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PHP : Function Reference : PHP Options&Information : dl

dl

Loads a PHP extension at runtime (PHP 4, PHP 5)
int 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()).

Parameters

library

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 sockets.so 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\ 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 (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.

Examples

Example 1832. dl() examples

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<?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);
}
?>


Notes

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:

As of PHP 5, the dl() function is deprecated in every SAPI except CLI. Use Extension Loading Directives method instead.

Note:

Since PHP 6 this function is disabled in all SAPIs, except CLI, CGI and embed.

Note:

dl() is case sensitive on Unix platforms.

Note:

This function is disabled in safe mode.

See Also
Extension Loading Directives
extension_loaded()

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Code Examples / Notes » dl

james
WARNING: enable_dl/dl()
*********************
There is an exploit circulating currently which takes advantage of dl() to inject code into Apache which causes all requests to all virtual hosts to be redirected to a page of the attackers choice.
All operators of shared web hosting servers with Apache and PHP should disable dl() by setting enable_dl to off otherwise your servers are vulnerable to this exploit.
This exploit is generally known as flame.so (the object that is loaded into Apache) and flame.php (the php script that loads it).
Google gives more information:
http://www.google.co.nz/search?q=flame.so+flame.php

docey
just some note to loading modules, they do not have to
be executable.
some examples below check for this but if an module is
not executable is does not mean you cant use it. it just
needs to be readable NOT executable.
although some modules might need this perhaps for some
reason i cannot think of, so here an example,
// fails to load mysql although it could be loaded.
if(is_executable("mysql.so")){
dl("mysql.so");
}
// loads mysql
if(is_readable("mysql.so")){
dl("mysql.so");
}
watch out with this, as you can see mysql.so would not be
loaded and the script would fail. because its checked for
executable permissions although these are not needed.

endofyourself
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()
-------------------------

buildsmart
I recently came across this under PHP 4.4.4, it seems that the dl(); function generates an error/warning about registering the function if a test is done on an extension that is pre-loaded in the php.ini file (extension=gd.so).
<?php
$gd_is_shared = "shared-library";
if (function_exists('ImageCreateFromPNG') && !@dl('gd.so')) {
$gd_is_shared = "embedded";
}
print $gd_is_shared;
?>
The only purpose of this test is to determine if it is an embedded extension or a loaded extension.
I don't see this error occur under PHP 5.1.6 or PHP 5.2.0.
The test platform is Mac OS X 10.3.9 and Mac OS X 10.4.8

nutbar
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 :)

tychay
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

prozente
a note for mag_2000 at front dot ru
the line
$currentExtPath = ini_get('extension_dir');
would be better to be
$currentExtPath = realpath(ini_get('extension_dir'));
I came across some hosts that had ./  set at the extension_dir

mag_2000
<?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()
?>

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