Read a file backwards line by line using fseek

Question

How do I read a file backwards line by line using fseek?

code can be helpful. must be cross platform and pure php.

many thanks in advance

regards

Answer 1

To completely reverse a file:

$fl = fopen("\some_file.txt", "r");
for($x_pos = 0, $output = ''; fseek($fl, $x_pos, SEEK_END) !== -1; $x_pos--) {
    $output .= fgetc($fl);
    }
fclose($fl);
print_r($output);

Of course, you wanted line-by-line reversal...

$fl = fopen("\some_file.txt", "r");
for($x_pos = 0, $ln = 0, $output = array(); fseek($fl, $x_pos, SEEK_END) !== -1; $x_pos--) {
    $char = fgetc($fl);
    if ($char === "\n") {
        // analyse completed line $output[$ln] if need be
        $ln++;
        continue;
        }
    $output[$ln] = $char . ((array_key_exists($ln, $output)) ? $output[$ln] : '');
    }
fclose($fl);
print_r($output);

Really though, Jonathan Kuhn has the best answer IMHO above. The only cases you'd not use his answer that I know of is if file or like functions are disabled via php.ini, yet the admin forgot about fseek, or when opening a huge file just get the last few lines of contents would magically save memory this way.

Note: Error handling not included. And, PHP_EOL didn't cooperate, so I used "\n" to denote end of line instead. So, above may not work in all cases.