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

unlink "./log.txt" or warn "$!";         # in case


open OUT, '>>', 'log.txt' or die $!;

{
    my $previous_default = select(OUT);  # save previous default
    $|++;                                # autoflush OUT
    select($previous_default);           # restore previous default
}

print OUT "before close";

open IN, '<', 'log.txt' or die $!;

my $read;

$read = <IN>;
chomp $read;
say "Before close: <$read>";

close OUT;