dl() - Load Module Dynamically

PHP Modules Tutorials - Herong's Tutorial Examples

∟dl() - Load Module Dynamically

This section provides a tutorial example on how to load a module dynamically using the dl() function.

If you have a module that is used occasionally, you can stop loading it through the .ini file. You can load it dynamically when it is needed in your PHP script by calling the dl() function. This will reduce the memory usage of the PHP runtime, if it is not needed and not loaded.

Here is an example that shows you how to call the dl() function:

<?php 
# dl-load-module.php
# Copyright 2009-2026 (c) HerongYang.com. All Rights Reserved.

  $module = $argv[1];
  if (dl($module)) {
    print("$module is loaded\n");
  } else {
    print("Failed to load $module\n");
  }
?>

Let's try to load the "JSON" module to parse HTML documents:

herong$ php dl-load-module.php json

PHP Warning:  dl(): Dynamically loaded extensions aren't enabled 
in /Users/herong/dl-load-module.php on line 6

Looks like the dl() is disabled by default. We can enable it in the php.ini file:

herong$ php -i | grep dl
  /etc/php/7.2/cli/conf.d/20-readline.ini,
  Zend Signal Handling => enabled

  enable_dl => Off => Off
  ...

herong$ sudo vi /etc/php/7.2/cli/php.ini

  ...
  enable_dl = On

Now, run the script again:

herong$ php dl-load-module.php json

PHP Warning:  Module 'json' already loaded in ...

Okay, I forgot to remove the loading directive for mysqli in the .ini file. Let's find the .ini file and disable the extension=json.so setting:

herong$ php --ini 
  Configuration File (php.ini) Path: /etc/php/7.2/cli
  Loaded Configuration File:         /etc/php/7.2/cli/php.ini
  Scan for additional .ini files in: /etc/php/7.2/cli/conf.d
  Additional .ini files parsed:      /etc/php/7.2/cli/conf.d/10-mysqlnd.ini,
  /etc/php/7.2/cli/conf.d/10-opcache.ini,
  /etc/php/7.2/cli/conf.d/10-pdo.ini,
  /etc/php/7.2/cli/conf.d/20-calendar.ini,
  /etc/php/7.2/cli/conf.d/20-ctype.ini,
  /etc/php/7.2/cli/conf.d/20-exif.ini,
  /etc/php/7.2/cli/conf.d/20-fileinfo.ini,
  /etc/php/7.2/cli/conf.d/20-ftp.ini,
  /etc/php/7.2/cli/conf.d/20-gettext.ini,
  /etc/php/7.2/cli/conf.d/20-iconv.ini,

  /etc/php/7.2/cli/conf.d/20-json.ini,

herong$ sudo vi /etc/php/7.2/cli/conf.d/20-json.ini 
  ; configuration for php json module
  ; priority=20
  ;extension=json.so

Run the script again. It should work now:

herong$ php dl-load-module.php json 

json is loaded

If you try to load module without its library file in the extension_dir directory, you will get an error:

herong$ php dl-load-module.php junk 

PHP Warning:  dl(): Unable to load dynamic library 'junk' 
  (tried: /usr/lib/php/20170718/junk (/usr/lib/php/20170718/junk: 
  cannot open shared object file: No such file or directory), 
  /usr/lib/php/20170718/junk.so (/usr/lib/php/20170718/junk.so: 
  cannot open shared object file: No such file or directory)) 
  in /home/herong/dl-load-module.php on line 6

Failed to load junk