Thanks to All for the suggestions, but i tried this way and its working good.

my $myproc = Proc::Simple->new();
$myproc->redirect_output ("/outcome1.txt");
$myproc->start(\&disk_use,"/usr/bin");
my $running = $myproc->poll(); ##to chk if process is still running.
my $pid= $myproc->pid; 
my $bk_id1=$pid;

sub disk_use
{
        my $path=shift;
        my $total_usage=du("$path");
        print "total disk uasge is $total_usage\n";
}
[download]

Its working:)