sub _system {
    my $prog = shift;
    my $rv = system( { $prog } $prog => @_ );
    if    ($rv == -1)         { die("Can't launch $prog: $!\n"); }
    elsif (my $s = $rv & 127) { die("$prog died from signal $s\n"); }
    elsif (my $e = $rv >> 8)  { die("$prog exited with code $e\n"); }
}