# this is my sample function i cannot modify
sub doIt() {
    print "blabla\n";
    print STDOUT "blabla2\n";
    #sample_app is a small script that writes some output to STDOUT and STDERR
    system("sample_app");
}

sub execute() {
    pipe(RDR, WTR);
    my $pid = fork();
    if ($pid == 0) {
        
        close STDOUT;
        open (STDOUT, '>&WTR');
        select STDOUT;
        $| = 1;

        doIt();

        print "child finished\n";
        exit;
    } else {

        my $buf = "";
        while ($buf !~ /child finished/) {
            $buf .= <RDR>;
        }
        sleep 2;
        print "parent got:\n$buf\n";
    }
}

##</code><code>##

use threads;
my $t = threads->new(\&execute);
$t->join();