Display the last 100 lines of a log file in real time

Question

I want to be able to display the last 100 lines of a log file in a div window, and have it update in real time, so if something would be written to the log, the window would write the new log content for the user to see. Currently I'm doing this only once but it works fine, I just need a way to update it real time every second:

<?php
$file = "logfile.log";
$f = fopen($file, "r");
while ($line = fgets($f, 100) ) {
    print $line . "<br/>";
}
?>

You'll have to use a timer + ajax via javascript to call a PHP script to get the latest lines. — aynber, Oct 16 '17 at 17:44
Possible duplicate of [PHP - Returning the last line in a file?](https://stackoverflow.com/questions/1062716/php-returning-the-last-line-in-a-file) — cmorrissey, Oct 16 '17 at 17:45
@cmorrissey OP states: *"Currently I'm doing this only once but it works fine, I just need a way to update it real time every second"*. — Funk Forty Niner, Oct 16 '17 at 17:45
You could add a header to auto-refresh the page at a certain interval. Simpler than ajax. https://www.w3schools.com/tags/att_meta_http_equiv.asp — Nic3500, Oct 16 '17 at 18:00
Also, your code reads the entire file from top to bottom in 99 Bytes incremets — AbraCadaver, Oct 16 '17 at 18:14
@Fred-ii- it defiantly doesn't work the way he has described it, its reading the entire file. Which is why I posted to close it as a duplicate as that has the correct answer on it — cmorrissey, Oct 16 '17 at 19:05
@cmorrissey alrighty ;-) if you're 100% sure of the dupe, let me know and I'll hammer it. Just say the word. — Funk Forty Niner, Oct 16 '17 at 19:06

score 3 · Accepted Answer · answered Oct 16 '17 at 20:04

This is a basic solution.

Here is your html and js index.php

<!doctype html>
<html>
<head>
<meta charset="UTF-8">
<title>Read Log File</title>

</head>

<body>
<div>
    <ul id="log">

    </ul>
</div>
<script src="./jquery-3.2.1.min.js"></script> 
<script>

    $(function(){

        setInterval(function(){
            $.getJSON( "./getLog.php", function( data ) {
              var $log = $('#log');
              $.each( data, function( key, val ) {
                $log.prepend( "<li>" + val + "</li>" );
              });
            });

        },5000);

    });

</script>
</body>
</html>

Here is your php file getLog.php

  <?php

  session_start();

  $file  = '/path/to/your/file_log';

  $total_lines = shell_exec('cat ' . escapeshellarg($file) . ' | wc -l');

  if(isset($_SESSION['current_line']) && $_SESSION['current_line'] < $total_lines){

    $lines = shell_exec('tail -n' . ($total_lines - $_SESSION['current_line']) . ' ' . escapeshellarg($file));

  } else if(!isset($_SESSION['current_line'])){

    $lines = shell_exec('tail -n100 ' . escapeshellarg($file));

  }

  $_SESSION['current_line'] = $total_lines;

  $lines_array = array_filter(preg_split('#[\r\n]+#', trim($lines)));

  if(count($lines_array)){
    echo json_encode($lines_array);
  }

  ?>

Display the last 100 lines of a log file in real time

1 Answers1