PHP - Shift lines in txt file to restricted amount of lines

Question

I am writing a chat in PHP and I want to restrict the amount of lines in a chat file:

<?php
    $filename = "chat.txt";

    file_put_contents($filename, file_get_contents($filename) . $_POST["message"] . "\r\n");

    $max_lines = 3;
    $lines = 0;

    $handle = fopen($filename, "r");
    while (!feof($handle)) {
      $line = fgets($handle);
      $lines++;
    }
    fclose($handle);

    $lines_over = $lines - $max_lines;
    if ($lines_over > 0) {
        while ($lines_over > 0) {
            file_put_contents($filename, implode("\r\n", file($filename, FILE_IGNORE_NEW_LINES)));

            $lines_over--;
        }
    }
?>

, I want to delete as many lines as needed in the beginning to make the file only have 3 lines.

Which apparently doesn't work with my current code and I don't know why, please help?

Answer 1

I didn't fully understand the logic you are trying use. If you want to delete lines from the beginning of the file you can use this. I have added explanation in the code.

$filename = "chat.txt";
$max_lines = 3;
//Read lines into an array
$lines = file($filename);
//trim your array to max_lines
$lines = array_slice($lines, -1 * $max_lines);
//check if we have max_lines
if (count($lines) == $max_lines){
    //remove one from the beginning
    array_shift($lines);
}
//add your new line
$lines[] = trim($_POST["message"]) . "\r\n";
file_put_contents($filename, implode($lines));

References: file , array_shift and array_slice

Edit: Another method without using array_shift

$filename = "chat.txt";
$max_lines = 3;
//Read lines into an array
$lines = file($filename);
//trim your array to just one less item than max lines
$lines = array_slice($lines, -1*($max_lines-1));
//confirm newline is available in the last line
$lines[count($lines)-1] = trim($lines[count($lines)-1]) . "\r\n";
//add your new line with newline
$lines[] = trim($_POST["message"]) . "\r\n";
file_put_contents($filename, implode($lines));

Edit2: Fixed issue with empty file and file not yet created.

$filename = "chat.txt";
$max_lines = 3;
//Read lines into an array only if file_exists
//On first run this file may not be there
if(file_exists($filename)){
    $lines = file($filename);
}
//trim your array to just one less item than max lines
//This is needed only if there are lines
if (!empty($lines)){
    $lines = array_slice($lines, -1*($max_lines-1));
    //confirm newline is available in the last line
    $lines[count($lines)-1] = trim($lines[count($lines)-1]) . "\r\n";
}
//add your new line with newline
$lines[] = trim($_POST["message"]) . "\r\n";
file_put_contents($filename, implode($lines));

Note: I have not added validation for preventing browser refresh and same message getting added multiple times. This is left for you to implement.