Initialising...\n
Progress: 0%\r
Progress: 1%\r
Progress: 2%\r
Progress: 3%\r

##</code><code>##

sub io_cb {
  my $fh = shift;
  local $/ = "\r";
  my $line = <$fh>; # blocks until there is a \r
  # update progress bar with $line
}