Your great blog enlightened me, but sadly my webhost doesn't allow shell_exec so I wrote a simple perl script instead, hope reader here find it useful.

My perl doing exactly the same as your php, however, instead of reading a live .htaccess file, my perl read from a template instead, of course, if you assign a live .htaccess as a template, it works as well.

Once it found the template file, it looks for any line(s) contains the word @@@DYNAMIC@@@ and then replace it with a new line below

allow from 1.2.3.4

The perl script is already running on my shared web hosting account :)

#!/usr/bin/perl

$htaccess = "/volume1/web/test/.htaccess";
$template = "/volume1/web/test/template";

# get ip address
$result=`host myhome.somedomain.com`;
@sp = split(/ /,$result);
$size = @sp;
$ip = $sp[$size-1];

open(TEMPLATE, $template) || die("Could not open file!");
@raw_data=;
close(TEMPLATE);

open(NEW, ">$htaccess") || die("Could not create file!");

foreach $line (@raw_data){
	if($line =~ /\@\@\@DYNAMIC\@\@\@/){
		print NEW "allow from $ip\n";
	}else{
		print NEW $line;
	}
}

close(NEW);