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

evalEvaluate a string as PHP code


eval(string $code): mixed

Evaluates the given code as PHP.

The code being evaluated inherits the variable scope of the line on which the eval() call occurs. Any variables available at that line will be available for reading and modification in the evaluated code. However, all functions and classes defined will be defined in the global namespace. In other words, the compiler considers the evaluated code as if it were a separate included file.


The eval() language construct is very dangerous because it allows execution of arbitrary PHP code. Its use thus is discouraged. If you have carefully verified that there is no other option than to use this construct, pay special attention not to pass any user provided data into it without properly validating it beforehand.



Valid PHP code to be evaluated.

The code must not be wrapped in opening and closing PHP tags, i.e. 'echo "Hi!";' must be passed instead of '<?php echo "Hi!"; ?>'. It is still possible to leave and re-enter PHP mode though using the appropriate PHP tags, e.g. 'echo "In PHP mode!"; ?>In HTML mode!<?php echo "Back in PHP mode!";'.

Apart from that the passed code must be valid PHP. This includes that all statements must be properly terminated using a semicolon. 'echo "Hi!"' for example will cause a parse error, whereas 'echo "Hi!";' will work.

A return statement will immediately terminate the evaluation of the code.

The code will be executed in the scope of the code calling eval(). Thus any variables defined or changed in the eval() call will remain visible after it terminates.

Return Values

eval() returns null unless return is called in the evaluated code, in which case the value passed to return is returned. As of PHP 7, if there is a parse error in the evaluated code, eval() throws a ParseError exception. Before PHP 7, in this case eval() returned false and execution of the following code continued normally. It is not possible to catch a parse error in eval() using set_error_handler().


Example #1 eval() example - simple text merge

= 'cup';
$name = 'coffee';
$str = 'This is a $string with my $name in it.';
$str. "\n";
"\$str = \"$str\";");
$str. "\n";

The above example will output:

This is a $string with my $name in it.
This is a cup with my coffee in it.


Note: Because this is a language construct and not a function, it cannot be called using variable functions, or named arguments.


As with anything that outputs its result directly to the browser, the output-control functions can be used to capture the output of this function, and save it in a string (for example).


In case of a fatal error in the evaluated code, the whole script exits.

See Also

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User Contributed Notes 7 notes

20 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
lord dot dracon at gmail dot com
8 years ago
Inception with eval()

Inception Start:
eval("echo 'Inception lvl 1...\n'; eval('echo \"Inception lvl 2...\n\"; eval(\"echo \'Inception lvl 3...\n\'; eval(\'echo \\\"Limbo!\\\";\');\");');");
7 years ago
At least in PHP 7.1+, eval() terminates the script if the evaluated code generate a fatal error. For example:
@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:
try {
'$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.
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:


= '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.';');
$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
6 years ago
It should be noted that imported namespaces are not available in eval.
divinity76 at gmail dot com
7 years ago
imo, this is a better eval replacement:

function betterEval($code) {
$tmp = tmpfile ();
$tmpf = stream_get_meta_data ( $tmp );
$tmpf = $tmpf ['uri'];
fwrite ( $tmp, $code );
$ret = include ($tmpf);
fclose ( $tmp );

- 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
darkhogg (foo) gmail (bar) com
14 years ago
The following code

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

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

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