how to keep last n number of line from log file in php

Question

hi i want to delete all lines from old log files and keep fresh 50 lines which is at the bottom

plz give me the php code do something like this and if possible can we change the orientation of these lines

normal input

111111
2222222
3333333
44444444
5555555

output like

555555
4444444
3333333
22222
111111

to see the fresh log at top and 50 or 100 lines only

Thanks alot

---

Added Comment from below

Thanks alot but how to join it with this one ?

// set source file name and path 
$source = "toi200686.txt"; 
// read raw text as array 
$raw = file($source) or die("Cannot read file"); 
// join remaining data into string 
$data = join('', $raw); 
// replace special characters with HTML entities 
// replace line breaks with <br />  
$html = nl2br(htmlspecialchars($data)); 

it make the output as a html file, so how ur code will run with this properly ? Thanks

Answer 1

$lines = file('/path/to/file.log'); // reads the file into an array by line
$flipped = array_reverse($lines); // reverse the order of the array
$keep = array_slice($flipped,0, 50); // keep the first 50 elements of the array

from there you can dow whatever with $keep. for example if you want to spit it back out:

echo implode("\n", $keep);

or

file_put_contents('/path/to/file.log', implode("\n", $keep));

Answer 2

This would work for truncating the log file:

exec("tail -n 50 /path/to/log.txt", $log);
file_put_contents('/path/to/log.txt', implode(PHP_EOL, $log));

This will return the output from tail in $log and write it back to the log file.

Answer 3

Optimal form is:

<?
print `tail -50 /path/to/file.log`;
?>

Answer 4

This is a bit more complex, but uses less memory as the entire file is not loaded into the array. Basically, it keeps an N length array, and pushes on new lines as they are read from the file while shifting one off. Because the newline is returned by fgets, you can simply do an implode to see your N lines, even with the padded array.

<?php
$handle = @fopen("/path/to/log.txt", "r");
$lines = array_fill(0, $n-1, '');

if ($handle) {
    while (!feof($handle)) {
        $buffer = fgets($handle);
        array_push($lines, $buffer);
        array_shift($lines);
    }
    fclose($handle);
}

print implode("",$lines);
?>

Just showing another way to do things, especially if you don't have tail at your disposal.

Answer 5

this method use associative array to store only $tail number of lines each time. It does not fill the whole array with all lines

$tail=50;
$handle = fopen("file", "r");
if ($handle) {
    $i=0;
    while (!feof($handle)) {
        $buffer = fgets($handle,2048);
        $i++;
        $array[$i % $tail]=$buffer;
    }
    fclose($handle);
    for($o=$i+1;$o<$i+$tail;$o++){
        print $array[$o%$tail];
    }
}