You might want to try Net::FTP::Robust. It will download complete directories or single file. If the download isn't completed, it will resume where it left off on the second try. For example, try this:

#!/usr/bin/perl

use strict;
use warnings;
use Net::FTP::Robust;

my $dir   = '/pub/CPAN/';
my $local = '/path/to/local_dir';

my $ftp = Net::FTP::Robust->new(
    Host => 'ftp.cpan.org',
);
$ftp->get($dir, $local);
$ftp->quit;
[download]