how to create a file handle with using file descriptor in perl?

[Chaofei]

open(INPUT, "< /etc/motd") or die "/etc/motd: $!";
if ($pid = fork) { wait }
else {
defined($pid) or die "fork:$!";
open(STDIN, "<&INPUT") or die "dup: $!";
exec("cat", "-n") or die "exec cat: $!";#or system(...);
}
i just want to pass a file handle into a parallel process.and how to pass a socket to a new process.
<unix networking programing v1> 2edition there is some detials about what i want in 14.7 in that book.
another way to do that is like this.
but i can't create a file handle with a file descriptor.it doesn't work in the new process.
if (defined($ENV{input_fdno}) && $ENV{input_fdno}) =~ /^\d$/) {
open(INPUT, "<&=$ENV{input_fdno}")
or die "can't fdopen $ENV{input_fdno} for input: $!";
}