#!/usr/bin/perl

close STDERR;
open AA,     ">/tmp/myfd2" or die $!;   # gets fd 2
open STDERR, ">/tmp/myfd3" or die $!;   # gets fd 3
warn "Hello";

##</code><code>##

$ strace -eopen,write ./849816.pl
...
open("/tmp/myfd2", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 2
open("/tmp/myfd3", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 3
write(3, "Hello at ./849816.pl line 6.\n", 29) = 29
      ^