#!/usr/bin/perl
use warnings;
use strict;
use IPC::Open2;

my $cmd = '/no/such/command';
my($out,$in);
open2($out, $in, $cmd) || die("I thought script should die here: $!");

print $in "the_string\n" || die ("print die here no fork: $!");
open(my $pipe, "$cmd|") || die("But it dies only here: $!");