#!/usr/bin/env perl
use warnings;
use strict;
use Fcntl qw(F_GETFD F_SETFD FD_CLOEXEC);

open my $fh,">&2";
unless (@ARGV && $ARGV[0] eq 'noset') {
  fcntl($fh, F_SETFD, ~FD_CLOEXEC) or die "Can't set flags: $!\n";
  print "Set no close on exec\n";
}

$ENV{myfd}=fileno($fh);
system 'print_to_3.pl';

print $fh "This is to fd $ENV{myfd} from the parent\n";