Question 187567 in PHP Versions Question posted in
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Php versions – Is PHP's $_SERVER superglobal guaranteed to be writeable?

My PHP scripts are able to write to the superglobal array $_SERVER.

Whilst messing with $_SERVER is pretty obviously a bad idea in almost all cases, there may be situations where it could be useful as a short-term band-aid or for some kinds of testing. Can I rely on it being writeable by scripts, or is this something that might be:

  • different for different servers or PHP versions?
  • controllable by some ini setting?

The PHP docs don’t appear to specify whether S_SERVER should be, or might be, read-only. They do imply that it’s just a variable, and therefore writeable like any other variable. However, since it’s a rather special variable, it seems reasonable to ask the question. It’s very easy to show $_SERVER being modified on a real PHP web page:

<?php
$uri = $_SERVER['REQUEST_URI'];
$_SERVER['REQUEST_URI'] = "test-value";

echo '<pre>
Before: "'.$uri.'"
After : "'.$_SERVER['REQUEST_URI'].'"
</pre>';

die();
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2

Answers


  1. 0

    All superglobals are writable.

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  2. 0

    I don’t think that PHP even supports read-only variables at all. The closest thing to an exception is that you can’t wipe out the entire $GLOBALS array, as in $GLOBALS = [] (but you can still create or edit individual array elements). And even this restriction does not affect $_SERVER, this is totally valid:

    $_SERVER = 'x';

    Of course, that doesn’t mean that editing a $_SERVER entry will necessarily have the same effect than the original value had. For example, $_SERVER['PATH'] contains the process PATH environment variable, but editing it to a different value will not change the env variable itself:

    var_dump(getenv('PATH'), $_SERVER['PATH']);
$_SERVER['PATH'] = '/opt/another/';
var_dump(getenv('PATH'), $_SERVER['PATH']);

    string(13) "/usr/bin:/bin"
string(13) "/usr/bin:/bin"
string(13) "/usr/bin:/bin"
string(13) "/opt/another/"

    Demo

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