writing to closed stdout (II): exit status

[kdevel]

Sometimes the file descriptor 1 is closed when a program is 
executed (cf. [1]). Due to buffering [2] a write error is not 
detected until the buffers are flushed. But the flushing occurs 
after the return from main:

```d
int main ()
{
    import std.stdio;
    writeln ("OK.");
    return 0;
}
```

(`1>&-` or `>&-` can be used to close stdout in BASH, likewise 
descriptor 1 can be closed in the D program using `extern (C) int 
close (int); close (1);`.)

```sh
$ dmd return0.d
$ ./return0 1>&-; echo $?
Failed to flush stdout: Bad file descriptor
1
$
```

Surprisingly when the return value is anything but 0 the exit 
code of the program becomes `rv & 255`. So in order to return 0 
one can return 256:

```d
int main ()
{
    import std.stdio;
    writeln ("OK.");
    return 256; // returns (256 & 0xff) == 0
}
```

Even more surprising is the fact that is behavior strongly 
resembles the Perl since v5.24.4 [3]


[1] Goodbye World! The perils of relying on output streams in C 
[PDF], p. 15 
https://www.gnu.org/ghm/2011/paris/slides/jim-meyering-goodbye-world.pdf
[2] What do fully buffered, line buffered and unbuffered mean in 
C? [closed] 
https://stackoverflow.com/questions/36573074/what-do-fully-buffered-line-buffered-and-unbuffered-mean-in-c
[3] 
https://stackoverflow.com/questions/50507849/weird-error-after-perl-upgrade-unable-to-flush-stdout/52106594#52106594