Error using $_SERVER in a variable variable (PHP)

I was开发者_开发技巧 trying to get the name of a superglobal variable through a GET parameter. I was told to pass only _VAR_NAME (without the $) in the get request, so in the program I have to access it through a variable variable: $$_GET['parameter_name'].

Everything went fine except with $_SERVER. To try what was wrong I just did a small php script to test what was happening. Here is the code:

<?php
    // ¡¡ This does not work !!
        $nombre = "_SERVER";
        $var = $$nombre;
        print_r($var);
    // This works 
        $nombre = "_GET";
        $var = $$nombre;
        print_r($var);
?>

Is there any reason for the _SERVER version not working? I get the following error:

Notice: Undefined variable: _SERVER in ...

I'm not sure why you need this, I don't use variable variables (there are usually better ways).

You could do a simple switch based on your $nombre variable, there are not so many superglobal variables!

switch ($nombre) {
  case "_SERVER" : 
    print_r($_SERVER);
    break;
  case "_GET" : 
    print_r($_GET);
    break;
  case "_POST" : 
    print_r($_POST);
    break;
  // ...
  default:
    echo "Unknown variable";
}

When auto_globals_jit directive is enabled, the SERVER and ENV variables are created when they're first used (Just In Time) instead of when the script starts. PHP Manual warns about variable variables:

Usage of SERVER and ENV variables is checked during the compile time so using them through e.g. variable variables will not cause their initialization.

Possible solutions are:

• Using the PHP function getenv() instead of the SERVER variable.
• Adding just the line $_SERVER; before, or at the beginning of the script.
• Disabled the directive (in php.ini: auto_globals_jit = Off, or inside the script: ini_set('auto_globals_jit',0);)
• Using the key '_SERVER' in the array $GLOBALS ($GLOBALS['_SERVER'])

You can try the alternative syntax:

$var = $GLOBALS["_SERVER"];
print_r($var);

This is functionally equivalent to $$varvar.

One more critical thing to check is if $_SERVER itself is there. (If not, place an empty count($_SERVER); expression at the start of your script.)

It can be absent if variables_order= was modified in the php.ini (though it should really just show up as empty array in recent PHP versions.)

It Works perfectly here for me. have you tried print_r ($_SERVER)

it might not be populated on your system.

make sure you have not unset it somewhere in your script.

Are you using it in a function or class?

The warning states that this cannot be used on superglobals within functions or classes.

Your best bet is the switch statement.