As a variation on using bytes_read(), one can use methods of the dataconn class of Net::FTP to report periodic progress of the transfer. For example, assuming an $ftp object has been created, one can use the read method for getting a file:

my $file = 'some_file';
my $size = $ftp->size($file);
my $bsize = 1024;
my $report_size = $bsize * 1000;
my ($len, $buffer);
my $so_far = 0;
my $chunk_size = 0;
$ftp->binary;
my $data = $ftp->retr($file);
open(my $fh, '>', $file) or die qq{Cannot open $file: $!};
binmode $fh;
do {
  $len = $data->read($buffer, $bsize);
  $so_far += $len;
  $chunk_size += $len;
  if ($chunk_size >= $report_size) {
    printf("Downloaded %d / %d so far\n", $so_far, $size);
    $chunk_size = 0;
  }
} while ($len > 0 && syswrite($fh, $buffer, $len) == $len);
print "Done!\n";
close($fh);
$data->close;
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while for uploading a file one can use the write method:

my $file = 'some_file';
my $size = -s $file;
my $bsize = 1024;
my $report_size = $bsize * 1000;
my ($len, $buffer);
my $so_far = 0;
my $chunk_size = 0;
$ftp->binary;
my $data = $ftp->stor($file);
open(my $fh, '<', $file) or die qq{Cannot open $file: $!};
binmode $fh;
while (sysread $fh, $buffer = "", $bsize) {
  $len = $data->write($buffer, length($buffer));
  $so_far += $len;
  $chunk_size += $len;
  if ($chunk_size >= $report_size) {
    printf("Uploaded %d / %d so far\n", $so_far, $size);
    $chunk_size = 0;
  }
}
print "Done!\n";
close($fh);
$data->close;
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