One neat perl trick is the ability to push elements onto an array while you iterate over it. Note don't try to do anything but push unless you are feeling *very* lucky. For example you can 'recurse' the file structure with a handful of lines:

sub recurse_tree {
    my @dirs = @_;
    my @files;
    for my $dir ( @dirs ) {
        opendir DIR, $dir or error("Can't open $dir\n");
        while ( my $file = readdir DIR ) {
          next if $file eq '.' or $file eq '..';
          next if -l "$dir/$file";
            push @dirs, "$dir/$file" if -d "$dir/$file";
            push @files, "$dir/$file" if -f "$dir/$file";
        }
        closedir DIR;
    }
  return \@dirs, \@files;
}
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One of the intersting features of this algorithm is that it proceeds width first, rather than depth first as with most recursive algorithms.