convert string into variable name

I am working on a function that takes a string as an argument, which I need to use to get the value of a variable of the same name.

For example

If the string $foo = "$_POST['email']"; is passed I need to retrieve the value of $_POST['email'] and store it as $example, so that $_POST['email'] == $example would return true. There is no feasable way of passing the value directly to function (the variable has to be dynamic to m开发者_运维问答ake the function worthwhile).

I did think of using variable variables but they don't work with super globals which will be the primary source of the values I need.

Basically is there a way to get the value of a variable (usually in a superglobal array) with the needed variable as a string?

Let me know if more detail is needed.

Thanks

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Variable variables would be the answer, but if you're after fetching values from $_POST array, why not pass just a key to a function?

Note: ths function is provided just for example, my actual recommendation is below.

function fetchFromPost($key) {
  if(isset($_POST[$key]) {
    return $_POST[$key];
  } else {
    return null; //or do whatever you want to do in case key is not found
  }
}

In fact filter_input(), which allows you to chose an input array, a key and a sanitaion filter to be used, is already there for you

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It is possible, although I seriously doubt you should use this. It allows for PHP injection and makes your source code very vulnerable if you don't know where the string came from:

<?
function eval_expression($expression)
{
    eval("\$temp = $expression;");
    return $temp;
}

// Usage:
echo eval_expression("\$_GET['plop']");