PHP: require_once

require_once

(PHP 4, PHP 5, PHP 7, PHP 8)

Der Ausdruck require_once entspricht im Wesentlichen require. PHP prüft hier allerdings, ob die gewünschte Datei bereits eingebunden wurde und wird sie in diesem Fall nicht ein weiteres Mal einbinden.

Nähere Informationen zum Verhalten von _once und wie es sich von seinem nicht-_once-Gegenstück unterscheidet, finden Sie in der Dokumentation zu include_once.

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User Contributed Notes 4 notes

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186

bimal at sanjaal dot com ¶

13 years ago

If your code is running on multiple servers with different environments (locations from where your scripts run) the following idea may be useful to you:



a. Do not give absolute path to include files on your server.

b. Dynamically calculate the full path (absolute path)



Hints:

Use a combination of dirname(__FILE__) and subsequent calls to itself until you reach to the home of your '/index.php'. Then, attach this variable (that contains the path) to your included files.



One of my typical example is:



<?php

define('__ROOT__', dirname(dirname(__FILE__)));

require_once(__ROOT__.'/config.php');

?>



instead of:

<?php require_once('/var/www/public_html/config.php'); ?>



After this, if you copy paste your codes to another servers, it will still run, without requiring any further re-configurations.



[EDIT BY danbrown AT php DOT net: Contains a typofix (missing ')') provided by 'JoeB' on 09-JUN-2011.]

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bobray99 at softville dot com ¶

2 years ago

Be careful when using include_once and require_once for files that return a value:

fiddle2.php
<?php
return "Some String";

fiddle.php
<?php
$s = require_once('fiddle2.php');
echo "\n" . $s;
$s = require_once('fiddle2.php');
echo "\n" . $s;

/* output  
 Some String
1 
*/

The second time require_once occurs, it returns 1 because the file has already been included.

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boda0128318 at gmail dot com ¶

3 years ago

1 - "require" and "require_once"  throw a fatal error if the file is not 
       existing  and stop the script execution

2 - "include" and "include_once" throw a warning and the execution 
       continues 

3 - "require_once" and "include_once" as their names suggests , 
      they will not include the file if the file was already included with 
      "require", "require_once", "include" or "include_once"

try the following code: 

create a file called "index.php" 

<?php

require "first.php";  // this will include the file

include_once "first.php";  // this will not as it was included using "require"

require_once "first.php";  // this will not as it was included using "require"

?>

and another file that is called "first.php" and write the following header

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

<h1>Hello every one</h1>

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

i hope this will help you

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powtac at gmx dot de ¶

9 years ago

"require_once" and "require" are language constructs and not functions. Therefore they should be written without "()" brackets!

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