connect( 'clicked' => sub {
    my $command = "tw pro:$currproj";
    my $ret = fork();
    if($ret == 0) {
        # this is the fork: become $command and go away.
        exec("gnome-terminal", "-e", "bash -c '$command; bash'");
    }
    else { # this is the parent: do nothing and go ahead. }
    return FALSE;
} );

##</code><code>##

 2504 ?        00:00:01 perl
 2509 ?        00:00:01 gnome-terminal <defunct>
 2573 ?        00:00:01 gnome-terminal <defunct>
 2638 ?        00:00:01 gnome-terminal <defunct>
 2702 ?        00:00:01 gnome-terminal <defunct>
 2767 ?        00:00:00 gnome-terminal
 2773 ?        00:00:00 gnome-pty-helpe