Re^3: Leaking a file descriptor into a child to use with /proc/self/fd/3

This worked:

open(my $in, '/etc/passwd');

my $flags = fcntl($in, F_GETFD, 0);
fcntl($in, F_SETFD, $flags & (~FD_CLOEXEC)) or die "Can't set flags: $
+!\n";

if (!fork()) {
        exec("grep", "root", "/proc/self/fd/" . fileno($in));
}
close($in);
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