tail-like

reader.pl

#!/usr/bin/env perl

use strict;
use warnings;

my $pid = $ARGV[0];
my $file = '/tmp/logfile.log';

open my $fh, '<', $file;
while (pid_exists()){
    while (my $line = readline($fh)) {
        print $line;
    }
    sleep 1;
    seek $fh, 0, 1; # this clears the eof flag on $fh
}

sub pid_exists {
    return kill 0, $pid;
}

writer.pl

#!/usr/bin/env perl

use strict;
use warnings;

$|++;

open my $log_fh, '>', '/tmp/logfile.log';
my $count = 1;

print $$, "\n";

while (1) {
    syswrite $log_fh, $count . "\n";
    $count++;
    sleep 2;
}

close $log_fh;