PHP Velho Oeste 2024

eval

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

evalExécute une chaîne comme un script PHP

Description

eval(string $code): mixed

Évalue le code fourni comme étant du code PHP.

Le code en cours d'évaluation hérite de la portée des variables de la ligne sur laquelle l'appel à eval() a lieu. Toutes les variables disponibles à cette ligne seront accessibles en lecture et modification dans le code évalué. Cependant, toutes les fonctions et classes définies seront définies dans l'espace de noms global. En d'autres termes, le compilateur considère le code évalué comme s'il s'agissait d'un fichier inclus séparé.

Attention

La construction de langage eval() est très dangereuse car elle autorise l'exécution de code PHP arbitraire. Son utilisation est vivement déconseillée. Si vous avez soigneusement vérifié qu'il n'y a pas d'autres options que de l'utiliser, gardez une attention toute particulière à ne pas y passer de données provenant d'un utilisateur sans les avoir précédemment validées minutieusement.

Liste de paramètres

code

Code PHP valide à évaluer.

Le code ne doit pas être entouré de balises PHP ouvrante et fermante, i.e. 'echo "Hi!";' doit être passé au lieu de '<?php echo "Hi!"; >'. Il est toujours possible de quitter et de retourner en mode PHP en utilisant les balises PHP appropriées, i.e. 'echo "En mode PHP !"; ?>En mode HTML !<?php echo "Retour en mode PHP !";'.

Mis à part cela, le code PHP passé doit être valide. Ceci inclut que toutes les instructions doivent se terminer par un point-virgule. 'echo "Hi!"' par exemple résultera en une erreur fatale, alors que 'echo "Hi!";' fonctionnera.

Une instruction return terminera immédiatement l'évaluation du code.

Le code sera exécuté dans le scope du code appelant la fonction eval(). Aussi, toutes les variables définies ou modifiées dans l'appel à la fonction eval() resteront visibles après la fin de l'exécution de la fonction.

Valeurs de retour

eval() retourne null sauf si return est appelé dans le code évalué, auquel cas la valeur passée à return est retournée. À partir de PHP 7, s'il y a une erreur de syntaxe dans le code évalué, eval() lance une exception ParseError. Avant PHP 7, dans ce cas eval() retourne false et l'exécution du code suivant continue normalement. Il n'est pas possible d'attraper l'erreur d'analyse de la fonction eval() en utilisant la fonction set_error_handler().

Exemples

Exemple #1 Exemple avec eval() - concaténation de texte

<?php
$string
= 'tasse';
$name = 'café';
$str = 'Ceci est une $string avec mon $name dedans.<br />';
echo
$str;
eval(
"\$str = \"$str\";" );
echo
$str;
?>

L'exemple ci-dessus va afficher :

Ceci est une $string avec mon $name dedans.
Ceci est une tasse avec mon café dedans.

Notes

Note: Comme ceci est une structure du langage, et non pas une fonction, il n'est pas possible de l'appeler avec les fonctions variables ou arguments nommés.

Astuce

Comme pour toutes les fonctions qui affichent directement des résultats au navigateur, les fonctions de gestion des sorties peuvent être utilisées pour capturer la sortie de cette fonction et l'enregistrer dans une chaîne de caractères (par exemple).

Note:

Dans le cas d'une erreur fatale dans le code évalué, l'ensemble du script se terminera.

Voir aussi

  • call_user_func() - Appelle une fonction de rappel fournie par le premier argument

add a note

User Contributed Notes 20 notes

up
468
Anonymous
19 years ago
Kepp the following Quote in mind:

If eval() is the answer, you're almost certainly asking the
wrong question. -- Rasmus Lerdorf, BDFL of PHP
up
42
lord dot dracon at gmail dot com
8 years ago
Inception with eval()

<pre>
Inception Start:
<?php
eval("echo 'Inception lvl 1...\n'; eval('echo \"Inception lvl 2...\n\"; eval(\"echo \'Inception lvl 3...\n\'; eval(\'echo \\\"Limbo!\\\";\');\");');");
?>
up
22
Jeremie LEGRAND
6 years ago
At least in PHP 7.1+, eval() terminates the script if the evaluated code generate a fatal error. For example:
<?php
@eval('$content = (100 - );');
?>

(Even if it is in the man, I'm note sure it acted like this in 5.6, but whatever)
To catch it, I had to do:
<?php
try {
eval(
'$content = (100 - );');
} catch (
Throwable $t) {
$content = null;
}
?>

This is the only way I found to catch the error and hide the fact there was one.
up
23
bohwaz
12 years ago
If you want to allow math input and make sure that the input is proper mathematics and not some hacking code, you can try this:

