#!/usr/bin/perl -l

use IPC::Open3 qw( open3 );

my $file = "file.txt";

print "before";

{
   open (my $fh, '>', $file) or die;
   my $pid = open3('<&STDIN', '>&'.fileno($fh), '>&STDERR', 'ls');
   waitpid($pid, 0);
}

print "after";