How to get output of piped process?

[kdevel]

On Saturday, 6 March 2021 at 01:53:15 UTC, Jesse Phillips wrote:
[...]
> I think this post is going to answer your need.
>
> https://dev.to/jessekphillips/piping-process-output-1cai
>
> I haven't read all the replies, so maybe you have it working 
> and this will benefit someone else.

If I understand your code correctly you have a program "reverse" 
writing
output to another program "check". I am wondering why you have 
two threads
shoveling data between pipes. In the example below data are read 
from stdin
by the first process and is piped to another one which is finally 
piped
into the program and copied into a string appender.

```pipechain.d
import std.stdio;
import std.process;
import std.conv;
import std.array;
import std.range;
import std.algorithm;

int main (string [] args)
{
    auto p = pipe ();
    auto proc1 = spawnProcess (["cat"], stdin, p.writeEnd);
    auto q = pipe ();
    auto proc2 = spawnProcess (["cat"], p.readEnd, q.writeEnd);
    auto os = appender!string;
    q.readEnd.byChunk (4096).copy (os);
    auto res2 = wait (proc2);
    auto res1 = wait (proc1);
    stderr.writeln ("res1 = ", res1, ", res2 = ", res2);
    write (os[]);
    stderr.writeln ("fin");
    return 0;
}
```

AFAICS this is immune to SIGPIPE. Do I miss anything?