use strict;
use warnings;
my $cmd = 'copy.exe';
my @args = ('from', 'to', '/z');
open(EXE, '-|', $cmd, @args) || die "$!";
while(<EXE>){
        print "read from program output: ".$_."\n";
}
print "done.\n";
close(EXE);
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(Update1) Alternatively, if in unix/bash, create a script which forks a copy process and a filestat process. When the copy process finishes, the filestat process is killed. You can use the above perl script to run it.

#!/bin/bash

FROM=$1
TO=$2

cp "${FROM}" "${TO}" &
wPID1=$!
echo "$0 : copy-process, pid is $wPID1"

(for((;;)); do stat -c '%s' "${TO}"; sleep 1; done) &
wPID2=$!
echo "$0 : filestat-process, pid is $wPID2"

wait ${wPID1} # wait for copy-process to finish
echo "$0 : copy-process is finished"
kill ${wPID2}
echo "$0 : filestat-process killed"
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You could also use the same logic of the bash script in Perl.