Since we're printing @entries to a file, we don't need to chomp it and put the \n's back. We can just leave them on.

# prepend $log_string to @entries
my @entries = "$log_string\n";
my $logfile = 'log.txt';
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Writing push @entries, <LOG>; would push the entire log onto @entries.
Writing push @entries, scalar <LOG>; would push one line of the log onto @entries.
Adding for 1 .. 10; adds 10 lines of the log to @entries.

open LOG, $logfile or die "Cannot open $logfile: $!";
    push @entries, scalar <LOG> for 1 .. 10;
close LOG;

open LOG, "> $logfile" or die "Cannot open $logfile: $!";
    print LOG @entries;
close LOG;
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I tested this on windows. You're on your own with flock.

HTH,
Charles K. Clarkson