Needed a function that could get me the last N lines of a log file. Wanted it to be efficient and not dependent on anything other than my code.
Found some versions, but they were either a bit messy or depended on unstable arithmetic (where filesize is greater than PHP_INT_MAX). So, I decided to take on the challenge and try to write one myself. Nice little exercise 🙂
My result looks a bit long, but that’s mostly because I have added lots of comments here so you can hopefully understand what’s going on 😛
{
// Open the file
$f = fopen($filename, "rb");
// Jump to last character
fseek($f, -1, SEEK_END);
// Read it and adjust line number if necessary
// (Otherwise the result would be wrong if file doesn't end with a blank line)
if(fread($f, 1) != "\n") $lines -= 1;
// Start reading
$output = '';
$chunk = '';
// While we would like more
while(ftell($f) > 0 && $lines >= 0)
{
// Figure out how far back we should jump
$seek = min(ftell($f), $buffer);
// Do the jump (backwards, relative to where we are)
fseek($f, -$seek, SEEK_CUR);
// Read a chunk and prepend it to our output
$output = ($chunk = fread($f, $seek)).$output;
// Jump back to where we started reading
fseek($f, -mb_strlen($chunk, '8bit'), SEEK_CUR);
// Decrease our line counter
$lines -= substr_count($chunk, "\n");
}
// While we have too many lines
// (Because of buffer size we might have read too many)
while($lines++ < 0)
{
// Find first newline and remove all text before that
$output = substr($output, strpos($output, "\n") + 1);
}
// Close file and return
fclose($f);
return $output;
}
Sample
You can try out a slightly modified version at samples.geekality.net/tail. Of course you won’t be able to try it on your multi-gigabyte-sized log file, but at least you can see if it does what it should 🙂
As usual, if you have any corrections or feedback, if you found it useful, please leave a comment!