How can I parse Apache's error log in PHP?

There are a few things to consider first:

1. Firstly, your PHP user may not have access to Apache's log files.
2. Secondly, PHP and Apache aren't going to tell you where said log file is,
3. Lastly, Apache log files can get quite large.

However, if none of these apply, you can use the normal file reading commands to do it. The easiest way to get the last error is

$contents = @file('/path/to/error.log', FILE_SKIP_EMPTY_LINES);
if (is_array($contents)) {
    echo end($contents);
}
unset($contents);

There's probably a better way of doing this that doesn't oink up memory, but I'll leave that as an exercise for the reader.

One last comment: PHP also has an ini setting to redirect PHP errors to a log file: error_log = /path/to/error.log

You can set this in httpd.conf or in an .htaccess file (if you have access to one) using the php_flag notation:

php_flag error_log /web/mysite/logs/error.log

for anyone else looking for a sample script, i threw something together, it's got the basics:

<?php
exec('tail /usr/local/apache/logs/error_log', $output);
?>
<Table border="1">
    <tr>
        <th>Date</th>
        <th>Type</th>
        <th>Client</th>
        <th>Message</th>
    </tr>
<?
    foreach($output as $line) {
        // sample line: [Wed Oct 01 15:07:23 2008] [error] [client 76.246.51.127] PHP 99. Debugger->handleError() /home/gsmcms/public_html/central/cake/libs/debugger.php:0
        preg_match('~^\[(.*?)\]~', $line, $date);
        if(empty($date[1])) {
            continue;
        }
        preg_match('~\] \[([a-z]*?)\] \[~', $line, $type);
        preg_match('~\] \[client ([0-9\.]*)\]~', $line, $client);
        preg_match('~\] (.*)$~', $line, $message);
        ?>
    <tr>
        <td><?=$date[1]?></td>
        <td><?=$type[1]?></td>
        <td><?=$client[1]?></td>
        <td><?=$message[1]?></td>
    </tr>
        <?
    }
?>
</table>

there are piles of php scripts that do this, just do a google search for examples. if you want to roll your own, it's nothing more complex than reading any other file. just make sure you know the location of your logfiles (defined in the httpd.conf file) and the format your log files are in. the format is also defined in httpd.conf