PHP 7.1.2 Released


(PHP 4, PHP 5, PHP 7)

La sentencia include_once incluye y evalúa el fichero especificado durante la ejecución del script. Tiene un comportamiento similar al de la sentencia include, siendo la única diferencia de que si el código del fichero ya ha sido incluido, no se volverá a incluir, e include_once devolverá TRUE. Como su nombre indica, el fichero será incluido solamente una vez.

include_once se puede utilizar en casos donde el mismo fichero podría ser incluido y evaluado más de una vez durante una ejecución particular de un script, así que en este caso, puede ser de ayuda para evitar problemas como la redefinición de funciones, reasignación de valores de variables, etc.

Véase la documentación de include para más información sobre cómo funciona esta función.


Con PHP 4, la funcionalidad de _once difiere entre sistemas operativos que ignoran las mayúsculas/minúsculas (como Windows). Por ejemplo:

Ejemplo #1 include_once con un SO que no distinque mayúsculas de minúsculas en PHP 4

include_once "a.php"// esto incluirá a.php
include_once "A.php"// esto incluirá a.php ¡otra vez! (sólo PHP 4)

Este comportamiento cambió en PHP 5, así que, por ejemplo con Windows primero se normaliza la ruta para que C:\PROGRA~1\A.php sea identificado con C:\Program Files\a.php y el fichero sea incluido sólo una vez.

add a note add a note

User Contributed Notes 7 notes

roach dot scott+spam at googlemail dot com
8 years ago
If you include a file that does not exist with include_once, the return result will be false.

If you try to include that same file again with include_once the return value will be true.

(include_once 'fakefile.ext'); // bool(false)
var_dump(include_once 'fakefile.ext'); // bool(true)

This is because according to php the file was already included once (even though it does not exist).
Greg McCarthy
26 days ago
In response to what a user wrote 8 years ago regarding include_once being ran two times in a row on a non-existent file:

Perhaps 8 years ago that was the case, however I have tested in PHP 5.6, and I get this:

$result = include_once 'fakefile.php';  // $result = false
$result = include_once 'fakefile.php'   // $result is still false
xcl_rockman at qq dot com
1 year ago
return array("test">1);

$config = include_once("config.php");

$config = include_once("config.php");

output will be

webmaster AT domaene - kempten DOT de
10 years ago
Since I like to reuse a lot of code it came handy to me to begin some sort of library that I stored in a subdir
e.g. "lib"

The only thing that bothered me for some time was that although everything worked all IDEs reported during editing
these useless warnings "file not found" when library files included other library files, since my path were given all relative to the corresponding document-root.

Here is a short workaround that makes that gone:

// Change to your path

if(strpos(__FILE__,'/lib/') != FALSE){
include_once (
// ... or any other include[_once] / require[_once]

just adjust the path and it will be fine - also for your IDE.

1083706899 at qq dot com
1 year ago
require_once() can check the file if once include ,or the file is wrong will tell a error and quit the script.
flobee at gmail dot com
11 years ago
i already had a discussion with several people about "not shown errors"
error reporting and all others in php.ini set to: "show errors" to find problems:
the answer i finally found:
if you have an "@include..." instead of "include..." or "require..('somthing') in any place in your code
all following errors are not shown too!!!

so, this is actually a bad idea when developing because paser errors will be droped too:
if(!@include_once('./somthing') ) {
'can not include';

if(!@file_exists('./somthing') ) {
'can not include';
} else {
emanuele at rogledi dot com
8 years ago
For include_once a file in every paths of application we can do simply this

include_once($_SERVER["DOCUMENT_ROOT"] . "mypath/my2ndpath/myfile.php");
To Top