use File::Path;

sub purge {
    my $n = shift; # 100, for example

    my @newest_first = do {
        my @dir = grep -d, </var/script/proc/*>;
        my @age = map -M, @dir;
        @dir[ sort { $age[$a] <=> $age[$b] } 0 .. $#dir ];
    };

    splice @newest_first, 0, $n;

    rmtree \@newest_first, 0, 1 if @newest_first;
}
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Makeshifts last the longest.