text file managment help

[ToeBee]

Ok I am working on making a auto delete function for a shoutbox script that uses a text file for the database. The function should delete any data that is greater than a set number. This is what I have now.

function deleteOld() {
    global $entriesFile;
        $limit = "10"; // Any key greater than 10 will be deleted
        $shout = file ($entriesFile);
    while (list ($key, $val) = each ($shout)) { 
            if ($key >= $limit) {
                list($id, $time, $shoutbox_name, $shoutbox_msg, $shoutbox_url, $shoutbox_ip) = explode("|",$val); 
                $fp = fopen($entriesFile, "r");
                $data = fread($fp, filesize($entriesFile));
                fclose($fp);

                $old = "$id|$time|$shoutbox_name|$shoutbox_msg|$shoutbox_url|$shoutbox_ip|";
                $new = "";

                $data = str_replace($old, $new, $data);
                    
                $fp = fopen($entriesFile, "w");
                fputs($fp, $data);
                fclose($fp);
            }
    }
} 

This seems to work fine for a bit, but then starts to slowly remove parts of the last $key.

example of the text file:
id|time|shoutbox_name|shoutbox_msg|shoutbox_url|shoutbox_ip|
id|time|shoutbox_name|shoutbox_msg|shoutbox_url|shoutbox_ip|
id|time|shoutbox_name|shoutbox_msg|shoutbox_url|shoutbox_ip|

What starts to happen:
id|time|shoutbox_name|shoutbox_msg|shoutbox_url|shoutbox_ip|
id|time|shoutbox_name|shoutbox_msg|shoutbox_url|shoutbox_ip|
id|time|shoutbox_name|shoutbox_msg|shoutbox_url|shoutbox_

Then:
id|time|shoutbox_name|shoutbox_msg|shoutbox_url|shoutbox_ip|
id|time|shoutbox_name|shoutbox_msg|shoutbox_url|shoutbox_ip|
id|time|shoutbox_name|shoutbox_msg|shoutbox_url|shou

I can't figure out why it is removing sections of the last $key like that. It seems to be random also, does it sometimes doesn't do it other times. Has anybody had a problem like this before? Or have any ideas of whats going on? Thanks.

[Sheldon]

wouldnt a mySQL database be a whole lot easier?

[ToeBee]

Yes but this shoutbox is using ajax to update the shouts without page refreshs. So the users can chat basically like a chat room. My host has a note about not using chat scripts on there mysql for extreme loads, so I would like to keep it on a text file.