my $ftp = Net::FTP->new($_[0], Debug => 1) or die "Cannot connect to $_[0]";
$ftp->login($_[1],$_[2]) or die $login_failed_message;
...
$ftp->put($_[3]) or die "get failed ", $ftp->message;

##</code><code>##

my $ftp_message = 'n/a';

eval {
  $ftp_message = upload_file($server_ip,$server_user,$server_pass,$file_to_upload,$os);
}; 

if ($@) { # catched an exception
   $ftp_message = "Error: $@";
   ...
} else {
   ...
}

##</code><code>##


{ # temporarily change Net::Cmd::debug_print
  my $log_buffer;

  local *Net::Cmd::debug_print = sub {
           my ($self, $dir, $text) = @_;
           $log_buffer .= ($dir ? 'snd --> ' : 'rcv <-- ') . $text;
        };

  my $ftp = Net::FTP->new($_[0], Debug => 1) or die "Cannot connect to $_[0]";
  ...
  $ftp->quit;

  print "Log:\n$log_buffer\n";
} # recovers previous behaviour of Net::Cmd::debug_print