#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

open my $OUT, '>', '1' or die $!;

my $child = fork;
if ($child) {
    sleep 1;
    my %new_name = map +($_ => $_ + 1), 1 .. 8;
    for my $old (1 .. 8) {
        rename $old, $new_name{$old} or die $!;
        say "$old renamed to $new_name{$old}.";
        sleep 1;
    }
    exit
}

defined $child or die "Can't fork";
for (1 .. 10) {
    say {$OUT} $_;
    say "Printed: $_.";
    sleep 1;
}