#!/usr/bin/perl

use 5.010;

use strict;
use warnings;

use IO::Handle qw( );

my $fn_log = 'perlogfile.rtf';

open(my $fh_log, '>>', $fn_log)
    or die("Can't append to log file \"$fn_log\": $!\n");
$fh_log->autoflush(1);

print($fh_log $_) while <STDIN>;