PHP eval() Function

PHP eval() function in PHP is an inbuilt function that evaluates a string as PHP code. 

Syntax: 

eval( $string )

Parameters: This function accepts a single parameter as shown in the above syntax and described below.

• $string: It must consist of a valid PHP code to be evaluated but should not contain opening and closing PHP tags.

Note: All statements must be properly terminated using a semicolon. For example, initializing the string as ‘echo “Geeks for Geeks”‘ will cause a parse error. To rectify, need to initialize as ‘echo “Geeks for Geeks”;’. 

Return Value: Returns NULL unless a return statement is called in the input string containing PHP code. Then the value is returned. In case of a parse error in the input string, the function returns FALSE. 

Examples:

Input : $age = 20; $str = "I am $age years old"
        eval("\$str = \"$str\";");
Output : I am 20 years old

Input : $str = 'echo "Geeks for Geeks";';
        echo eval($str). "\n";
Output : Geeks for Geeks

Below programs illustrate the use of eval() function: 

Program 1: 

php

<?php

$age = 20;
$str = 'My age is $age';
echo $str. "\n";

eval("\$str = \"$str\";");
echo $str. "\n";
?>

Output:

My age is $age
My age is 20

Program 2: 

php

<?php

$str = 'echo "Geeks for Geeks";';
echo eval($str). "\n";
?>

Output:

Geeks for Geeks

Reference: http://php.net/manual/en/function.eval.php