Kepp the following Quote in mind:
If eval() is the answer, you're almost certainly asking the
wrong question. -- Rasmus Lerdorf, BDFL of PHP
eval
(PHP 4, PHP 5, PHP 7, PHP 8)
eval — 文字列を PHP コードとして評価する
説明
指定した code
を PHP コードとして評価します。
評価されるコードは、eval() がコールされた行における 変数のスコープ を継承します。コールされた時点で利用可能なあらゆる変数が、 評価されるコード中で読み取ることができますし、変更することもできます。 しかし、定義されている全ての関数やクラスは、グローバル名前空間で定義されます。 言い換えると、コンパイラは評価されるコードを include された別のファイルのようにみなすということです。
警告
eval() は非常に危険な言語構造です。 というのも、任意の PHP コードを実行できてしまうからです。 これを使うことはおすすめしません。 いろいろ検討した結果どうしても使わざるを得なくなった場合は、細心の注意を払って使いましょう。 ユーザーから受け取ったデータをそのまま渡してはいけません。 渡す前に、適切な検証が必要です。
パラメータ
-
code -
有効な PHP コード。これを評価します。
PHP 開始タグを含めてはいけません。つまり、
'<?php echo "Hi!"; ?>'ではなく'echo "Hi!";'を渡さなければならないということです。 適切に PHP タグを使えば、PHP モードからいったん抜けてもう一度 PHP モードに戻るということも可能です。 たとえば、このようになります。'echo "PHP モード!"; ?>HTML モード!<?php echo "ふたたび PHP モード!";'それはさておき、渡すコードは PHP として有効な形式でなければなりません。 つまり、すべての文はセミコロンで終了する必要があるということです。 たとえば
'echo "やあ!"'はパースエラーになりますが、'echo "やあ!";'は動作します。return文は、コードの評価をただちに終了します。コードの実行は、eval() を呼び出したスコープ内で行われます。 したがって、eval() の中で定義したり変更したりした変数は eval() を抜けた後でも参照可能です。
戻り値
評価されるコードの中で return が
コールされない限り、eval() は null を返します。
return がコールされた場合は、その値を返します。
PHP 7 以降、評価されるコードの中でパースエラーが発生した場合は、
eval() は ParseError 例外をスローします。
PHP 7 より前のバージョンでは、この場合に
eval() は false を返していました。
それ以降のコードは通常通り実行されます。
eval() の中でのパースエラーを
set_error_handler()
で捕捉することはできません。
例
例1 eval() の例 - 簡単なテキストのマージ
<?php
$string = 'cup';
$name = 'coffee';
$str = 'This is a $string with my $name in it.';
echo $str. "\n";
eval("\$str = \"$str\";");
echo $str. "\n";
?>上の例の出力は以下となります。
This is a $string with my $name in it. This is a cup with my coffee in it.
注意
注意:
評価されるコードの中で致命的なエラーが発生した場合は、 スクリプト全体が終了します。
add a note
User Contributed Notes 20 notes
Anonymous ¶
20 years ago
lord dot dracon at gmail dot com ¶
9 years ago
Inception with eval()
<pre>
Inception Start:
<?php
eval("echo 'Inception lvl 1...\n'; eval('echo \"Inception lvl 2...\n\"; eval(\"echo \'Inception lvl 3...\n\'; eval(\'echo \\\"Limbo!\\\";\');\");');");
?>
Jeremie LEGRAND ¶
7 years ago
At least in PHP 7.1+, eval() terminates the script if the evaluated code generate a fatal error. For example:
<?php
@eval('$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.
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
{
$result = false;
}
?>
I can't guarantee you absolutely that this will block every possible malicious code nor that it will block malformed code, but that's better than the matheval function below which will allow malformed code like '2+2+' which will throw an error.
catgirl at charuru dot moe ¶
7 years ago
It should be noted that imported namespaces are not available in eval.
darkhogg (foo) gmail (bar) com ¶
14 years ago
The following code
<?php
eval( '?> foo <?php' );
?>
does not throw any error, but prints the opening tag.
Adding a space after the open tag fixes it:
<?php
eval( '?> foo <?php ' );
?>
remindfwd ¶
3 years ago
Note that
<?php
echo eval( '$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 " __ " . $var = 10;' ); // 15 __ 10 someString otherString ...
?>
divinity76 at gmail dot com ¶
7 years ago
imo, this is a better eval replacement:
<?php
function betterEval($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
xxixxek at gmail dot com ¶
1 year 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.
xxixxek at gmail dot com ¶
1 year 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, $somecode));
echo "</pre>";
}
I know it is terrible but I didn't have much of a choice. None of the try...catch solutions worked for me; the solution above shows the exact lines with numbers and it is easy to find what's wrong with the code.
stocki dot r at gmail dot com ¶
2 years ago
You can use `eval()` to combine classes/traits dynamically with anonymus classes:
<?php
function init($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'
?>
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 $end
?>
solobot ¶
7 years ago
eval() is workaround for generating multiple anonymous classes with static properties in loop
public function generateClassMap()
{
foreach ($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.
php at rijkvanwel dot nl ¶
14 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;
}
?>
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 :/
php at stock-consulting dot com ¶
16 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;
?>
greald at gmail dot com ¶
3 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 . $colorStr();
?>
Patanjali ¶
2 years ago
eval() is useful for preprocessing css (and js) with php to embed directly into a style tag in the head tag (or script tag at the bottom of body tag) of the HTML of the page.
This:
a. Prevents Flash of White in Chrome or Firefox (where an external css file arrives briefly too late to render the HTML).
b. Allows radical minifying by testing the page source to see if whole blocks of rules or code are even required, such as for tables.
c. Allows custom source-content-dependent css rules to be created on the fly. (I use this to create rules for positioned labels over an image that scale with it)
d. Allows generation of a hash of the processed css or js for use in the page's CSP header for style-src or script-src to prevent injection attacks.
Here eval() is safe because it is not using user-supplied (person or browser) information
Ipseno at yahoo dot com ¶
16 years ago
If you attempt to call a user defined function in eval() and .php files are obfuscated by Zend encoder, it will result in a fatal error.
Use a call_user_func() inside eval() to call your personal hand made functions.
This is user function
<?php
function square_it($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( $code );
?>
marco at harddisk dot is-a-geek dot org ¶
16 years ago
eval does not work reliably in conjunction with global, at least not in the cygwin port version.
So:
<?PHP
class foo {
//my class...
}
function load_module($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!
