<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<title>Predefined Variables</title>
</head>
<body><div class="manualnavbar" style="text-align: center;">
<div class="prev" style="text-align: left; float: left;"><a href="language.variables.basics.html">Basics</a></div>
<div class="next" style="text-align: right; float: right;"><a href="language.variables.scope.html">Variable scope</a></div>
<div class="up"><a href="language.variables.html">Variables</a></div>
<div class="home"><a href="index.html">PHP Manual</a></div>
</div><hr /><div id="language.variables.predefined" class="sect1">
<h2 class="title">Predefined Variables</h2>
<p class="simpara">
PHP provides a large number of predefined variables to any script
which it runs. Many of these variables, however, cannot be fully
documented as they are dependent upon which server is running, the
version and setup of the server, and other factors. Some of these
variables will not be available when PHP is run on the
<a href="features.commandline.html" class="link">command line</a>.
For a listing of these variables, please see the section on
<a href="reserved.variables.html" class="link">Reserved Predefined Variables</a>.
</p>
<div class="warning"><strong class="warning">Warning</strong>
<p class="simpara">
In PHP 4.2.0 and later, the default value for the PHP directive <a href="ini.core.html#ini.register-globals" class="link">register_globals</a> is
<em class="emphasis">off</em>. This is a major change in PHP. Having
register_globals <em class="emphasis">off</em> affects the set of predefined
variables available in the global scope. For example, to get
<var class="varname"><var class="varname">DOCUMENT_ROOT</var></var> you'll use
<var class="varname"><var class="varname"><a href="reserved.variables.server.html" class="classname">$_SERVER['DOCUMENT_ROOT']</a></var></var> instead of
<var class="varname"><var class="varname">$DOCUMENT_ROOT</var></var>, or <var class="varname"><var class="varname"><a href="reserved.variables.get.html" class="classname">$_GET['id']</a></var></var> from
the URL <em>http://www.example.com/test.php?id=3</em> instead
of <var class="varname"><var class="varname">$id</var></var>, or <var class="varname"><var class="varname"><a href="reserved.variables.environment.html" class="classname">$_ENV['HOME']</a></var></var> instead of
<var class="varname"><var class="varname">$HOME</var></var>.
</p>
<p class="simpara">
For related information on this change, read the configuration entry for
<a href="ini.core.html#ini.register-globals" class="link">register_globals</a>, the security
chapter on <a href="security.globals.html" class="link">Using Register Globals
</a>, as well as the PHP <a href="http://www.php.net/releases/4_1_0.php" class="link external">» 4.1.0
</a> and <a href="http://www.php.net/releases/4_2_0.php" class="link external">» 4.2.0</a> Release
Announcements.
</p>
<p class="simpara">
Using the available PHP Reserved Predefined Variables, like the
<a href="language.variables.superglobals.html" class="link">superglobal arrays</a>,
is preferred.
</p>
</div>
<p class="simpara">
From version 4.1.0 onward, PHP provides an additional set of predefined arrays
containing variables from the web server (if applicable), the
environment, and user input. These new arrays are rather special
in that they are automatically global--i.e., automatically
available in every scope. For this reason, they are often known as
"superglobals". (There is no mechanism in PHP for
user-defined superglobals.) The superglobals are listed below;
however, for a listing of their contents and further discussion on
PHP predefined variables and their natures, please see the section
<a href="reserved.variables.html" class="link">Reserved Predefined Variables</a>.
Also, you'll notice how the older predefined variables
(<var class="varname"><var class="varname">$HTTP_*_VARS</var></var>) still exist.
As of PHP 5.0.0, the long PHP
<a href="language.variables.predefined.html" class="link">predefined variable</a>
arrays may be disabled with the
<a href="ini.core.html#ini.register-long-arrays" class="link">register_long_arrays</a>
directive.
</p>
<blockquote class="note"><p><strong class="note">Note</strong>:
<strong>Variable variables</strong><br />
<p class="para">
Superglobals cannot be used as
<a href="language.variables.variable.html" class="link">variable variables</a>
inside functions or class methods.
</p>
</p></blockquote>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
Even though both the superglobal and <em>HTTP_*_VARS</em> can exist at the same
time; they are not identical, so modifying one will not change the other.
</p>
</p></blockquote>
<p class="para">
If certain variables in <a href="ini.core.html#ini.variables-order" class="link">variables_order</a> are not set, their
appropriate PHP predefined arrays are also left empty.
</p>
</div><hr /><div class="manualnavbar" style="text-align: center;">
<div class="prev" style="text-align: left; float: left;"><a href="language.variables.basics.html">Basics</a></div>
<div class="next" style="text-align: right; float: right;"><a href="language.variables.scope.html">Variable scope</a></div>
<div class="up"><a href="language.variables.html">Variables</a></div>
<div class="home"><a href="index.html">PHP Manual</a></div>
</div></body></html>
