PHP: dl - Manual

Description

int dl ( string library )

Loads the PHP extension given by the parameter library. The library 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 sockets.so on Unix platforms whereas it is called php_sockets.dll on the Windows platform.

Returns TRUE on success or FALSE on failure. If the functionality of loading modules is not available (see Note) or has been disabled (either by turning it off enable_dl 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.

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()).

The dl() function is deprecated as of PHP 5. Use Extension Loading Directives method instead.

Example 1. dl() examples


<?php

// Example loading an extension based on OS

if (!extension_loaded('sqlite')) {

    if (strtoupper(substr(PHP_OS, 0, 3) == 'WIN')) {

        dl('php_sqlite.dll');

    } else {

        dl('sqlite.so');

    }

}



// 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);

}

?>

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\ 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.

Note: dl() is not supported in multithreaded Web servers. Use the extensions statement in your php.ini when operating under such an environment. However, the CGI and CLI build are not affected !

Note: dl() is case sensitive on Unix platforms.

Note: This function is disabled in safe mode.

User Contributed Notes
dl

nutbar at innocent dot com
18-Mar-2004 04:22


For those who are tearing their hair out due to the extension_dir being set to "./", here's a somewhat graceful fix that will be portable:



dl(preg_replace('/\/([^\/]+)/', '../', dirname(__FILE__)) . __FILE__ . '/../some/path/dll.so');



You could alternatively make that preg_replace part into a separate function and call it something like dirname_rel() or whatever.  It basically replaces all the path components with ".." and spits out a relative path, so that when mixed with the "./" part of the extension_dir setting, it puts you at the root folder "/" so that you know where you are :)

endofyourself at yahoo dot com
18-Oct-2003 07:12


If you need to load an extension from the CURRENT local directory because you do not have privelages to place the extension in your servers PHP extensions directory, this function i wrote may be of use to you



---------------

/*

    Function: dl_local()

    Reference: http://us2.php.net/manual/en/function.dl.php

    Author: Brendon Crawford <endofyourself |AT| yahoo>

    Usage: dl_local( "mylib.so" );

    Returns: Extension Name (NOT the extension filename however)

    NOTE:

        This function can be used when you need to load a PHP extension (module,shared object,etc..),

        but you do not have sufficient privelages to place the extension in the proper directory where it can be loaded. This function

        will load the extension from the CURRENT WORKING DIRECTORY only.

        If you need to see which functions are available within a certain extension,

        use "get_extension_funcs()". Documentation for this can be found at

        "http://us2.php.net/manual/en/function.get-extension-funcs.php".

*/



function dl_local( $extensionFile ) {

    //make sure that we are ABLE to load libraries

    if( !(bool)ini_get( "enable_dl" ) || (bool)ini_get( "safe_mode" ) ) {

     die( "dh_local(): Loading extensions is not permitted.\n" );

    }



     //check to make sure the file exists

    if( !file_exists( $extensionFile ) ) {

     die( "dl_local(): File '$extensionFile' does not exist.\n" );

    }

    

    //check the file permissions

    if( !is_executable( $extensionFile ) ) {

     die( "dl_local(): File '$extensionFile' is not executable.\n" );

    }



 //we figure out the path

 $currentDir = getcwd() . "/";

 $currentExtPath = ini_get( "extension_dir" );

 $subDirs = preg_match_all( "/\//" , $currentExtPath , $matches );

 unset( $matches );

 

     //lets make sure we extracted a valid extension path

    if( !(bool)$subDirs ) {

     die( "dl_local(): Could not determine a valid extension path [extension_dir].\n" );

    }

 

 $extPathLastChar = strlen( $currentExtPath ) - 1;

 

    if( $extPathLastChar == strrpos( $currentExtPath , "/" ) ) {

     $subDirs--;

    }



 $backDirStr = ""; 

     for( $i = 1; $i <= $subDirs; $i++ ) {

     $backDirStr .= "..";

        if( $i != $subDirs ) {

         $backDirStr .= "/";

        }

    }



 //construct the final path to load

 $finalExtPath = $backDirStr . $currentDir . $extensionFile;

 

    //now we execute dl() to actually load the module

     if( !dl( $finalExtPath ) ) {

     die();

    }



 //if the module was loaded correctly, we must bow grab the module name

 $loadedExtensions = get_loaded_extensions();

 $thisExtName = $loadedExtensions[ sizeof( $loadedExtensions ) - 1 ];

  

 //lastly, we return the extension name

  return $thisExtName;



}//end dl_local()



-------------------------

tychay at php dot net
05-Jul-2003 11:15


Alan isn't 100% correct (though he's close). The exception is Mac OS X. This operating system makes a distinction between dynamically loadable shared libraries and and loadable modules of code (bundles). The former has an extension .dylib and the latter has an extension .so. The former is in Mac-O and the latter is in ELF.



Thus PHP's extensions are built as .so whereas the symbol PHP_SHLIB_SUFFIX is bound (currently) to .dylib. I don't think this is the correct behavior, but nonetheless, it is the behavior as of PHP-5.0.0b2-dev. Right now, the config binds to SHLIB_SUFFIX_NAME (which is correctly bound to .dylib on Mac OS X). I imagine this is related to why there is so much trouble getting dl() to work on Mac OS X. (For instance, I have no trouble phpizing in a new shared library, but when compiling in stuff as shared... much evilness!)



BTW, to get dl() to work in Mac OS X you need to install the dlcompat library (via Fink, DarwinPorts, or Gentoo ports). Remember in the case of Fink, you better make sure your environment variables are adjusted to point to where dlcompat (and your other fink libraries) are.



terry