This works:

use IO::Handle;
use strict;
use warnings;

my $x= IO::Handle->new();
$x->fdopen(fileno(DATA), "r");

my $y= IO::Handle->new();
$y->fdopen(fileno(DATA), "r");

my $pos= tell *DATA;

my $pid= fork();
die unless defined $pid;
if ($pid == 0) {
  seek $x, $pos, 0;
  print "Start c\n";
  while (<$x>) {
    print "c: $_"; sleep 1;
  }
  print "stop c\n";
}
else {
  seek $y, $pos, 0;
  print "Start p\n";
  while (<$y>) {
    print "p: $_"; sleep 1;
  }
  print "stop p\n";
}
__DATA__
a
b
c
d
e
[download]

Simply reposition the filepointer…

The docs on fork perlfork say that parent and child share the same seek pointer:

Any filehandles open at the time of the fork() will be dup()-ed. Thus, the files can be closed independently in the parent and child, but beware that the dup()-ed handles will still share the same seek pointer. Changing the seek position in the parent will change it in the child and vice-versa. One can avoid this by opening files that need distinct seek pointers separately in the child.

So I find it surprising that this version works.

> So I find it surprising that this version works.

It works sometimes . I've run it 10 times and got the following output twice:

Start p
p: a
Start c
stop c
p: b
p: c
p: d
p: e
stop p
[download]

map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]