PHP: How to read a file live that is constantly being written to

Question

I want to read a log file that is constantly being written to. It resides on the same server as the application. The catch is the file gets written to every few seconds, and

Answer 1

you can close the file handle when it is not used(once a portion of data has been written). or you can use a buffer to store the data and put it to the file only when it's full. this way you won't have the file open all the time.

if you want to get everything that is written to the file as soon as it is written there, you might need to extend the code, writing the data, so that it would output to other places too(screen, some variable, other file...)

Answer 2

Yes, you need to sleep some time in the loop but you don't have to reopen the file. I was just looking for a similar problem. I wanted to read a file that might have been changed since last read.

The problem is that the resource has reached end of file (EOF). And does not continue to read. The solution is to reset the pointer with fseek($fh, ftell($fh)).

A complete program that waits for input in a text file might look like this one:

<?php

$fh = fopen('/var/log/system', 'r');
while (true) {
    $line = fgets($fh);
    if ($line !== false) {
      // show the line or send it via email or to a websocket..
    } else {
        // sleep for 0.1 seconds (or more?)
        usleep(0.1 * 1000000);
        fseek($fh, ftell($fh));
    }
}

Answer 3

For example :

$log_file = '/tmp/test/log_file.log';

$f = fopen($log_file, 'a+');
$fr = fopen($log_file, 'r' );

for ( $i = 1; $i < 10; $i++ )
{
    fprintf($f, "Line: %u\n", $i);
    sleep(2);
    echo fread($fr, 1024) . "\n";
}

fclose($fr);
fclose($f);

//Or if you want use tail

$f = fopen($log_file, 'a+');

for ( $i = 1; $i < 10; $i++ )
{
    fprintf($f, "Line: %u\n", $i);
    sleep(2);
    $result = array();
    exec( 'tail -n 1 ' . $log_file, $result );
    echo "\n".$result[0];
}

fclose($f);

Answer 4

Just an idea..

Did you think of using the *nix tail command? execute the command from php (with a param that will return a certain number of lines) and process the results in your php script.

Answer 5

You need to loop with sleep:

$file='/home/user/youfile.txt';
$lastpos = 0;
while (true) {
    usleep(300000); //0.3 s
    clearstatcache(false, $file);
    $len = filesize($file);
    if ($len < $lastpos) {
        //file deleted or reset
        $lastpos = $len;
    }
    elseif ($len > $lastpos) {
        $f = fopen($file, "rb");
        if ($f === false)
            die();
        fseek($f, $lastpos);
        while (!feof($f)) {
            $buffer = fread($f, 4096);
            echo $buffer;
            flush();
        }
        $lastpos = ftell($f);
        fclose($f);
    }
}

(tested.. it works)