$GLOBALS

References all variables available in global scope

Description

An associative array containing references to all variables which are currently defined in the global scope of the script. The variable names are the keys of the array.

Examples

Example #1 $GLOBALS example

<?php

function test()
{
    $foo = "local variable";

    echo '$foo in global scope: ' . $GLOBALS["foo"] . "\n";
    echo '$foo in current scope: ' . $foo . "\n";
}

$foo = "Example content";
test();

?>

The above example will output something similar to:

$foo in global scope: Example content
$foo in current scope: local variable

Warning

As of PHP 8.1.0, write access to the entire $GLOBALS array is no longer supported:

Example #2 writing entire $GLOBALS will result in error.

<?php

// Generates compile-time error:
$GLOBALS = [];
$GLOBALS += [];
$GLOBALS =& $x;
$x =& $GLOBALS;
unset($GLOBALS);
array_pop($GLOBALS);
// ...and any other write/read-write operation on $GLOBALS

?>

Notes

Note:
This is a 'superglobal', or automatic global, variable. This simply means that it is available in all scopes throughout a script. There is no need to do global $variable; to access it within functions or methods.

Note: Variable availability

Unlike all of the other superglobals, $GLOBALS has essentially always been available in PHP.

Note:
As of PHP 8.1.0, $GLOBALS is now a read-only copy of the global symbol table. That is, global variables cannot be modified via its copy. Previously, $GLOBALS array is excluded from the usual by-value behavior of PHP arrays and global variables can be modified via its copy.
<?php

// Before PHP 8.1.0
$a = 1;

$globals = $GLOBALS; // Ostensibly by-value copy
$globals['a'] = 2;
var_dump($a); // int(2)

// As of PHP 8.1.0
// this no longer modifies $a. The previous behavior violated by-value semantics.
$globals = $GLOBALS;
$globals['a'] = 1;

// To restore the previous behavior, iterate its copy and assign each property back to $GLOBALS.
foreach ($globals as $key => $value) {
    $GLOBALS[$key] = $value;
}

?>