Reading large files from end

Question

Can I read a file in PHP from my end, for example if I want to read last 10-20 lines?

And, as I read, if the size of the file is more than 10mbs I start getting erro

Answer 1

Following snippet worked for me.

$file = popen("tac $filename",'r');

while ($line = fgets($file)) {

   echo $line;

}

Reference: http://laughingmeme.org/2008/02/28/reading-a-file-backwards-in-php/

Answer 2

Well while searching for the same thing, I can across the following and thought it might be useful to others as well so sharing it here:

/* Read file from end line by line */

function tail_custom($filepath, $lines = 1, $adaptive = true) {
        // Open file
        $f = @fopen($filepath, "rb");
        if ($f === false) return false;

        // Sets buffer size, according to the number of lines to retrieve.
        // This gives a performance boost when reading a few lines from the file.
        if (!$adaptive) $buffer = 4096;
        else $buffer = ($lines < 2 ? 64 : ($lines < 10 ? 512 : 4096));

        // 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($f);     
        return trim($output);

    }

Answer 3

You can use fopen and fseek to navigate in file backwards from end. For example

$fp = @fopen($file, "r");
$pos = -2;
while (fgetc($fp) != "\n") {
    fseek($fp, $pos, SEEK_END);
    $pos = $pos - 1;
}
$lastline = fgets($fp);

Answer 4

As Einstein said every thing should be made as simple as possible but no simpler. At this point you are in need of a data structure, a LIFO data structure or simply put a stack.