sub hooked_system(&@)
{
    my ($hook,@args)=@;
    my $pid=fork() // die "Can't fork: $!";
    if ($pid) {
        # (parent)
        waitpid($pid,0);
        # plus whatever is needed to collect data from the child
    } else {
        # (child)
        $hook->();
        exec { $args[0] } @args or die "exec failed: $!";
    }
}