how to creat php function to edit config.php - php

Question

In a project, I need to load some basic config without database query, how to creat a function to edit this file.
config.php may like this:
<?php
define(DEBUG, TRUE);
define (LANG, 'en');
define(THEME, 'joy');
define(DB_NAME, 'cms');
define(DB_USER, 'root');
define(DB_PASSWORD, '000');
define(DB_HOST, 'localhost');
define(CACHE, '3600');
define(CLOSE, TRUE);
.....
ajax.php
$key = $_POST['key'];
$value = $_POST['value'];
function change_config($key,$value){
// how ?
}
if I want to change cache time, I can run change_config('CACHE','1800')
if I want to change debug value, I can run change_config('DEBUG',false)

Answer 1

You could always take the easy route and use runkit_constant_redefine
runkit_constant_redefine($key, $value);
But of course, constants were built to be static. Editing that file directly means properly sanitizing input, and rewriting the file from the top to bottom every time. If the file size doesn't change and nor does the constant value's length, then you can use fwrite to write at the exact block where it exists, but that's generally not a solution. That said, use a database. they're not hard to learn.
Edit
When I was referring to using a database, I was implying the settings other than the DB connection, which should be static, or should change using something like Environment Variables, not being edited manually.

Answer 2

You could do something like this:
<?php
$key = $_POST['key'];
$value = $_POST['value'];
require_once 'config.php';
function change_config($key,$value){
$newContent = "<?php \n
define(DEBUG, " . ($key == "DEBUG"?$value:DEBUG) . "); \n
define(LANG, '" . ($key == "LANG"?$value:LANG) . "'); \n
define(THEME, '" . ($key == "THEME"?$value:THEME) . "'); \n";
file_put_contents('config.php', $newContent);
}
Your overwriting the file with the new content. We create an string wich will hold the content of the NEW config.php file. The \n are for new lines.
Then we go past all the define lines and put them in the string. For the value we use an Ternary Operator. Simply said, that's an if statement which will check if the key is corresponding the define where building. If so we will put the new value in it. If not, we will enter the OLD CONFIG.php value.