pipe B,A;

my $child = fork;

die "fork: $!" unless defined $child;

if ($child != 0)
{
        use IO::Handle;
        close B;
        print A "hello\n";
        A->flush;
        sleep 1;
        print A "world\n";
        exit;
}

close A;
while (<B>)
{
        print;
}