my %dependencies = (
   item1 => [ 'item2' ],
   item2 => [ qw' item3 item4 ' ],
);
my %done;

sub act_on {
   my $item = shift;

   $done{$item} = undef;    # mark it early to avoid circular dependencies

   if (exists $dependencies{$item}) {
      foreach my $dep (@{$dependencies{$item}}) {
         warn "Circular dependency $item => $dep"
            if exists $done{$dep} and !$done{$dep};

         &act_on($dep) unless exists $done{$dep};
      }
   }

   # Dependencies satisfied, do whatever on $item
   print "Doing $item...\n";

   $done{$item} = 1;         # really done
}  

act_on "item1";

Doing item3...
Doing item4...
Doing item2...
Doing item1...