<?php

$test
= '2+3*pi';

// Remove whitespaces
$test = preg_replace('/\s+/', '', $test);

$number = '(?:\d+(?:[,.]\d+)?|pi|π)'; // What is a number
$functions = '(?:sinh?|cosh?|tanh?|abs|acosh?|asinh?|atanh?|exp|log10|deg2rad|rad2deg|sqrt|ceil|floor|round)'; // Allowed PHP functions
$operators = '[+\/*\^%-]'; // Allowed math operators
$regexp = '/^(('.$number.'|'.$functions.'\s*\((?1)+\)|\((?1)+\))(?:'.$operators.'(?2))?)+$/'; // Final regexp, heavily using recursive patterns

if (preg_match($regexp, $q))
{
$test = preg_replace('!pi|π!', 'pi()', $test); // Replace pi with pi function
eval('$result = '.$test.';');
}
else
{
$result = false;
}

?>

I can't guarantee you absolutely that this will block every possible malicious code nor that it will block malformed code, but that's better than the matheval function below which will allow malformed code like '2+2+' which will throw an error.
up
7
catgirl at charuru dot moe
6 years ago
It should be noted that imported namespaces are not available in eval.
up
6
darkhogg (foo) gmail (bar) com
13 years ago
The following code

<?php
eval( '?> foo <?php' );
?>

does not throw any error, but prints the opening tag.
Adding a space after the open tag fixes it:

<?php
eval( '?> foo <?php ' );
?>
up
1
remindfwd
3 years ago
Note that

<?php

echo eval( '$var = (20 - 5);' ); // don't show anything

echo ' someString ' . eval( 'echo $var = 15;' ); // outputs 15 someString

//or
echo ' someString ' . eval( 'echo $var = 15;' ) . ' otherString '; // 15 someString otherString

//or
echo ' someString ' . eval( 'echo $var = 15;' ) . ' otherString ' . '...' .eval( 'echo " __ " . $var = 10;' ); // 15 __ 10 someString otherString ...

?>
up
2
divinity76 at gmail dot com
6 years ago
imo, this is a better eval replacement:

<?php
function betterEval($code) {
$tmp = tmpfile ();
$tmpf = stream_get_meta_data ( $tmp );
$tmpf = $tmpf ['uri'];
fwrite ( $tmp, $code );
$ret = include ($tmpf);
fclose ( $tmp );
return
$ret;
}
?>

- why? betterEval follows normal php opening and closing tag conventions, there's no need to strip `<?php?>` from the source. and it always throws a ParseError if there was a parse error, instead of returning false (note: this was fixed for normal eval() in php 7.0). - and there's also something about exception backtraces
up
0
xxixxek at gmail dot com
11 months ago
I happened to work on a very old code that, for many reasons, couldn't be rewritten and the only way of showing the exact error in eval that worked for me was:

$res = eval($somecode);

if(!$res) {
echo "<pre>";
print_r(explode(PHP_EOL, $somecode));
echo "</pre>";
}

I know it is terrible but I didn't have much of a choice. None of the try...catch solutions worked for me; the solution above shows the exact lines with numbers and it is easy to find what's wrong with the code.
up
-1
xxixxek at gmail dot com
11 months ago
I happened to work on a very old code that, for many reasons, couldn't be rewritten and the only way of showing the exact error in eval that worked for me was:

$res = eval($somecode);

if(!$res) {
echo "<pre>";
print_r(explode(PHP_EOL, $somecode));
echo "</pre>";
}

I know it is terrible but I didn't have much of a choice. None of the try...catch solutions worked for me; the solution above shows the exact lines with numbers and it is easy to find what's wrong with the code.
up
0
stocki dot r at gmail dot com
1 year ago
You can use `eval()` to combine classes/traits dynamically with anonymus classes:

<?php

function init($trait, $class) {
return (
trait_exists($trait) && class_exists($class))
? eval(
"return new class() extends {$class} { use {$trait}; };")
:
false;
}

trait
Edit {
function
hello() { echo 'EDIT: ' . $this->modulename; }
}
trait
Ajax {
function
hello() { echo 'AJAX: ' . $this->modulename; }
}
class
MyModule {
public
$modulename = 'My Module';
}
class
AnotherModule {
public
$modulename = 'Another Module';
}

init('Edit', 'MyModule')->hello(); # 'EDIT: My Module'
init('Ajax', 'AnotherModule')->hello(); # 'AJAX: Another Module'

?>
up
1
Karel
9 years ago
For them who are facing syntax error when try execute code in eval,


