How do I compose pipes?

[Anthony]

This post https://dlang.org/library/std/process/pipe.html 
mentions:

>Pipes can, for example, be used for interprocess communication 
>by spawning a new process and passing one end of the pipe to the 
>child, while the parent uses the other end. (See also 
>pipeProcess and pipeShell for an easier way of doing this.)

```
auto p = pipe();
auto outFile = File("D downloads.txt", "w");
auto cpid = spawnProcess(["curl", 
"http://dlang.org/download.html"],
                          stdin, p.writeEnd);
scope(exit) wait(cpid);
auto gpid = spawnProcess(["grep", "-o", `http://\S*\.zip`],
                          p.readEnd, outFile);
scope(exit) wait(gpid);
```

How am I able to compose the pipes from pipeProcess if I can't 
pass in an existing pipe into the function. Eg.

```
auto p = pipeProcess("ls");
auto q = pipeProcess("cat", stdin = p.stdout); //it would be good 
to do this or something like it
```

Do I need to manually extract the output from pipes.stdin.readln 
and place it in pipes.stdout.writeln?
Or is there an easier way to do this?

Thanks