#! perl -slw
use strict;
use threads;
use threads::shared;

my $outfile = 'output.txt';

unlink $outfile ;

my $done:shared = 0;
async{
    system("dir /s  > $outfile");
    $done =1;
};
sleep 1 until -e $outfile;
printf STDERR "\r%d\t", -s( $outfile ) and sleep 1 until $done;
print STDERR 'Output complete';