#!/usr/bin/perl -wT

use strict;
use File::Spec::Functions qw(catdir rootdir no_upwards);

use constant START_DIR => catdir(rootdir, qw(users foo));

opendir DIR, START_DIR
  or die 'Could not open directory ', START_DIR, ": $!";

while( defined(my $file = readdir DIR) ) {
  next unless no_upwards($file);
  print "$file\n";

  #...do something with $file
}

closedir DIR;