Logging IP Addresses w/o Duplicates

<?php
$ip = $_SERVER['REMOTE_ADDR'];  
$file = fopen("log.txt", "a");
fwrite($file, 'IP: '.$ip.');
fclose($file);
?>

Code (markup):

A very simple code, but how can I make this not record duplicate IP entries?


Also, if I was trying to make this record IPs referred only from a certain domain, how can I do that?

 

I would use preg_match in this case but the best solution is to use a mysql db with a table to store ip's and checking when adding a new entry for existing ip before

 

You can read the content and use strpos (http://us2.php.net/strpos) or preg_match (http://us3.php.net/manual/en/function.preg-match.php) to find out whether or not an IP exists in the file.

With strpos:

$content = fread($file, filesize("log.txt"));
if (strpos($content, $ip) === false)
{
fwrite($file, 'IP: '.$ip.');
}
else
{
echo "There was an IP match.";
}

Code (markup):

With preg_match:

$content = fread($file, filesize("log.txt"));
if (preg_match("/{$ip}/", $content) == 0)
{
fwrite($file, 'IP: '.$ip.');
}
else
{
echo "There was an IP match.";
}

Code (markup):

 

Use the $_SERVER['HTTP_REFERER'] variable in addition to check for a certain domain. (http://us.php.net/manual/en/reserved.variables.server.php)

 

personally, i'd just log the IP addresses into the database, and make sure the IP address field is set to unquie, it's nasty and quick, but would work.