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Tailing Log File and Write results to new file

由 血红的双手。 提交于 2019-11-29 13:24:33

Introduction

You can tail a file by tracking the last position;

Example 

$file = __DIR__ . "/a.log";
$tail = new TailLog($file);
$data = $tail->tail(100) ;
// Save $data to new file

TailLog is a simple class i wrote for this task here is a simple example to show its actually tailing the file

Simple Test

$file = __DIR__ . "/a.log";
$tail = new TailLog($file);

// Some Random Data
$data = array_chunk(range("a", "z"), 3);

// Write Log
file_put_contents($file, implode("\n", array_shift($data)));

// First Tail (2) Run
print_r($tail->tail(2));

// Run Tail (2) Again
print_r($tail->tail(2));

// Write Another data to Log
file_put_contents($file, "\n" . implode("\n", array_shift($data)), FILE_APPEND);

// Call Tail Again after writing Data
print_r($tail->tail(2));

// See the full content
print_r(file_get_contents($file));

Output 

// First Tail (2) Run
Array
(
    [0] => c
    [1] => b
)

// Run Tail (2) Again
Array
(
)

// Call Tail Again after writing Data
Array
(
    [0] => f
    [1] => e
)

// See the full content
a
b
c
d
e
f

Real Time Tailing 

while(true) {
    $data = $tail->tail(100);
    // write data to another file
    sleep(5);
}

Note: Tailing 100 lines does not mean it would always return 100 lines. It would return new lines added 100 is just the maximum number of lines to return. This might not be efficient where you have heavy logging of more than 100 line per sec is there is any

Tail Class

class TailLog {
    private $file;
    private $data;
    private $timeout = 5;
    private $lock;

    function __construct($file) {
        $this->file = $file;
        $this->lock = new TailLock($file);
    }

    public function tail($lines) {
        $pos = - 2;
        $t = $lines;
        $fp = fopen($this->file, "r");
        $break = false;
        $line = "";
        $text = array();

        while($t > 0) {
            $c = "";

            // Seach for End of line
            while($c != "\n" && $c != PHP_EOL) {
                if (fseek($fp, $pos, SEEK_END) == - 1) {
                    $break = true;
                    break;
                }
                if (ftell($fp) < $this->lock->getPosition()) {
                    break;
                }
                $c = fgetc($fp);
                $pos --;
            }
            if (ftell($fp) < $this->lock->getPosition()) {
                break;
            }
            $t --;
            $break && rewind($fp);
            $text[$lines - $t - 1] = fgets($fp);
            if ($break) {
                break;
            }
        }

        // Move to end
        fseek($fp, 0, SEEK_END);

        // Save Position
        $this->lock->save(ftell($fp));

        // Close File
        fclose($fp);
        return array_map("trim", $text);
    }
}

Tail Lock

class TailLock {
    private $file;
    private $lock;
    private $data;

    function __construct($file) {
        $this->file = $file;
        $this->lock = $file . ".tail";
        touch($this->lock);

        if (! is_file($this->lock))
            throw new Exception("can't Create Lock File");

        $this->data = json_decode(file_get_contents($this->lock));

        // Check if file is valida json
        // Check if Data in the original files as not be delete
        // You expect data to increate not decrease

        if (! $this->data || $this->data->size > filesize($this->file)) {
            $this->reset($file);
        }
    }

    function getPosition() {
        return $this->data->position;
    }

    function reset() {
        $this->data = new stdClass();
        $this->data->size = filesize($this->file);
        $this->data->modification = filemtime($this->file);
        $this->data->position = 0;
        $this->update();
    }

    function save($pos) {
        $this->data = new stdClass();
        $this->data->size = filesize($this->file);
        $this->data->modification = filemtime($this->file);
        $this->data->position = $pos;
        $this->update();
    }

    function update() {
        return file_put_contents($this->lock, json_encode($this->data, 128));
    }
}

Not really clear on how you want to use the output but would something like this work .... 

$dat = file_get_contents("tracker.dat");
$fp = fopen("/logs/syst.log", "r");
fseek($fp, $dat, SEEK_SET);
ob_start();
// alternatively you can do a while fgets if you want to interpret the file or do something
fpassthru($fp);
$pos = ftell($fp);
fclose($fp);
echo nl2br(ob_get_clean());
file_put_contents("tracker.dat", ftell($fp));

tracker.dat is just a text file that contains where the read position position was from the previous run. I'm just seeking to that position and piping the rest to the output buffer.

Use tail -c <number of bytes, instead of number of lines, and then check the file size. The rough idea is:

$old_file_size = 0;
$max_bytes = 512;

function last_lines($path) {
  $new_file_size = filesize($path);
  $pending_bytes = $new_file_size - $old_file_size;
  if ($pending_bytes > $max_bytes) $pending_bytes = $max_bytes;
  exec("tail -c " + $pending_bytes + " /path/to/your_log", $output);
  $old_file_size = $new_file_size;
  return $output;
}

The advantage is that you can do away with all the special processing stuff, and get good performance. The disadvantage is that you have to manually split the output into lines, and probably you could end up with unfinished lines. But this isn't a big deal, you can easily work around by omitting the last line alone from the output (and appropriately subtracting the last line number of bytes from old_file_size).

标签
php
jquery
logging
tail
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