Something like:
$log = fopen('log_file_name', 'r');
$newLog = fopen('new_log_file_name', 'w');
while(!EOF)
{
$line = fgets($log);
if(strpos($line, $ipAddress) !== false)
{
fputs($newLog, $line);
}
}
fclose($log);
fclose($newLog);
Heh, that one minute it took to look up whether it's strpos(needle, haystack) or strpos(haystack, needle) let Halfabee beat me to it. 😉