I was not aware Windows reports incorrect filesizes. Then you have to rely on copy's reporting. Use this pipe-open form instead:

use strict;
use warnings;
my $cmd = 'copy.exe 'from', 'to', '/z' |';
open(EXE, $cmd) || die "$!";
while(<EXE>){
        print "read from program output: ".$_."\n";
}
print "done.\n";
close(EXE);

[download]

Or use IPC::Run or any other IPC::* module mentioned here or there.

In reply to Re^3: Reading progress of "copy" executed asynchronously by bliako
in thread Reading progress of "copy" executed asynchronously by neWerminder

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