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PHP Manual


(PHP 4, PHP 5)

dlLoads a PHP extension at runtime


bool dl ( string $library )

Loads the PHP extension given by the parameter library.

Use extension_loaded() to test whether a given extension is already available or not. This works on both built-in extensions and dynamically loaded ones (either through php.ini or dl()).


This function has been removed from some SAPIs in PHP 5.3.



This parameter is only the filename of the extension to load which also depends on your platform. For example, the sockets extension (if compiled as a shared module, not the default!) would be called on Unix platforms whereas it is called php_sockets.dll on the Windows platform.

The directory where the extension is loaded from depends on your platform:

Windows - If not explicitly set in the php.ini, the extension is loaded from C:\php4\extensions\ (PHP 4) or C:\php5\ (PHP 5) by default.

Unix - If not explicitly set in the php.ini, the default extension directory depends on

  • whether PHP has been built with --enable-debug or not
  • whether PHP has been built with (experimental) ZTS (Zend Thread Safety) support or not
  • the current internal ZEND_MODULE_API_NO (Zend internal module API number, which is basically the date on which a major module API change happened, e.g. 20010901)
Taking into account the above, the directory then defaults to <install-dir>/lib/php/extensions/ <debug-or-not>-<zts-or-not>-ZEND_MODULE_API_NO, e.g. /usr/local/php/lib/php/extensions/debug-non-zts-20010901 or /usr/local/php/lib/php/extensions/no-debug-zts-20010901.

Return Values

Returns TRUE on success or FALSE on failure. If the functionality of loading modules is not available or has been disabled (either by setting enable_dl off or by enabling safe mode in php.ini) an E_ERROR is emitted and execution is stopped. If dl() fails because the specified library couldn't be loaded, in addition to FALSE an E_WARNING message is emitted.


Example #1 dl() examples

// Example loading an extension based on OS
if (!extension_loaded('sqlite')) {
    if (
strtoupper(substr(PHP_OS03)) === 'WIN') {
    } else {

// Or, the PHP_SHLIB_SUFFIX constant is available as of PHP 4.3.0
if (!extension_loaded('sqlite')) {
$prefix = (PHP_SHLIB_SUFFIX === 'dll') ? 'php_' '';
dl($prefix 'sqlite.' PHP_SHLIB_SUFFIX);


Version Description
5.3.0 dl() is now disabled in some SAPIs due to stability issues. The only SAPIs that allow dl() are CLI and Embed. Use the Extension Loading Directives instead.



dl() is not supported when PHP is built with ZTS support. Use the Extension Loading Directives instead.


dl() is case sensitive on Unix platforms.

Note: This function is disabled when PHP is running in safe mode.

See Also

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