use strict ;
use warnings ;

my $dir = "/var/tmp/monk";
chdir("$dir") or die "$!";
opendir(DIR, $dir) or die "Can't open $dir: $!";

sub task {
  my $entry = shift || 'n/a' ;
  # got an entry, do something
  print 'got one: ', $entry, "\n" ;
}

sub check {
  my $entry = readdir DIR ;
  while ($entry && ($entry eq '.' || $entry eq '..')) {
    $entry = readdir DIR ;
  }
  if ($entry) {
    task($entry) ;
    check() ;
  }
  else {
    close DIR ;
    # uncomment for a script you can daemonize
    #sleep 1 ;
    #opendir(DIR, $dir) or die "Can't open $dir: $!";
    #check() ;
  }
}

check() ;
[download]

P.S. This takes the previous example and makes it recursive which is what the OP asked for.