Try this:

#! perl
use strict;
use Win32::Console;

my $cons = new Win32::Console( STD_OUTPUT_HANDLE );

$cons->Cls;

$cons->WriteChar( 'Downstream: 0    Upstream: 0', 12, 3 );

my( $up, $dn ) = (0) x 2;

for ( 1 .. 1000 ) {
    Win32::Sleep 100;
    $cons->WriteChar( $up += int rand 100, 24, 3 );
    $cons->WriteChar( $dn += int rand 100, 40, 3 );
}
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Obviously this won't work on *nix. You might find Win32::Console::ANSI makes it easier ot write a portable script.