sub single_thread {
    for my $line (@_) {
        my $pid = open3(my $wtr, my $rdr, undef, 'cat', '-v');
        print $wtr $line;
        close $wtr;

        my $content=do{local $/;<$rdr>};

        local $\;
        print "STDOUT: $content\n";
    }
}