#!/usr/bin/env perl

use strict;
use warnings;
use autodie;
use utf8;
use constant DELAY => 2;

my @ascii_texts = map "text#$_", 0 .. 9;
my @unicode_texts = map "🅃🄴🅇🅃#️$_", qw{0️ 1️ 2️ 3️ 4️ 5️ 6️ 7️ 8️ 9️};

for my $i (0 .. 9) {
    write_ascii_log($ascii_texts[$i]);
    write_unicode_log($unicode_texts[$i]);
    sleep DELAY;
}

close_ascii_log();
close_unicode_log();

sub now {
    return scalar localtime();
}

# Log file routines
#   Note anonymous block

{
    my ($asc_filename, $uni_filename);
    BEGIN {
        ($asc_filename, $uni_filename) = qw{ascii.log unicode.log};
    }
    my ($ascii_fh, $unicode_fh);

    sub _open_asc {
        open $ascii_fh, '>>', $asc_filename;
        $ascii_fh->autoflush();
        # For demo only:
        print "Run 'tail -f $asc_filename' in a separate window.\n";
        print 'Hit <Enter> when ready: ';
        (undef) = scalar <STDIN>;
        return;
    }

    sub write_ascii_log {
        my ($text) = @_;
        _open_asc() unless defined $ascii_fh;
        $ascii_fh->print(now(), ": $text\n");
        return;
    }

    sub close_ascii_log {
        return unless defined $ascii_fh;
        undef $ascii_fh;
        # For demo only:
        print "Stop 'tail -f $asc_filename'.\n";
        print 'Hit <Enter> when ready: ';
        (undef) = scalar <STDIN>;
        return;
    }

    sub _open_uni {
        open $unicode_fh, '>>:encoding(UTF-8)', $uni_filename;
        $unicode_fh->autoflush();
        # For demo only:
        print "Run 'tail -f $uni_filename' in a separate window.\n";
        print 'Hit <Enter> when ready: ';
        (undef) = scalar <STDIN>;
        return;
    }

    sub write_unicode_log {
        my ($text) = @_;
        _open_uni() unless defined $unicode_fh;
        $unicode_fh->print(now(), ": $text\n");
        return;
    }

    sub close_unicode_log {
        return unless defined $unicode_fh;
        undef $unicode_fh;
        # For demo only:
        print "Stop 'tail -f $uni_filename'.\n";
        print 'Hit <Enter> when ready: ';
        (undef) = scalar <STDIN>;
        return;
    }
}

##</code><code>##

ken@titan ~/tmp/pm_11154936_buffering
$ ./log_example1.pl
Run 'tail -f ascii.log' in a separate window.
Hit <Enter> when ready:
Run 'tail -f unicode.log' in a separate window.
Hit <Enter> when ready:
Stop 'tail -f ascii.log'.
Hit <Enter> when ready:
Stop 'tail -f unicode.log'.
Hit <Enter> when ready:
ken@titan ~/tmp/pm_11154936_buffering
$

##</code><code>##

ken@titan ~/tmp/pm_11154936_buffering
$ tail -f ascii.log
Fri Oct 13 23:07:47 2023: text#0
Fri Oct 13 23:08:07 2023: text#1
Fri Oct 13 23:08:09 2023: text#2
Fri Oct 13 23:08:11 2023: text#3
Fri Oct 13 23:08:13 2023: text#4
Fri Oct 13 23:08:15 2023: text#5
Fri Oct 13 23:08:17 2023: text#6
Fri Oct 13 23:08:19 2023: text#7
Fri Oct 13 23:08:21 2023: text#8
Fri Oct 13 23:08:23 2023: text#9