<?php

$str
= '<?php echo "test"; ?>';

eval(
'?>'.$str.'<?php;'); // outputs test
eval('?>'.$str.'<?'); // outputs test
eval('?>'.$str.'<?php');// throws syntax error - unexpected $end

?>
up
0
solobot
6 years ago
eval() is workaround for generating multiple anonymous classes with static properties in loop

public function generateClassMap()
{
foreach ($this->classMap as $tableName => $class)
{
$c = null;
eval('$c = new class extends \common\MyStaticClass {
public static $tableName;
public static function tableName()
{
return static::$tableName;
}
};');
$c::$tableName = $this->replicationPrefix.$tableName;
$this->classMap[$tableName] = $c;

}
}

thus every class will have its own $tableName instead of common ancestor.
up
0
php at rijkvanwel dot nl
13 years ago
To catch a parse error in eval()'ed code with a custom error handler, use error_get_last() (PHP >= 5.2.0).

<?php
$return
= eval( 'parse error' );

if (
$return === false && ( $error = error_get_last() ) ) {
myErrorHandler( $error['type'], $error['message'], $error['file'], $error['line'], null );

// Since the "execution of the following code continues normally", as stated in the manual,
// we still have to exit explicitly in case of an error
exit;
}
?>
up
-1
Uther
8 years ago
eval'd code within namespaces which contain class and/or function definitions will be defined in the global namespace... not incredibly obvious :/
up
-2
php at stock-consulting dot com
15 years ago
Magic constants like __FILE__ may not return what you expect if used inside eval()'d code. Instead, it'll answer something like "c:\directory\filename.php(123) : eval()'d code" (under Windows, obviously, checked with PHP5.2.6) - which can still be processed with a function like preg_replace to receive the filename of the file containing the eval().

Example:

<?php
$filename
= preg_replace('@\(.*\(.*$@', '', __FILE__);
echo
$filename;
?>
up
-1
greald at gmail dot com
2 years ago
to avoid the evil eval() you may use the fact that function names, variable names, property names and method names can be handled strings.

<?php
class Fruit
{
public
$tomato = "Tomatos";

public function
red() {return " are red. ";}
}

$fruit = new Fruit;
$fruitStr = "tomato";
$colorStr = "red";

echo
$fruit->$fruitStr . $fruit->$colorStr();

// and procedural //////////////////////////////////////////

$lemon = "Lemons";

function
yellow() {return " are yellow. ";}

$fruitStr = "$lemon";
$colorStr = "yellow";

echo
$fruitStr . $colorStr();
?>
up
-2
Patanjali
1 year ago
eval() is useful for preprocessing css (and js) with php to embed directly into a style tag in the head tag (or script tag at the bottom of body tag) of the HTML of the page.

This:

a. Prevents Flash of White in Chrome or Firefox (where an external css file arrives briefly too late to render the HTML).

b. Allows radical minifying by testing the page source to see if whole blocks of rules or code are even required, such as for tables.

c. Allows custom source-content-dependent css rules to be created on the fly. (I use this to create rules for positioned labels over an image that scale with it)

d. Allows generation of a hash of the processed css or js for use in the page's CSP header for style-src or script-src to prevent injection attacks.

Here eval() is safe because it is not using user-supplied (person or browser) information
up
-13
Ipseno at yahoo dot com
15 years ago
If you attempt to call a user defined function in eval() and .php files are obfuscated by Zend encoder, it will result in a fatal error.

Use a call_user_func() inside eval() to call your personal hand made functions.

This is user function
<?php

function square_it($nmb)
{
return
$nmb * $nmb;
}

?>

//Checking if eval sees it?
<?php

$code
= var_export( function_exists('square_it') );

eval(
$code ); //returns TRUE - so yes it does!

?>

This will result in a fatal error:
PHP Fatal error: Call to undefined function square_it()
<?php

$code
= 'echo square_it(55);' ;

eval(
$code );

?>

This will work
<?php

$code
= 'echo call_user_func(\'square_it\', 55);' ;

eval(
$code );

?>
up
-11
marco at harddisk dot is-a-geek dot org
15 years ago
eval does not work reliably in conjunction with global, at least not in the cygwin port version.

So:
<?PHP
class foo {
//my class...
}
function
load_module($module) {
eval(
"global \$".$module."_var;");
eval(
"\$".$module."_var=&new foo();");
//various stuff ... ...
}
load_module("foo");
?>

becomes to working:

<?PHP
class foo {
//my class...
}
function
load_module($module) {
eval(
'$GLOBALS["'.$module.'_var"]=&new foo();');
//various stuff ... ...
}
load_module("foo");
?>

Note in the 2nd example, you _always_ need to use $GLOBALS[$module] to access the variable!
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