This strips off the last directory if more than one directory in path:

foreach my $path (<DATA>) {
    chomp($path);
    $path =~ s{(?<=[^/])/[^/]+/?$}{}xms;
    print $path . "\n";
}

__DATA__
/rootdir/sub funky ---doodash/la la la/Proposal for Buttering My Feet
/rootdir/sub1/sub2/sub3/sub4/
/rootdir/sub1/sub2/sub3/sub4/file/
/rootdir/
/
[download]

Hope this helps