sub purge {
  my $n = shift; # 100, for example
  my @newest_first =
    map $_->[0],
    sort { $a->[1] <=> $b->[1] }
    map [$_, -M],
    </var/script/proc/*>;
  system "/bin/rm", "-rf", @newest_first[$n..$#newest_first]
    if @newest_first > $n;
}